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THE DESIGN AND APPLICATION OF A

PROGRAINABLE COULOSTATIC POLARIZER

Ching-Cherng Lii

A DISSERTATION
Submitted to
liehigmn State University
in pertiel fulfillment of the requirements
for the degree of
DOCTOR OF PHILOSOPHY

Depertment of Chemistry

1982

ABSTRACT

THE DESIGN AND APPLICATION OF A

PROGRAIIABLB COULOSTATIC POLARIZER

By

Ching-Cherng Lii

A microcomputer controlled coulostatic electrochemical
instrument has been slightly modified. The design
principles and applications of the instrument. the
programmable coulostatic polariaer (PCP). will be discussed.
The PCP consists of an electrochemical cell. a digitally
controlled charge generator for adding charge to the
electrode, a voltage measurement system to monitor the
working electrode potential. a real time clock to control
the timing of experiments. and a microcomputer system to
control the operation of charge generator. voltage
measurement system and real time colck.

Ihen an electrochemical cell is controlled by a
potentiostat vhich is generally employed in conventional

instruments. an 12 error vhich is the product of the portion

L5
u.

of current and the portion of resistance sensed by the
reference electrode always exists. This error can be
significant if the solution resistance is high or if the
current is large. The PCP is based on the coulostatic
polarization method which employs the addition of charge
pulses to the electrode and measures the electrode potential
between charge additions when there is no current in the
solution. The potentials measured with coulostatic method
are thus free from IR error.‘

The PCP can be operated in ways analogous to many
electrochemical polarisation modes where the charge.
current. or potential must be measured or controlled. These
can be accomplished without modification of the instrument
hardware.

Some applications of the PCP have been achieved as follows:
1. Fast measurement of electrode capacitance:

Capacitance measurements for mercury electrode in 1.0 I
[Cl eolution can be obtained within 8 seconds with 2 $ RSD.
2. Electrode capacitance measurements for low

concentration of electrolyte solution:

The concentration of [Cl solution for capacitance
measurement on mercury electrode can be as low as 10 pl.

3. Charging current compensation for constant
chronopotentiometry:

Compensation of charging current using blank

electrolyte ([01) solution has been performed for the

solutions of TlCl in 0.1 I RC1. A dramatic correspondance
of transition times with theory is obtained. In-situ
compensation of charging current allows the detection limit

for cadmium to be as low as 0.25 pl.

ACKNOWLEDGEMENTS

I would like to express my sincere appreciation to
Profesaor Christie G. Enke for his help. encouragement. and
friendship throughout my graduate study. Thanks go to
Professor lichael 'eaver for his helpful suggestions as a
second reader. Thanks also go to Professor Eugene LeGoff,
Professor Donald Farnum, and Professor Gerald Babcock aa my
guidance committee.

I would likc to thank Dr. Thomas Atkinson and the
members of Professor Enke's research group for their help
and friendship. especially Robert Engerer, Peter Aiello,
Sechoing Lin. Kane-Yang Liu. Bruce Newcomc. and Hugh Gregg.

I would like to thank Dr. Verdun Erle Leichty for his
valuable help in grammer correction.

Thanks go to my wife, Lily, for her help in drawing
figures, continuous support, and love. Thanks go to my
parents. brothers. and sisters for their support throughout

my life.

TABLE OF CONTENTS

LIST OF TABLES O O O O O O O O O 0 O O O O O O O O O 0

LIST OF FIGURES O O O O O O O O O O O O O O O O O 0 0

CHAPTER

CHAPTER

CHAPTER

1
A.

D.
E.
F.

3

INTRODUCTION . . . . . . . . . . . . . . .
Coulostatic lethod . . . . .'. . . . . . .
A licrocomputer Controlled Instrument:

A Programmable Coulostatic Polarixer (PCP)

OPERATIONAL lODES OF THE PCP . . . . . . .
Description of the Charge Generator and the
Voltage leasurement System . . . . . . . .
Controlled Charge lode . . . . . . . . . .
Controlled Current lode . . . . . . . . . .
Controlled Potential lode . . . . . . . . .
Open Circuit lode . . . . . . . . . . . . .
Combination of lodes . . . . . . . . . . .

EXAlPLE OF CONTROLLED CHARGE EXPERIlENT:

ELECTRODE CAPACITANCE lEASURElENTS . . . . . .

A.

Introduction . . . . . . . . . . . . . . .
General Background on Double Layer
Capacitance . . . . . . . . . . . . . . . .
l. Qualitative Description of Electrode
Double Layer . . . . . . . . . . . . . .
2. Usefulness of Double Layer Studies . . .
3. lethods for the leasurements of Double

Layer Capacitance . . . . . . . . . . .

iii

Page
vi

vii

13

13
19
20
20
21

21

22

22

23

23

25

26

CHAPTER

CHAPTER

4.

Description and Test of the Technique
Developed in this Research Work . . . . . .
Double Layer Capacitance leasurements for
lcrcury Electrode in (CI Solutions . . . .
Discussion . . . . . . . . . . . . . . . .

EXAlPLE OF CONTROLLED CURRENT EXPERIlENT:

CONSTANT CURRENT CHRONOPOTENTIOlETRY 'ITH

CHARGING CURRENT COlPENSATION . . . . . . . .

A.
B.
C.

D.

Introduction . . . . . . . . . . . . . . .
Historical Background . . . . . . . . . . .
Description and Test of the Technique . . .
Compensation of Charging Current for the
System TlCl in 0.1 l [Cl Solution . . . . .
In Situ Compensation of Charging Current as
Sensitive Technique for the Detection
of ca*’ . . . . . . . . . . . . . . . . . .
Discussion . . . . . . . . . . . . . . . .
SOlE POSSIBLE APPLICATIONS OF THE PCP . .
The Applications of the Controlled
Charge lode . . . . . . . . . . . . . . . .
1. Traditional Coulostatic lethod . . . . .
2. Electrode Capacitance leasurements . . .
3. Coulometric Titrations . . . . . . . . .
The Applications of the Controlled
Current lode . . . . . . . . . . . . . . .

1. Constant Current Chronopotentiometry . .

iv

Page

30

47

62

65
65
66

73

93

101
110

116

116
116
117

118

119

119

CHAPTER 6

B.
C.

APPENDIX A

APPENDIX B

Page

2. Programmed Current Chronopotentiometry . 120

3. Electrode Pretreatment . . . . . . . . . 120

The Applications of
Potential lode . .
The Applications of
The Applications of
of lodes . . . . .
DESCRIPTION OF THE
lodification of the
Voltage leasurement
Interface Circuits
The Real Time Clock

- Equation and Some

the Controlled

. . . . . . . . . . . . 121
the Open Circuit lode . 123
the Combination

. . . . . . . . . . . . 124
SYSTEl HARD'ARE . . . . 128
Charge Generator and the
System . . . . . . . . 128
. . . . . . . . . . . . 131
. . . . . . . . . . . . 136

Examples for the

Calculation of linimum values of tdl for

Chronopotentiometric Experiments . . . . 138

- Programs for Data

Data Analysis . .

LIST OF REFERENCES . . . . . .

Acquisition and
O O O O O O O O O O O O 139

O O O O I O O O O O O O 172

Table

LIST OF TABLES

Page
Estimated Error due to the switch
current leakage for the capacitance
leasurement . . . . . . . . . . . . . . . 61
Transition time (seconds) of various
concentrations of TlCl as a function of
number of charging current compensations . 99
List of if, 1b/1f. r, 1:"‘ for cac:,
solutions . . . . . . . . . . . . . . . 110
The names and functions of the data
acquisition programs . . . . . . . . . . 139
The names and functions of the data

analysis programs . . . . . . . . . . . 140

vi

Figure

LIST OF FIGURES

Equivalent circuit for an
electrochemical cell controlled

by a potentiostat . . . . . . . . . . .
An equivalent circuit and an example

of charge pulse for coulostatic method .
Block diagram of the programmable
coulostatic polarixer (PCP) . . . . . .
The charge generator and the voltage
measurement system . . . . . . . . . . .
The first part of the flow chart of the
program for the capacitance measurement
The second part of the flow chart of the
program for the capacitance measurement
The third part of the flow chart of the
program for the capacitance measurement
Calibration error in analog-to-digital
converter (ADC) . . . . . . . . . . . .
Effect of Calibration error in
analog-to-digital converter on

the capacitance measurement . . . . . .
Dummy cell configuration for testing

the capacitance measurement technique .
Results of removing calibration error of

ADC O O O O O O O O O O O O I O O O O 0

vii

Page

11

14

32

33

34

37

39

40

42

Figure

3-8

3-10

Page
Capacitance ratio obtained with
N1'100. Ndz-loOOg ‘nd td'Oes .' e e e e e ‘5
Capacitance ratio obtained with
Ndl-IOOOg NdZ'looo' .nd td'Oms .‘ m o e o 46
Capacitance curves of HlDE in 1.0 l RC1
solution obtained with Ndl-lOO. Nd2'1000'
and td - 0.4. 0.8. 1.6. 3.2 ms with the
higher capacitances corresponding to
the longer times . . . . . . . . . . . . . 49
Capacitance curves of ElDE in 0.1 l RC1
solution obtained with Ndl-lOO. Ndz-IOOO,
‘nd td - 002g 00" 0.8, 1.6. 302. 6.4 .‘ 'ith
the higher capacitances corresponding
to the longer times . . . . . . . . . . . 51
Capacitance curves of HlDE in 0.01 l RC1
solution obtained with Nd1-100. Nag-1000.
.nd td - 0.2g 00" 008, 1.6g 302' 6.4.
12.8 ms with the higher capacitances
corresponding to the longer times . . . . 52
Capacitance curves of nuns in 10’3 l xc1
solution obtained with Nd1-100, Nd2-1000,
.nd td - 0.4. 008. 1.6g 3.2g 6.4. 1208'
25.6 ms with the higher capacitances

corresponding to the longer times . . . . 53

viii

Figure

3-14

Cdpaoitance curves of 10'3 l RC1 solution
obtained with improved cell geometry
These curves are obtained with Nd1-100.
Nd2-1000. and td - 0.2. 0.3. 0.4. 0.8.
1.6. 3.2 ms with higher capacitances
corresponding to the longer times . . . .
Capacitance curves of HlDE in 10.4 l
RC1 solution obtained with Nd1-20.
Nd2-1000. and td - 0.8. 1.6. 3.2. 6.4.
12.8. 25.6 ms with the higher capacitances
corresponding to the longer times . . . .
Capacitance curves of HlDE in 10'5 l

RC1 solution obtained with Nd1-20.
Nd2-1000. and td - 12.8. 25.6. 51.2.

102.4 ms with the higher capacitances
corresponding to the longer times . . . .
Capacitance curves of RC1 solutions with
concentrations of 1. 0.1. 0.01. 10'3.
10". end 10'5 u . . . . . . . . . . . . .
Capacitanccs of mercury electrode in

0.1 l RC1 solution

.... this work;

+++. Grahame's data . . . . . . . . . . .
Illustration of the compensation of

charging current. the first part . . . . .

ix

Page

55

57

58

59

63

74

Figure

4-4

Illustration of the compemsation of
charging current. the second part . . . .
Flow chart of the program

for the measurement of integral

capacitive charge; the first part . . . .
Flow chart of the program for the
measurement of integral capacitive

charge. the second part . . . . . . . . .
Flow chart of the program for
chronopotentiometry with charge-

ing current compensation . . . . . . . . .
Flow chart of the program for data
acquisition of a chronopotentiogram . . .
Circuits of dummy cell for the test of
charging current compensation for
chronopotentiometry

cdml: the charging capacitor

Cd.2: the Faradaic capacitor . . . . . . .
Voltage-time curve obtained with

one dummy capacitor. Cd.2 . . . . . . . .
Voltage-time curves obtained with

two dummy capacitors

Curve 0: no charging current compensation
Curve 1: the first compensation

Curve 2: the second compensation

Curve 3: the third compensation . . . . .

x

Page

75

_77

78

82

83

87

89

9O

Figure

4-10

4-11

4-13

Page
Voltage-time curves
Curve 1: only Cd‘z in the feedback loop
Curve 2: both capacitors in the feedback
loop and with the compensation
for Cd.1 . . . . . . . . . . . . 92

Integral capacitive charge of SlDE in
0.1 l RC1 solution . . . . . . . . . . . . 95
Chronopotentiograms of 10"4 l TlCl solution
Curve 0: No charging current compensation
Curve 1: the first compensation
Curve 2: the second compensation
Curve 3: the third compensation . . . . . 97
Faradaic charge curves for SlDE in
10“ a 1101 and 0.1 l xc1 solution
Curve 0: no charging current compensation
Curve 1: the first compensation
Curve 2: the second compensation
Curve 3: the third compensation . . . . . 98
itl/ZIC vs. log concentration (I) of Tl+
o. with charging current compensation
x. without charging current

compensation . . . . . . . . . . . . 100
Chronopotentiograms of 2010-5 l CdClz
The number besides the curve corresponding
to the number of charging current

compensation . . . . . . . . . . . . . . 103

xi

Figure

4-8

4-10

4-13

Page
Voltage-time curves
Curve 1: only Cd.2 in the feedback loop
Curve 2: both capacitors in the feedback
loop and with the compensation
for Cd.1 . . . . . . . . . . . . 92

Integral capacitive charge of SlDE in
0.1 l RC1 solution . . . . . . . . . . . . 95
Chronopotentiograms of 10"4 l TlCl solution
Curve 0: No charging current compensation
Curve 1: the first compensation
Curve 2: the second compensation
Curve 3: the third compensation . . . . . 97
Faradaic charge curves for SlDE in
10"4 s TlCl and 0.1 x xc1 solution
Curve 0: no charging current compensation
Curve 1: the first compensation
Curve 2: the second compensation
Curve 3: the third compensation . . . . . 98
itllz/C vs. log concentration (l) of Tl+
o. with charging current compensation
x. without charging current

compensation . . . . . . . . . . . . 100
Chronopotentiograms of 2-10'5 l CdClz
The number besides the curve corresponding
to the number of charging current

compensation . . . . . . . . . . . . . . 103

xi

Figure

4-14

4-18

6-1

Page
leasured integral capacitive charge for
0.01 l RC1 solution
Curve 1: without CdClz
Curve 2: with 2-10'5 I cac12 . . . . . . 105
leasured integral capacitive charge for
0.01 l RC1 solution
Curve 1: without CdClz
Curve 2: with 5-10" I cac12 . . . . . . 106
Chronopotentiograms of 10" u cac12
The number besides the curve corresponding
to the number of charging current
compensation . . . . . . . . . . . . . . 107
Chronopotentiograms of 5°10-7 l CdClz
with charging current compensation . . . 109
i-rll2 vs. concentration of Cd+2 . . . . 111
The bipolar Digital-to-Analog
Converter . . . . . . . . . . . . . . . 129
The voltage measurement system . . . . . 130
Interface logic for the DAC and
the ADC . . . . . . . . . . . . . . . . 132

Switch decoding circuits . . . . . . . . 134

xii

- d.-

CHAPTER 1
INTRODUCTION

Electrochemical instruments are often based on the
potentiostat which tries to maintain the potential of the
working electrode equal to a control voltage provided by a
signal generator. The control signal may have a constant
value or vary with time. Figure 1-1 shows an equivalent
circuit for an electrochemical cell which is controlled by a
potentiostat(not shown). The solution resistance is
represented by R'. The resistance of an electrochemical
reaction which depends on the kinetics and the availability

e' The double

of electroactive species is represented by R
layer capacitance of the working electrode appears in the
equivalent circuit as Cdl' On the solution side of the
electrode/solution interface. there are ionic species and
solvent dipoles. A change in the electrode potential causes
a change in the distribution of ions and the orientation of
solvent dipoles. Thus. the electrode/solution interface
responds like a capacitor. A detailed discussion of the
double layer capacitance can be found in Chapter 3. In a
potentiostat. the electrochemical cell is part of a feedback
loop in which the cell current is continuously controlled in

order to minimize the difference between the measured value

of the electrode potential and the desired (control signal)

COUNTER REFERENCE WORKING
ELECTRODE ELECTRODE ELECTRODE

 

 

 

 

 

 

 

 

 

Figure 1-1. Equivalent circuit for an

electrochemical cell controlled

by c potentiostat

potential. However. the actual potential of the working
electrode deviates from the measured value (and thus from
the desired value) whenever there is a current in the cell.
This deviation is caused by the IR drop which is the product
of current I and the portion of the solution resistance 5
sensed by the reference electrode. In order to reduce the
IR component of the measured voltage. solvents with high
dielectric constant and high concentrations of supporting
electrolyte are used. In some cases. a Luggin capillary
reference electrode must be used to minimise the distance
between the working and reference electrodes.

'hen the supporting electrolyte concentration is below
0.01 l (as is often the case when nonaqueous solvents are
used). the IR drop can introduce a significant error in
potential control.

Some electrochemists have tried to use potentiostats
with positive IR compensating feedback (1-6) to reduce the
error in potential control and enhance the system response.
However. it has been found that the circuit tends to
oscillate (3.5.6). A common method to compensate the
solution resistance is to increase the level of compensation
until the potentiostat/cell system is no longer stable. It
was pointed out in a review paper (7) that this can be a
rather inaccurate procedure. as many systems can be unstable
at rather less than 100% compensation and. conversely. some

systems are stable even beyond 100% compensation.

A. Coulostatic lethod

In the early 1960's P. Delahay and I. H. Reinmuth each
published a series of papers in which they described the
theory and applications of a new method. the coulostatic
polarisation method (8-12). Figure 1-2 shows an equivalent
circuit of an electrochemical cell and an example of charge
pulse for the coulostatic method. In the coulostatic
method. a brief charge pulse (microsecond range) of qp
coulombs is injected into the cell and then the cell is kept
in an open circuit condition. The quantity of charge may be
controlled by applying a constant current i for a short
period of time t or by injecting a known quantity of charge
with a capacitor charged to a known voltage. After the
charge pulse is injected. the Faradaic current if. or the
charge consumed by the Faradaic process. is supplied by the
charge on the double layer capacitor cdl' The original
coulostatic method usually involved the injection of a large
charge pulse to alter the potential of an electrode from
several to several hundred millivolts followed by the
open-circuit monitoring of the potential. The
potential/time curve can then be related to the electrode
reaction processes of charge transfer. diffusion. and
chemical kinetics (8.10.12). For example. for a simple
redox system Red + ne- t 0x. with both species soluble. with
mass transport by semi-infinite diffusion. and with a

constant double layer capacitance cdl' the potential/time

i q-p=J‘i-dt

 

 

 

 

 

 

Ref Col
if
“9 —W‘——
Re
Figure 1-2. An equivalent circuit and an example

of charge pulse for coulostatic method

relationships were derived for the following situations:

1. 'ith a small potential perturbation AE (nFAE/RT << 1)
and with fast charge transfer reaction (12) (the rate of the
reaction is completely limited by the diffusion of Red to

the electrode surface).
AE - AEi-exp(tltd)-erfc(t/td):/3 (1-1).

where AB is the change of potential from its initial value.
AEi is the initial potential perturbation. t is the time

after charge injection. and

(td)1/: ' (RTCdl/naF‘)'
<(cnod)“<on,d)“"+(c°x)“(n°,>“") (1-2).
where n is the number of electrons transfered. cRed and cox
are the initial concentrations. other terms have their usual

meaning.

2. With a small potential perturbation AE and when the

rate of charge transfer is limiting (12).

AE - AEi-exp(-t/rc) (1-3).

where

to - [Teal/HFI. (1-4),
where i. is the exchange current density for the charge
transfer process.

3. Vith a large potential perturbation AE. and with a fast

charge transfer reaction.

AB - (2nF(DRCd)1I’cRCd/(x):lacd1)t1/: (1'5).

For cdl - 20 uF/cm'. ”Red - 10 cm'lsec. and n - 2. AB is

equal to 0.344 t"’, o_0344 t‘l’. 0 00344 ti]:

1/3 for cRed . 10", 10", 10" moles/liter.

volts[(sec)
respectively (8.10).

The potential-time relaxation is a function of the
double layer capacitance which is a function of potential.
One of the major disadvantages of the original coulostatic
method is that the variation of double layer capacitance
with potential complicates the analysis of the desired
parameters.

The coulostatic method reduces the effect of solution
resistance because the current is zero when the electrode
potential is measured. Therefore. the coulostatic method

can be applied to most non-aqueous solutions and lower

concentrations of supporting electrolyte can be used to

reduce contaminations from the addition of the supporting
electrolyte. In spite of the above advantages. which make
the coulostatic polarisation an attractive technique for
analytical applications. only a few applications of this
method have been reported (some examples can be found in
References 11.13-16). This may be due to the lack of rapid
and intelligent control system with which to produce the
traditional varieties of polarizing potential or current
waveforms through charge pulse injection.

Charge pulse injection. which is used in traditional
coulostatic method to change the potential of a working
electrode to a new value. can be used as well to maintain
the electrode potential at a desired value as long as the
sire of the injected charge is small and the frequency of
injection is sufficiently high.

The idea of controlling the electrode potential by
charge injection has been used by Goldworth and Clem to
develop the 'bipolar digipotentiogrator' (17). The system
uses the charge injection technique to maintain a desired
potential and simultaneously serves as a current-to-digital
converter. The system injects small charge pulses of
constant size to the working electrode as often as needed to
keep its potential at the desired value. The design of the
bipolar digipotentiogrator is based on dedicated hardware

logic.

B. A licroccmputer Controlled Instrument:

A Programmable Coulostatic Polarixer (PCP)

In order to enhance the flexibility of the coulostatic
method. a general purpose electroanalytical system based on
a microcomputer-controlled coulostatic generator has been
developed by Spyros Houdakis (18). This first
microcomputer-controlled instrument has been improved
substantially in this thesis work. The goals of the
research work described here were to develop a flexible
electrochemical instrument around the computer-controlled
charge injection principle and to apply this instrument to
some electrochemical experiments which standard
electrochemical instruments cannot easily perform.

Computers have been used heavily during the last decade
in the development of modern automated instruments. The
dedicated computer can operate the instrument. calibrate the
instrument. collect data. and make decisions during the
course of the experiment. licroprocessors with greatly
improved performance have been introduced into the market in
recent years. Some microprocessors have an instruction
cycle as low as 0.8 us. licroprocessors. with the aid of
supporting chips such as memory. input-output registers.
buffers. communication chips. interrupt controllers. timing
controllers. etc.. can be used as an intelligent controller
for virtually any instrument. The microcomputer used in

this instrument is a single microcomputer segment of a

lO

multi-microcomputer system that has been developed in our
research group (19). These microcomputers are based on the
8085 microprocessor chip first manufactured by Intel Corp.
The block diagram of the instrument is shown in Figure
1-3. It consists of:
1. an electrochemical cell with working. reference.
and counter electrodes (I. R. and C).
2. a charge generator for the injection of charge
to the electrode.
3. a voltage measurement system to monitor working

electrode potential between charge injections.

4. a keyboard (RB) and a display (CRT) to allow

operator communication.

5. a graphic controller to present the results of

experiments in graphic form on the CRT.

6. a real time clock to control the timing of

experiments. and

7. a floppy disk to store data.

The instrument is interfaced to a PDP I 11/40
minicomputer to allow loading programs from its mass
storage. and to use the minicomputer for faster data
analysis and for hard copies of experimental results.

The instrument will be called the programmable
coulostatic polarixer (PCP) since it is flexible through
programming and can generate many types of coulostatic

polarisation waveforms. Several modes of operation of the

‘ a-v.‘ _ ‘ ..

 

 

 

 

 

VOLTAGE
o
CHARGE W ; R 5 MEASUREMENT
GENERATOR ‘ SYSTEM
AA~ " C /A\

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

KB ‘Lll' ‘v"
l_.|
CRT } NHCROCOMPUTER SYSTEM
GRAPHIC
REA
FLOPPY 1WM: PDP
DISK 11/40
CLOCK
Figurel-J. Block diagram of the programmable

coulostatic polarizer (PCP)

11

12

PCP will be described in Chapter 2. examples of applications
will be presented in Chapters 3 and 4. and some possible

applications will be discussed in Chapter 5.

CHAPTER 2
THE DESIGN AND THE OPERATIONAL lODES OF THE PCP

A. Description of the Charge Generator and the Voltage
leasurement System

Figure 2-1 shows a diagram of the charge generator and
the voltage measurement system. The charge generator and
the voltage measurement system are essentially the same as
those designed by Spyros Hourdakis (18) except that a few
components have been changed; a separate power supply is
used. and grounding circuits have been redesigned and
constructed in order to reduce noise. A detailed
description of the circuits can be found in Hourdakis'
thesis (18). Some modifications to these circuits will be
discussed in Chapter 6. The design principles and important
characteristics of the components and circuits will be
discussed in this chapter.

The charge generator consists of a 10-bit digital-
to-analcg coverter (DAC) and several capacitors. switches.
and operational amplifiers. The microcomputer can control
the DAC to produce a programmable voltage V. If the data
for the DAC control is stored in the computer memory. the
process of reading the data and controlling the DAC takes
about 17 us. The DAC is of bipolar construction with a

maximum output voltage of x 2.5 V. It has a quantization

13

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15

level of 4.88 mV. It is based on the AD7522 chip from
AnalOg Devices which has maximum differential non-linearity
of 1 1/2 LSB and an overall non-linearity of less than 0.05%
full scale range.

The inverter. which consists of Operational amplifier
A2. and resistors R1 and R2. converts the programmed voltage
V to the voltage -V of equal magnitude. but with opposite
polarity. Both . voltages V and -V are available
simultaneously in order to save the time of reprogramming
the DAC if the opposite polarity of voltage is needed.

The microcomputer can control the closing of switches
by which the capacitors C1 or C2 can be charged to -V or the
capacitors C3 or C4 charged to +V. A capacitor which has a
capacitance below 0.01 pH. takes less than 13 us to reach
1/2 LSB (2.44 mV) for a step change of 2.5 V or less.

The switches are SIGNETICS SD5000 FET analog switches
with on resistance of 30 O and off resistance of 10" O.
The leakage current is below 1 nA. The input capacitance is
below 2.4 pF and the output capacitance is below 1.3 pF.
Probably due to the coupling of the switch capacitance with
the power sources (1 15V). a small amount of charge (about
20 pC) is always injected to the working electrode together
with of the desired charge. This error is corrected by
adjusting the baseline value of the DAC for a specific size
of capacitor used. The adjustment can be performed

automatically with the program BLVC.lAC which can be found

16

in Appendix B. The operational amplifier A3 is a Datel Al
405-2 FET input. high-speed amplifier with high input
impedance of 101: O and a fast slew rate of 120 V/ps. The
amplifier can supply a continuous current of t 10 mA and a
peak current of t 50 mA.

The microcomputer can connect the capacitor which has
been charged to the inverting input of operational amplifier
A3 by closing the proper switch (e.g.. switch 8'2 for the
capacitor C1). The connection of the capacitor to the
amplifier makes the voltages different at the two inputs of
the amplifier. 'hen the operational amplifier A3 detects a
voltage difference between its two inputs. it amplifies this
difference by a very large gain which is usually between 10‘
and 10‘. The voltage of the capacitor (one of- C1-C4)
usually exceeds 1 100 mV and the result of this
amplification exceeds the power supply voltage (1 15V). In
this situation. the output voltage limits at 1 or 2 V less
than the power supply voltages. The change of output
voltage of A3 creates a potential drop across the solution
and charge flows from the output of A3 through the counter
electrode. through the solution. through the working
electrode to the capacitor in order to reduce the voltage
difference between the inputs of the amplifier A3. The
current continues until the voltages at both inputs of A3
are equal. A consequence of this process is that the

capacitor (one of Cl-C4) is discharged and the charge is

17.

transfered to the working electrode. If the working
electrode is an ideal pclarixable electrode (an electrode
which does not leak any charge across the electrode solution
interface). the charge is accumulated on the electrode. If
it is not. the accumulated charge is equal to the charge
injected minus the charge consummed by the Faradaic process.
A capacitor C5 is placed in the feedback loop of amplifier
A3 to prevent oscillation. The capacitor does not slow down
the response of the circuit significantly if its value is
small (such as below 1000 pF). The recommended value for
this capacitor is between 100 and 1000 pF which is usually
much less than the value of the electrode double layer
capacitance. When a charge pulse is injected. a very small
portion (between 0.01 and 0.1 $) of the charge goes to the
capacitor C5 if the electrode capacitance has a value of 1
uF. This error is so small that it can be neglected. Using
this circuit. a charge can usually be injected to the
working electrode within 50 us for solutions with an
electrolyte concentration above 0.01 l.

