137
536

 

THS

POLAROGRAPHiC STUDIES 0?
METALLEC 3M9URE'E‘IE” IN NICKEL
SULFATE SOLUTiCN

Thesis {0? the Degree cf M. 3.
MICHEGAN S?A"’i‘3 C LL53
Ciyde B. Anderson

{94!

 

 

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PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date If requested.

 

DATE DUE

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6101 czr’ClFICDaIeDue p65-p 15

 

 

 

POLAROGRAPHIC STUDIES OF METALLIC IMPURITIES

IN NICKEL SULFATE SOLUTION

by
4’“

Clyde B.Ugnderson

A THESIS
Submitted to the Graduate School of Michigan
State College of Agriculture and Applied
Science in partial fulfilment of the
requirements for the degree of

MASTER OF SCIENCE

Department of Chemistry
1941

v
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Una («ukv ,. 1 L5 1 UL‘tl" I,

T546
A5Z“

ACKNOWLEDGMENT
The writer wishes to express his sincere appreciation

to Dr. D. T. Ewing, Professor of Physical Chemistry, for

his able guidance and materials furnished.

134206

TABLE OF CONTENTS

IntrOduCtiono I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 0
Description of Apparatus.........................
Procedure. 0 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 0 O O 0

Preparation Of materialSOOOOOOOOOOOOOOOOOOOOOO...

rm 0) (n e: Ia

EXPerimental-O...00.0.0.0...OOOOOOOOOOOOOOOOOOOOO.

summarYOOOOOOOOOOOOOOO00....0.00.00.00.000000000064

Literatllre...000......0.0...00.00.00.00000000000025

INTRODUCTION

The polarographic method of analysis developed by
Heyrovsky has been brought into prominence in this country
largely due to the work of men like Kolthoff and Lingane.(l)
Lingane and Kerlinger<7have applied this method to the
determination of nickel in alloys. Others such as Muller(3)
have worked with organic compounds. Recently Lingane and
Davis(6)have determined Vitamin B complexes by the use of the
polarograph. This instrument is still being applied in various

new fields.

DESCRIPTION OF APPARATUS

The simplified wiring diagram helps explain the method
and principles of polarographic analysis. The electrolysis
cell containing the solution to be analyzed is denoted by
D in the diagram. The cell consists of a dropping mercury
electrode as the cathode. This electrode must deliver small
drops of mercury at the rate of one drop in every three to
four seconds. The tip of this electrode is placed beneath
the surface of the solution being analyzed. Two nitrogen
inlets are shown. The first inlet N1 is used to bubble
the nitrogen through the solution. This is necessary since
the dissolved oxygen would be reduced at the dropping mercury
cathode during the analysis, giving troublesome maxima.
The second inlet N2 is used during the actual run. This
insures the exclusion of oxygen during the run and also

allows the solution to be quiet. An undisturbed solution

is essential since galvanometer readings are affected by
disturbances or jarring. The layer of mercury at the
bottom of the cell serves as the anode.

This mercury anode is connected to the wire wound
cylinder at B by means of a movable disk. Standard re-
sistance wire is wound on the cylinder. If the total
voltage of the battery is three volts and if thirty turns
of standard resistance wire on the cylinder are just equal
to three volts, then each turn would correspond to 0.1
volt. The cylinder is essentially a potentiometric bridge.

By this cylinder arrangement, the applied E.M.F. is
increased gradually and uniformly by means of the synchro-
nous motor A. This increasing voltage is synchronized
with the moving chart paper. One revolution of the
cylinder B, as previously stated, is equal to 0.1 volt, and,
by the proper gear ratio, is also made equal to one division
of the chart paper. This makes possible an exact knowledge
of the applied E.H.F. at any time.

The current passes through a galvanometer whose
deflections are mechanically amplified T and transmitted
to the inking pen by the automatic recorder R. The
displacement of the inking pen is directly proportional to
the amount of current flowing. The total range of the
recorder varies from two to one hundred microamperes. The
recorder range or sensitivity of the system is regulated
by varying the shunt resistance S. The larger the shunt
resistance, the more sensitive is the system; 1.9., a
larger fraction of the current is forced through the

recorder galvanometen

Current voltage curves are simply the curves obtained
by gradually increasing the applied E.M.F..and noting the
current corresponding to each E.M.F. applied. As shown
by the diagram, the Leeds-Northup electro-chemograph
makes a permanent record of the current-voltage curve at
the time of the analysis. Manually operated polarographic
systems can also be used to obtain these curves, which
would then consist of a series of points rather than a

continuous curve.

 

 

 

 

 

 

 

 

 

 

Fig. 1

In this polarogram, curve 1, the applied E.M.F.
volts are plotted on the ordinate and the corresponding

current on the abscissa. This solution is .OO2N cadmium

chloride in O.lN potassium chloride. When the line denoted
by A traces a straight line on the ordinate of the graph
paper, this is a check that shows the electrical balances

have been correctly made. The polarizer was snapped on

at point 0 and the curve started. At first only a small
current flowed through the cell and was carried by the
potassium chloride. When the decomposition potential

of cadmiu m B was-reached, continuous electrolysis began.