The voltage measurement system consists of a voltage
follower A4. an amplifier A5 with a gain of 2. a sample and
hold circuit. and a 12-bit analog-to-digital converter
(ADC). The ADC is a DATEL ADC-HleBC 12-bit successive
approximation analog-to-digital converter with a conversion
time of 8 us and an input range of 1 5 V. The voltage of

the reference electrode is amplified with a gain of 2 before

18

it is fed in the input of the ADC. The resolution of the
ADC is 2.44 mV which corresponds to 1.22 mV resolution in
the electrode potential measurement. The purpose of using
the amplifier with a gain of 2 and the low pass active
filter is to reduce noise. The operator can regard the
quantitixation level of the voltage measurement system and
of the electrode potential as 1.22 mV.

The microcomputer can command the ADC to convert the
electrode potential to digital form. The microcomputer can
then store the data. or compare the measured potential to
the desired value and use this information to control the
potential or make other types of decisions.

Several capacitors and associated switches can be used
in the charge generator to enable the injection of both
positive and negative polarities and different sizes of
charge.

The charge generator and the voltage measurement system
perform only two simple operations on the electrochemical
cell: inject charge pulses to the working electrode and
measure the potential of the working electrode. The use of
a microcomputer as the control element of the operation of
the PCP gives greater flexibility than it is found in
conventional instruments. The operator has the ability. by
programming. to determine how the operations of the charge

generator and the voltage measurement system are to be used

in order to perform an experiment. and he or she can program

19

the instrument to produce and apply any complex potential or
current waveforms to the electrode. The flexibility of the
PCP allows the operator to perform whichever electrochemical
technique provides the best response for the investigated
chemical system and also to perform some experiments which
are difficult to perform with other instruments.

In addition to the flexibility of implementing a
variety of polarisation modes. the PCP maintains the
characteristic advantages of coulostatic method. i.e.. IR
drop errors can be eliminated so that higher solution
resistance causes fewer problems and double layer
capacitance information is available to aid in separating
double layer charging and Faradaic current. Several

operational modes are discussed in this chapter.

B. Controlled Charge lode

The operator can program the DAC to obtain a voltage V.
and select a switch to charge a capacitor C. in order to
produce a charge of value C-V coulombs which can then be
transferred to the double layer of the working electrode.
By choosing the capacitor value and the DAC voltage. the
operator has the flexibility of generating a charge that can
vary in size over several orders of magnitude. This allows
the effect of the charge injection on the electrode
potential to be varied from a fraction of a millivolt to

several volts. The electrode potential is monitored both

20

before and after the charge injection.
The application of this operational mode to electrode

capacitance measurement will be discussed in Chapter 3.

C. Controlled Current lode

The equivalent of controlled current can be obtained
either by controlling the quantity of charge per pulse to be
injected to the working electrode and keeping charge
injection rate constant. or by keeping the quantity of
charge constant and controlling the charge injection rate.
The current applied is equal to the charge per pulse times
the frequency of pulse injection.

The application of this operational mode to constant

current chronopotentiometry will be discussed in chapter 4.

D. Controlled Potential lode

Controlled potential experiments can be achieved by
comparing the measured potential to the desired potential at
any specific time. If there is a difference. an appropriate
amount of charge (e.g.. the amount to make 1 mV potential
perturbation) can be injected to the electrode in order to
reduce the difference. This process can be repeated to
within the resolution of the charge injection or potential
measurement. whichever is larger. The desired potential can
then pregrammed to vary with time. Virtually all kinds of

controlled potential experiments (e.g.. cyclic voltammetry.

21

pulse polarography. chronocoulometry. rotating disk
voltammetry. etc.) can be performed in this way by using the

PCP.

E. Open Circuit lode

If no charge is injected on the electrode. the cell is
in an open circuit condition. The measured potential is
then obtained when there is no current passing through the
solution. In this mode. the PCP can be used for the
potentiometric measurements of a PH electrode or other ion

selective electrodes.

F. Combinations of lodes

The PCP can switch from one mode of operation to
another by changing from the program for one mode to that of
the other. There are several advantages associated with
this: First. the switching of the PCP from one mode of
operation to another is fast. In most cases. the switching
time is between 10 us and 1 ms. Second. the switching is
done by software and involves no undesired charge added to
the cell. Third. due to this flexibility. the PCP at times
can perform some types of multi-mode' experiments which
cannot be carried out with other instruments. Fourth. the
need for several differential instruments to perform various

kinds of experiments can be avoided.

CHAPTER 3

EXAlPLE OF CONTROLLED CHARGE EXPERIlENT:

ELECTRODE CAPACITANCE lEASURElENTS

A. Introduction

A capacitance measurement technique developed in this
thesis work is discussed in this chapter. The technique is
based on the charge injection method. Because charge pulses
can be applied to the electrode automatically and very
rapidly. capacitance measurements can be made very quickly.
The potential is measured when there is no current passing
through the solution so solution resistance causes fewer
problems than with continuous current methods. Electrode
capacitances can thus be obtained in solutions of quite
dilute electrolyte. For example. capacitance measurements
were obtained from a hanging mercury drop electrode (HlDE)
in various concentrations of RC1 solution down to 10" N.
For concentrations of RC1 above 0.01 l. 37 equally spaced
data points with 2 S relative standard deviation over a 1.45
V potential range were obtained within 30 seconds. The
capacitances of a HlDE in dilute potassium chloride
solutions were obtained within 150 seconds for a 10" l

solution and within 30 minutes for a 10' l solution.

22

 

'- «any. _.._..-

23

B. Background on Double Layer Capacitance leasurements
1. Qualitative Description of Electrical Double Layer

'Electrical double layer' is a term used to describe
the array of charged particles and oriented dipoles which
exist at any material interface. The modern qualitative
picture of the electrical double layer at a
metal-electrolyte solution interface is based on the model
proposed by D. C. Grahame (20-22). The model is a
modification of previous ones proposed by Gouy. Chapman. and
Stern (23-26). The interface consists of several regions:
(a) the metallic region. and. on the solution side. (b) an
inner layer region of a few A next to the metallic surface.
and (c) an outer. or diffuse layer region which extends into
the bulk solution a distance of several A to a few hundred
l.

The metallic surface may bear positive or negative
electric charge resulting from an excess or deficiency of
electrons. The electric charge may be imposed on the metal
by an external source of electric charge or current. or it
may be generated by a Faradaic reaction at the interface.
The inner layer. which is on the solution side of the
interface next to the metallic surface. contains solvent
molecules and sometimes other neutral molecules. Ihen the
electrode potential is near or more positive than the
potential of zero charge. in most electrolyte solutions the

inner layer also contains a fractional monolayer of ions

24

(usually anions) which are said to be specifically adsorbed.
The plane which is formed by the electric centers of these
adsorbed ions is called the inner Helmholtz plane (IHP).

'hen the interaction between an ion and the metal is
not strong enough to desolvate the ion. the ion can not come
as close to the metal as can those ions which are
specifically adsorbed. The plane passing through the
electrical centers of these solvated ions is called the
outer Helmholtz plane (OHP). The principal interaction
between the metal and the solvated ions is the ordinary
long-range cculombic force and this is the basis of the
Gouy-Chapman theory (23-25). The interaction of these ions
with the metal is essentially independent of their chemical
properties but dependent on their ionic charges andr radius.
The solvated ions near the electrode are said to be
nonspecifically adsorbed. Due to the thermal motions of
these ions. not all of them are located at the OHP. instead.
they are contained in a three dimensional region. the
diffuse layer. which extends from OHP into the bulk of the
solution. The diffuse layer is very thin. For example.
99.99 i of excess charges in the diffuse layer for a
uni-valent electrolyte at a concentration of 10':L l is
within 8.9°10-' cm. and at 10" l is within 8.9-10“ cm from
the surface of the metallic electrode.

The metallic surface may bear a net electric charge and

the solution side may have an excess of charged particles or

25

a net orientation of dipoles. The electrode interface looks
like a capacitor and has the property of capacitance under
equilibrium conditions. The differential capacitance of an
electrode at constant chemical composition is defined as
(3q‘l3E)n. where q. is the charge density on the metallic
electrode. and E is the electrode potential. This term is
very similar to (Q/V). the capacitance for an ideal
capacitor.
2. Usefulness of Double Layer Studies

The measured fundamental parameters of electrode
kinetics may be strongly dependent on the structure of the
‘double layer. The rate constant k for a given electrode
reaction might be a function of supporting electrolyte or
its concentration. Then there is no apparent reaction
involving the electroactive species of interest (e.g.
complexation or ion-pairina). a non-linear plot of the
logarithm of the rate constant k versus potential can be
observed.

lost of these effects can be understood and interpreted
in terms of the effect of electrolyte on the potential
profile in the double layer region. In addition to the
means of controlling electrode potential. double layer
studies will provide chemists with a means to affect an
electrochemical reaction through the variation in
electrolyte composition.

In trace analysis. adsorption of electroactive species

26

sought may become a predominant factor for some
electroanalytical techniques. A For example. in
chronOpotentiometry. adsorption of an electroactive

constituent can give rise to an increased transition time.
Failure to take account of adsorption can lead to serious
errors. If the adsorption is properly interpreted. the
sensitivity of an electroanalytical technique may be
enhanced. A

The double layer charging current. which is a
non-Faradaic current required by the electrode during a
change of electrode potential or area. is involved in all
controlled potential techniques. The measurement of the
double layer capacitance can help one to be aware of the
relative magnitudes of the charging and Faradaic currents in
an experiment. loreover. a knowledge of the double layer
capacitance may be used for the compensation of the double
layer charging as will be demonstrated in chapter 4.
3. lethods for the leasurement of Double Layer

Capacitance

If the phenomena predicted by a theory do not agree
with the experimental results. the theory is considered
deficient. Double layer capacitance measurements are
generally used in electrochemistry to test how good a theory
on double layer structure is. A number of methods for the
measurement of double layer capacitance have been developed

and the more important ones will be discussed.

27

One type of capacitance measurement is performed by
taking the second derivative of a curve of surface tension
versus electrode potential. Let us consider the situation
of a liquid mercury electrode in an electrolyte solution.
The interfacial tension 1 of a mercury-solution interface
varies with the electrode potential E. If 1 is plotted
vs. E. the result is known as an electrocapillary curve.
All electrocapillary curves may be described by the
electrocapillary equation developed by Grahame and 'hitney
(27). which is a differential equation relating the
interfacial tension to the temperature. pressure. electrode
potential. and chemical potentials of the components. The
starting point of the derivation of the electrocapillary
equation is the Gibbs adsorption equation. Some important
relationships have been derived from the electrocapillary

equation. e.g.:

qIll - (av/OE)“ (3-1)
cdl I (327/3E2)ll and (3-2)
1 - 1,,c - jj§,°cd1-dsz (3-3)

where q“ is the charge density on the mercury electrode. Cdl
is the double layer capacitance. and psc represents the

potential of zero charge on the electrode.

28

The capacitance of an electrode can be obtained by
measuring the surface tension 7 of the electrode. and then
taking the second derivative of the electrocapillary curve.
(321/3E2)". The limitation of this method is that it can
usually be applied to liquid electrodes only.

Capacitance measurements are commonly performed with an
AC bridge. Bridge measurements provide a direct way to
compare unknown impedances with known standard impedances.
The impedance may be supplied by a pure resistor. capacitor.
or inductor. or may be supplied by a circuit represented by
some series or parallel combination of resistors.
capacitors. and inductors. The major advantage of this
method is that it allows one to very accurately obtain
electrode capacitance and kinetic parameters at high
concentrations of electrolyte solution (e.g. above 10" l).
This method has several disadvantages: First. it is tedious
to adjust the values of resistors and capacitors in order to
match the unknown impedance of 'the cell. Second. it
requires significant skill to perform the experiment.
Third. it can require more than 30 minutes to take data for
the entire potential range (usually between 1 V and 2 V) and
the electrode (especially for a solid one) may be more
subject to the adsorption of organic impurities if it is
left in the solution so long. Fourth. it cannot generally
be applied to the determination of double layer capacitance

with media of low conductivity or dilute electrolyte

29

' l for strong electrolyte).

solutions (e.g. below 10'

lost commercial instruments presently available use a
lock-in amplifier technique to measure electrode
capacitance. The capacitance measurement can usually be
completed within a few minutes. But again. these
instruments are not well suited for very dilute electrolyte

solutions.

L. Ramaley and co-worker (28) developed two methods of

capacitance measurement. One method involved the
application of a rectangular current waveform to the
electrode. The capacitance cdl was obtained by measuring

the slope of the electrode potential vs. time curve:

where i is the current density applied to the electrode. and
dE/dt is the slope of the potential time curve. Because a
constant current is applied to the electrode and the
solution resistance does not change during the current
pulse. the IR drop is constant and it does not affect the
value of dE/dt. This can be very important in high
resistant solutions. The other method involved the use of
small sinusoidally varying potential of constant amplitude.
With an oscilloscope as a fast detection system. they
measured electrode capacitance with a sweep speed of a volt

per second or more for solutions with high conductivity.

30

The speed and ease of measurement is importment for the
measurement of capacitance of silver in perchlorate solution
(29).

P. Delahay and co-workers (30) used a coulostatic
charging method to change the electrode potential slightly
(5-15 mV) and measure the potential change due to a known
charge. The charge 0 on a small capacitor (500 pF) which
had been charged to at least 1 V was transfered to the
working electrode by a differential electrometer-amplifier.
leasurements were read out on an oscilloscope and compared
with those obtained with a dummy cell. Because of the
temporary overload of the amplifier. they took readings 50
to 100 ms after the pulse and extrapolated the results back
to time zero when necessary. The capacitance cdl of the
electrode is Q/V3. where Q is the charge transfered to the
electrode and Va is the potential change resulting from the
charge addition. The major advantage of this method is that
double layer capacitance can be measured in media of low

conductivity.

C. Description and Test of the Technique:

The technique for capacitance measurement developed in
this research work is based on the ideas of P. Delahay and
his co-workers (30). except that we have used a
microcomputer for automatic charge injection and data

collection. These allow the capacitance to be measured very

31

quickly. Because a fast response amplifier (Al 405-2) was
used. the overloading of the amplifier is not the limiting
factor in the delay time required for potential measurement.
The potential perturbation can be measured at a shorter time
after the charge pulse using this technique than the method
developed by P. Delahay and co-workers. For example. with a
concentration of RC1 of 10" l. the delay time can be as
short as 6.4 ms. (The shortness of delay time is limited by
the resistance of the electrolyte. not by the amplifier
overloading.)' lultiple measurements also enhance the
precision of the results.

Figures 3-1 to 3-3 show a flow chart of the program
which was used for the capacitance measurement. The
operator sets up the parameters such as initial potential
Einit' final potential Efinal' potential perturbation AE for
capacitance measurement. potential interval Binc between two
adjacent data points. desired minimum number of repetitive
measurements Nd for each potential. delay time td between
charge injection and voltage measurement. etc.. before
starting the data acquisition.

After the operator starts the program. the PCP measures
the electrode potential and compares it to the desired
initial value Einit' If there is any difference in the
potential values. the PCP injects charge pulses of proper
.polarity in order to bring the electrode potential to the

initial value. After the initial potential is reached. the

 

 

 

SET up )
PARAMETERS {START

Ed'Einit
AEnog-O

 

 

Einit: Initial potential

 

E130“: final potential

AEflog: flag for calculation

 

 

of charge size in

  

order to start at

 
 

APPROACH

E proper potential
init

 

    

 

E: Electrode potential

Ed‘ desired potential for

 

taking data
AE: potential perturbation
ASH”: potential

increment to next

  

 

 

TELL‘OPERATOR '
IT'S READY data point
AEd: desired potential
perturbation

 

max- AEd+1.22mV

 

 

desired time

 

delay between

 

charge injection

 

and voflage

measurement
N(E): number of data

RESULTS
ON CRT

 
   
  

 

PAGES)
points at potential
E
Na: desired minimum

number of data

   

 

 

, points
F
91:32.35 0: charge to be injected
AND EXP. Gina: charge increment
RESULTS
Figure 3-1. The first part of the flow chart of the

program for the capacitance measurement

32

FROM THE
Q FIRST PART

SET UP REAL
TIME CLOCK

L

REACH Ed
PROM

' SETL UP
THE THIRD CHARG

. BE lNJ CTED
PART

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

INJECT
CHARGE
”°
YES
MEASURE E.
CALC AE 1‘
CALC
PROPER
AMOUNT OF
CHARGE o

 

 

 

1‘

 

THIRD PART

Figure 3-2. The second part of the flow chart of the
program for the capacitance measurement

33

FRON THE
2nd PART

Lance-0

_SP_,
REACH E

 

 

 

 

 

 

)lSET UP 0
1

 

    
    

   
 

 

ACCUHULATE 0.
N(E)-N(E)+l

Ed"Ed'*Einc
INJECT o ,
1

 

 

 

 

 

 

 

 

 

 

 

 

TO THE 2nd
PART

MEASURE E.
CALC AE

 

TO THE FIRST

 

Figure 3-3.

PART

 

The third part of the flow chart of the
program for the capacitance measurement

3b.

' "‘“W— W...,_. _._—- ‘—

35

PCP keeps the electrode potential at this value by adding
charge as needed until the operator commands the PCP to
execute data acquisition. An amount of charge previously
specified by the operator is injected to the electrode and
the potential E is measured after some delay time td. The
potential perturbation AE due to the charge injection is
calculated and compared to the desired value AEd. The
computer automatically calculates the amount of charge 0 to
be injected on the electrode in order to make AE - AEd -
3.66 mV. For a typical measurement. AEd - 9.77 mV which
corresponds to 8 times the least significant bit (LSB). The
quantization level of the voltage measurement system is 1.22
mV. A potential change of 9.77 mV is selected because it is
not large and can be used for differential capacitance
measurements. The value AEd - 3.66 mV is chosen for two
reasons: The first is because the quantity of charge 0 to
be injected will be incremented and the number of charge
injections which will make AE within AEd t 1.22 mV will be
counted. The value AEd - 3.66 mV is not too far from the
value AEd - 1.22 mV and starting the charge incrementation
from the amount of charge which will achieve this potential
perturbation can save experimental time. The second reason
is that the value AEd - 3.66 mV differs from the value AEd -
1.22 mV by 2.44 mV. which corresponds to 2 L83. This
difference can provide some noise rejection.

The size of charge Q is incremented automatically after

36

AB = AEd - 3.66 mV is reached. the potentials are measured
before and after charge injection. and the potential
perturbation is calculated for each injected charge pulse.
If AB is within AEd t 1.22 mV. the amount of injected charge
is accumulated and the counter is incremented by 1. As soon
as AB 2 AEd + 3.66 mV. the computer will read N(E). the
content of the counter for potential E. The computer
compares N(E) to Nd. the desired minimum number of data
points previously specified by the operator. If N(E) z Nd'
the control will go to the next potential and perform charge
injections and data collection until the final potential is
reached. If N(E) < Nd' more data points will be taken
before going to the next potential. The results are plotted
on a CRT display immediately after the experiment is
completed to allow the operator to observe the experimental
results.

According to the manufacturer. the calibration of the
analog-to-digital converter (ADC) is accurate to 1 1/2 least
significant bit (LSB) which corresponds to t 0.61 mV of
electrode potential in this instrument design. Although it
is possible to reduce this uncertainty by using an ADC with
higher resolution. the cost will be higher. The voltage
differences AV1 and AV: shown on Figure 3-4 may not be equal
even if they give the same results in the conversion to the
digital domain. The consequence of this is that different

amounts of charge 0‘ and Ob are required to make the voltage

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

average value of

/ individual level Of
ADC

 

 

 

 

7F
7" 7r
1?
1.22 mv
AL Av1
9.77 mV AV2
AL
All.
AL
ideal ADC real
Figure 3-4. Calibration error in anolog-to-digital

converter (ADC)

37

38

perturbation AV1 and AV2 respectively although the ADC
reports them as the same. This can introduce error in the
calculation of capacitance if the results are interpreted as
Q‘I(AVid°‘1°A) and Qb/(Avideal'A)' where A is the area of
the electrode and AVid°.1 is the ideal voltage perturbation
corresponding to the obtained digital result from ADC.
Figure 3-5 shows the capacitance curve obtained for a

0.995 pF capacitor using the equation:
C ' Q1/(N1.Av2d0I1) (3‘5):

where C is the calculated capacitance. Q. is the accumulated
charge. The number of charge injections is N:. and
Avideal'9'77 mV. A dummy cell shown in Figure 3-6 with the
capacitor Cd. in the feedback loop was used and more than
1000 data points were taken for each voltage. The capacitor
Cd. is mylar and the capacitance is constant throughout the
voltage range used in all of the following experiments.

A method to reduce this calibration error was needed in
order to improve the results. Equation 3-6 shows the double
layer capacitance Cd1(E) at potential E in terms of the
accumulated charge injected to the electrode 0.1. the number

of charge injections N the potential perturbation AE. and

'9
the electrode area A. A dummy cell with capacitance cdm is
used to perform a similar experiment. Equation 3-7 relates

the accumulated charge Qdm' the number of charge injections

1.60 --

1.4o -—

1.20 --

11F

0.80 --

0.60 --

0.40 -—

DUMMY CELL.

+
. O O -;H+++H++H+*++T++HW+W++W*

Cd

m 0.995 UF

 

 

Figure 3-5.

Effect of Calibration error in
analog-to-digital converter on

the capacitance measurement

39

To vonage

measurement
system

c -o.995pr
d'" “(.52

—H w»—

Programmed
——/ ——.0_—\
voltage
‘—-‘+
0.01pF

 

 

 

 

 

 

 

V

Figure 3-6. Dummy cell configuration for testing

the capacitance measurement technique

40

41

N1. and the voltage perturbation AV. which is equal to AE at
the same voltage or potential. If Equation 3-6 is devided

by Equation 3-7. Equation 3-8 is obtained.
Q01/(NB.AE.A) - cdl (3-6)

cd./(N.-AV) - cd <3-7)

I
0.1.N1.cd.l(N3.A.Qd-) ' cdl (3-8)

By doing this. the error or uncertainty in AE or AV. in the
calibration of ADC is cancelled out. If Cd. is known. cdl
can be calculated accurately without being affected by the
calibration error.

Two identical experiments were performed with the same
dummy capacitor. The capacitance of the capacitor Cd.2(V)
at voltage V is calculated by assuming that the capacitance
cdml of the capacitor is constant (0.995 pH) and by using

Equation 3-9 which is similar to Equation 3-8.
Cd.2(V) - 0,-N1-Cd31/(Nath) (3-9).

where Q: and Q, are accumulated charges for individual
experiments. N1 and N3 are the number of charge injections
for individual experiments. and Cdml - 0.995 uF.

Figure 3-7 shows the results obtained by this method.

11F

.80

.60 -L

.00 --

.60 -—

.4o --

.20 --

.80 --

.4o -—

 

Figure 3-7.

0.995 uF

DUMMY CELL. cdm

.00 ‘WMWHWWW

Results at
ADC

removing calibration error of

42

43

In each experiment. the desired minimum number of charge
injections. Nd' is 1000. The method clearly removes the
effect of calibration error in ADC.

Quantization error is encountered in all
analog-to-digital conversions. A common method to reduce
the quantization error is to add to the signal white random
noise whose amplitude is comparable to the quantization
level of the ADC and then average repetitive measurements.
The standard deviation of the average from a number of
measurements can be less than the quantization level of the
ADC.

Although AAE. the difference in potential perturbations
of two adjacent charge injections. is usually smaller than
the quantization level of the voltage measurement syetem (in
this instrument design. the quantization level is 1.22 mV).
the quantization error is less for two reasons: First. the
amount of charge injected to the electrode is incremented
and averaged through the potential difference window AEd
1 1.22 mV several times until the number of data for each
potential is greater than Nd‘ Second. the potential before
charge injection to make the perturbation AE has a small
random variation.

According to Relly and Horlick (31). the standard
deviation of quantization noise is v1/12o'5 . where v1 is
the magnitude of the quantization level. In this case. v1 =

1.22 mV. Since voltage differences are taken. the standard

44

deviation should be 1.22-20-5/120-5 mV. If N is the number
of data points to be averaged. the estimated standard

deviation is
1.22-20-5ll(N-1)°°5-1z°°5) mV (3-10).

For a typical application where AE I 9.77 mV and N I 20. the

estimated I relative standard deviation (i RSD) is
(1.22-(2)'5/(lzo-1)'5-9.77-(12)'5)-1oos - 1.175 (3-11).
For AE I 9.77 mV and N I 100. it is
(1.22-(2)'5/((1oo-1)'5-9.77-(12)°5)-1oos . .512s (3-12).
For AE I 9.77 mV and N I 1000. it is
(1.22-(2)'5/((1ooo-1)'5-9.77-(12)-5)-1oos = .161s <3-13).
By choosing the value of N. the desired precision of
the measurement can be obtained. Figures 3-8 and 3-9.
illustrate the precision of this technique. The
experimental results were calculated using Equation 3-9.
Figure 3-8 shows the results obtained with Ndl I 100 and "dz

I 1000. where Ndl is the desired minimum number of charge

injections for the first scan and Nd2 is the desired minimum

DUMMY CELL

 

 

1.06 --
.4.—
1 04 --
O ——
E 1.02 “P
a: __ +
23' "i- + +++ ++ ++ +
zl.OO--+ +++ + + +++++++
g "+ + + +++ + +
2 -I— + + + +
% .1-
o O 98 --
0.96 --
-L
.. . I . 1 . l . l . l
0.94 T l I I l l l l I l
0.0 -0.3 -O 6 -O.9 —1 2 -1
VOLTS
Figure 3-8. Capacitance ratio obtained with

Nd1-1oo. Nd2=IOOO. and td=O.8 ms

45

DUMMY CELL

++
. + ++ ++ ++ ++ + +
1-00 ++++++ ++++++ + ++ + ++ + + +

CAPACWANCE RAUO

 

Figure 3-9. Capacitance ratio obtained with
"6131000' NdZCTOOO. and td30.3 ms

1+6

47

number of charge injections for the second scan. The
average relative standard deviation was found to be 0.54 i.
Figure 3-9 shows the results obtained with Ndl I 1000 and
"d2 I 1000. The average relative standard deviation was
found to be 0.19 i. The capacitance measurement results
obtained in the next section are all performed using "dz I

1000 for the dummy cell measurements.

D. Double Layer Capacitance leasurements for lercury
Electrode in RC1 Solutions

Ihen the capacitance measurement technique was tested
with a mercury electrode in RC1 solutions. a hanging mercury
drop electrode (HlDE) was used as a working electrode and
the capillary of the HlDE was siliconized on a daily basis
to prevent capillary action of the test solution. A
micrometer drive HlDE was used. The weight of mercury with
the turning of 200 divisions of the micrometer drive was
measured (0.2112 grams). The weight (8.45 mg) of each
mercury drop with the turning of 8 divisions was calculated
by dividing the weight (0.2112 g) by 25 (assuming that the
micrometer drive is uniform). The area (0.0352 cm’) of the
mercury drop was calculated by assuming that it has a
spherical shape. The reproducibility of the area was
determined by measuring the amount of charge required to
make a potential perturbation of 400 mV (for details. see

the integral capacitive charge measurement in Chapter 4) in

48

0.1 l RC1 solution for 20 different mercury drops under the
same experimental condition. The relative standard
deviation of the area was found to be 1.1%.

A saturated calomel electrode (SCE) was used as the
reference electrode. A 1.0 cm: platinum gauze was used as a
counter electrode. Potassium chloride solutions were used
because RC1 is the most commonly used supporting electrolyte
for analytical work. By using RC1 solutions. the leakage of
a trace amount of RC1 from the SCE reference electrode
causes fewer problems. Sodium fluoride solutions are
generally used to test Gouy-Chapman double layer theory
(23-25) because it is believed that sodium fluoride does not
adsorb on the mercury surface. However. for experimental
simplicity. RC1 solutions were used to test the performance
of the PCP for capacitance measurements. Reagent grade
potassium chloride had been recrystallized before it was
used. Solutions were prepared with de-ionized water which
had been passed through an ion-exchange column manufactured
by lillipore. The solution in the cell was de-aerated with
nitrogen gas which had been passed through a vanadous
chloride solution to remove trace oxygen. All experiments
were performed at room temperature between 20.5 and 21.5 'C
except when noted otherwise.

Figure 3-10 shows the capacitance curves obtained with
1.0 l RC1 solution. These curves were obtained with Ndl I

100. Ndz - 1000. and td - 0.4. 0.8. 1.6. 3.2 ms. The

1.0 M KCI

 

 

50.0 --
40.0 -- .“g '
-- l
N 30.0 "" ,
E
0 ‘_ 1
\ .
Li. I
320.0 -- -
10.0 --
l | l I I l J l l J
0.0 l I I I I I l I I I
0.0 -O.3 -O.6 —0.9 -1.2 -1.5
POTENTIAL vs. SCE (VOLTS)
Figure 3—10. Capacitance curves at HMDE in 1.0 M KCI

solution obtained with Nd1IIOO. NdzIIOOO.
and ‘d - Oe4. 0.8. 1e6. 3oz "‘8 With the
higher capacitances corresponding to

the longer times

49

50

capacitance values increased with increasing values of td
(the delay time between charge injection ‘and voltage
measurement) Ndl is the minimum number of charge injections
for the electrochemical cell. and "d2 is the minimum number
of charge injections for the dummy cell.

Figure 3-11 shows the capacitance curves obtained with
0.1 l RC1 solution. These curves were obtained with Ndl I
100. N42 I 1000. and td I 0.2. 0.4. 0.8. 1.6. 3.2. 6.4 ms.

Figure 3-12 shows the capacitance curves obtained with
0.01 l RC1 solution. These curves were obtained with Ndl I
100. Nd2 I 1000. and td I 0.2. 0.4. 0.8. 1.6. 3.2. 6.4. 12.8
us.

The capacitance approaches a fairly constant value
after some delay time.. This is because it takes some time
for the charge to be injected to the electrode and the
charge needs to be distributed evenly on the electrode
before an accurate reading can be taken. For lower
concentrations of RC1 solution. it takes longer to get a
constant capacitance value (equal charge distribution)
because the solution is less conductive.

Figure 3-13 shows the capacitance curves obtained with
10" l RC1 solution. These curves are obtained with Ndl I
100. "d2 I 1000. and td I 0.4. 0.8. 1.6. 3.2. 6.4. 12.8.
25.6 ms.

In order to speed up the cell response. the first

attempt was to decrease the solution resistance between the

0.1 M KCI

 

 

50.0 --
40.0 __-°i.6'.?::1
° .° .1
__ 'O‘.4 .
l
N 30.0 "L— .0..2 . I
E .
o __ l
\ I
u. .1,
320.0 -— .;',I .
.Of:"'tlsltl'!'i;f
10.0 --
t l . l t l l l t l
0.0 I l r I l I I f I I
0.0 —0.3 -O.6 -0.9 -1.2 -1.5

POTENTIAL vs. SCE (VOLTs)

Figure 3-11. Capacitance curves at HMDE in 0.1 M KCI
solution obtained with Nd1-1OO. NdzIIOOO.
and id - 0.2. 0.4. 0.3. 1.6. 3.2. 6.4 ms
with the higher capacitances corresponding

to the longer times

51

 

0.01 M KCI

 

50.0 --
40.0 —-—:.12;5.
-- .1°.'s' -.
.013"
N 30.0 --
E . 0.4
0 III)- e
\ O..2 :
“- f
120.0 --
1 £ 2 :'-.. .
.- u“...:.'-:%:522:.:s.:.=
10.0 --
. I . I . I A I . I
0.0 I I I I I I I I j I
0.0, -—0.3 -0.6 -0.9 -1.2 -1.5

Figure 3-12.

POTENTIAL vs. SCE (VOLTS)

Capacitance curves at HMDE in 0.01 M KCI
solution obtained with N‘HIIOO. Nd2I1000.
and td I 0.2. 0.4. 0.8. 1.6. 3.2. 6.4.
12.8 ms with the,higher capacitances

corresponding to the longer times

52

0.001 M KCI

50.0 --
40.0 ‘-

30.o +0,

uF/ cm2

0 o 0 O
.........
....................

10.0 -F-

O P 0 e
eeeeeeeeeeeeeee

 

 

O.o -o.3 -0.5 -0.9 -1.2 —1.5
POTENTIAL vs. SCE (VOLTS)

“9"" 3‘13- Capacitance curves at HMDE in 10"3 M KCI
solution obtained with Nd1-100. NdzIIOOO.

and id - 0.4. 0.8. 1.6. 3.2. 6.4. 12.8.
25.6.ms with the higher capacitances

corresponding to the longer times

53

 

54

working electrode end the counter electrode by putting the
counter electrode es close to the HIDE working electrode es
possible. The shortest distence between the counter
electrode end the HIDE wes epprorinetely 0.15 on end the
cepecitence curves for [C1 solutions nentioned previously in
this section were ell obteined by this cell geonetry.
However. this cell geonetry wee ectuelly found to slow down
the cell response beceuse of the leek of unifornity of the
current density.

In order to obtein e nore uniforn current density. e
cell with the counter electrode ebout 1.0 on ewey from the
HIDE end with the SCE reference electrode on the other side
of the HIDE wes used for the following erperinents of
cepecitence neesnrenent. A selt bridge filled with the sene
concentretion of test solution wes pleced between the SCE
end the test solution in order to reduce the leekege of [Cl
fro: the SC! to the test solution. This selt bridge wes
used for ell [Cl concentretions below 10" I.

Figure 3-14 shows the cepecitence curves obteined with
10-. I (Cl solution end with the improved cell geonetry.
These curves were obteined with Ndl - 100. Ndz - 1000, end
td - 0.2. 0.3. 0.4. 0.8. 1.6, 3.2 Is. The cepecitence curve
obteined_with td - 6.4 ns elnost coincides with thet
obteined with td - 3.2 us. For clerity. it hes been onitted
fro. the figure. If we conpere these results to those shown

on Figure 3-13, cleerly. we find thet the new cell geonetry

0.001 M KCI

 

 

50.0 'h"
40.0 ‘73.?.
.-_;.:..
0.6“.
r .
NE30'0 '0‘; ..
o -h
\
u.
120.0 “'-
-. 013‘ .s""355512"121::--
.* :3 ..
10.0 -— .' '''''''' ..... '°
.1!
'1” °
0.2
"H.”“l ....... l ....... I°°'°.""I"".'°J
o o I l l I I. I I I I l
0.0 -0.3 -O.6 -0.9 —1.2 -1.5
POTENTIAL vs. SCE (VOLTS)
“9“" 3-1% Capacitance curves of 10"3 M KCI solution

obtained with improved cell geometry
These curves are obtained with Nd1-1OO.
"dz-1000. and td - 0.2. 0.3. 0.4. 0.3.
1.6. 3.2 ms with higher capacitances

corresponding to the longer times

55

56

improves the cell response significently.

Figure 3-15 shows the cepecitence curves obteined with
10“ l [Cl solution. These curves were obteined with Ndl -
20. Nd: - 1000. end td - 0.8. 1.6. 3.2. 6.4. 12.8. 25.6 ms.
The number 20 insteed of 100 wes used for Ndl to reduce
erperimentel time elthough this resulted in some secrifice
in precision. A typicel time spent for dete collection et
10“ I with td - 12.8 ms is 150 sec. The estimeted
precision due to quentiretion error for Ndl I 20 is 1.17 i
[8D eccording to Equetion 3-11.

Figure 3-16 shows the cepecitence curves obteined with
10" I [Cl solution. These curves were obteined with Ndl -
20. Ndz - 1000. end td - 12.8. 25.6. 51.2. 102.4 ms.

Figure 3-17 shows the cepecitence curves for e renge of
[C1 solution concentretions. Bech curve wes obteined from
the cepecitence velues which epproeched e reletively
constent velue et the longer deley times. The deley times
td were 0.4. 1.6. 6.4 ms for 1.0. 0.1. 0.01 I [Cl solutions
respectively, end the td's were 6.4. 12.8, 102.4. ms for
10". 10". 10" u rc1 solutions with improved cell
geometry. For e 10" I [Cl solution, the cepecitence did
not quite reech e constent velue. especielly et the more
positive potentiels. This mekes the determinetion of the
cepecitence velue somewhet difficult.

The mejor sources of error will be discussed. The i

[SD of the eree of HIDE is 1.1 i. The estimeted

10—4 M KCI

 

 

50.0 --
40.0 ‘-
"2.5.5
N 30.0 -i-:"
E 3.2
o d-
\
“a - '
20.0 d_1.6'
.. . ..:! Itel. it! I; 'o
10.0 -- .
0.0 'i:
'"'.""I"".'"l"'.°"'l‘"'.""l"".'° I
O O I I I I l l I I l I
O O —0.3 -O.6 --O.9 --12 ——1 5
POTENTIAL vs. SCE (VOLTS)
7390" 3-15- - Capacitance curves 0! HMDE in 10"4 M

KCI solution obtained with Nd1-20.
”d2'1000' and td a- 0.8. 1.6. 3.2. 6.4.
12.8. 25.6 ms with the higher capacitances

corresponding to the longer times

57

10—5 M KCI

 

 

50.0 --
40.0 *-
N 30.0 "Ercaa
E .53.:
\ . - . -
L 25.0-
1 20.0 -- .
_°_..'.- .
10.0 _— : .::::°.‘..o ..... ..
1 L l . L . l . l
O O I I r I I I l I I l
0.0 -O.3 -O.6 —O.9 —1.2 -—1.
POTENTIAL vs. SCE (VOLTS)
F390" 3-15- Capacitance curves of HMDE in 10-5 M

KCl solution obtained with Nd1-20.
"dz-1000. andtd :- 12.8. 25.6. 51.2.

102.4 ms with the higher capacitances

corresponding to the longer times

58

KCI SOLUTIONS

50.0 --

40.0

30.0

uF/cm2

 

 

 

 

10.0 --
l l 1 4L 1 l l I L I
0.0 I I T I l I 1 I l 1
0.0 -O.3 -O.6 -0.9 -1.2 —-1.5
POTENTIAL vs. SCE (VOLTS)
Figure 3-17. Capacitance curves of KCI solutions with

concentrations of 1, 0.1, 0.01, 10-3,

10“, and 10"5 M

59

60

quentiretion error for Ndl I 20 is 1.11 i BSD end for Ndl I
100 is 0.51 5 [SD eccording to Bquetions 3-11 end 3-12. The
impurities in the [Cl solutions mey be en importent
consideretian when [Cl concentretion is high, e.g. ebove
10" I; however. no significent drift of cepecitence curves
were observed efter the cepecitence reeched e constent
velue. The leekege current (1.9 nA) from the enelog
switches is the mein source of error when the concentretion
of :01 is low (below 10" I) end td is 1:2... The reduction
of oxygen or reduction of other electroective species is the
second; fortunetely. it tends to cencel out the error of
current leekege. The meesurement error of the double leyer
cepecitence. Acdl' due to the current leekege cen be

estimeted by the equetion
Acdl I (1.9 nA)°td/(A-(0.00977 V)) (3-14).
where A is the electrode eree 0.0352 cm’. Teble 3-1 lists

the expected error due to the leekege of current of the

switch.

61

Teble 3-1 Estimeted error due to the switch current

leekege for the cepecitence meesurement

 

 

td (ms) Error (uF/cm’)
1.6 0.0088
3.2 0.018
6.4 0.035
12.8 0.071
25.6 0.14
51.2 0.28
102.4 0.57

This error eetimetion suggests thet the cepecitence cen
be obteined eccuretely for concentretions of [C1 solutions
ebove 10" I if the leekege of current is the only concern.
The lergeet reletive error for 10" I [Cl solution due to

the current leekege is
(0.071 uF/cm’)/(2.95 uF/cm’)-100$ - 2.4% (3-15).

where 2.95 93/013 is the minimum cepecitence of 10" I [Cl
solution within the potentiel window tested. The estimeted
h [80 for individuel potentiel due to the quentiretion error
of ADC is 0.51 I for Ndl I 100. end 1.17 i for "dz I 20.

For 10“ I [Cl solution. the error in the cepecitence

meesurement due to the switch leekege current cen be es high

62

es 0.57 uF/cm'. Some uncerteinty in the cepecitence velue
is elso observed et potentiels more positive then -0.15 V

vs. 8C8.

E. Discussion

Figure 3-18 shows the results obteined with this
technique end the results obteined by D. C. Greheme (32) for
0.1 I [C1 solution et 25 'C. These results egree with eech
other within experimentel error.

The edventeges of the technique ere: First. the
tedious menuel work in edjusting resistors end cepecitors to
metch up the cell impedence cen be evoided. Second. the
computer cen teke dete eutometicelly end humen error cen be
evoided. Third. no speciel skill is required to teke dete.
Fourth. fest dete collection ellows better results to be
obteined. It is known thet the cepecitence of en electrode
usuelly chenges with time due to the edsorption of
impurities. For e solid electrode. it is more difficult to
renew the electrode surfece then for e nercury electrode.
Fester dete collection will be subject to less error beceuse
the electrode hes less time to edsorb impurities. For
concentretions of [Cl solutions ebove 10"3 I. dete cen be
obteined within 30 seconds for N41 I 100. end within 8
seconds for Ndl I20. For 10'”4 I. s typicel experiment time
is 150 seconds for Ndl I 20. Although usesurements et e

stetionery mercury electrode ere probebly subject to some

0.1 M KCl

50.0 '1-

 

 

__+
40.0 _- +*°_+]_.+.+'+
_, il-
N 30.0 "'"" .+.
E
U -- 4:
\ +
I...
120.0 -- +~+
'4'. _
-_ .*-+..++.+. + '+
10.0 --
I l I I . l . l 1 ’J
0.0 I l I I I I I I I I
0.0 -O.3 -0.6 -0.9 —1.2 —1.
POTENTIAL vs. SCE (VOLTs)
Figure 3-18. Capacitances of mercury electrode in

0.1 M KCI solution
“II this work;

+++. Grahame's data

63

64

poisoning. in this reseerch work no significent time
dependence effects on cepecitence meesurements were
observed.

For some solid electrodes. meesurement speed mey be
more importent then eccurecy or precision of meesurement.
(Errors of severel percent of error mey be tolereble.) With
some secrifice in precision (using Ndl I 20. the expected
precision due to the quentireticn of ADC is 1.17 i RSD). e
cepecitence profile (37 dete points) cen be obteined within
8 seconds for 1 I [Cl solution.

Besed on the cherge injection principle. further
enhencement of the speed of cepecitence meesurenent cen be
echieved by using e higher resolution ADC which would
require less dete evereging.

The mejor disedventege of this technique is thet it is
not suiteble for cepecitence meesurements with electroective
species in the solution.

The cell geonetry cen probebly be improved further to
provide more uniform current density end fester response by
using e fine-tipped cepillery (33) with e cylindricel

counter electrode surrounding the cepillery.

CHAPTER 4

EXAIPLE OF CONTROLLED CURRENT EXPERIMENT:
CONSTANT CURRENT CERONOPOTENTIOIETRT 'ITE

CHARGING CURRENT COIPENSATION

A. Introduction

Ihen e constent current is epplied to en electrode.
pert of the current goes to cherge the double leyer
cepecitence. The desired constent Feredeic current is no
longer constent beceuse of the cherging current. The
chronopotentiogrem (potentiel vs. time curve) obteined is
distorted by the cherging current. As will be noted leter
in this chepter. the trensition time (the time intervel
between two sherp potentiel chenges) is longer then thet
predicted by the theory.

A method hes been developed in this thesis work to
compensete the cherging current in order to meke the
Feredeic current constent using the cherge injection method.
Cherge pulses ere injected et e constent rete. The portion
of the cherge which hes been consuned by Feredeic process
from the beginning of the experiment to eny specific
injection time hes been celculeted by subtrecting the cherge
which hes gone to cherge the double leyer cepecitor from the
totel cherge injected. If there is eny devietion between

the desired Feredeic cherge end ectuelly consumed Feredeic

65

66

cherge. e mechenism to minimize this devietion hes been
developed end used to meke the Feredeic current constent.
The mechenism of cherging current compensetion will be
discussed in section C.

A greet improvement of the correspondence between the
meesured trensition times with the trensition tines
predicted by the theory for e series of concentretions of
TlCl in 0.1 I [Cl solution is demonstreted in Section D.
In-situ compensetion of cherging current ellows the

detection limit for cedmiun to be es low es 2.5-10-7 I.

B. Historicel Beckgrcund

If we epply e controlled current to en electrochemicel
cell end plot the potentiel es e function of time, we obtein
s so celled chronopotentiogrem. As the neme of
chronopotentiometry infers. the potentiel is monitored es s
function of time.

The most commonly used chronopotentiometric technique
is to epply e constent current to en electrochemicel cell.
Let us suppose thet we heve e solution which conteins
sufficient supporting electrolyte end en electroective
species in the oxidized form Or. The species 0x cen undergo
the resction. 0x + ne- I Red. by supplying electrons to the
electrode. Ihen e constent current i is epplied to the
electrode, the species 0x is reduced et e constent rete.

The potentiel of the electrode moves repidly to some velue

67

which is e cherecteristic of the redox couple. The
potentiel veries with time es the 0x/Red concentretion retio
chenges et the electrode surfece es s result of the
conversion of 0x to Red. After the concentretion of 0x et
the electrode surfece drops to zero. the flux of 0x to the
electrode is no longer sufficient to beer the impressed
current end the electrode potentiel chenges very repidly
until the reduction of enother electroective species (when
there is such e species which is reducible et more negetive
potentiel) or the decomposition of the solvent occurs. The
time intervel between these two sherp chenges of the
potentiel is celled the trensition time, t. The trensition
time t is releted to e number of veriebles including the 0x
concentretion by the Send equetion (34):

i:"‘ - ntl'nFADgé‘C 12 (4-1)

or
where i is the epplied constent current, 3 is the number of
electrons involved in the electrochemicel reection. E is the
Feredey. A is the eree of the working electrode, Dox is the
diffusion coefficient of 0x. end Cox is the bulk
concentretion of Or.

The meesured r cen be used to determine the number of
electrons involved in the reection. or the diffusion

coefficient nox' or the concentretion cox“ The trensition

tine does not depend on the reversibility of the

68

electrochemicel reection since e constent current is forced
through the cell to ceuse e constent rete of reection. The
independence of the trensition time on reversibility is en
edventege in enelyticel epplicetions. especielly for
reections which ere not very reversible. The potentiel of
the electrode during the trensition. on the other hend.
depends on the reversibility of the reection. Therefore.
chronopotentiometry cen be used for studying the kinetics of
electrochemicel reections. For e reversible reection. the
reletionship between the electrode potentiel E end the time

t (35) is:

a - 3,,4 + Int/up)-1n((c"’-t"’)/t"’) (4-2).
where Er/4' the potentiel et the time 1/4. is:

at,4 - a; - (RT/2nF)(Dox/Dn.d) (4-3).
_where E; is the formel potentiel of the redox couple, end
”Red is the diffusion coefficient of Red.

For e totelly irreversible reection. the reletionship

between the potentiel E end the time t (36) is:

69

3 - a; + (RT/cn‘F)ln(nFACoxk'/i)
+ (RT/cn‘F)ln(1-(t/t)1/') (4-4).

where a is the trensfer coefficient. n‘ is the number of
electrons involved in the rete determining step.-ko is the
stenderd heterogeneous rete constent. The electrode
potentiel shifts negetively with increesing current.
Chronopotentiometry cen be used for the meesurement of
edsorption end surfece film formetion (37). By impressing
high current to the electrode, the electrons consumed by the

diffusion of 0x to the electrode surfece cen be minimised.

Thus.
lim1,.it I nFFA (4-5).

where F is the surfece excess, in moles/cm’. of the edsorbed
meteriel.

If e reverse current is epplied to the electrode efter
some experinentel time t1, some of the Red formed during the
forwerd period is oxidized to Or. The potentiel chenges
repidly when the concentretion of Red et the electrode
surfece drops to zero. The seperetion of the forwerd end
reverse weves on the potentiel exis cen be releted to the
reversibility of the electrochemicel reection.

If both the forwerd end reverse processes ere diffusion

70

controlled. if both currents heve the seme megnitude. end if
the reection hes n0 chemicel complicetions. the trensition
time for the reverse process. T,. is releted t0 the time t1.

the time of epplying the reverse current. by (38)
t: a t1/3 (t1st) (4-6)e

If the Red undergoes some chemicel reection to form
products PRed which do not reset in the seme menner es Red
does. the effect will be evident in the resulting
chronopotentiogrem. For exemple. if Plea does not oxidise
within the renge of potentiels in the experiment. the
trensition time s, will be shorter then ttl3. The
chronopotentiometric. potentiel/time reletionships for e
number 0f common electrochemicel reection mechenisms heve
been derived by severel chemists (38-42). Current reversel
chronopotentiometry end cyclic chronopotentiometry cen be
used for studying the kinetics of electrochemicel reections
(43.44).

Chronopotentiometric techniques heve not been widely
used for the pest 10 to 15 yeers. A mejor reeson thet they
heve not is thet the electrode potentiel chenges during e
chronopotentiometric experiment end e frection of the
impressed current is elweys consumed by the cherging of
double leyer cepecitor end not by the Feredeic process.

Theoreticelly. e chronopotentiogrem rises very repidly et

71

the beginning end et the end. However. due to the cherging
current which decreeses the rete of the Feredeic process.
the chronopotentiogrem rises slower especielly et the
beginning end et the end where the repid voltege chenge
requires more cherging current. The chronopotentiogrem
distortion mekes the determinetion of trensition time more
difficult end less eccurete when the concentretion is below
10" I. Chronopotentiometric techniques cen be useful if
the effect of double leyer cherging cen be removed.

The effect of double leyer cepecitence on the
distortion of chronopotentiogrems hes been considered by
severel chemists (45-50). All euthors heve essumed thet the
double leyer cepecitence is independent of electrode
potentiel. If one tekes 10 seconds es the trensition time.
the lower limit for precticel enelyticel epplicetions is et
ebcut 10" I concentretion level (51).

Severel grephicel methods (36.45.48.52-55) heve been
proposed to determine the trensition time from e
chronopotentiogrem. However. none of these methods yield e
constent velue for 1:"’/c which should be constent
eccording to the Send's equetion (Equetion 4-1).

Severel chemists heve tried to generete e constent
Feredeic current by edding the required cherging current.
L. Gierst (56) end P. Iechelynck (57) developed e device
with e cepecitor perellel to the electrochemicel cell in the

circuit. A cepecitor with cepecitence epproximetely equel

72

to the double leyer cepecitence of the working electrode wes
chosen for the device. The current needed for cherging the
cepecitor wes edded to, the constent current end the
resulting current wes impressed on the electrochemicel cell.
The mejor dissdventeges of this technique ere: 1. The
correction of cherging current is not exect beceuse the
double leyer cepecitence chenges es'e function of potentiel.
2. The device cen not hendle chronopotentiometric
experiments with short trensition time (below e few
seconds).

I. D. Shults end co-workers (58) developed en epperetus
with e function similer to the ones developed by L. Gierst
(56) end P. Iechelynck (57). Insteed of e cepecitor. they
used e blenk cell with the seme electrode eree end with e
solution conteining only the supporting electrolyte. The
chenge of double leyer cepecitence with potentiel cen be
teken into eccount by this method.

The epperetus developed by Gierst end Iechelynck end by
Shults tend to ceuse the problem of overshooting due to the
positive feedbeck. Then there is some smell time deley in
the eddition of cherging current. the reduction of Or will
be subject to e suddenly increesed current which ceuses e
smeller trensition time then there should be. Shults end
co-workers used their epperetus only for long trensition
time such es 6 - 40 seconds. According to I. R. Reinmuth

(59). these epperetus cen only be epplied to long trensition

73

tine beceuse of the inherent instebility.

P. Dos end E. Ven Delen (60) developed en epperetus
besed on the seme principles es the one of I. D. Shults end
co-workers. The epperetus wes protected egeinst overloeding
by the cherging current. The shortest trensition time cen
be es short es 0.1 second. 'ith the trensition time et
ebout 11 seconds. the former obteined feirly constent
ir‘I'IC velues (1.9 I RSD) for e mercury electrode in Tl+
end [N0, solution with Tl+ in the concentretion renge
between 3.25-10" I end 6.5-10" I. There ere still some
disedventeges in using this method: 1. Two cells must be
used. 2. The srees end the cepecitences of both electrodes
cen be difficult to metch, especielly for solid electrodes.
3. The shortest trensition time (0.1 second) which cen be

epplied is not very short.

C. Description end Test of the Iethod

In this section e method for obteining e constent
Feredeic current besed on e cherge injection method will be
discussed.

The cepecitive cherge hes been given this neme beceuse
it is directed to the double leyer cepecitence. The cherge
required to chenge the potentiel of en electrode from one
fixed potentiel to eny other potentiel will be designeted es
en integrel cepecitive cherge. Before the cherging current

compensetion is eccomplished, the integrel cepecitive

    

 

 

 

 

 

   
 

 

 

 

 

 

 

A QT curve A
Desired of the let 5
econ E
D
a» 9 -
u o .E
3 olnl(En) -; °
is
O
(t > '
0' n .5 I
‘ O (E)
1' int n
to 1,, Einit En
Time Potential E
4—lo 4-10
A
'6
'5 En
B
. I
'3 i Controlled
0.
COMVOHNI / | current mode
liini‘l } I I
potentiel mode '
l l >
4-1c Time
_ A
.5
a
e
S
0
Potential controlled -= l I l ll l l l
I o
I r T '
0* Einit ’LTIPD t“ 9': T 1 {FT T
4-": Set up n ‘n+1
' timer th1;:
Figure 4-1. Illustration of the compensation of

charging current. the first port.

714

Charge

   
   
  
  

A 1 th
OT of the OT 0 e
2nd scan

2nd scan

 
  
  
  
 

01 ol the

1st scan and
Desired 0‘

  

 

 

 

 

 

    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

OT 0' Th0 .
oI
1st scan 3
Desired .c
0' 0 /
0' 01 the
0, ol the let econ ‘.‘ soon
> . >
‘ni ‘n
1"“. Tim.
4-1e Graph for the simple 4-11 Graph for the method
method of compensation actually ,used
I\
E
0'
e
'3
o
£
t)
Potential controlled ll'l'
r , 3'
0‘ E30" Time
4-10
.A
'3
:3
e
a»
b
o
1.:
Potential controlled 0
at £30" T T T Time

 

Kin 9|

Illustration of. the compemsation of

Figure 4-1.
the second part

charging current.

75

76

cherges of the working electrode must be meesured over the
potentiel renge of interest. The results ere stored in the
memory of the computer. Figure 4-1b illustretes the
integrel cepecitive cherge Qint required to meke the
potentiel perturbetion from the potentiel Einit to the
potentiel E for e working electrode in e solution. The
solution mey be e blenk solution conteining only the
supporting electrolyte end the solvent. or it mey be the
solution to be tested. Although the integrel cepecitive
cherge meesurement mey be subject to some error when the
test solution conteins electroective meteriels. the error is
smell for low concentretions of electroective species es
will'be shown in Figures 4-14 end 4-15 (less then 11 i error
for 2°10" I Cd+3 end less then 4 I error for 5°10" I Cd+‘
in 0.01 I [Cl solution).

Figure 4-2 shows the process of meesuring the integrel
cepecitive cherge. The operetor sets up the peremeters such
es initiel potentiel Einit' finel potentiel Efinel' cherge
to be injected 01. deley time for cherge injection td. etc.
For the reection 0x + ne- 9 Red, Efinel is more negetive
then Binit end 01 is negetive. After the operetor sterts
the progrem. the PCP meesures the electrode potentiel end
comperes it to the desired initiel velue Binit’ If there is
eny difference in these two potentiel velues. the PCP
injects enough cherge pulses of proper polerity to bring the

electrode potentiel to the initiel velue. After the initiel

 

< )

 

 

SET UP 0;: charge to be
PARAMETERS
injected
II! n: number of charge
injection
hIi
Einit: initial potential

 

 

 

 
   
 

APPROACH
Einit

 

    

 

 
 

TELL OPERATO
IT'S READY

  

 

 

KEEP
Einit

 

Figure 4-2.’

   
 

DATA ACQUISITION
(NEXT PAGE)

Flow chart of the program
lor the measurement of integral
capacitive charge; the first part

77

 

 

 

 

 

 

 

 

 

 

 

 
 
 
 

 

 

integral capacitive

 

     

 

 

charge
potenial before
charge injections.
_> ”HOE-CT should be equal
' 5° Einit
E2“. potentiuiafter
t NO char e in'ections
REACilED? ‘ 9 J
Etinal‘ final potential
YES td: delay time
n
NJECTIONS?
YES
MEASURE
PRINT E“, E Edwin-Em
and E2" 2n

 

 

i

 

 

 

 

CALCULATE INDIVIDUAL 05M
BETWEEN EintTEdn—t and

RESULTS IN MEMORY

 

 

 
    

 

 
 

E2mand N

 

STOP

 

Figure 4-2. Flow chart of the program for the

measurement of integral capacitive

charge. the second part

78

79

potentisl is resched, the PCP reports to the aperstor thst
it is resdy to execute dsts scquisition. The PCP keeps the
electrode potentisl st Einit by sdding chsrge pulses ss
needed until the operstor con-snds the PCP to execute the
dsts scquisition. After the dsts scqusition stsrts. the PCP
nskes sure thst the potentiel 811 before chsrge injection is
equsl to Einit' then injects the chsrge Qi to the electrode
snd nessures the potentisl 821 sftcr some slight delsy tile
td. The ninilun tine required by the conputer progrsnling
is shout 50 us for esch chsrge injection. The PCP
cslculstes the potentisl difference Edl resulting from one
injection of chsrge Q1 by the equstion: Edl - 821 - £11
(Edi should hsve s negstive vslue). The integrel cspscitiwe
chsrge Qint for the individusl vslue of potentisls between
Binit ‘“‘ Einit * Edl '“°h " Einit' Einit ’ 1°22 'V' Binit
- 2.44 'v""Binit + Edl' is cslculsted by sssuning thst
Qint is lines: within the potentisl rsnge. The results sre
stored in the Ie-ory of the co-puter. 0n the screen. the
PCP reports the vslues 811 snd 321. the potentisls before
snd sfter chsrge injection. A sinilsr nth process is
performed to bring the electrode potentisl to Einit' to
inject chsrge Qi n times. to nessure the electrode potentisl
sfter chsrge injections BZn' to cslculste the potentisl
difference Edn - EZn - Eln (Eln - Einit” to cslculste the
individusl cspscitive chsrge for the potentisls within the

rsnge Einit + Bdn-l - 1.22 IV snd Einit + Edn' snd to report

80

the vslues Eln snd E2n' the potentisls before snd sfter
chsrge injections. Ihen the process hss been caIpleted for
s potentisl which is Iore negstive thsn Efinsl - 24.4 IV.
the PCP reports the vslue N. the nuIber of chsrge injections
thst hsve been perforIed during the Iost recent series of
chsrge injections. When this occurs. the IessureIent of the
integrsl cspscitive chsrge hss been coIpleted. The
cspscitive chsrge for the individusl potentisl between Einit
snd Efinsl - 24.4 IV such ss Einit' Einit - 1.22 IV.....
Efinsl""' Efinsl - 24.4 IV. is stored in the IeIory of the
IicrocoIputer during the execution of this progrsI. In
order to provide s wider rsnge of cspscitive chsrge IeIory
file. the vslue Efinsl - 24.4 IV is selected to be Iore
negstive thsn Efinsl’ To obtsin fsirly sccurste cspscitive
chsrge for the individusl potentisl. s vslue of 10 IV to 20
IV for the potentisl rsnge between Edn-l snd Edn is
suggested for sny electrode which hsve fsirly constsnt wslue
of double lsyer cspscitsnce within the potentisl rsnge (such
ss Iercury electrode in 0.1 I or 0.01 I [Cl solutions).

For the caIpensstion of chsrging current using s blsnk
cell. the integrsl cspscitive chsrge should be Iessured
before testing the solution of ‘ interest. For the
caIpensstion of chsrging current in-situ. the integrsl
cepecitive chsrge Isy be Iessured sfter esch
chronOpotentiOIetric scsn.

To perforI chsrging current caIpensstion. the

81

operstor prepsres the solution to be tested snd sets up the
psrsIeters such ss the initisl potentisl Einit' the finsl
potentisl Efinsl' the tiIe intervsl between two potentisl
IessureIents tdl' stiIuI nuIber of chsrge injections within
the period tdl' s nuIber TIPD for the sIount of delsy tiIe
TIPD-tdl to keep the electrode potentisl st Einit sfter
setting up the tiIer snd before executing dsts collection.
etc. The cperstor then initistes the progrsI to perforI
chsrging current caIpensstion. The process of perforIing
the first chronopotentionetric scsn is shown in Figures
4-lc. 4-ld. snd 4-4. The PCP brings the electrode potentisl
to the initisl vslue Einit snd inforIs the aperstor thst it
is resdy to begin the dsts scquisition. The operstor csn
stsrt the dsts scquisition sfter this' point hss been
resched; however, it will be found sdvsntsgeous to wsit for
s while (e.g.. 10 seconds) for the electrode to reduce sny
inurities which sre present in its vinicity snd sre
reducible st Einit' After the operstor caIIsnds the PCP to
stsrt the dsts scquisition. the PCP sets up the tiIer. keeps
the potentisl st Einit for s period TIPD-tdl. The PCP
Iessures the electrode potentisl st the tiIes t. snd stores
it in the aoIputer IeIory. injects s chsrge pulse or s
nuIber of chsrge pulses to the electrode. wsits until t1 is
resched, then Iessures the electrode potentisl snd injects
snother chsrge pulse or Iore chsrge pulses. The PCP

continues to Iessure the electrode potentisl snd to inject s

 

 

 

 

    
   

let Scan?

 

    

SET UP CALC & SEND
CONSTANT 030} o, to PDP 11

LIBRARY

 

 

 

 

 

 

 

 

 

REACH Einit CONSTRUCT

THE NEW
r 01’ vs. t curv

| KEEP NO COLPISIIION

Ehfil suooru
YES QT VI. I can

DATA ACQUISITION
(NEXT PAGE) 7 EL
SET UP 0303

REACH Emu Library
(See Fig 4-1g]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PLOT
RESULTS
: char e
SEND a Q 9
DATA 10 Of: Faradaic charge
POP 11 o, ,. . .
.nJ-charge to be injected
L Qinfiintegral capacitive
Oint charge
_ REACH E°nn
""0“" FE— . 01-: Total charge

 

 

ment
(Fig 4-2)

Einit. \' NO

 

 

 

 

 

Figure 4-3. Flow chart of the program for
' chronopotentiometry with charge-
ing current compensation.

82

 

     
      
 
   
        
     

APPROACH From Figure

Einit

 

"4-3

 

 

ITELL OPERATOR I
n"s READY KEEP

Ehfit

 

 

 

 

 

 

 

 

KEEP E30"
tor a period
TlPD-tdt

l MEASURE E

 

 

 

 

    

Ta Figure
4-3

512
potential

meesure-
memts?

YES

 

 

INJECT law's
(See Figure. 4-1d
and 4-1n)

 

 

 

| N0 “ YES

REACHED?

Figure 4-4.‘ Flow chart of the program for data

 

 

acquisition of a chronopotentiogram

83

84
constsnt qusntity of chsrges within tdl tiIe intervel until
the electrode potentisl is equsl to or more negstive thsn
Efinsl' or until 512 potentisls sre Iessured. whichever
occurs first. The electrode potentisls st the tiIe t.. t1,
t,. ...._ etc. sre stored in the IeIory during the dsts
scquisition.

For the injection of s chsrge pulse between two
sdjscent potentisl IessureIents. the IiniIuI vslue of tdl is
156 us. For the injection of two chsrge pulses. it is 205
us. For the injection of 10 chsrge pulses. it is 601 us. A
detsiled cslculstion of the IiniIuI vslue of tdl csn be
found in Appendix A.

After the first scsn. in order to restore the desired
initisl concentrstion of 0x in the vinicity of the electrode
surfsce. the electrode potentisl is brought to the vslue
Einit to oxidize Red beck to 0x for s reversible resction.
or not to reduce 0x sny Iore for sn irreversible resction.
This is necesssry in the situstion in which sn HIDE is used
snd the ssIe Iercury drop will be used. or in the situstion
in which s solid electrode is used. becsuse the solution
nesr the electrode is not well stirred. After the potentisl
resches Binit' the chronopotentiogrsI. the E vs. tiIe curve.
will be plotted on the screen. The operstor Isy ssve the
results. The PCP holds the electrode potentisl st Einit'
The operstor Isy perforI the cspscitive chsrge IessureIent

with the ssIe solution when the in-situ coIpensstion is

85

desired. It is sdvsntsgeous to do so for in-situ
coIpensstion of cherging current since the probleI of drift
of electrode cspscitsnce csn be reduced.

As shown on Figures 4-1 snd 4-3 the PCP identifies the
electrode potentisl En st the tiIe tn (Figure 4-1c) snd

locstes the integrsl cspscitive chsrge Qint(En) for the

potentisl E (Figure 4-1b). The Fsrsdsic chsrge Qf(tn)

n
(Figure 4-1s). which hss been consuIed st the tiIe tn, is
cslculsted by the equstion:

Qf(tn) ' °T(tn) ’ Qint(En) (4'7):

where QT(tn) is the totsl chsrge injected st the tiIe tn of
the Iost recent scsn (In the first scsn, the QT vs. tiIe
curve is the desired 0: curve).

There sre Isny possible Iethods of sdjusting the totsl
chsrge curve in order to Iske the Fsrsdsic chsrge curve
spprosch the desired strsight line. As shown on Figure
4-1e. s sinle Iethod is to sdd the chsrge difference
between Qf(tn) snd the desired at vslue to QT(tn) of the
Iost recent scsn. Instesd of this sinle Iethod. I used s
Iethod which provides fsster coIpensstion. This Iethod is
illustrsted in Figure 4-1f. The PCP locstes the tiIe t. st
which Qf(tn) should hsve been consuIed. For the next scsn.
the totsl chsrge st t will be the totsl chsrge which hss

been injected st tn of the previous scsn. The QT vs. t

86

curve is extended to s higher qusntity of chsrge by
extrspolsting the end portion of the curve.

If the potentisl Enl (not shown) st the tiIe tnl is
Iore negstive thsn the potentisls before tnl' snd if Enz is
the first potentisl which is Iore negstive thsn Enl' the
cspscitive chsrge corresponding to the potentisl chsnge is
divided evenly in the tiIe period between tnl snd tIZ' (tIl
snd tI2 sre deterIined in the ssIe Isnner ss tII is
deterIined.) The totsl chsrge curve is sIoothed snd then
divided into sIsll chsrge segIents to be injected in the
next scsn ss shown in Figures 4-1g snd 4-lh. The sIoothing
is perforIed by using s sIsll tiIe window to sversge the
dsts within it. If the cspscitive chsrge is not distributed
evenly within tIl snd tIZ' or if the sIoothing is not
perforIed. the injection of s lsrge chsrge pulse or lsrge
chsrge pulses resulting froI the coIpensstion of chsrging
current Isy generste s potentisl spike of s few Iillivolts
in the next chronopotentiogrsI. A tiIe window of less thsn
5 S of the trsnsition tiIe is suggested for sIoothing. This
kind of chsrging current coIpensstion csn be repested s
nuIber of tiIes until the Fsrsdsic chsrge curve is close to
the desired strsight line or until the chronopotentiogrsI
rises rspidly st the beginning snd st the end.

This Iethod of chsrging current caIpensstion wss tested
with s duIIy cell whose configurstion is shown in Figure

4-5. The chsrge injected into the cspscitor chl wss

Cdm1-0.995pF
I +—
|

Cdm2-0.976flr

 

1K. 5%

i m

 

SWA
——o/<>
swa
»—</c
From-O/ o__0.__\
DAC

0.01pF I /

 

 

 

 

 

Figure 4—5. Circuits of dummy cell for the test of
charging current compensation for
chronopotentiometry
cdml‘ the charging capacitor
cdm2‘ the Faradaic capacitor

87

88

considered ss the cspscitive chsrge which would be
coIpenssted. The chsrge injected into the cspscitor ch2
wss considered ss the Fsrsdsic chsrge. Vith both cspscitors
in the feedbsck loop snd sfter coIpenssting for the chsrging
current. the results should look ss if only the cspscitor
ch2 were present.

Figure 4-6 shows the voltsge vs. tiIe curve obtsined by
epplying s constsnt current to the duIIy cell with only the
cspscitor can: in the feedbsck loop (only the switch B wss
closed).

The integrsl cspscitive chsrge wss obtsined with only
the cspscitor chl in the feedbsck loop. Both cspscitors
chl snd ch2 were then put in the feedbsck loop snd the
caIpensstion of the cspscitive chsrge of chl wss perforIed.
Curve 0 of Figure 4-7 shows the voltsge vs. tiIe curve
obtsined by spplying the constsnt current to both cspscitors
snd without sny chsrging current caIpensstion. The
cspscitive chsrge of the cspscitor Cd.1 wss coIpenssted in
the subsequent scsns sccording to the Iethod described
sbove. In Figure 4-7. the curve 1 corresponds to the
results obtsined in the first coIpensstion the chsrging
current. curve 2 corresponds to the second coIpensstion. snd
so on. The fsct thst curves 1. 2. snd 3 slIost coincide
suggests thst the effect of the presence of the cspscitor
chl in this cell configurstion csn be eliIinsted with just

one caIpensstion. The fsct thst one caIpensstion is

Y3
8’°°5°
>

-0.40
0.000

Figure 4-6.

DUMMY CELL

0.025 0.050 0.075 0.100 0.125
TIME ($50.)

Voltage-time curve obtained with

one dummy capacitor. Cdm2~

89

f’.’
—'—O.60
9

-0.40

DUMMY CELL

x
r' f'
. I
.' .’
o' J’
I ”.
I

0.000 0.050 0.100 0.150 0.200 0.250

Figure 4—7.

TIME ($50.)

Voltage-time curves obtained with

two dummy capacitors

Curve 0: no charging current compensation

Curve 1 the first compensation

Curve 2: the second compensation
3

Curve : the third compensation

90

91

sufficient for this cell configurstion csn also be predicted
through sinle geoIetry.

Curve 1 of Figure 4-8 (the ssIe es the curve of Figure
4-6) shows the results obtsined with only Cd.1 in the
feedbsck loop. Curve 2 of Figure 4-8 is equivslent to the
curve 3 of Figure 4-7 snd shows the results obtsined with
both cspscitors in the feedbsck loop snd with the
coIpensstion of the cspscitive chsrge of chl' Clesrly,
this Iethod of chsrging current caIpensstion reIoves the
cspscitsnce effect.

The spplicstion of this Iethod to two cheIicsl systeIs
will be discussed in Sections D snd B. Resgent grsde
csdIiuI chloride snd thslliuI chloride were used. Resgent
grsde potsssiuI chloride hsd been recrystsllixed once before
its use ss s supporting electrolyte. Solutions were
prepsred with de-ionised wster which hsd been psssed through
sn ion-exchsnge coluIn Isnufsctured by lillipore. The tiIe
windows for sIoothing the totsl chsrge curve wss less thsn 5
h of the trsnsition tiIe for ThslliuI solutions snd for
csdIiuI solutions with concentrstion shove 10" I. For
lower concentrstions of csdIiuI solution. tiIe windows were
less thsn 15 i of the trsnsition tiIe. Esch solution wss
de-sersted with nitrogen gss which hsd been psssed through s
vsnsdous chloride solution to reIove oxygen. All
experiIents were perforIed st rooI teIpersture between 20.5

snd 21.5 'c.

DUMMY CELL

-0.80
-0.70
235.1
.‘2
51-050
>
-0.50
—0.40 '
0.000 0.025 0.050 0.075 0.100 0.125
TIME (5150.)
Figure 4-8. I Voltage-time curves

Curve 1: only Cdmz in the feedback loop
Curve 2: both capacitors in the feedback
loop and with the compensation

IOI’ Cdm1

92

93

D. CoIpensstion of Chsrging Current for the System

TlCl in 0.1 l [Cl solution.

The Iethod of caIpensstion of chsrging current wss
tested with TlCl in 0.1 I KCl solution snd with s sitting
Iercury drop electrode. The chsrging current wss
coIpenssted with s blsnk solution (0.1 M KCl). If the’
effect of chsrging current is reIoved. the vslue it‘l'ICox
should be constsnt sccording to the Ssnd's equstion
(Equstion 4-1). As long ss there is no sdsorption of 0x
(Tl+). the presence of 0x (Tl+) does not chsnge the
cspscitsnce of the electrode.) snd proper experiIentsl
precsutions hsve been observed (e.g.. use s short trsnsition
tiIe to svoid possible convection). 'Isny cheIicsl systeIs
could be selected to test the Iethod of chsrging current
caIpensstion for chronopotentioIetry since the reversibility
of the resction 0x + ne- # Red is not sn inortsnt issue.
The chsrging current hss s Iore profound effect on the
chronopotentiogrsI of one electron trsnsfer resction thsn on
thsn of s Iulti-electron trsnsfer resction. Tl+ is selected
becsuse its reduction involves only one electron trsnsfer.
The tested concentrstion rsnge of Tl+ wss between 10" I snd
10" I. Since [Cl snd TlCl sre both uni-vslent electrolyte
snd the concentrstion of KCl (0.1 I) is st lesst 100 tiIes
higher thsn thst of Tl+. the selection of KCI concentrstion
should effectively reIove the Iigrstion of T1+ ss s result

of chsnging the electricsl field in the vicinity of the

94

electrode surfsce during s chronopotentioIetric experiIent.
To svoid the tediuI of costing the contsct for s
hsnging Iercury drop electrode (HIDE). s sitting Iercury
drop electrode (SIDE) wss used. A plstinuI wire of 0.01
inch in disIeter sesled in soft glsss wss used to construct
the sitting Iercury drop electrode. One end of the soft
glsss snd the sesled plstinuI wss ground with 3 Iicron
sluIinuI oxide then bent to s U-shspe. The plstinuI wire of
the other end wss soldered with s copper wire which
fscilitsted sn electricsl connection to the PCP. The ground
plstinuI tip wss casted with Iercury sccording to Isng's
Iethod (61). This bsckground current of the SIDE is not
significsnt coIpsred to the desired Fsrsdsic current (the
bsckground current wss 1.4 i of the desired Fsrsdsic current
st 10" I Tl+ concentrstion level). A fresh Iercury drop
wss obtsined by trsnsferring s fixed voluIe of Iercury froI
sn HIDE to the SIDE. The potentisl of the SIDE wss kept st
Einit for 10 seconds to reduce inurities before stsrting
the soquisition of dsts. The bsckground current wss
corrected by sdding it to the desired Fsrsdsic current.
Figure 4-9 shows the cspscitive chsrge obtsined with
the SIDE in 0.1 I [Cl solution with td - 1.24 Is (see Figure
4-2). Forty chsrge increIents were used to Iessure the
integrsl cspscitive chsrge for the potentisl perturbstion
froI -0.325 V to -0.725 V vs. SCE. The tiIes required for

this potentisl perturbstion sre 4.6 Is snd 49.6 Is for td

0.1 M KCI

-0.425 -0.525 -0.625

—0.325

—0.725

 

 

 

@5053 “.8210 ”$555 .2532.

 

- n - bL b b (P B — p p n p — b n p b r. b F b
u d u — q u q u — u q a - — fififi q — - q u u — - u a a
II II
II II
II I
.1 .fi
II II
II II
II LI
II JI
II II
[I '1!
J II
.fi :
LI II
II JI
II 11'.
Ir .1
II II
II II
II II
[I [I
II II
U- I-
II II
II III
II II
I1. II
Lu 1...
III IJI
I:l JI
II II
II II
41 IT
1' ll
JI II
II 1...
JI II
II p p n p — p p p r— n b h b — b p b b — p n L P — n F b _ II
- - u q — q u u u — 4 4 d 1— u u d d — u a u u — - u - a
O O O O O O 0
n4 0. Ru .0 4. 9. AU
1. 1 _ _ _ _
_ _

-0.525 -0.525 —0.725
POTENTIAL vs. so: (VOLTS)

-0.425

-0.325

in

capacifive charge of SMDE

Integral

0.

Figure 4-9.

solution

M KCI

1

95

96

0.115 Is snd 1.24 Is respectively. The curve of integrsl
cspscitive chsrge wss not chsnged significsntly by chsnging
td (within 2.2 i for td between 0.115 Is snd 1.24 Is).

Figures 4-10 snd 4-11 show sn estple of the
caIpensstion of chsrging current for 10" I TlCl in 0.1 I
[C1 solution. Curve 0 of Figure 4-10 shows the
chronopotentiogrsI obtsined without sny caIpensstion of
chsrging current. Curve O‘of Figure 4-11 is the Fsrsdsic
chsrge vs. tiIe curve of the first scsn (without sny
chsrging current caIpensstion). Curve 1 of Figure 4-10
shows the chronopotentiogrsI obtsined with the first
caIpensstion of chsrging current. Curve 1 of Figure 4-11 is
the Fsrsdsic chsrge curve corresponding to the first
caIpensstion. Curve 2 of Figure 4-10 shows the
chronopotentiogrsI obtsined with the second caIpensstion.
etc. After s few caIpensstions. the trsnsition tiIe
spprosched s constsnt vslue.

stle 4-1 lists the trsnsition tiIes corresponding to
the nuIber of chsrging current caIpensstions for s nuIber of
concentrstions. In esch csse. the ssIe i/C vslue of 1.02
A'CI-’°I010-1'11t0r wss used. The trsnsition tiIes were
obtsined by the grsphicsl Iethod of Delshsy snd Isttsx
(36.54). The Iethod is deIonstrsted by the grsphing snd
finding of the tiIe intervsl corresponding to the line
segIent AB for curve 0 of Figure 4-10. After s few

caIpensstions. the trsnsition tiIe spprosched s constsnt

.
AmFJO>v MOW

. .
. m) Jilb ZNFOQ

Fi

10‘4 M TlCl in 0.1 M KCI

 

 

0.00 0.05 0.10 0.15 0.20 0.25 0.50
-0.725 1..
:: 1 ‘ I
“—0 525 1i- i
g j: i
3 .‘L. 0
Lu 2:
0 -.
m CII- /
d-O°525 1;-
) q.
_, --
< ..::.
.5. -~ J 7
L‘.‘ 3: A B
8-0 425 -’
' 'I/ , h%AB*—-—%AB———~l g
—0.325 'g
0.00 0.05 .10 0.15 0.20 0.25 0.30

TIME (SE0)

Figure 4—10. Chronopotentiograms of 10" M TlCl solution

Curve
Curve
Curve

Curve

0:

No charging current compensation

1: the first compensation
2:
3

the second compensation

the third compensation

97

10"4 M TICI in 0.1 M KCI

 

 

0.00 0.05 0.10 0.15 0.20 0.25 0.50
—30.0 -r
- .0 . 55—

25 DeSIred of curve ——> '2‘;

.q‘ ::

g 55

g-20.0 :2 g:-

0 EE

LIJ 1 ..

g ::

(’15 O '2'.-

I Z:

0 ::

2 5E

E‘s-10.0 e:—

< ..

a: If ::

E a;

-5.0 €3—
0.0 :—
0.00 0.05 0.10 0.15 0.20 0.25 0.30

Figure 4-11.

TIME (SE0)

Faradaic charge curves for SMDE in

10"4 14 um and 0.1 u KCI solution
0:

Curve
Curve
Curve

Curve

no charging current compensation

1: the first compensation
2:
3

° the third compensation

the second compensation

98

1:1

Tab

 

C0111
com;
com;
The
Oth
9 t1
t1’11
P101

Chi:

99

vslue.
stle 4-1. Trsnsition tiIes (seconds) of vsrious
concentrstions of TlCl ss s function of

nuIber of chsrging current caIpensstions

 

  
 

 

 

 

 

 

 

 

 

 

I n"
hunter 10" 5-10" 2-10" 10" 5-10"
of cOI ensstion
0 0.121 0.126 0.128 0.133 0.145
1 0.111 0.110 0.109 0.113 0.112
2 0.112 0.108 0.108 0.112 0.106
3 0.112 0.108 0.108 0.112 0.106
Figure 4-12 shows s plot of it"‘/c vs. log
concentrstion of T1+ with snd without chsrging current

caIpensstion. The trsnsition tiIes with chsrging current

caIpensstion were the constsnt vslues schieved sfter scsns.

The sversged trsnsition tiIe for esch concentrstion wss
obtsined by tsking the sversge of 9 trsnsition tiIes. These
9 trsnsition tiIes were obtsined frOI 3 solutions with 3

trsnsition tiIe frOI esch solution. It is clesr thst the

plot of it‘l'lc vs. C is Iore drsIsticslly constsnt with

chsrging current caIpensstion.

TlCl in 0.1 M KCI

 

0.60

E

50.55

'2 I

o

E3 0.50

N

\

o

o

‘I’ 0.45 I

‘7‘

E

‘3

$0.40 I

o i X

N\ ’ x
,\_ 0 55 I g i m 0
.5 I

0.30
-5.5 -5.0 -4.5 -4.0 -3.5 ~3.0 -2.5
LOGC

I".3913” 4'12- it1/2/C vs. log concentration (M) of TIT

o. with charging current compensation

1:. without charging current compensation

100

CI
IC

CI

it
to
th.
thI
It
Ihg

01:

101

E. In-Situ COIpensstion of Chsrging Current es s

Sensitive Technique for the Detection of Cd+3

In order to test the sensitivity of the Iethod. longer
trsnsition tiIes were used to enhsnce the rstio of the
Fsrsdsic to the cspscitive chsrges. Trsnsition tiIes
between 1.6 sec snd 7.5 sec were used. These trsnsition
tiIes were kept short in order to svoid the effect of
nstursl convection. Concentrstions of csdIiuI solutions
between 2-10" I snd 2.5-10" I in 0.01 I [Cl solution were
tested with sn HIDE. A low concentrstion of supporting
electrolyte solution of 0.01 I [Cl wss used in order to
decresse the introduction of inurities with the supporting
electrolyte. In order to svoid the uncertsinty of integrsl
cspscitive chsrge due to the vsristion of electrode sres. s
single Iercury drop wss used for esch solution in both
cspscitive chsrge IessureIents snd chronopotentiOIetric
scsns (This could be done becsuse the concentrstion of
csdIiuI is low). The electrode potentisl wss brought to
Einit (-475 IV vs. SCE) sfter esch chronopotentioIetric
scsn. The electrode potentisl wss then kept st Einit for 10
to 20 seconds before Iessuring the integrsl cspscitive
chsrge of the electrode in the ssIe solution. It wss found
thst if the electrode wss kept st Einit for s tiIe ss short
ss 2 seconds. the Iessured cspscitive chsrge is essentislly
the ssIe. After the cspscitive chsrge wss Iessured. the

electrode potentisl wss held st Einit for 3 Iinutes before

102

stsrting the next chronopotentiOIetric scsn for those scsns
whose trsnsition tiIe slIost spprosched s constsnt vslue.
For the first few scsns, only one Iinute tiIe intervsl wss
used in order to ssve tiIe. The purpose of doing this is to
strip out Iost of the csdIiuI which hsd been deposited on
the Iercury drop.

Figure 4-13 shows the chronopotentiOgrsIs obtsined with
2-10" I CdCl, in 0.01 I rc1 solution. A desired Fsrsdsic
current density of 3.5 uA/cIa wss used. Curve 0 shows the
results obtsined without sny caIpensstion of chsrging
current. Curve 1 shows the results obtsined with the first
caIpensstion of chsrging current. curve 2 chows the results
obtsined with the second caIpensstion of chsrging current.
etc.

The integrsl cspscitive chsrge of the HIDE in the
solution contsining 2°10" I CdCla snd 0.01 I [C1 decresses
sbout 2g$ during the tiIe intervsl between two sdjscent
chronopotentiOIetric scsns. The rste of decresse is so
sIsll thst it does not introduce significsnt error in the
chsrging current caIpensstion.

For the cspscitive chsrge IessureIent, between 20 snd
25 chsrge increIents (see Figure 4-2) were used to chsnge
the electrode potentisl frOI -475 IV snd -775 IV vs. SCE.
The tiIe required to Iske the potentisl perturbstion is
between 1.3 Is snd 1.6 Is which is considersbly less thsn

the trsnsition tiIe used (between 1.7 snd 7.4 seconds);

2110'"5 M CdCI2 in 0.01 M KCI

10.012.014.0

6.0 8.0

4.0

0.0 2.0

 

-0.775

.675

0

.
6596 wow .2,

 

-0.575

.22.th9;

IIIITIIIIIIIIIIIIIIIII!IIIIIIIIIIIIIIITI'IIII'IIIIIIIII'IIIIIIIIIIIIIIIIIII

0.0 2.0

IIII'IIIIIIIIIIIIIIIIIIIIIIILIIIIIIIIIIIIIIIIIIIIIIIII'IIII‘IIIIIIIIIIlllrb

 

-0.475

10.012.014.0

6.0 8.0

4.0

TIME (SE0)

Chronopotentiograms of 2-10'5 M CdCl2

Figure 4-13.

besides the curve corresponding

The number

to the number of charging current

compensation

103'

104

therefore. the Fsrsdsic chsrge consumed in the tiIe intervsl
for cspscitive chsrge IessureIent is Iuch less thsn the
Fsrsdsic chsrge consuIed in the chronopotentiOIetric
experiIent.

Figure 4-14 shows the caIpsrison of the Iessured
integrsl cspscitive chsrge obtsined with s fresh Iercury
drop in 0.01 I [Cl solution (curve 1) snd in 2-10" I CdCla
snd 0.01 I [Cl solution (curve 2). The fsct thst the
Iessured integrsl cspscitive chsrge is higher for csdIiuI
solution thsn for plsin supporting electrolyte solution is
principslly due to the reduction of sons csdIiuI ions during
the period of cspscitive chsrge IessureIent.

For lower concentrstion of csdIiuI solutions. the error
involved in the cspscitive chsrge IessureIent .due to
Fsrsdsic resction is less. For estple. the integrsl
cspscitive chsrge Iessured with 5-10" I CdClz hss s lower
error ss shown in Figure 4-15. Even with the solution of
2-10-‘ I CdCla in 0.01 I [01. it is still sdvsntsgeous to
caIpensste for the chsrging current becsuse the chsrging
current is still the Isjor error.

Figure 4-16 shows snother estple of in-situ chsrging
current caIpensstion. The test solution contsined 10" I
CdCla snd 0.01 I [C1. A stesdy stste bsckground current of
0.017 uA/cI’ (10 i of the desired Fsrsdsic current) wss
deterIined st Einit {-475 IV vs. SCE). The bsckground wss

corrected by sdding it to the Fsrsdsic current of 0.17

0.01 M KCI w 0 2140"“5 M CdCI2

-0.575 -0.675 -0.775

-0.475

 

 

 

 

. p . — F p p p — - p p L b - n - p — L p p n — F b n -
IT a — q q . u — q q u u — q u - _ — _ - - . —J _ - .II
II II
II 11
El IT
4.. -1
l... .1
II J-
II II
LV h“
II II
II II
H H
II 1 I.
II II
II II
II II
II 2 11
I] 11
1' I-
”n “H
II II
“n “n
“u mu
LP 1P
II I...
II II
II II
II II
II I1.
II L1
II I1
I I
.n Mr
[I I].
“n “n
II II
H um
I I
“n H
In 1'
I] 1'
II II
1' IE
IT I...
II II
11 II
II II
II II
II II
II p p P P — b p p p PL b b b — p p p p — b p b PB b p P P I
- _ u a — 1 u - - — u u u - — a u _ _ — d - a u — u u u u
0 0 O 0 O 0 0
e . e e e e e e
6 5 4 3 2 el 0
_ _ _ _ _

_
ANEO \ 03

mom<Io m>Eo<a<o I_<mou._.z_

-0.575 -0.675 —0.775

--0.475

POTENTIAL vs. SCE (VOLTS)

capacHive charge for

integral

Measured
0.01 It KCI

Figure 4-14.

solution

without Cd012

Curve 1:

with 2-10'5 M CdC12

Curve 2:

105

0.01 M KCI w 0 5*10’5 M CdCI2

-O.575 -O.675 -O.775

—O.475

 

 

 

 

P PL F — b b h p — n L P p — n p p p — n — h b — L n p p
11 . . . 4 . . . _ . . . . — . . . . _ . . a u _ A q a . 1'
II II
II II
”n -1
Ir II
II I?!
II II
II II
II II
II II
II I1
II II
II II
II II
II II
II II
1T 2 11
II II
If! II
II II
H H
H H
JI II
II II
Ln. H1
II II
“n u:
.- .H
II II
“H “V
II II
II II
II II
IT II
II II
LT- II
II II
II II
“n UH
LI II
II I.
II 1W
II I
11 II
um um
II II
I1 II
II II
1.. P p r . — p _ b b — . p p b — p b h P — p p b . b p p I p l
u q u n d d u u - — d u d - — — q u - — u - u d — a - q a
O O O 0 O O 0
e e e e o o o
6 5 4 3 2 4| 0
_ _ _ _ _

_
AmEo \ 01V

wom<Io w>:._0<n.<o ._<mmvm.—Z_

- O . 5 7 5 - O . 7 7 5
POTENTIAL vs. SCE (VOLTS)

-O.575

-O.475

capacHive charge for

integral
Ia KCI

Measured
0.01

Ffigure 4-15.

solufion

without CdCl2

Curve 1:

with 5 10'6 u caclz

Curve 2:

106

10’5 M CdCIZ in 0.01 M KCI

 

O
4;
0
+0
(11
O
O

\
lllLlliL

IIFIUITUI IIIUTIUIT IIUITI'III FITI‘IIII IIUFIIIII IIIITTIII
I I I I I I

l
0
05
\I
(II

\ ,.~

 

I
O
U1
\I
U"

POTENTIAL vs. SCE (VOLTS)
1‘
V

‘ ""N:

llllllllllLlllllllllllllJllllllllllllllllllllLllL

 

-O.475
0.0 10.0 20.0 30.0 40.0

TIME (350.)

0'
O
0

Figure 4-15. Chronopotentiogrome of 10"6 M CdClz
' The number besides the curve corresponding
to the number of charging current

compensation

. 107

108

nA/cn'. Curve 0 sho's the chronopotentiogram obtained
without any charging current compensation. Curve 1 is
obtained uith the first compensation of charging current,
curve 2 is obtained with the second compensation. etc.

Figure 4-17 shows a chronopotentiogram of 5-10” I Cd+3
obtained after the transition tine approached a constant
value.

Table 4-2 lists the desired Faradaic current if applied

it‘l’. and the

to the electrode, the transition tine 1.
ratio of background current ib to if for a number of

concentrations.

5*10—7 M CdCl2 in 0.01 M KCI

 

 

 

 

.pp.»ppP.—.nu-hbbph—ppp-b-bub—pupphpb-pbp—pnpp-pp—P-pp-pbbb
Ila-J.-_.-ud_-—d_dq-—-dju-u-——_d__-d-:—-_—__--—-._—_qu-Il
11a 1'
ll 41
III I]
III 1'
IT IT.
[T If
Ill II
II. ll-
lvl 1'
[I 1'
1T ll
1T ll.
Ira III
II II
III 1'
Ill 1'
ll- 1'
If. a..-
ll Ill-I.
J' 1'
1' LI-
1' ll
41 1.-
1' ll
1' III
11- II.
I." Jul
11: I...
I] I]
1' Jr!
Ila II
1' ll-
I... [TI
[I II
.I I]
U- 11!
ll- l
L- -fl
II I]
III 0 III
I] O 1..
11. e I...-

ppLP—.ppb—bbppppppp—p-nppppt—l—E—-pC——_P—-P;~—-pPh_-b-—

d-uuu_-d—-_-__-—dqu---—-quad-q-—q-J--d_—fiud--u¢
5 5 5 5
7 6 5 4.

e e e s

O 0 0 0

_ _
6503 wow .2, ._<:zm:om

TIME (Si-2C.)

Figure 4-17.

Chronopotentiograms of 5010’7 M CdCl2
with charging current compensation

109

110

Table 4-2. List of if, ib/if. t, it”3 for CdCl3 solutions.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

u ca+’ 2-10" 1.5-10" 10" 5-10"

1 (uA/cl') 3.5143 2.614% 1.7143 0.8714$

1b/1f-100s - 05 as as as

1 (sec) 6.2 6.5 6.6 7.4
1:"’ (pi-sec‘l'lcu’) 8.6 6.6 4.5 2.4

x ca“ 2-10" 10" 5-10" 2.5-10"

1 (pl/en’) 0.35:4s 0.17:41 0.17:4s 0.03737s

1b/1f-100s 5s 10$ 10s 30s

1 (sec) 7.2 6.1 1.7 2.2
a:"' (pa-soc"’/cn’) 0.93 0.43 0.22 0.13

 

 

 

 

 

 

 

7" vs. concentration of

Figure 4-18 shows a plot of it
cad-inn. Theoretically. ir1I' should be proportional to the
concentration according to Equation 4-1. A fairly linear

it‘l' vs. C relationship was obtained.

F. Discussion

The nethod of charging current compensation can
effectively renove the effect of double layer charging as it
was shown in the previous two sections. The potentials are
nonitored while there is no current passing through the
solution. As a result of this, potential neasurenents can

be nade more accurately. and the solution resistance causes

7.00
6.00
5.00
4.00 '

3.00

i 731/2 (pA°sec1/2/cm2)

2.00

Figure 4-18.

4 .

CdCl2 in 0.01 M KCI

Concentration of QT"2 (0M)

331/2 vs. concentration of C

111

0 8.0 12.0 16.

0

d+2

20.

112

fewer problcns. Therefore. this nethod can be applied to
solutions of non-aqueous solvents, which nay not be able to
dissolve nuch electrolyte (the concentration of electrolyte
nay be as low as 0.1 II).

According to Dos and Van Dalen (60). for the reaction
0: + ne- 9 Red, it is advantageous to keep the electrode
potential at a value which is somewhat (e.g.. 100 IV to 200
nV) ncre positive than the E. of the redox couple to reduce
impurities which react rapidly at this potential. They used
a potentiostat to control the potential before the cell was
switched to an anpercstat. The PCP serves both as a
potentiostat and an galvanostat. Switching from the
controlled potential node to the controlled current node by
the PCP is practically instantaneous and does not cause any
problcns such as a current spike.

Dos and Van Dalen's apparatus (60) can perfcrn charging
current ccnpensated chronopotentionetric experinents whose
transition tines are as short as 0.1 second. The method
developed in this thesis work can handle
chronopotentionetric experinents at least 10 tines faster.
For example.‘ if 30 potential neasurenents are desired. the

nininun tine required for taking these data is
0.156 ns 0 30 . 4.7 as (4-8).

where 0.156 as is the nininun tine required between two

113

adjacent potential measurements.

If the has and Van Dalen's device is used for charging
current compensation. two cells must be used. One of them
contains the solution of interest. Another is the blank
cell which contains solution of supporting electrolyte only.
The blank cell is used for generating charging current. The
areas and the surface conditions of the working electrodes
in these two cells must be identical; otherwise, the
compensation will be subject to error. 'hen solid
electrodes are used. it is difficult to match electrodes
because of the surface roughness. the adsorption. and the
oxide film formation.

'ith the technique of in-situ compensation of charging
current developed in this thesis work. the capacitive charge
was measured with the same electrode in the same solution.
The effort of preparing a blank cell can be saved. 'hen the
solution does not contain high concentrations of
electroactive species (upper limit about 2°10" I). the
charging current can be compensated more accurately with
this method since the capacitive charge of the same
electrode is used. The drift of the quantity of measured
capacitive charge was not a serious problem for mercury
electrode since the time interval between two adjacent
chronopotentiometric scans was four minutes or less. A
drift of less than 2 i was observed in that time interval.

The time interval can be shortened to enhance the speed of

114

analysis or to reduce the drift of capacitance value in the
following situations: 1. A shorter transition time is used.
(smaller diffusion layer thickness makes it quicker to
restore the initial 0x concentration.) 2. A solid electrode
is used and with knocking the electrode after each scan (to
restore the initial 0: concentration at the electrode
surface).

Iith the technique of in-situ compensation of charging
current. the effect of adsorption of non-electroactive
materials on the capacitance measurement can be taken into
account since the capacitive charge is measured with the
same electrode between two chronopotentiometric scans. In
the situation in which the electroactive species is adsorbed
on the electrode and it reacts rapidly. the charge consumed
by this Faradaic reaction is included in the measured
capacitive charge. The measured capacitive charge will be
compensated in the next scan. Thus. the effect of the
adsorption of this type of electroactive species is removed.
In this situation, the method only takes the diffusion of
electroactive species into account. As a result of this. it
gives a better analytical working curve. These reasons.
discussed above. probably explain why this technique
improves the sensitivity of chronopotentiometry by more than
one order of magnitude. The sensitivity of this technique
is similar to that of pulse polarography.

The major limitation of the PCP is that high current

115

densities cannot be employed. For example. in the case of a
chronopotentiometric experiment. current densities above
mA/cma range cannot be applied. The program for performing
a chronopotentiometric experiment involves reading the DAC
values from the computer memory. calling a program to inject
charge pulses. calling a program to measure the potential.
etc. All of these processes require time. Ihen high
concentrations of supporting electrolytes are used (e.g..
above 0.01 I), the speed of cperation of the PCP is mainly
limited by the speed of the microcomputer. The maximum
current which can be applied to an electrode is limited by
the speed of the PCP. A large potential perturbation, due
to each charge injection. is certainly not desirable in any
chronopotentiometric experiments. If 3 mV is set as the
tolerable potential perturbation resulting from a charge
injection, and if the electrode capacitance is 20 uF/cm'.

the maximum current that can be applied to the electrode is

(3 mV)-(20 pF/o-')/(156 p8) - 0.33 mA/cm’ (4-9).

where 156 us is the minimum time required between two
adjacent voltage measurements. If higher current densities
are desired. a faster computer or a hardware charge

injection and measurement system should be used.

\

CHAPTER 5

SOME POSSIBLE APPLICATIONS OF THE PCP

Several operational modes of the PCP have been
discussed in Chapter 2. In this chapter. some possible
applications of these operational modes will be discussed.
lost of them have not been investigated. However. the
expected performance will be discussed at the best of my

knowledge.

A. The applications of the controlled charge mode
1. Traditional Coulostatic Iethod

A large charge pulse can be applied to the working
electrode in order to bring the electrode potential to a
value where the species of interest will react. The
potential can then be monitored as a function of time. The
decay of potential can be related to the kinetics of the
reaction (12.62) or the concentration of the electroactive
species (8.11.14.63). The time required for the voltage
measurement system (VHS) is 8 us. The minimum sampling time
required for each data point is between 20 and 25 us if the
time required for commanding the VHS to convert data. for
reading the converted data. and for storing the data are
included. The voltage sampling speed is moderate. For very

fast reactions. the PCP is not suitable. The resolution of

116

117

VHS is 1.22 mV which should be adequate for most
experiments. The DAC has lO-bit resolution and is bipolar.
The uncertainty in output voltage for each digital data is
1 1/2 LSB which corresponds to 1 2.5mV. The relative error
of charge can easily be less than 1% if proper voltage of
DAC is selected (e.g.. more than 0.5V out of the full range
2.5V).

2. Electrode Capacitance Heasurement

For the measurement of differential capacitance. as
discussed in Chapter 3. the PCP can inject an amount of
charge appropriate for the desired potential perturbation
(e.g.. 10mV). The entire capacitance-voltage profile of an
electrode can be obtained-in as little as 8 seconds. The
capacitance measurement is very accurate since the
calibration error of the ADC is reduced (see Chapter 3) and
the operator can select the number of iterations of
measurement in order to attain the desired precision.
Usually. the experimental technique is the main source of
error.

For the measurement of integral capacitance. a method
has been discussed in Chapter 4 which requires a few
milliseconds for a potential perturbation of 0.4V. A faster
program could be developed which would reduce the time to
about 50 us. If only one measurement is performed for each
potential and if the potential perturbation is large (e.g..

more than lOOmV). the relative error in capacitance

118

measurement is not large since the potential uncertainty is
only 1.22 mV.
3. Coulometric Titrations

Precise amounts of charge can be used to generate
titrant electrochemically. The electrode potential can be
monitored as a function of time or as a function of charge
added.

A four electrode system can be employed with a very
small change to the basic electronic circuitry. The current
applied between the working and counter electrodes generates
the desired titrant at the working electrode. In order to
prevent the reaction products at the counter electrode from
getting into the sample solution, the counter electrode can
be separated from the sample solution by a fritted glass. A
simple differential amplifier is needed. The reference
electrode and the indicator electrode can be connected to
the inputs of this differential amplifier and the output of
the differential amplifier can be connected to the VHS.
Using a computer controlled system such as the PCP. a high
current can be applied to generate titrant very quickly at
first and then the current or the rate of charge injection
can be decreased around the end point to allow the solution
well mixed. By doing this. the analysis time can be
shortened. A computer based instrument such as the PCP also
provides advantages in the continuous monitoring of analyte,

some of these advantages are automatic current range

119

selection. recording and warning. In the monitoring of
olefins and surfur compounds in petroleum using coulometric
titration. electrochemically generated bromine can be added
to petroleum streams (64). The bromine in the solution
reacts with the sample components and causes a decrease in
the concentration of bromine. The PCP can adjust the rate
of generating of bromine in order to maintain its
concentration at a specific level. One problem in using a
conventional coulometric titrator is that the current

applied between the working and counter electrodes generates

an IR drop between them. The reference and indicator
electrode should be positioned on an equal potential
contour. This consideration caused by simultaneous

electrochemical generation and detection has prompted the
use of spectrophotometric end point detection in some
applications of coulometric titration. Using the PCP. the
current between working and counter electrode is zero at the
moment when potential is sampled so the problem of IR drop

would be eliminated.

B. The Application of the Controlled Current Hode
l. Constant Current Chronopotentiometry

The application of PCP to constant current
chronopotentiometry has been discussed in Chapter 4. A

major advantage is that it is free from IR drop.

120

2. Programmed Current Chronopotentiometry

An instrument has been constructed by a group of
electrochemists (65) for chronopotentiometry with current
that varies along with any selected power of time. tq. The
transition time t, which is the time interval between two

sharp potential changes. is related to the concentration C

by

1(q+1/2) - kC (5-1).

where k is a constant.

The advantage of this method is that a wide range of
concentrations can be measured on a convenient time scale.

Iith PCP, a simple method to obtain a programmed
current is to vary the quantity of charge to be injected to
the electrode and keep the time interval between two
adjacent charge injections constant. The main disvantage
using PCP is that a high current density (above about 1
mA/cm’) cannot generally be employed partially due to the
inherent complication of the programming.
3. Electrode Pretreatment

Sometimes a clean and a reproducible electrode surface
can be obtained by heavily anodizing (e.g.. 1 sec at 10 to
100 mA/cm’) the electrode surface to remove adsorbed
material. This current density for this application is not

anticipated to be a problem since the programming is not as

121

complicated and the potential variation of the electrode is
not as vital as that of controlled current experiments. The
electrode's oxide layer is then reduced at a potential
sufficient to remove it. but neither the hydrogen ions or
the solvent are reduced. The pretreatment cycle is repeated
before every experiment, usually in the test solution.
Through the use of the PCP. complex current or
potential waveforms with precise timing control can be
applied to the electrode for pretreatment. The experiment
following the pretreatment can be carried out with the same
instrument and can be completed automatically. This special
capability results from the PCP's ability to switch
polarisation modes without disconnecting the cell or causing

any undesirable electrical stress at the working electrode.

C. The Application of the Controlled Potential Hode

Virtually all kinds of controlled potential experiment
(e.g.. cyclic voltammetry. pulse polarography.
chronocoulometry. rotating disk voltammetry. etc.) can be
performed using the PCP.

For pulse polarography. the PCP can usually attain a
potential step within the resolution of VHS (1.22 mV) in a
few milliseconds. This is not extremely fast compare to
most commercial instruments although most of them sample the
current between 30-50 ms after the pulse. For solution of

lower conductivity, the PCP has advantages over most

122

commercial instruments since it is applicable to these
solutions. One disadvantage of the PCP is that the
resolution of the VHS is not high. A certain amount of
electroactive species must be reacted before the PCP can
detect it. The lower limit of detectable concentration
depends on the technique applied. Generally. The PCP could
be well suited for concentration of electroactive species
above 10" H for direct analysis (For anodic stripping
voltammetry. much lower concentration can be achieved.). If
a lower detection limit is desirable. a higher resolution
ADC could be used. However, there may not be much advantage
to do so. In most cases. the background current is about
the same level as the Faradaic current generated by this low
concentration of electroactive species.

The PCP may have great advantages in the
electrochemical detection for liquid chromatography.
Because the coulostatic method does not require high
solution conductance. the PCP can be well suited for a wide
range of solutions. The differential pulse detection for
liquid chromatography can eliminate some electrode fouling
problems (66). The PCP can be well suited for this
application since it can step potential faster than most
commercial instruments under the condition of high solution
resistance.

One favorable aspect of the PCP for controlled

potential experiments is that the charging current can be

123

integrated over a short period of time (e.g.. 2 ms) after a
potential step. The resulting information may be used to
study either electrode capacitance or surface adsorption.
However. because some Faradaic reaction will occur during
this period. the PCP can not be applied to this method of
studying surface phenomena accurately if the concentration
of electroactive species is roughly above 10" H. For small
potential steps. the measured capacitive charge is subject
to significant error because the resolution of VHS is 1.22
mV which imay be a large fraction of size of the potential

step.

D. The Applications of the Open Circuit Hode

Under the open circuit condition. the PCP can be used
for the potentiometric measurements of PE electrode or other
ion selective electrodes.

In normal pulse polarography. a potential waveform with
potential pulses superimposed on' a constant potential is
applied to a working electrode. An operator with little
experience may sometimes select an initial potential at
which the electrode will dissolve. or the solvent will
decompose, or the electroactive species of interest will
start to react. If the potential in the open circuit
condition is used as the initial potential. these problems

can be avoided.

124

E. The Applications of the Combination of Hodes

The PCP can switch from one mode of operation to
another without any difficulty. The switching is achieved
by software. Also, it is fast and produces no electrical
stress on the working electrode.

Examples of possible application can be as follows:

The PCP can keep the working electrode potential at a
desired value (controlled potential mode) then automatically
switch to controlled current mode. During the controlled
potential period. impurities easier to react than the
species of interest can be consumed at the electrode
surface. Thus, the interference of impurities can be
reduced.

In controlled potential experiments. .the information
about the current can be the basis for some control
decisions. For example. in cyclic voltammetry. if the
current drops to a certain fraction of the peak current. the
potential can start scanning in the reverse direction.
Another example is for the preparations of desired
concentrations of electrochemical species at the electrode.
For example. the potential of the electrode can be kept at a
value to achieve the desired initial concentration before
switching to an experiment which could be a controlled
charge experiment such as traditional coulostatic
experiment. The amount of current at the potential for

preparing the desired concentration. can be used for the

125

decision of switching to the experiment. 'ith the PCP. a
series of experiments of this kind with different initial
condition can be performed automatically.

The PCP can keep the potential of the working electrode
at a desired value (controlled potential mode). then inject
a charge pulse to the electrode either for capacitance
measurement or for traditional coulostatic method
(controlled charge mode).

In the compensation of charging current for
chronopotentiometry which has been discussed in chapter 4.
controlled charge mode is used to measure the capacitance of
the working electrode. The measured capacitance is used in
the controlled current mode to perform constant current
chronopotentiometry with charging current compensation.

For normal pulse polarography. the open -circuit mode
can be used to obtain the potential at zero current. The
potential may be used as the potential before voltage pulses
are applied (controlled potential mode).

For charge step pclarography (14). the potential of the
electrode can be held at a value (controlled potential mode)
where the electroactive species do not react before
injection of increasing quantities of charge pulses
(controlled charge mode). The slope of the potential decay
after each charge pulse is injected can be monitored and
plotted as a function of potential.

H. A. Schreiber and T. A. Last developed a computer

126

controlled cculostat (67). The basic design of their
instrument is patterned after the one used by
S. E. Eourdakis and C. G. Enke (18). They performed linear
sweep anodic stripping voltammetry with a thin film
mercury/wax-impregnated graphite electrode. The linear
potential scan was achieved by injection of calculated
quantity of charge at constant rate to keep the linear
potential scan. The potential decay after each charge pulse
injected was used to calculate the Faradaic component of the
injected charge. The detection limit was 100 parts per
trillion for cadmium.

The PCP can be used as a drop fall detector for
dropping mercury electrodes as it was performed by Spyros
Hourdakis (18). The idea is to inject a proper fixed
quantity of charge to the electrode and measure the
electrode potential difference before the charge injection
and after the charge injection. The area of a drop of
mercury is very small immediately after the previous drOp
falls. The potential change due to the injection of the
charge pulse is more when the drop size is small than it is
when the drop size is large. A sudden change of potential
difference can be used for the detection of the time at
which a drop falls.

The applications mentioned above are only a few of the
many possible applications. Any complex potential or

current waveform or any combination of the operational modes

127

which will give the best response to the chemical system can
be used either for electroanalytical work or for fundamental

electrochemical research.

CHAPTER 6
DESCRIPTION OF THE SYSTEH HARD'ARE

A. Hodification of the Charge Generator and the Voltage

leasurement System

Figure 6-1 shows the circuits of the Digital-to-Analog
Converter (DAC) of the charge generator. The AD 7522 chip
is a 10-bit converter manufactured by Analog Devices. The
DAC is bipolar with maximum output voltage of i 2.5 V. The
output voltage V is converted to - V by the inverter A4 so
that both polarities of the voltage are available
simultaneously. The circuits have been modified from S.
Eourdakis' original design to provide faster responses for
the application of this thesis work. The capacitor 01- has
been changed from 560 pF to 150 pF and the capacitor C2 has
been changed from 56 pF to 150 pF. These changes give the
amplifier A1 a faster response. The output of A1 can come
within 1/2 LSE (2.44 mV) of any output) voltage in 9 us
compared with 35 us in the original design. Resistors R6
and R7 have been changed from lOKO. 5% to 25:0. 1% to
provide better accuracy for the inverted voltage -V. A
capacitor C3 of 50 pF has been added in the feedback loop of
A4 to improve the signal.

Figure 6-2 shows the modified circuit of the

Analog-to-Digital Converter (ADC). A resistor R5 of 1K0 is

128

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added betwween the output of amplifier A2 and the 5.1 V
Zener diodes to limit the output current for A1. A
capacitor C1 of 100 pF is added in the feedback loop of A2
to reduce noise. These changes make the noise level very
low without excessive reducing in the response speed. 'hen
the concentrations of [Cl solution are above 0.01 H and the
electrochemical cell has not been shielded. the noise level
of the electrode potential is below 0.1 mV which is much
less than the resolution of the VHS (1.22 mV). For very low
concentration of supporting electolyte such as 10" H [Cl
solution. a shield on the electrochemical cell is required
to reduce noise level below 1.22 mV. The switch S'A is
added between the non-inverting input of the amplifier A2
and the 12 V Zener diodes. Ihen a very dilute electrolyte
solution (such as below 10" H) is used. S'A can be kept

open to prevent leakage current through the Zener diodes.

E. Interface Circuits

The circuits that interface the microcomputer to the
DAC and the ADC provide the necessary digital signals to
control them. Figure 6-3 shows the interface logic.
Connections A6-A9 are address lines. Signal ES is the board
select signal for the charge generator and the voltage
measurement system. 'hen A9 is high and US is low. the
74LSl38 decoder chip is selected. Under this condition. one

of the outputs of 74LSl38 can be selected (active low)

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133

through proper signal levels on lines of A6-A8. Each output
(Io-15) of the 74L8138 chip is gated with ii or ii signal to
make sure that the address lines are stable in order to
provide a proper control signal. DAC LBS is for the loading
the low byte (S-bit) data to the input buffer of the DAC.
DAC RES is for the loading of the high byte (2-bit) data to
the input buffer of the DAC. The low byte should be loaded
first. The DAC RES also triggers a monostable (74LS221) to
generate a 5 us duration pulse for loading the DAC register
from DAC input buffer. The falling edge of ADC START
triggers the ADC to begin the conversion. The rising edge
of the ADC START triggers a D flip-flop (74LS74) to hold the
voltage which the ADC is converting. The ADC LEEN enables
the reading of low byte (S-bit) data of the ADC. It also
clears the 0 output of the 74LS74 to change the SIR chip to
the sample state. The ADC EDEN enables the reading of the
high byte (4-bit) data of the ADC. The ADC EOCEN enables
the user to check the status of the end of conversion signal
of the ADC. These control signals are connected to the DAC
and ADC boards. Letter w indicates a connection to the wire
wrap side of the board. and letter c indicates a connection
to the component side of the board. The number which
follows the letter c or w gives the pin number.

The switch decoding circuits are shown in Figure 6-4.
The microprocessor can turn on the desired switch by writing

proper digital data to the latch (74174). Only one switch

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135

can be turned on at any time.

'hen the proper address is sent to the decoder chip
(74LSl3S) for programming the switches. the output (I6) of
74LSl38 goes low. The output is gated by the 7R signal to
make sure that the address lines are stable and the computer
is sending data. The duration of the low pulse of the
output of the OR gate is about 500 us. This signal is
inverted by the NAND gate. The 74174 chip is used to latch
data when the microprocessor programs the switches. The
7442 decoder chip selects one of the outputs through the
input data. Only one switch is active (active low) at any
time. The tri-state driver (74LS241) is used to drive the
switch controlling signals and to turn its own output off
when the data is being loaded into the the latch (74174).
'hen the inputs of 7442 change. its outputs also change.
The transitions of the outputs of 7442 is gated off by the
tri-state driver in order to avoid the situation that a
switch is being turned on while another switch is being
turned off. The 74LS221 monostable multivibrator chip is
used to generate ,a delayed (about 150 ns) low-to-high
transition of the output) (pin 8) of the NAND gate. This
delayed transition makes sure that the data (DO-D3) are
correct at the time of loading the latch. The delay (150
us) is much shorter than the gating off time of the 74L824l
chip. The outputs of 7442 will be stable before the gates

of 74LS241 are turned on again.

 

136

A power-up clear and a switch for hardware clear are
connected to the latch. The switch 0 is selected when the
latch is cleared. The switch 0 is used to connects a 1K0
feedback resistor between the output and the inverting input
of the charging amplifier (the amplifier for adding charge
to the electrode) to protect the amplifier (see Figure 35 of

S. Eourdakis's dissertation (18)).

C. The Real Time Clock

The real time clock is based on the AH 9513 system
timing controller chip manufactured by the Advanced Hicro
Devices. Inc. The chip includes five general-purpose 16 bit
counters. A variety of internal frequency sources and
external pins may be selected as inputs for individual
counters. Both hardware and software gating of each counter
is available. The counters may be programmed to count up
and sown in either binary or BCD. The usage of this chip
allows complex timing ccntroll to be feasible.

In order to make the programming easy. a crystal of
1.000000 HEz is selected to generate an accurate counting
source. The anti bus lines (030-037) and 55, ii inputs of
AH 9513 are connected to the microcomputer bus. The CS of
AH 9513 comes from one of the UNQUAL (not gated with HR or
RD) outputs of the CS board designed by Bruce Newcome (19).
Each pin of the outputs (OUTl-OUTS). of the source inputs

(SRCl-SRC5) and of the gate inputs (GATEl-GATE5) is

 

Ir? ._—

137

connected to 4 patch wire sockets to enable interconnection
between them or to other sources. A 50 pin connector is
soldered on the real time clock board to make any connection
to any device which needs accurate timing control or
provides pulses to be counted.

The usage of AH9513 and the design of the real time
clock board allow a flexible timing control for most
electrochemial experiments. Detail programming of the
timing controller and the connections between the outputs.
sources and gates can be found in the programs TICP.HAC and

TIH12.HAC in Appendix B.

 

APPENDIX A

Equation and Some Examples for the calculation
of minimum values of tdl for

Chronopotentiometric Experiments

H is the number of charge injections between two adjacent

potential measurements. N is the number of extra software

 

loop for charging the capacitor and injection of charge to
the electrode (N - S'DLYI + S'DLY2 - 2). See programs
CEOADH.HAC and S'DLYB.HAC in Appendix B.

Hinimum tdl - 155.5 + 49.5(H-l) + H-N-4.55 us

Hinimum tdl (us)

H-l 155.53 +1-N'4.55
H-2 205.03 +2-N°4.55
H-3 254.53 +3°N°4.55
H-4 304.03 +4°N°4.55
H-5 353.53 +5-N-4.55
H86 403.03 +6-N-4.55
H-7 452.53 +7'N°4.55
H-8 502.03 +8°N°4.55
H-9 551.53 +9°N°4.55
H-lO 601.03 +10°N°4.55

Hinimum tdl (us) for 0.01 H [Cl solution (SlDLYl - 2.
SIDLY2 - 3).

H-l: 169.18 H-2: 232.33 H-3: 295.48
H-4: 358.63 H-5: 421.78 H-6: 484.93
H-7: 548.48 H-8: 611.23 H-9: 674.38
H-lO: 737.53 H-ll: 800.68 H-12: 863.83
H-13: 926.98 H-l4: 990.13

138

APPENDIX B
Programs for Data Acquisition and Data Analysis

The names and the functions of the programs for data

acquisition and data analysis are listed below.

 

Table B-1. The names and functions of the data

acquisition programs

 

 

Name Function

CAPSEQ Controlls the sequential operations for
capacitance measurements

TIH12 Sets up timer for capacitance measurements

BLVC Calibrates DAC baseline values

CAP Heasures capacitances

TICP Sets up timer for chronopotentiometric
experiment

ICAPN Heasures integral capacitive charges

CPSEQB Controlls the sequential operations for
chronopotentiometric experiment

CPADCN Heasures electrode potential and stores it
in memory

CBGADH Injects a charge pulse or charge pulses
to the electrode

VBACK Bring the potential back to the initial
value

 

139

 

 

 

140
Table B-2. The names and functions of the data analysis
programs
Name Functions
CAP.FTN 1. Divides one binary file by another for

capacitance measurements; one data set
is from the results of an electrochemical
experiment. the other is from the
results of a dummy cell

2. generates a C. 0. Enke 8 Co. standard
data file and a parameter file

 

CONCPAD.FTN l. Converts ADC values obtained in a
chronopotentiometric experiment to a
C. 0. Enke 0 Co. standard data file
and a parameter file

CAPSEG:

CAPSOO:

CAPSOl:

CAPSGZ:

CAPSGG:

CAPSG7:

CAPSNO:

5
i

SUBR CAPSEO

PUSH
PUSH
LXI

CALL

LDA
CPI
JNZ
CALL
LXI
CALL
LDA
RRC
JNC
LDA
CPI
J2
CPI
JNZ
CALL
LXI
CALL
NVI
LXI
CALL
DCR
JNZ
LDA
RRC
JNC
LDA
CPI
CZ
CPI
C2
C2
NVI
CALL
LXI
CALL
CALL
CALL
JMP
NVI
CALL
POP
POP
RET

.ASCIZ

H

PSN
HoVINIT
VAPR

VAPFLO
O
CAPSGO
READY
HoVINIT
VAPR

'EFLAGS

CAPSGl
BUFO
CTRZ
CAPSO7
CAPSOl
CAP
HoCAPSNO
PRINT
AoSO.
HolOOOO.
DELAY

A
CAP802
EFLAGS

CAPSGS
BUFO
’b
BLANK
CLEAR
BLANK
AIEFUO
EFCLR
HolOOOO.
DELAY
CAPGR
CAPUL
CAPSGO
AIEFUO
EFCLR
PS“

H

ICLEAR?/

141

iSAVE REGS

i

i

iAPPROACH THE INITIAL
JVOLTAGE

iGET THE FLAG

iGET THE VOLTAGE?
:NO. DO IT AGAIN

3

5

z

i

i

iKEY BOARD IS NOT TYPED
iGET THE CHARACTER
iCONTROL Z

IEXIT

300

:NO

1

i

iCLEAR GRAPHICS?
iDELAY FOR 3 SEC.

1

.e ‘e .e ‘0 Q.

zKEYBOARD IS NOT TYPED
iGET THE CHARACTER

i

iCLEAR SCREEN

i

iCLEAR SCREEN

iCLEAR THE SCREEN

i

iCLEAR KB

iDELAY

iFOR .1 SEC.

iDRAN THE RESULTS
iSEND DATA TO 11
iLOOP AROUND

iCLEAR KB EVENT FLAG

iRESTORE REGS
i

i

3TINING PROGRAM FOR THE CAPACITANCE MEASUREMENT

 

 

142

:CONNECT GATES 1 AND 2 TO +5 V

SUBR TIM12
TIM12: PUSH H
PUSH D
PUSH PSN
CALL TIRSET
MVI A31
STA TICMD
LXI HaTIDATA
MVI Mp242
MVI "0233
XCHG
LHLD TIPD
XCHG
MOV MaE
MOV MaD
MOV MoE
MOV "ID
MVI "3202
MVI Ma220
XCHG
LHLD TIDD
DCX H
XCHG
MOV MoE
MOV Mob
MOV MoE
MOV MoD
POP PSN
POP D
POP H
RET

i

iSAVE REGS

i

I

JRESET TIMER

iCOUNTER #1 MODE REG

3

iGET ADDR OF TIMER DATA

iPORT

iENABLE SPECIAL GATE

iFROM LOAD REG.REPETITIVELY

iBIN. DONN. ACTIVE HIGH

:TOGGLE. DELAYED .
iACTIVE HIGH LEVEL GATE NOFI :
I i
scar TIMER DELAY .
i 9.41“
iTO LOAD REG

3

iTO HOLD REG

3

iCDUNTER #2 MODE REG

iENABLE SPECIAL GATE

iFROM LOAD REG: ONCE

iBIN. DONN. ACTIVE HIGH

iTOGGLE. DELAYED

iACTIVE HIGH LEVEL GATE N

zTCN-l

i

iGET TIMER DELAY

:DECREMENT TO MATCH

iDELAY I TIPD * TIDD

3

:TO LOAD REG

3

3

:RESTORE REGS

i

i

iAND GO HOME

iTHIS ROUTINE DETERMINES THE DAC VALUE

iFOR ADDING ZERO CHARGE

SUBR BLVC
BLVC: PUSH H
PUSH D
PUSH B
PUSH PSN
CALL LPTI
CALL BLVCl

iSAVE REGISTERS

i

i

i

iOUTPUTS TO TERMINAL ONLY
iCOMPARE VINIT &VFINAL

BLVC4:

JM

JNZ
MVI
STA
MVI
STA
JMP

BLVCS
BLVCll
A01
BLDARl
AoO
BLDAR2
BLVC47

143

sVFINAL IS MORE POSITIVE
iVFINAL IS MORE NEGATIVE
ISTORE THE RATIO

5

i

i

iGET TO THE DESIRED VOLTAGEoADD CHARGE AND CHECK

iTHE DIRECTION OF VOLTAGE
HaBLADl

BLVCl:

BLVC2:

BLVCS:

sVFINAL IS MORE POSITIVE

LXI

MVI
CALL

CALL
CALL
CALL
DCR
JNZ
MVI
CALL
DCR
JNZ
CALL
XCHG
SHLD
LHLD

XCHG
LDA
MOV
LDA
MOV
CALL

CALL
LHLD
XCHG
PUSH
LXI

CALL
CALL
CALL
LXI

CALL
POP

XCHG
CALL
CALL
CALL

RET

A1100
VAPR

ADCbDE
ADCBDP
CRLF
A
BLVC2
A1377
VAPR

A
BLVCS
ADCbDE

BLVCVl
BLDAl

BLSU
BOA
BLNUMI
CoA
CGADDC

ADCbDE
BLVCVl

H

HoVINITM

PRINT
ADCBDP
CRLF

HoVFINLM

PRINT
H

ADCBDP
CRLF
DCMP

JADD FOR VOLTAGE TO BE
iAPPROACHED

5100 TIMES

:APPROACH THE DESIRED
iVOLTAGE

iGET ADC VALUE IN DE
iPRINT THE VALUE
iCARRIAGE RETURNiLINE FEED
i

sLOOP ARROUND TILL DONE
3255 TIMES AGAIN

i

1

i

iGET ADC VALUE INTO DE
iGET INTO HL

sSTORE IT

iDAC VALUE FOR ADDING
iCHARGE

i INTO DE

58“ #

INUMBER OF CHARGE ADDITIONS

iADD CHARGE HLIDAC VALUE
3CI# OF LOOP

iGET ADC VALUE IN DE
iGET VINIT

3(DE)IVINIT (HL)IVFINAL
iSAVE V FINAL

i

iPRINT VINIT

i

(DE)IVFINAL (HL)IVINIT

.mmfiomseuo

1(DE)-(HL) FLAGS BASED ON
BRESULTS
iAND GO HOME

 

 

BLVCS:

iVFINAL
BLVCll:

BLVC47:

BLFLG:
BLVCVl:
i

i
sBLDAl:
1M0:
3N0:
3N1:
1N2:
:SNA:
iSNDLYl:
3

CALL
MOV
STA

LXI
CALL

CALL
JM
J2
CALL
CALL
MOV
STA

JMP

IS MORE

CALL
CALL
MOV
STA

LXI
CALL

CALL
J2
JP
CALL
MOV
STA

LXI

CALL
POP
POP
POP
POP
RET

.BLKB l
.BLKB 2

BASELINE VOLTAGE FOR DAC

DSUB
A:L

BLDARl

H.DLDA1

DCXM

BLVCl
BLVCD
BLVC4

DSUB

HLTCMP

AoL

BLDAR2

BLVC47
NEGATIVE

DSUB

HLTCMP

AaL

BLDAR2

HiBLDAl

INXM

BLVCl
BLVC4
BLVCll

DSUB
AoL

BLDARl

HoBLDAl

DCXM
PS“
B

D

H

144

3(HL)=(HL)-(DE)

I

iSTORE THE RATIO FOR MORE
iPOSITIVE V

iGET ADDRESS OF DAC VALUE
iINCREASE MEMORY NORD.
tDECREASE DAC VALUE

IDO IT AGAIN

JSTILL MORE POSITIVE
IVFINAL-VINIT

IHLIHL-DE

ITWO’S COMPLEMENT OF HL

3

iSTORE THE RATIO FOR
IMORE NEGATIVE V

tFINISH

iHLIHL-DE

:TNO’S COMPLEMENT OF HL
3

iSTORE THE RATIO FOR
iMORE NEGATIVE V

:GET ADDRESS OF DAC VALUE
iDECREASE MEMORY WORD.
ilNCREASE DAC VOLTAGE
iDO IT AGAIN
iVFINALIVlNIT

)STILL MORE NEGATIVE
iHLIHL-DE

i

:STORE THE RATIO FOR
:MORE POSITIVE V
iADJUST DAC TO BE
:MORE POSITIVE

i

iRESTORE REGISTERS

2

2

t

iAND GO HOME
il:VFINAL+.O:VFINAL-
iTEMP VOLTAGE STORAGE

MINIMUM DATA POINTS FOR EACH POTENTIAL STEP
SHORTER * OF LOOPS FOR KEEPING POTENTIAL
LONGER # OF LOOPS FOR LEEPING POTENTIAL

DAC INCREMENT FOR CAPACITANCE MEASUREMENT
SWITCH H FOR ADDING CHARGE: USE #4

DELAY FOR CHARGING CAPACITOR:

.1 OF CAP

iVSTPO: VOLTAGE STEP FOR CAPACITANCE MEASUREMENT

USE 10 IS ENOUGH FOR

145

iVSTPl: VOLTAGE STEP FOR POTENTIAL SCANNING
i

iMTMP: VOLTAGE APPROXIMATION FLAG 1I>ADJUSTED

3 OTHERS I) NOT ADJUSTED

TMTMPl: TEMPORARY CHG QUANTITY

JMXTMP: POTENTIAL BEFORE CHG ADD

IMXTMP1:DAC VALUE FOR CHARGE ADDITION

tMXTMP2zADDR FOR STORING SUMMATION OF CHARGE

IMXTMPazADDR FOR STORING # OF DATA POINTS FOR THE POTENTIAL

IDELAY I TIPD * TIDD

.TIPD >- 32. TIDD >- 4
SUER CAP f
CAP: PUSH H .SAUE REGS 5
PUSH D 3 ;
PUSH D 2 LI
PUSH PSN : “‘
LHLD VINIT iINITIAL VOLTAGE
SHLD MXTMP .
LXI H.ADCLID iSTARTING ADDR FOR STORING
iSUMMATION OF CHG
SHLD MXTMP2 ;
LXI D.CAPEND .ENDINc ADDR
CAPi: MVI ".0 zCLEAR MEM
lNX H :INCREASE MEM ADDR
CALL DCMP zDE-HL
JNZ CAPl s
LXI H.i .
SHLD DATAN tCLEAR 3 OF DATA POINTS
LXI HI 0 I
SHLD MX2TM3+2 :CLEAR HIGH NORD FOR A00
"VI A: O I
STA MTMP tCLEAR VOLTAGE
iAPPROXIMATION FLAG
51-) ADJUSTED
zo-> NOT ADJUSTED
CALL TIH12 TSET UP COUNTER s: s e:
MVI A.141 1
STA TICMD .LOAD AND ARM COUNTER e1
LXI H.TCLIS zSTARTING ADDR FOR STORING
.3 OF DATA POINTS FOR
JEACH VOLTAGE
SHLD NXTNPS ;
LXI D.TCLID+4ooo ;
CAP2: MVI N.o iCLEAR MEM
INX H zINCREASE MEM ADDR
CALL DCMP iDE-HL
JNZ CAP2 ;
CAPS: LXI H.MXTMP .
CALL VAPNl iKEEP AT THE POTENTIAL
sFOR A WHILEtLONGER)
LHLD DAO iGET DAC VALUE

CAPSA:

CAPSB:

CAPSC:

CAP4:

iCHG NOT ENOUGH:

z
CAPb:

XCHG
CALL
LDA
ANI
JNZ
LDA
ANI
J2
JMP
LDA
ANI
JNZ
MVI
STA
MVI
STA
LDA
STA
LDA
ANI
JNZ
CALL
LHLD

XCHG
CALL
LXI
CALL
JM

LHLD
XCHG
LHLD
CALL
XCHG
MVI

CALL
LHLD
CALL
SHLD
JMP

SHLD
LDA
DCR
DCR
DCR
CMP
JZ
JP

DACSUP

TICMD
2
CAPSB
TICMD
2
CAPSA
CAPSC
TICMD
2
CAPSB
A1352
TICMD
Aol42
TICMD
SHA
SN
TICMD
4
CAP4

ADCbDE

MXTMP

DSUB
D.O

DCMP
CAP6

ADD MORE

DAO

BLDAl
DSUB

Aa2
DMULT
BLDAl
DSUB
DAO
CAPS

MXTMP4

VSTPO
A
A
A
L
CAP2O
CAPIS

zINTO DE

sSET UP DAC AND CHG CAP
iGET TIMER STATUS

iOUTl

:1. CHECK FOR 1 -> O

I

l

:0 -> 1

iCHECK FOR 1 -> O

i

i

iSET OUT2

zLOAD AND ARM COUNTER #2
i

i

iSEND THE CHG TO ELECTRODE
z

iCOUNTER #2 STATUS BIT
)NDT YET. WAIT

iMEASURE THE POTENTIAL
iGET POTENTIAL BEFORE
iCHARGE ADDITION

i

iGET VOLTAGE DIFFERENCE
i

i

iO.K.

iGET DAC VALUE FOR CAP
iINTO DE

iGET BASELINE DAC VALUE
iHL-DE

i

i

JDEIDE*A

iGET BASELINE DAC VALUE
:CALC NEH DAC FOR CAP
tSTORE IT

iADD CHG AGAIN

iSTORE POTENTIAL DIFFERENCE
iVOLTAGE STEP FOR CAP
tSTART FROM SLSB LESS

i

i

:PROPER VOLTAGE TO START
IVOLTAGE TOO LITTLE

iCHECK APPROXIMATION FLAG

TVOLTAGE TOO MUCH. CALC PROPER CHARGE

CAPlO:

MVI

A11

3

 

 

 

iVOLTAGE TOO LITTLE:
iIF APPROXIMATED.

CAPlS: LDA MTMP

CPI 1

JNZ CAPlO
CAP20: MVI AoO

STA MTMP
iSTARTING ADDING INCREMENTING CHG
CAP21: LHLD DAO

SHLD MXTMPl
CAP22: LHLD MXTMPl

XCHG

LHLD BLDAl

CALL DSUB

XCHG

LHLD BLDAl

DAD D

CALL CGADD

LDA SHDLYS

CPI 0

J2 CAP22D

CALL VAPDEL
CAP22D: LXI HoMXTMP

CALL VAPNO

LHLD MXTMPl

XCHG

CALL DACSUP

LDA TICMD

ANI 2

JNZ CAP22B

STA

LHLD
XCHG
LHLD
CALL
XCHG
LDA

DCR
DCR
DCR
CALL
LDA
CALL
LHLD
CALL
SHLD
JMP

MTMP
DAO

BLDAl
DSUB

VSTPO

A

A

A
DMULT
MXTMP4
DIV
BLDAl
DSUB
DAO
CAPS

147

3337 APPROXIMATION FLAG
iGET DAC VALUE FOR CAP

iINTO DE

tGET BASE LINE DAC VALUE
iHL‘HL-DE

I

iDESIRED VOLTAGE STEP

3

FOR CAP

:DECREMENT BY 3

I
I

iDEIDE*A

IGET ACTUAL VOLTAGE STEP

iDEIDE/A

IGET BASELINE DAC VALUE
iCALC THE DAC VALUE FOR CAP

I

iTRY TO APPROXIMATE THE CHG
iADD AGAIN

CHECK APPROXIMATION FLAG:
GO AHEAD AND DO IT
:GET APPROXIMATION FLAG

iAPPROXIMATED?
tNOT YET.
tONCE

I

iCLEAR APPROXIMATION FLAG
IN ORDER TO MEASURE CAP

APPROXIMATE IT

iGET DAC VALUE

I

IGET DAC VALUE FOR CHG ADD

iINTO DE

iGET DAC BASELINE VOLTAGE

iHL-DE

iRESULTS INTO DE

IOET BASELINE DAC VALUE

iCALC DAC VALUE FOR
iREVERSE CHARGE

iADD THE CHG TO ELECTRODE

iGET SWITCH DELAY

iNO DELAY?

iYES
iDELAY FOR A WHILE
iGET POTENTIAL BEFORE
iCHARGE ADDITION

IAPPROACH THE POTENTIAL
3(SHORTER)

TGET DAC VALUE
sINTO DE

ISET UP DAC:

CHG CAP

:GET TIMER STATUS
iOUTl

510

CHECK FOR 1-> O

 

CAP22A:

CAP22B:

CAP22C:

CAP24:

tVOLTAGE WITHIN

CAP24A:

LDA
ANI
J2
JMP
LDA
ANI
JNZ
MVI
STA
MVI
STA
LDA
STA
LDA
ANI
JN2
CALL
LHLD

XCHG
CALL

LDA
SUB
JNZ

LHLD
XCHG
LHLD
CALL
SHLD
LHLD
LXI

MVI

CALL

CALL
LHLD
XCHG
LXI

CALL
LHLD

CALL
LHLD
LDA
MOV
MVI
CALL
LXI
CALL

TICMD
2
CAP22A
CAP22C
TICMD
2
CAP22B
A. 352
TICMD
Aol42
TICMD
SWA

SW
TICMD
4
CAP24
ADCbDE
MXTMP

DSUB
VSTPO

L
CAPSO

148

he 5e §e

30 -> 1

:CHECK FOR 1 -> O
i

i

iSET OUT2

iLOAD AND ARM COUNTER #2

i

iADD CHG TO ELECTRODE
iCHECK COUNTER S2

iCOUNTER #2 STATUS BIT
INOT YET: WAIT

iGET THE POTENTIAL

iGET POTENTIAL BEFORE
TCHARGE ADDITION

i

iPOTENTIAL AFTER CHG ADD -
iPOTENTIAL BEFORE CHG ADD
TVOLTAGE STEP FOR CAP

I

iVOLTAGE NOT EQUAL DESIRED
iVALUE

DESIRED VALUE +- lLSB

MXTMPl

BLDAl
DSUB
MX2TM3
MXTMP2
DoMX2TM4
A34

MTRF

DDADD
MXTMP2

HD"X2TM6
MTRF
MXTMPS

INXM
MXTMPI
N2
E:A
DoO
DSUB
DOO
DCMP

iGET DAC VALUE FOR CAP
iINTO DE

iGET BASELINE DAC VALUE
iHL'DE

i

tGET ADDR FOR CHG SUMMATION
i

i

iTRANSFER PREVIOUSLY
iSUMMED CHG

iINTO MX2TM4

3(6) I (4) + (5)

iGET ADDR OF SUM OF CHG
iFDR DESTINATION

iGET ADDR OF SOURCE
iTRANSFER 4 BYTES OF MEM
iGET ADDR OF COUNTER OF
1“ OF CHG ADD

tINCREMENT THE COUNT
iGET DAC VALUE

iHL-DE
iDE-HL

 

CAP25:

CAP26:

J2

JP
SHLD

JMP
CALL
JMP

TVOLTAGE NOT

CAPSO:

CAPSl:

CAP40:

CPI
J2
CPI
J2
CPI
JM
LHLD
LDA
MOV
MVI
CALL
LXI
CALL
J2
JP
SHLD

JMP

LHLD

MOV
INX
MOV
LHLD

CALL
JM

CAP25

CAP26
MXTMPl

CAP22
ERROR
CAP41
WITHIN TO THE DESIRED VALUE +- lLSB

l

CAP24A

-1

CAP24A

-2

CAP4O
MXTMPl

N2
E.A
D.O
DSUB
D.O
DCMP

CAPSl
CAP26
MXTMPI

CAP22
iVOLTAGE HIGH ENOUGH.
EGO TO NEXT VOLTAGE STEP
MXTMPS

E.M
H
D.M
MO

DCMP

CAP2l

149

iMOST NEGATIVE VOLTAGE
iALLOWED

TOUT OF BOUNDARY

iSTORE DAC VALUE FOR NEXT
iCHG ADD

iADD MORE CHG TO GET CAP
tSEND ERROR MESSAGE

iGO TO NEXT VLOTAGE STEP

I

may...»

.’”—.'7 V

iVOLTAGE HIGH ENOUGH
:GET DAC VALUE

:GET DAC STEP

3

i

iCALC NEXT DAC VALUE
iMOST NEGATIVE DAC VALUE
iDE-HL

THIGHEST VOLTAGE ALLOWED
IERROR. GO TO NEXT STEP
iSTORE DAC VALUE FOR NEXT
iCHG ADD

iADD MORE CHG TO GET CAP

Jami-'30

—.

J5

CHECK H OF DATA. IF ENOUGH.

IOET ADDR FOR STORING

3% OF DATA POINTS

3* OF DATA POINTS INTO DE
1

3

:GET MINIMUM DATA POINTS
iDESIRED

iDE-HL

iNOT ENOUGH DATA POINTS.
iGET THE STARTING POTENTIAL
TGUICKLY AND DO IT MORE

3* OF DATA POINTS IS ENOUGH FOR THE VOLTAGE OF INTEREST.
300 TO NEXT VOLTAGE

CAP41:

LHLD

LDA
CALL
XCHG
LHLD
CALL
JP
XCHG
SHLD
LHLD

MXTMP

VSTPl

HLPA

VFINAL

DCMP

CAPSO

MXTMP
DATAN

:GET THE VOLTAGE BEFORE
iCHG ADD ‘

iVOLTAGE STEP FOR SCANNING
iCALC VOLTAGE FOR NEXT STEP
iRESULTS INTO DE

iGET FINAL VOLTAGE

iDE-HL

iVOLTAGE HIGH ENOUGH

iNEXT VOLTAGE INTO HL
iSTORE IT

IGET * OF VOLTAGE STEP

CAPSO:

I
I

INX
SHLD
LHLD

INX
INX
SHLD
LHLD

INX
INX
INX
INX
SHLD
MVI
STA

JMP
POP
POP
POP
POP
RET

H
DATAN
MXTMPO

H
H
MXTMPS
MXTMP2

IIII

MXTMP2
A.O
MTMP

CAPS
PS“

150

ITIMER FOR CHRONOPOTENTIOMETRY.
iOATES 1: 2:

30UT4 TO GATE 3.

AND 4 TO +5V
-OUT4 TO IRS.

.INCREMENT ONE

ISTORE IT

zGET ADDR FOR STORING # OF
:DATA POINTS IN EACH STEP
:INCREMENT BY 2

;

ISTORE IT

zGET ADDR FOR STORING SUM
:OF CHG FOR THE VOLTAGE
:STEP

:INCREMENT BY 4

1

z

z

:STORE IT

, .

tCLEAR VOLTAGE
zAPPROXIMATION FLAG

:GO TO NEXT VOLTAGE STEP
tRESTORE REGS

t

z

3

:AND GO HOME

CONNECT OUT2 TO SRC2.
OUTS TO IR4

iIRS AND IR4 ARE INPUTS OF THE INTERRUPT CONTROLLER OF 8259

TICP:

SUDR
PUSH
PUSH
PUSH

CALL‘

MVI
STA
LXI

MVI

MVI
XCHG
LHLD
XCHG
MOV
MOV
MOV
MOV
MVI

TICP

H

D

PS“
TIRSET
A.2
TICMD
H.TIDATA

H.242

M.233
TIDD

M.E
M.D
M.E
M.D
H.242

:SAVE REGS

1

:

iRESET TIMER

:COUNTER 2 MODE REG

I

:GET ADDR OF TIMER DATA
:PORT

IENABLE SPECIAL GATE.
:FROM LOAD. REPETITIVELY.
zBIN. DONN. ACTIVE HIGH
:TOGGLE. DELAYED
:ACTIVE HIGH LEVE GATE N.F1
:SAVE ADDR OF TIDATA
zDATA DELAY

1

ITO LOAD REG

3

3T0 HOLD REG

I

:COUNTER 3 MODE REG
sSAME AS COUNTER 2

3

I

151

‘ soars IS CONTROLLED 3v 0014

MVI H.233 3
HOV M.E 3DATA DELAY TO
HOV M.D 3 LOAD REG
HOV M.E 3TO HOLD REG
MOV "a D I
MVI H.302 ICOUNTER 4 MODE REG
iENABLE SPECIAL GATE
3RELOAD FROM LOAD OR HOLD
3COUNT ONCE.BIN.DOHN.ACTIVE
IHIGH TOGGLE. DELAYED
MVI H.202 ISRC2(CONNECT OUT2 TO SRC2)
3RISING EDGE.
3ACTIVE HIGH GATE N
XCHG ISAVE ADDR OF TIDATA '
LHLD TIPD 3PRE EXP DELAY j
XCHG 3 f;
MOV M.E 3TO HOLD REG. FROM TIPD '*
MOV H: D I
MVI M.O 3512 DATA POINTS. LOAD REG
WI "3 2 I
MVI A.156 3
STA TICMD 3LOAD AND ARM COUNTER 4.3.2
POP PSH 3
POP D 3
POP H .
RET 3AND GO HOME

3THIS ROUTINE ADDS CHARGE TO THE ELECTRODE AND CALCULATE
3THE INTEGRAL CAPACITIVE CHARGE FOR EACH VOLTAGE
3MXTHP1: COUNTER FOR THE VOLTAGE

3HXTHP2: THE SECOND VOLTAGE DIFFERENCE

3HXTMP3: CHARGE QUANTITY OF ONE ADDITION

3MXTHP4: ADDRESS FOR INTEGRAL CAPACITIVE CHARGE

3MXTMP5: ADDRESS FOR THE DIFFERENCE OF ADJACENT VOLTAGE

SUBR ICAPN
ICAPN: PUSH H 3SAVE REGISTERS

PUSH D 3

PUSH B 3

PUSH PSH .

LXI H.O 3CLEAR MEMORY

SHLD BICAP 3 .

SHLD BICAP+2 3

LXI H.1 3SET UP COUNTER FOR VOLTAGE

SHLD MXTMPI 3

LDA ICAPCI 3GET NUMBER OF CHARGE

3ADDITIONS

LXI H.ICAPDA 3

CALL SMDAC 3SET DAC PARAMETERS

MVI A.1 3RESET

STA ICAPC2 3 # OF CHARGE ADDITION LOOP
ICPNOA: LXI H.VINIT 3APPROACH THE VOLTAGE

ICPNO:

ICPNI:

ICPN2:

ICPNS:

ICPNSA:

ICPNSB:

ICPN3C:

CALL
CALL
LXI
CALL
CALL
JNC
CPI
JNZ
LXI
CALL
LHLD
XCHG
LXI
CALL
CALL
LHLD
XCHG
CALL
JNZ

SHLD
LDA
PUSH
LDA
HOV
LDA
STA
LDA
STA
POP
PUSH
LDA
HOV
MVI
STA
LDA
DCR
JN2
HOV
STA
CALL
DCR
JNZ
POP
DCR
JNZ
CALL
LHLD
MVI
CALL
CALL

JP

152

VAPNO
READY
H.VINIT
VAPR
CHARIN
ICPNO
’9
ICPNO
H.VINIT
VAPNO
ADCTHP

H.VINIT
VAPNI
ADCbDE
VINIT

DCMP
ICPN2

ADCTHP
ICAPC2
PSW
ICAPSW
B.A
ICAPDA
DACLB
ICAPDA+1
DACHB
PSW
PSW
ICAPCI
C.A
A.1

SW
SWDLYI
A
ICPN3C
A.B

SW
SWDLYB
C
ICPNSB
PSW

A
ICPN3A
ADCbDE
VFINAL
A.20.
HLPA
DCMP

ICPNII

3
3TELL US IT'S READY
3APPROACH THE VOLTAGE

3

318 KEYBOARD TYPED?

3N0. WAIT

3GO?

3NO.WAIT

3

3APPROACH THE VOLTAGE
3GET THE VOLTAGE
3(DE)-TEMP VOLTAGE.
3APPROACH THE VOLTAGE

3

3GET THE DAC VALUE

3GET INIT VOLTAGE
3(HL)-DAC VALUE
3(VINIT)-ADC VALUE

3ADC VALUE IS NOT EQUAL
3TO VINIT. DO IT AGAIN
3STORE BEGINING POTENTIAL
3GET NUMBER OF CHARGE LOOP
3SAVE # OF CHARGE LOOP
3GET SW G

3 INTO B

3GET DAC LOW BYTE

3

3GET DAC HIGH BYTE

3

3GET G OF CHARGE LOOP
3SAVE G OF CHG LOOP LEFT
3GET 0 OF SMALL CHG LOOP
3SAVE IT

3

3CHARGE UP CAPACITOR

3GET SWITCH DELAY

3

3

3GET SWITCH NUMBER

3

3

3DECREASE SMALL CHG LOOP
3ND FINISH YET.DO IT AGAIN
3GET R OF CHG LOOP

3ALL DONE?

3NO DO IT SOME MORE

3GET DAC VALUE

3GET FINAL VOLTAGE

3ADD ABOUT 20 mV MORE

3

I DE’HL:
3RESULTS
3VOLTAGE IS MORE NEGATIVE

FLAGS BASED ON

CALL

JMP

ICPN4

-ICPN1

153

3OR EQUAL TO VFINAL
3CALCULATE THE CAP CHARGE &
3STORE THEM

3DO IT SOME MORE

3CALCULATE CAPACITIVE CHARGE.STORE THEM AND

3INCREMENT NUMBER OF CHARGE LOOP

ICPN4:

ICPNS:

ICPNb:

LHLD
XCHG

PUSH
LDA
CPI
J2
CALL
XCHG
CALL
XCHG
CALL
POP
CALL
JM
SHLD
LHLD

CALL

SHLD
LDA
DCR

MOV
MVI
CALL
SHLD
HOV
HOV
SHLD
LHLD
DCX

XCHG
LHLD
CALL
SHLD
LHLD
XCHG
MVI

CALL
LXI

DAD
SHLD

ADCTHP

PSW
DAADBF
2
ICPNS
ADCBDP

ADCBDP

LPCRLF
PSW
DSUB
ICPNIO
MXTMP2
ICAPDA

CGCALN

MXTMP3
ICAPC2
A

C.A
B.O
DDHULT

HX2TH4+2

L.C
H.B
MX2TM4
MXTMP1
H

MXTMP2
DSUB

MXTMPS
MXTMP1

A.4
DMULT

H.BICAP

D
HXTMP4

3
3HL-POTENTIAL AFTER CHG ADD
3DE-BEGINING POTENTIAL

3SAVE REG

3GET BIN/DEC FLAG

3

3N0 PRINTING ’
3PRINT BEGINNING POT

3

3PRINT POT AFTER CHG ADD

3

3CARRIAGE RETURN. LINE FEED
3RESTORE REG

3HL-HL-DE

3NOT ENOUGH CHARGE

3STORE 2nd VOLTAGE

3GET THE DAC VALUE &

3% OF CHARGE ADD

3CALCULATE THE NUMBER

30F CHARGE. HL=NEG CHARGE
3CHG QUANTITY OF ONE ADD
3GET Q OF CHARGE LOOP
3DECREMENT ONE CHG t FOR
3THE FIRST COLTAGE

3

3

3(HLBC)-(HL)*(BC)

o
i

’11

It

i

3GET THE IST VOLTAGE
3DECREMENT ONE IN ORDER

3TO MAKE PROPER VOLTAGE
3DIFFERENCE

3INTO DE

3GET THE END VOLTAGE

3CALC THE DIFFERENCE

3STORE THE DIFFERENCE

3GET Ist VOLTAGE DIFFERENCE
3 INTO DE

34 BITS FOR EACH DATA POINT
3DE-DE*A

3GET BASE MEMORY ADDR FOR
3ICAP '
3(HL)<-(HL)+(DE)

3STORE ADDR FOR INT CAP CHG

 

ICPNbl:

ICPN62:

ICPN7:

3NOT ENOUGH CHARGE

ICPNIO:

ICPNII:

MVI C.1

MVI B.O

LHLD MXTMP3
PUSH B

CALL DDHULT
PUSH H

LHLD MXTMPS
XCHG

POP H

CALL DDIVHB
SHLD HX2TM5+2
CALL HLXBC
SHLD HX2TM5
POP B

INR C

CALL DDADD
LHLD HXTHP4
MOV E.L

HOV D.H

MVI A.4

CALL HLPA
SHLD MXTMP4
LXI H.HX2TH6
CALL MTRF

LXI D.HXTMPI
LXI H.HXTMP2
CALL DCHPH

JP ICPN7
XCHG

CALL INXH

JMP ICPN61
XCHG

CALL INXM

LXI H.ICAPC2
INR H

RET

POP PSW

LXI H.ICAPC2
INR H

JMP ICPNI
LDA DAADBF
PUSH PSW

MVI A.O

STA DAADBF
CALL ICPN4
POP PSW

STA DAADBF

154

3COUNTER

3GET CHG OF ONE ADD
3STORE COUNTER COUNTER
3(HLBC)=(HL)*(BC)

3

3GET VOLTAGE DIFFERENCE
sINTO DE

3

3(HLBC)-(HLBC)/(DE)

3

3(HL)<=>(BC)

3

3

3INCREMENT COUNTER

3(4) + (5) I) (6)

3GET ADDR FOR INT CAP CHG
3INTO DE

3

34 BYTES EACH DATA POINT
3CALC NEXT ADDR

3STORE NEW CAP CHG ADDR
3

3TRANSFER RESULTS TO MEM
3

3((DE))-((HL))

318k VLOTAGE EQUAL TO OR
3GREATER THAN 2nd VOLTAGE
3GET ADDR OF VOLTAGE
3COUNTER

3INCREMENT ONE
3CALCULATE TILL ITS DONE
3GET ADDR OF VOLTAGE
3COUNTER

3INCREMENT ONE

3

3INCREMENT CHARGE LOOP
3AND GO HOME

3REMOVE JUNK

3GET ADDR OF # OF CHARGE

3LOOP

3INCREASE IT

3PROCEED THE EXP

3GET BIN/DEC FLAG

3SAVE IT

3

3MAKE IT PRINT ADC VALUES
3PRINT VOLTAGES

3RESTORE ORIGINAL BIN/DEC
3FLAG

3AND STORE THEM

 

 

 

I
3

I

CPSEQB:
CPSEBI:

CPSEB2:

CPSEB4:

CPSB4A:

LXI
CALL
POP
POP
POP
POP
RET

SUBR
PUSH
PUSH
LXI

CALL
CALL

CPI
JN2
CALL
LXI
CALL
CALL
LDA
RRC
JNC
LDA
CPI
J2
CALL
LXI
CALL
CALL
LDA
RRC
JNC
LDA
CPI
CZ
CPI
C2
C2
MVI
CALL
CALL
CALL
CALL
CALL
LXI
SHLD
CALL
CALL
CALL

H.PICAP2
SPRMPR
PSW

B

D

H

CPSEQB

H

PSW
H.CPSEBM
PRINT
CHARIN
CPSEBI
CPSEB2
CPSDLB
H.CPSEH2
PRINT
DELAY2
EFLAGS

CPSEB4
BUFO

’u
CPSEB7
CPB
H.CPSEMI
PRINT
DELAY2
EFLAGS

CPSB4A
BUFO
’b
BLANK
I
CLEAR
BLANK
A.EFUO
EFCLR
DELYPI
ADGR
CPADUL
CRLF
H.PCPCO2
APARAM
PARHPR
TTYINB
PARHCH

155

3PRINT G OF LOOP

3

3RESTORE REGISTERS
3

3

3

3AND GO HOME

3SAVE REGS
3
3NITIALIZE?
3

3

3 ,5
3YES a
3NO

3SET CP INITIAL LIB

3

3EXIT?

3DELAY FOR 2 SEC

3GET EVENT FLAG

3CARRY KEY BOARD IS TYPED

3ND

3GET THE CHARACTER

3EXIT?

3YES

3GP & VOLTAGE BACK

3

3CLEAR GRAPHICS?

3DELAY FOR 2 SEC.

3GET EVENT FLAGS

 

3KEYBOARD IS NOT TYPED
3GET THE CHARACTER

I

3CLEAR VRAM

5

3CLEAR GRAPHICS

3CLEAR VRAM

3CLEAR KB

3DELAY FOR .1 SEC

3DRAW THE VOLTAGE GRAPH
3SEND ADC VALUES
3CARRIAGE RETURN.
3CORRECTION RATIO
3ADDR FOR THE PARH
3PRINT THE PARAMETER
3INPUT A LINE. BREAK DOWN
3CHANGE THE PARAMETER

LINE FEED

CPSEBS:

CPSEB7:

CPSEBM:
CPSBHI:
3

CALL
LXI
SHLD
CALL
CALL
CALL
CALL
LXI
CALL
CALL
JNC
CPI
C2
CALL
CALL
CALL
CALL
CALL
CALL
CALL

.3319
POP
POP
RET

.ASCIZ
.ASCIZ

VBACK

H.PAVEW

APARAM
PARHPR
TTYINB
PARHCH
VBACK

H.CPSBHI

PRINT
CHARIN
CPSEBS
ICAPN
CPFCUL
CPTCNX
CPTCSM
VBACK
CPTCCF
CPTCAV
CPDTC

CPSEB2
PSW
H

ICPSDLB?/
IICAPN?/

156

3KEEP VINIT FOR A WHILE
3AVERAGE WIDTH

3ADDR OF THE PARM
3PRINT THE PARAMETER
3INPUT A LINE. BREAK DOWN
3CHANGE THE PARAMETER
3KEEP VINIT FOR A WHILE
3PRINT ICAPN?

3

3

3

3YES

3GET NEW CAPACITIVE CHG
3SEND FC VALUES
3EXTRAPLOATE TC

3SMOOTH CHARGE JUMP
3KEEP VINIT FOR A WHILE
3CLEAR FLAGS

3AVERAGE TC

3CHOP OFF TCLIB AND
3FILL DAC LIB

3LOOP AROUND

3RESTORE REGS

3

3

3THIS ROUTINE TAKES THE ADC VALUES FOR CHRONOPOT AND STORE

3IT IN MEMORY REFERED BY DE

CPADCN:

CPADN2:

SUBR
STA
LDA
MOV
NOP
NOP
NOP
NOP
NOP
LDA
ANI
STAX
INX
CMP

J2

JP
LDA
STAX
INX
RET
LDA

CPADCN
ADCST

VFINAL+1

C.A

ADCHB
17

D

D

C

CPADN2
CPADN3
ADCLB
D

D

VFINAL

3STARTS ADC

3GET FINAL VOLT HIGH BYTE
3STORE IT

3WAIT FOR ADC TO CONVERT
3

3

3

3

3GET ADC HIGH BYTE

3MASK OUT ALL BUT ADC BITS
3STORE ADC HIGH BYTE

3INC MEM ADDR

3COMPARE WITH VFINAL
3HIGH BYTE

3HIGH BYTE EQUAL.
3COMPARE LOW BYTE

3ALL DONE

3GET ADC LOW BYTE

3STORE ADC LOW BYTE

sINC MEM ADDR

3AND GO HOME

3GET FINAL VOLTAGE LOW BYTE

 

CPADN3:

I

3ADD CHARGE

MOV
LDA
STAX
INX
CMP

RC
JMP
LDA
STAX
INX
JMP

3HL I HL+2

CHGADM:

CGADMI:

CGADH2:

i
i

SUBR
MOV
STA
INX
HOV
STA
INX
ANI

RRC
RRC
HOV

MVI
STA
LDA
DCR
JN2

MOV
STA

CALL
DCR

JN2
RET

C.A
ADCLB
D

CP4O
ADCLB
D

D
CP4O

CHGADM
A.M
DACLB
H

A.M
DACHB
H

374

C.A

A.1
SW

SWDLYI'

A
CGADM2

A.B
SW

SWDLYB
C

CGADMI

157

3STORE IT

3GET ADC LOW BYTE
3STORE ADC LOW BYTE
3INC HEM ADDR
3VOLTAGE MORE NEG
3THAN FINAL?
3RETURN IF LESS NEG
3EXP IS DONE. LEAVE
3GET ADC LOW BYTE
3STORE IT

3INC MEM ADDR

3EXP IS DONE. LEAVE

TO ELECTRODE. DAC VALUE & G OF CHG ADD FORM MEM

3
3SET DAC LOW BYTE

3

3SET DAC HIGH BYTE

3

3INC MEM ADDR

3MASK DAC HIGH BYTE TO GET
3* OF CHARGE ADDITIONS
3ROTATE TO THE RIGHT
3POSITION

3SAVE NUMBER OF CHARGE
3ADDITIONS

3

3

3GET DELAY VALUE

3

3LOOP AROUND TILL IT IS
3DONE

3SW # FOR CHARGING AMPLIFIER
3DUMP CHARGE TO

3WORKING ELECTRODE

3DELAY

3CHECK IF NUMBER OF CHARGE
3ADDITIONS ARE DONE

3ND DO IT AGAIN

3AND GO HOME

3THIS ROUTINE COLLECTS DATA FOR CHROPOTENTIOHETRY EXP

CP:

SUBR
PUSH
PUSH
PUSH
PUSH
LXI

DAD

SHLD

OF

H

D

B
PSW
H.O
SP
SSAV

3SAVE REGS
3

3 .
3CLEAR REG

3AND GET STACK POINTER
3AND SAVE IT

 

 

CPO:

CPI:

0P2:

CPS:

CP4:

CPSO:

LXI
CALL
LDA
CPI
JN2
CALL
LXI
CALL
CALL
JNC

CPI
J2
CPI
J2
CPI
C2
JMP
CALL
DI
CALL
LDA
ANI
JN2
CALL
CALL
MVI
STA
STA
MVI
STA
STA
LXI

SHLD

LXI
SHLD

LXI
MVI
MVI
INX
HOV
ANI
HOV
EI
LXI
CALL
JMP
POP
LXI
SHLD

158

H.VINIT
VAPR
VAPFLG
O

CPO
READY
H.VINIT
VAPR
CHARIN
CPI

'0
CP2

’9
CP2

'b
BLANK
cm
arr-'1 1

TICP
TICMD

10

CPS
CLRINS
CLRIN4
A.Béa
INTTLB+14
INTTLB+2O
A.BOS
INTTLB+15
INTTLB+21
H.CP4O

INTTLB+16

H.CPSO
INTTLB+22

H.INTCMD
H.143
H.144

H

A.M

347

H.A

H.VINIT
VAPR

CP4

H

H.CP32
INTTLB+22

3GET ADDR FOR INIT VOLTAGE
3APPROACH THE VOLTAGE
3GET THE VOLT FLAG
3EQUAL?

3NO. WAIT

3TELL US IT’S READY

3GET ADDR FOR INIT VOLTAGE
3APPROACH THE VOLTAGE
3KEY BOARD TYPED?

3NO. KEEP AT DESIRED
3POTENTIAL

3GO?

3YES

3G0?

3YES

3BLANK?

3CLEAR VRAM

3NO.WAIT

3INGORE INTERRUPT FROM 11
3DISABLE INT

3SET UP TIMER FOR CHRONOPOT
3GET TIMER OUTPUT STATUS
3OUT 3
3NOT CORRECT.
3CLEAR INS
3CLEAR IN4
3GET A DI COMMAND

3DI AT LEVEL 3

3 & 4

3GET A JUMP COMMAND

3

3

3JMP TO SETTING UP

3PARM ADDR FOR

3 CHARGE ADD & VOLTAGE

3 MEASUREMENT

3

3LAST DATUM HAS BEEN TAKEN.
3FINISH UP EXP

3

3RESET IS FF 3 & 4

3

3

3INT MASK

3ENABLE LEVEL 3 & 4

3

3 ENABLE INTERRUPT

3

3KEEP AT INIT VOLTAGE

3

3REMOVE CALL

3

3JMP TO CP82 ON NEXT INT

DO IT AGAIN

 

CPSI:

CP32:

CP40:

CP41:

LXI
LXI
LDA
MOV
MVI
STA

NOP
NOP

JMP

CALL
CALL
LDA
STA

STA

EI
RET
DI
MVI
STA
DCX
DCX
LXI
CALL
CALL
SHLD
CALL
MVI
STA
CALL
CALL
MVI
STA
STA
LXI
MVI
MVI
INX
HOV
ORI
HOV
LHLD
SPHL
CALL
CALL
LXI
CALL

159

H.DACLIB
D.ADCLIB
SWA

B.A
A.EOI
INTCHD

CP31

CPADCN
CHGADM
SWC

SW

A.EOI
INTCHD

A.EOI
INTCMD
H

H
D.DACLIB
DSUB
RHLR
DATAN
TIRSET
A.EOI
INTCHD
CLRINS
CLRIN4
A.377
INTTLB+14
INTTLB+2O
H.INTCMD
H.143
H.144

H

A.M

30

H.A

SSAV

ONII
CPADFX
H.PDATAN
SPRMPR

3

i

3GET SWITCH G
3STORE IT IN B
3

69%...

348 MORE NOP’S ARE OMITTED
3

3

3GET POTENTIAL

3ADD CHARGE

IIF'73

3TURN OFF SWITCH TO AVOID
3LEAKAGE

3GET AN END OF INTERRUPT
3FLAG

3AND TELL THE INTERRUPT
3CONTROLLER

3

3RETURN TO DUMMY ROUTINE
3

3GET AN END OF INT FLAG
3AND TELL INT CONTROLLER
3-1 DATA POINT

3

3

3HL-DE

3ROTATE HL RIGHT. DIS-O
3NUMBER OF DATA

3RESET TIMER

3GET AN END OF INT FLAG
3AN TELL INT CONTROLLER
3CLEAR INS

3CLEAR IN4

3SET A RESTART 7

3FOR LEVEL 3

3 & 4

3

3RESET IS FF 3

3 a 4

3INT MASK

3

3DISABLE LEVEL 3 & 4

3

3GET ORIGINAL STACK POINTER
3MOV HL TO SP

3

3FIX ADC LIB

3GET ADDR OF PARM DATAN
3STORE IT.

 

 

160
3AND PRINT THE PARM

POP PSW 3RESTORE REGS

POP B 3

POP D 3

POP H 3

E1 3ENABLE INT

RET 3AND GO HOME

3

3

3ROUTINE TO BRING VOLTAGE BACK
SUBR VBACK

 

VBACK: PUSH H 3SAVE REGS
PUSH D 3
PUSH PSW 3
MVI D.5 3COUNTER
MVI E.S77 3
VBACKI: LXI H.VINIT 3APPROACH THE INITIAL
3VOLTAGE
CALL VAPR 3
LDA VAPFLG 3GET VOLTAGE FLAG
CPI O 3EQUAL?
JN2 VBACKI 3NOT YET
DCR E 3
JN2 VBACKI 3
LXI H.TIDD 3TIMER DELAY
CALL DELAY 3WAIT FOR A WHILE
DCR D 3DECREMENT COUNTER
JN2 VBACKI 3
POP PSW 3RESTORE REGS
POP D 3
POP H 3
RET 3
3
SUBR CPB
CPB: CALL CP 3CHRONOPOTIONMETRY EXP
CALL VBACK 3BRING VOLTAGE BACK
RET 3AND GO HOME
C********
C
C CAP.FTN
C THIS ROUTINE DIVIDE ONE SET OF AVERAGED DATA .
C BY ANOTHER
C
C C.C.LII 7/31/81
C REVISED 10/24/81
C
C********
C DECLARE VARIABLES

BYTE INFILE(32) . INFIL(32) . OTFILE(32). OTFIL1(32)
BYTE IDAT(6144).DATE(IO).CONC(40).TEHP(IO)
REAL'RB DI: D23 DP": DP": DPO: DPP: DPG: "F

O
O

0 0 0 03 0000
(I

0

0

0000

161

INTEGER IDATA(SO72).IDATA1(3072).IERR.ITABLE(96)
INTEGER IERRI.ITABLIC96).ND.II.I2.ND2
INTEGER VINIT.VFINAL.VSTPO.VSTP1.MO.BLDA1
INTEGER TIPD.TIDD.NO.N1.SWDLYI.SWDLY2.VAPDA.VAPDA1
INTEGER VAPN.VAPN1.N2.SWDLY3.SWDLY4
EQUIVALENCECINFILEII).TEST)

DATA EXl’EX’l

LUNI'I

LUN2-2

LUNS-S

LUN4-4

LUNSIS

LUNé-b

ASK FOR INPUT FILE NAME

WRITE(LUN5.900)

FORMAT(’$FILE/FILE1. INPUT FILE: ’)

READ THE INPUT FILE NAME
READ(LUN5.905)INFILE

FORMAT(32A1)

CHECK IF USER HAS TYPED EXIT TO LEAVE ROUTINE
IF(TEST.EQ.EX)GOTO 50

CALL UNFORH TO OPEN FILE TO READ ENABLE
CALL UNFORM(O.IERR.ITABLE.INFILE.O.1.LUN3)
CHECK FOR ERRORS

IF(IERR.NE.O)GOTO 10

READ IN THE DATA USING UNFORH

NUM=6144

CALL ~ UNFORM(1.IERR.ITABLE.IDATA.NUH)
CHECK FOR ERRORS

IF(IERR.NE.O)GOTO 2O

ASK FOR 2nd INPUT FILE NAME
WRITE(LUN5.906)

FORMAT(’$INPUT FILE1: ’)

READ THE INPUT FILE NAME
READ(LUN5.907)INFIL

FORMAT(32A1)

CALL UNFORH TO OPEN FILE TO READ ENABLE
CALL UNFORM(0.IERR1.ITABL1.INFIL.O.1.LUN2)
CHECK FOR ERRORS

IF(IERR1.NE.O)GOTO 11

READ IN THE DATA USING UNFORH,

NUM=6144

CALL UNFORM(1.IERR.ITABL1.IDATA1.NUM)
CHECK FOR ERRORS

IF(IERR.NE.O)GOTO 2O

CLOSE INPUT FILE

CALL UNFORM(2.IERR.ITABLE)

OPEN INPUT FILE AGAIN

CALL UNFORM(O.IERR.ITABLE.INFILE.O.1.LUN3)
READ IN DATA USING UNFORH

NUM=6144 '

CALL UNFORM(1.IERR.ITABLE.IDAT.NUH)
IF(IERR .NE. 0) GO TO 20

 

 

162

C ASK FOR MULTIPLYING FACTOR
WRITE(LUN5.9OS)

908 FORMAT(’GMULTIPLYING FACTOR(CAP/CH**2): ’)

C READ THE FACTOR
READ<LUN5.909)MF

909 FORMAT(F15.7)

C ASK FOR OUTPUT FILE

6 WRITE(LUN5.910)

910 FORMAT(’$OUTPUT FILE: ’)

C READ THE OUTPUT FILE NAME
READ(LUN5.903)OTFILE

C OPEN OUTPUT FILE USING ASSIGN
CALL ASSIGN(4.0TFILE.32)

C SEND HEADER TO OUTPUT FILE
WRITE<LUN4.913)INFILE

915 FORMAT(’HD '.S2A1)
WRITE(LUN4.915)INFIL
ND-IDATA(1) '
NDO=ND~30

C GET PARAMETERS
J33
DO 110 I'1.10
DATE(I)-IDAT(J)
J-J+1

110 CONTINUE
DO 115 I81.4O
CONC(I)-IDAT(J)
JIJ+1

115 CONTINUE
DO 120 131.10
TEMP(I)-IDAT(J)
JIJ+1

120 CONTINUE
VINIT
VFINAL
VSTPO
VSTP1
HO
BLDAI
TIPD
TIDD
N0
N1
N2
SWDLYI
SWDLY2
SWDLYS
SWDLY4
VAPDA

IDATA(32)
IDATA(33)
IDATA(34)
IDATA(35)
IDATA(36)
IDATA(37)
IDATA(38)
IDATA(39)
IDATA(40)
IDATA(41)
IDATA(42)
IDATA(43)
IDATAI44)
IDATA(45)
IDATA(46)
IDATA(47)
VAPN IDATAC4S)
VAPDA1 IDATA(49)
VAPNI 8 IDATA(50)
C SEND NUMBER OF DATA POINTS TO OUTPUT FILE

 

163

WRITE(LUN4.920)NDO

920 FORMAT(’NU ’.I15)

IF(VFINAL .GT. VINIT)GO TO 205
C D5: AVERAGE VOLTAGE FOR CAPACITANCE MEASUREMENT
C SCAN POSITIVELY

D5BVINIT*1.0-VSTP0*.5
D68-VSTP1*1.0
GO TO 207
205 D5-VINIT41.0+VSTPO*.5
D6-VSTP1*1.0
207 VOLT82.4988-D5*.0012207031
C READ IN THE DATA POINTS CONVERT THEM INTO VOLTAGE
C AND SEND THEM TO THE OUTPUT FILE
ND2=ND*S+1
DO 100 1.9235102! S
I2-IDATA(I)
IF(I2.GE.0)GO TO 55
D2-655S6.+1.*I2

GO TO 56
55 D2-I2
56 II-IDATA(I+1)

IF(I1.GE.0)GO TO 60
DI-(65536.+1.*I1)*65536.
GO TO 61

60 D1-I1*65536.

61 DPN=DI+D2
DPH'IDATA(I+2)*1.0
DPO-DPN/DPH
I2-IDATA1(I)
IF(I2.GE.0)GOTO 65
D2-65536.+1.*I2

GOTO 66
65 D2-I2
66 I1-IDATA1(I+1)

IF(I1.GE.0)GOTO 70
D1-(65536.+1.*I1)*65536.
GOTO 71

70 D1-Ilfi65536.

71 DPN-D1+D2
DPM-IDATA1(I+2)*1.0
DPP'DPN/DPM
DPQ-DPO*MF/DPP
WRITE<LUN4.925)VOLT.DPQ

925 FORMAT(’RD’.2E15.7)

C CALCULATES NEXT VOLTAGE
D5-D5+D6
VOLT=2.49SS-D5*.0012207031

100 CONTINUE.

WRITE(LUN5.800)

800 FORMAT<1X.’PARAMETERS TO 1.TI 2.LP 3.NO OUTPUT ’)
READ(LUN5.805)I5

805 FORMAT(I5)

IF(I5 .EQ. 3)GO TO 190

125
130
810

811
812

815

816

820

821

822

823

824

830

835

836

837

164

IF(I5 .EQ. 2)GO TO 125

LU-LUNS

GO TO 130

LU-LUN6

WRITECLUN5.810)
FORMAT(1X.’OUTPUT FILE1: ’)
READ(LUN5.905)OTFIL1

CALL ASSIGN(LUN1.0TFIL1.32)
WRITE(LUN1.915)INFILE
WRITE(LUN1.920)NDO
WRITE(LU.811)INFILE
FORMAT(1X.’FILE’.12X.32A1)
WRITE<LU.812)(DATE(I).I-1.10)
FORMAT(1X.’DATE’.12X.10A1)
WRITE<LUN1.812)(DATE(I).I-I.10)
WRITE<LU.815)(CONC(I).I-1.40)
FORMAT(1X.’CONC’.12X.40A1)
WRITE(LUN1.815)(CONC(I).I'1.40)
WRITE(LU.816)(TEMP(I).III.10)
FORMAT(1X.’TEMP’.12X.10A1)
WRITE¢LUN1.816)(TEMP(I).III.10)
VIN-2.4988-VINIT*.OO12207031
WRITE(LU.820)VIN
FORMAT11X.’VINIT’.11X.F15.7.7X.’V’)
WRITE€LUN1.820)VIN
VFI82.4988-VFINAL4.0012207031
WRITE(LU.821)VFI

FORMAT(1X. ’VFINAL’. 10X. F15. 7. 7X. ’V’)
WRITE(LUN1.821)VFI
WRITEILU.822)VSTPO
FORMAT(1X.’VSTPO’.11X.I15)
WRITE<LUN1.822)VSTPO
WRITE(LU.823)VSTP1
FORMAT(1X.’VSTP1’.11X.I15)
WRITE(LUN1.823)VSTP1
WRITE(LU.824)M0
FORMAT(1X.’H0’.14X.II5)
WRITE(LUN1.824)MO
DASi-(BLDA1-512)*4.8828125
WRITE(LU.830)DA3
FORMAT(1X.’BLDA1’.11X.F15.7.6X.’mV’)
WRITE(LUN1.830)DA3
TI-1.*TIPD*TIDD
WRITE(LU.835)TI
FORMAT<1X.’TIME DELAY’.6X.F15.0.5X.’US.’1
WRITE(LUN1.835)TI
WRITE(LU.836)TIPD
FORMAT(1X.’TIPD!.12X.I15)
WRITE<LUN1.836)TIPD
WRITE(LU.837)TIDD
FORMAT(1X.’TIDD’.12X.I15)
WRITE(LUN1.837)TIDD
WRITE(LU.845)N0

845

846

853

847

848

854

855

850

851

849

930
935

1D
94D

11

20
945

165

FORMAT(1X.’N0’.14X.I15)
WRITE(LUN1.845)NO

WRITE(LU.846)N1
FORMAT‘IX.’N1'.14X.IIB)
WRITE(LUN1.846)N1

WRITE(LU.853)N2
FORMAT(1X.’N2’.14X.II5)
WRITE(LUN1.853)N2
WRITE<LU.847)SWDLY1
FORMAT(1X.’SWDLY1’310X3115)
WRITE<LUN13847)SWDLY1
WRITE(LU.848)SWDLY2
FORMAT(1X.’SWDLY2'.10X.I15)
WRITE(LUN1.848)SWDLY2
WRITE(LU.854)SWDLY3
FORMAT(1X.’SWDLYS’.10X.II5)
WRITE(LUN1.854)SWDLY3
WRITE(LU.855)SWDLY4
FORMAT(1X.’SWDLY4’.10X.I15)
WRITE(LUN1.855)SWDLY4
DA3I-(VAPDA-512)*4.8828125
WRITE(LU.850)VAPN.DA3
FORMAT<1X.’VAPDA’.6X313.’ *’.F15.7.6X.’mV’)
WRITE(LUN1.850)VAPN.DA3
DASS-(VAPDA1-512)*4.8828125
WRITE(LU.851)VAPN1.DA3

FORMAT1 1X. ’VAPDAI ’3 5X. IS. ’ *’1 F15. 73 6X0 ’MV’)
WRITE(LUN1.851)VAPN1.DA3
WRITE(LU.849)MF
FORMAT(1X.’MF(CAP/CH**2)’.3X.F15.7)
WRITE<LUN1.849)HF

CALL CLOSE(LUN1)

GO TO 190 '

NOW CLOSE THE STILL OPEN INPUT FILE USING UNFORH
CALL UNFORM(2.IERR.ITABLE)

CHECK FOR ERRORS

IF‘IERR.NE.0)GOTO 30

CALL UNFORM(2.IERR1.ITABL1)

CHECK FOR ERRORS

IF(IERR1.NE.0)GOTO 30

SEND END OF DATA MAKER TO OUTPUT FILE
WRITE(LUN4.930)

FORMAT(’ED ’)

WRITE(LUN5.935)

FORMAT(' DATA CONVERSION COMPLETE ’)
GOTO 40

WRITECLUN53940)

FORMAT(’ INPUT FILE NOT FOUND ’)
GOTO 5

WRITEILUN5.940)

GOTO 7

WRITE‘LUN5.945)

FORMAT(’DATA CAN NOT BE READ OUT OF INPUT FILE ’)

30
950
C
40
C

50

166

GOTO 50

WRITE(LUN5.950)

FORMAT(' INPUT FILE CAN NOT BE CLOSED ’)
ADN CLOSE THE OUTPUT FILE

CALL CLOSE(4)

RETURN TO BEGINNING TO CONVERT ANOTHER FILE
GOTO 5

CALL EXIT

END

C {an} ”*flr‘i

00000000000

0
O

O
(I

0~OO~0 0 0 00 0000
3..
O

CONCPAD.FTN

THIS ROUTINE CONVERTS BINARY FILE OF

ADC VALUES TO C.G.ENKE & CO. STANDARD DATA FILE
AND A PARAMETER FILE

C.C.LII 4/22/81 J
REVISED 10127131 I

m*****

DECLARE VARIABLES

BYTE INFILEC32).OTFILE(32).OTFIL1(32)

BYTE IDAT(1204).DATE(10).CONC(40).TEMP(10)
BYTE NCAP(20)

INTEGER IDATA(602).IERR.ITABLE(96).ND

INTEGER VINIT.VFINAL.AVEW.BLDA1.CADDMN.CGMAX
INTEGER CHGN.CHGQ.CPCOR1.CPCOR2.ICAPC1.ICAPC2
INTEGER ICAPDA.ICDN.ICAPSW.SWA

INTEGER SWDLY1.SWDLY2.TCENW.TIDDA.TIPD
INTEGER VAPDA.VAPDN.VAPDA1.VAPD1N
EQUIVALENCE(INFILE(1).TEST)

DATA EXI’EX’I

LUN1 I
LUNS I
LUN4 I
LUN5 I
LUN6 I
ASK FOR INPUT FILE NAME

WRITE<LUN5.900)

FORMAT(’$INPUT FILE: ’)

READ THE INPUT FILE NAME

READ(LUN5.905)INFILE

FORMAT(S2A1)

CHECK IF USER HAS TYPED EXIT TO LEAVE ROUTINE
IF(TEST.EQ.EX)GOTO 50

CALL UNFORH TO OPEN FILE TO READ ENABLE

CALL UNFORHCO.IERR.ITABLE.INFILE.0.1.LUN3)
CHECK FOR ERRORS

IF(IERR.NE.0)GOTO 10

ASK FOR OUTPUT FILE

WRITE(LUN5.910)

FORMAT(’$OUTPUT FILE: ’)

READ THE OUTPUT FILE NAME

00¥Ufl

0000

110

120

125

130

167

READ(LUN5.905)OTFILE

READ IN THE DATA USING UNFORH

NUMI1204

CALL UNFORHCI.IERR.ITABLE.IDATA.NUH)
CHECK FOR ERRORS

IF(IERR.NE.0)GOTO 20

CLOSE INPUT FILE

CALL UNFORM(2.IERR.ITABLE)

OPEN FILE AGAIN

CALL UNFORM(0.IERR.ITABLE.INFILE.O.1.LUN3)
READ IN DATA USING UNFORH

NUMI1204

CALL UNFORM(1.IERR.ITABLE.IDAT.NUH)
IFCIERR .NE. 0)GO TO 20

GET PARAMETERS

JI3

DO 110 II1.10
DATE(I)IIDAT(J)
JIJ+1

CONTINUE

DO 120 II1.40
CONC‘I)IIDAT(J)
JIJ+1

CONTINUE

DO 125 II1.10
TEMP(I)IIDAT(J)
JIJ+1

CONTINUE

DO 130 II1.20
NCAP(I)IIDAT(J)
JIJ+1

CONTINUE

VINIT I IDATA(42)
VFINAL I IDATA(43)
AVEW I IDATA(44)
BLDA1 I IDATA(45)
CADDMN I IDATA(46)
CGMAX I IDATA(47)
CHGN I IDATA(48)
CHGQ I IDATA(49)
CPCOR1 I IDATA(50)
CPCOR2 I IDATA(51)
ICAPC1 I IDATA(52)
ICAPC2 I IDATA(53)
ICAPDA I IDATA(54)
ICDN I IDATA(55)
ICAPSW I IDATA(56)
SWA I IDATA(57)
SWDLY1 I IDATA(58)
SWDLY2 I IDATA(59)
TCENW I IDATA(60)
TIDDA I IDATA(61)
TIPD I IDATA(62)

126
127

915

920

925
100
800
805

806
807
808

135
140
810

811

168

VAPDA I IDATA(63)
VAPDN I IDATA<64)
VAPDA1 I IDATA(65)
VAPDIN I IDATA(66)
BLDA3 I IDATA(67)

IF(TIDDA .GE. 0)GO TO 126
TIDDI65536.+1.*TIDDA

GO TO 127

TIDDITIDDA

OPEN OUTPUT FILE USING ASSIGN
CALL ASSIGN(LUN4.0TFILE.32)
SEND HEADER TO OUTPUT FILE
WRITE<LUN4.915)INFILE

FORMAT(’HD ’.32A1)

NDIIDATA(1)

NDOIND-90

SEND NUMBER OF DATA POINTS TO OUTPUT FILE
WRITE(LUN4.920)NDO

FORMAT(’NU '.II5)

READ IN THE DATA POINTS CONVERT THEM INTO VOLTAGE
AND SEND THEM TO THE OUTPUT FILE
NDIND+1

TI1I0.0

DO 100 II92.ND

AIIDATA(I)
BI2.4988-A*.0012207031
WRITECLUN4.925)TI1.B
FORMAT(’RD’.2E15.7)
TI1ITI1+TIDD*2.0*10.**(-6)
CONTINUE

WRITE(LUN5.800)
FORMAT(1X.’PARAMETERS TO 1.TI 2.LP 3.NO OUTPUT ’)
READ(LUN5.805)I5

FORMAT(I5)

IF(I5 .EQ. 3)GO TO 190
WRITE(LUN5.806)
FORMAT(1X.’CAPACITANCE FOR CHG ADD/ELECTRODE’.)
WRITE(LUN5.807)
FORMAT<1X.’AREAqu/CM**2): ’)
READ(LUN5.808)C1

FORMATCF15.7)

IF(I5 .EQ. 2)GO TO 135

LUILUN5

GO TO 140

LUILUN6

WRITE(LUN5.810)
FORMAT(1X.’OUTPUT FILE1: ’)
READ(LUN5.905)OTFIL1

CALL ASSIGN(LUN1. OTFIL1. 32)
WRITE(LUN1.915)INFILE
WRITE(LUN1.920)NDO
WRITE(LU.811)INFILE
FORMAT(1X.'FILE’.12X.32A1)

“‘11

.1...

 

812

815

816

817

818

819

820

821’

822

823

828

824

825

826

827

169

WRITE‘LU3812)(DATE(II.III.IO)
FORMAT<IX3’DATE’.12X.10A1)
WRITECLUNI.812)(DATE(I)3III.10)
WRITE(LU.815)(CDNC(I)3II134O)
FORMAT(1X. ’CONC ’3 12X. 4OA1)
WRITECLUN13915)(CONC(I)31.1.40)
WRITE(LU3816)(TEMP(I)31'13IO)
FORHAT‘IX.’TEMP’312X310A1)
WRITE<LUN13916)(TEMP(I)3III.IO)
WRITE‘LU3917)(NCAP(I)31'1320)
FORMAT(1X. 'NCAP '3 12X. 20A1 )
WRITECLUN13817)(NCAP(I)31.1320)
WRITE‘LU3318IC1
FOR"AT(1X3’CAP/AREA'IBXIF15.7IBXI’UP/CN**2’)
WRITE1LUN13818)C1
TIENTI2.*TIDD*IO.**(-6)
CURNTIC1*(CHGN*CHGQ*1.O)*.OOGBBEBIED/TIENT
WRITE1LU.BI9)CURNT
FORMAT(1X.'CURRENT’.9X.F15.7.8X.'UA/CM**2')
WRITE‘LUN13819)CURNT
VINIZ.4983-VINIT*.0012207031
WRITECLU382O)VIN
FORMAT11X.’VINIT'.11X.F15.7.15X.’V’)
WRITE(LUN1.820)VIN
VFII2.4988‘VFINAL*.OOI2207031
WRITE(LU.821)VFI
FORMAT(1X.'VFINAL'310X3F15.7315X3'V’)
WRITE(LUN1.821)VFI

WRITEILU3822)AVEW
FORMAT1IX3'AVEW’JIZXIIIS)
WRITE1LUNI.822)AVEH
DASI-(BLDA1-512)*4.8828125
WRITEILU38231DA3
FOR"AT(1X3'BLDAI’IIIX3F15.7314XJ’MV’)
WRITE1LUN1.823)DA3
DAGI-(BLDA3-512)*4.8828125
WRITEILU.828)DA3
FORMAT1IX.'BLDA3'311X3F15.7314X3'mV’)
WRITEILUN13828)DA3
WRITE1LU3824ICADDMN
FORMAT(1X.’CAQPHN’310X3I15)
WRITE(LUNI.824)CADDMN
DASI—(CGHAXIDI2)*4.8828125
WRITE(LU.825)DA3
FORMAT‘IX:'CQHAX'311X3F13.7314X3'MV')
WRITE(LUN1.825)DA3

WRITE‘LU3826ICHGN
FORMAT(IX.’CHGN’.12X.I15)
WRITE(LUN1.826)CHGN
WRITE(LU3827)CHGG
FDRMAT(1X.’CHGQ’.12X.I15)
WRITE(LUN1.827)CHOG
WRITE(LU3830)CPCDR1

830

831

832

833

840

841

842

847

848

849

850

851

852

853

854

170

FORMAT(1X.’CPCORI’.10X.I15)
WRITE(LUN1.830)CPCOR1
WRITE(LU.831)CPCOR2
FORMAT(1X.’CPCOR2’o10X.I15)
WRITE(LUN1.831)CPCOR2
WRITE(LU.832)ICAPC1
FORMAT(1X.’ICAPC1’.10X.II5)
WRITE(LUN1.832)ICAPC1
WRITE(LU.833)ICAPC2
FORMAT(1X.’ICAPC2’o10X.I15)
WRITEILUN1.833)ICAPC2
DA3I-(ICAPDA-512)*4.8828125
WRITE(LU.840)ICDN.DA3
FORMAT<1X.’ICAPDA’.5X.I3.’ *’.F15.7.14X.’mV’)
WRITE(LUN1.840)ICDN.DA3
WRITE(LU.841)ICAPSW
FORMAT(1X.’ICAPSW’.10X.I15)
WRITE(LUN1.841)ICAPSW
WRITE(LU.842)SWA
FORMAT(1X.’SWA’.13X.I15)
WRITE(LUN1.842)SWA
WRITE(LU.847)SWDLY1
FORMAT(1X.’SWDLYI’.10X.I15)
WRITE(LUN1.847)SWDLY1
WRITE¢LUo848)SWDLY2
FORMAT(1X.’SWDLY2’.10X.I15)
WRITE<LUN1.848)SWDLY2
WRITE(LU.849)TCENW
FORMAT(1X.’TCENW’.11X.I15)
WRITE(LUN1.849)TCENW
WRITE(LU.850)TIDD

FORMAT‘IX: ’TIDD’: 12X. F15 13 14X. '05,)
WRITE(LUN1.850)TIDD
WRITE(LU.851)TIPD
FORMAT(1X.’TIPD’.12X.I15)
WRITE<LUN1.851)TIPD

TII2*TIDD

WRITE(LU.852)TI

FORMAT(1X.’TIME DELAY’.6X.F15.1.14X.'us’)
WRITE<LUN1.852)TI
DA3I-(VAPDA-512)*4.8828125
WRITE(LU.853)VAPDN.DA3
FORMAT(1X.’VAPDA’.6X.I3.’ *’.F15.7.14X.’mV’)
WRITE(LUN1.853)VAPDN.DA3
DASI-(VAPDA1-512)*4.8828125
WRITE(LU.854)VAPD1N.DA3
FORMAT(1X.’VAPDA1'.5X.IS.’ *’.F15.7.14X.’mV’)
WRITE(LUN1.854)VAPD1N.DAS

CALL CLOSE(LUNI)

GO TO 190

NOW CLOSE THE STILL OPEN INPUT FILE USING UNFORH
CALL UNFORH‘2.IERR.ITABLE)~

CHECK FOR ERRORS

 

930
935

10
940

20
94s

30
950

40

50

171

IF(IERR.NE.0)GOTO 30

SEND END OF DATA MAKER TO OUTPUT FILE
WRITE<LUN4.930)

FORMAT(’ED ’)

WRITE(LUN5.935)

FORMAT(’ DATA CONVERSION COMPLETE ’)
GOTO 40

WRITE(LUN5.940)

FORMATI’ INPUT FILE NOT FOUND ’)

GOTO 5

WRITECLUN5.945)

FORMAT(’DATA CAN NOT BE READ OUT OF INPUT FILE ’)
GOTO 50

WRITE(LUN5.950)

FORMAT(’ INPUT FILE CAN NOT BE CLOSED ’)
ADN CLOSE THE OUTPUT FILE

CALL CLOSE(4)

RETURN TO BEGINNING TO CONVERT ANOTHER FILE
GOTO 5

CALL EXIT

END

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1. G. L. Boo-an and I. B. Bolbrook. A3311__hgg1. 1_.
1793 (1963).

2. G. L. Boo-an and I. B. Bolbrook. 5331‘_£hgg1. _1.
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3. J. I. Hayes and C. N. Roilloy, 13311_£hgn1.11.
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4. D. Pauli, J. R. Buff, and I. C. Pearson. Ag;L‘_§hgl‘.

5. G. Lunar and R. A. Ostoryoung, Aggl1_£hgl1. 13.
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6. B. R. Brown. T. G. lcCDrd. D. E. 831th. and D. D.
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7. D. I Brits. IE_ELLELEDEDEII_£1221. ii. 309

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8. P. Dolnhay, A331, Ch1n, A059. 11, 90 (1962).
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10. P. Delahay. An‘l‘_£hgg‘. 11, 1267 (1962).

11. A. Art-atn. and P. Delahay, 53311_gng;1. 11, 1117
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12. I. B. Rein-nth, Ag;1‘_£3331, 11, 1272 (1962).
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14. I. I. Indirka, R. Abel. and C. G. Enke. 61112.21211.
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15. J. I. Intzonbergor and P. B. Dunn. _g;11_§hgg1.11.
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16. I. Astrno. F. Del Ray End I. Bonastro, 1‘_fi1ggggg;n;1‘
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17. I. I. Goldsvorthy and R. G. Clan. Aggl1_£hgg1. 11.
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18. 8. B. Bonrdnkis. Dissertation. Iichigan State
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22.

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H0

D. C. Grnhnne. Proe. 3rd fleeting CITEC, Berne, 1951,
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G. Gouy. 11_£h1;1_311113. g. 457 (1910).
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D. L. Chip-an. £h111_!311. $1. 475 (1913).
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D. C. Grnhene and B. B. Ihitney. 1‘_An1_£hg|._§3314.§AJ
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L. 24-4191 and C. G. Enke. 12.211211221131_§991.
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L. Bentley and C. G. Enke. 1. Elgggggghel. figg..
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P. Delnhny. R. d1 Lvie. and A.-I. Giuliani.
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P. C.Ie11y and Gary Borliek.An;11_£hgl1.11.
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D. C. Grahame, J, Aggg. ghga. £29..1_.
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D. C. at‘h“°o Ii-A!££‘_£h£l&_§2£$' 12'
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B. I. 8. Sand, Phi; Nag..‘1. 45 (1901).

Z. Intaoglnnoff. Z. Blghgrggggg,. 1_. 5 (1906).

P. n.1‘h‘y ‘nd I 39:3133' l&—A£££&—£h——&—§££L' 120
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I. L. B. Rae. A. Dnnjnnovie, and J. 0'!. Boektis.
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T. Berzins and P. Delnhny. I;_A§1_£h__1_§gg1. 11.
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39.

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41.

42.

43.

44.

45.

46.

47.

48.

49.

50.

51.

52.

53.

54.

55.
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57.

174

I. B. Reinmuth. An11‘_£hgg‘. 12. 1514 (1960).

A. C. Tests and I. H. Beinnuth.1I Amer, Chem, 899,.

_1. 783 (1961).

B. B. Bernen end A. J. Bard. 1‘_£_1;‘_£Lgn‘. 12.
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J V Ashley and C N Bailey. 11.319911913111_21221.

l. 253 (1964).

 

L. Gieret. Thesis. Univ. Libre Bruxelles. 1952.

B. B. Ber-en and A. I. Berd. 1. ElegtrochenI $00., 115.
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I. B. Rein-nth, Ana}. C§e3,. 31. 485 (1961).

R. 8. Rogers and L. leitee, C
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I. T. DeVriee. B 0 Che Interfe el
Electrochen.. 11, 31 (1968).

I. T. DeVriee, 1. Elggtroenel. Chen, Igterfeoiel
£11£££2£h£5. 1!. 459 (1963)-

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