The cadmium ions were dischargaior "plated off" on the
cathodic drops of mercury, forming a dilute cadmium amalgam.
After the decomposition potential was slightly exceeded,

the current carried by the indifferent salt and the cadmium
reached a limiting value and became constant. This difference
between this limiting current D and the current just before
the decomposition potential is reached is directly proportional
to the concentration of the reducible substance. This is

the basis of quantitative polarography.

The limiting current is often called a diffusion current.
Lingane(l)states that "when an indifferent electrolyte is
used the current is practically entirely carried by the
indifferent ions and the electrical forces on the reducible
ions is nullified. Under the/ignditions the reducible ions
reach the electrical surface only by diffusion and hence
the limiting current is called a diffusion current."

After the limiting current is reached the cadmium ions are

reduced as fast as they reach the mercury drop by diffusion,

and the effect is then a constant effect.

The identifying parts of curve 1 are first the
decomposition potential B. This is characteristic for
each element and for cadmium in this solution it is -.64
volts. Many workers use the half-wave potential C
rather than the decomposition potential as the identifying
method.

The half wave potential is less affected by such
factors as the capillary used and the dr0p timefl)The half
wave potential as used throughout this thesis is the value
of the applied E.H.F. of the dropping mercury electrode
at that point on the current voltage curve where the
current is one half of its limiting value.

Curve 2 shows the simultaneous determination of .OOlN
lead chloride and .OOlN cadmium chloride in 0.1N potassium
chloride. The first diffusion current F is for the lead
ions and the second diffusion current G is for the cadmium
ions. The decomposition potential of cadmium is the same
in each case. The diffusion current G is half that shown
in curve 1. This is in direct agreement with their

concentrations.

PROCEDURE

The general procedure for the run for the .OO2N
cadmium chloride solution is as follows. The electrical
balances are made as specified by the Leeds-Northup Co.
Enough mercury was poured into the electrolyzing cell
to form a layer at the bottom. A measured volume of the
cadmium chloride solution was pipetted into the cell.
Next nitrogen was bubbled through the solution by inlet 1
as show n on the diagram for a period of 10 minutes.

The incoming nitrogen was changed to inlet 2 and the first
inlet stoppered. The dropping electrode was next intro‘
duced, its tip being placed 5 mm. below the surface of

the solution. The cell was then connected to the
electrical system and allowed to come to equilibrium over
a period of five minutes. During this time the drop rate
of the mercury electrode was checked. The drop rate must
be between three and four seconds as the time per drop.
After this check the polarizing unit was snapped on and
the resulting current-voltage curve obtained. At the
completion of the analysis the polarizing unit was snapped
off, the outside glass of dropping mercury electrode was
cleaned. Then the tip was immersed in pure mercury and

thus kept free from contamination until the next analysis.

PREPARATION OF MATERIALS
The mercury was purified according to the following

procedure. Very fine drops of mercury from the capillary

stem of a funnel reservoir were allowed to fall through_

a glass tube 150 cms in length that contained a 40%
nitric acid solution. Next the mercury was electrolyzed
with mercury as the anode. A 4% nitric acid solution was
used with a current density of two amperes per square
decimeter for a period of twelve to sixteen hours. After
electrolysis, the mercury was dried and distilled under
vacuum.

The nitrogen used was taken from a commercial nitrogen
pressure tank. This nitrogen was bubbled through two
separate flasks each containing alkaline pyrogallic acid
to remove oxygen. Then the gas was bubbled through a
flask containing water to remove the vapors of pyrogallic
acid. From this flask the nitrogen was introduced into the

electrolyzing cell.

DETERMINATION OF METALLIC IONS IN NICKEL SULFATE

The nickel sulfate solution used throughout the research
was made by dissolving 479.5 grams of nickel sulfate in
two liters of water. This is equivalent to two pounds of
nickel sulfate per gallon and is the concentration often
used in plating solutions. Sulfate solutions are commonly
used in the determination of cadmium.

Cadmium was the first ion tried in the nickel sulfate
solution. Excellent current-voltage curves were obtained
as shown by Fig. 2. The amount of cadmium or of any other
metallic ion will be expressed in mg. per liter throughout
this thesis.

For cadmium the simple conversion was made:

 

At. rt. Cd (112.41) x 877.6 = 449.6
Mol. wt. Cd012.2H20 (219.4) Wt. CdClg. mg Cd per
2Hc0 mg per liter
li er

Cadmium at the above concentration was added to nickel
sulfate solutions at various pH's. The nickel sulfate
solutions of pH 1.22 and 2.85 were acidified by the addition
of C.P. hydrochloric acid. The nickel sulfate solution of
pH 6.70 was obtained by the addition of 0.125N sodium
hydroxide drop by drop using a mechanical stirrer. The pH
6.70 was considered as the upper limit since above this pH
nickel precipitated in appreciable amounts.

The diffusion current of cadmium at the same concentra-
tion was the same regardless of the acidity as shown by

curves f or these three pH's.

The diffusion current at each pH was directly
preportional to the amount of cadmium present over the
range of 12 to 450 mg of cadmium per liter. Current voltage
curves are shown in Fig. 2. Acidity had no definite effect
on either the decomposition potential or the half-wave

potential as shown by Table 1.

 

 

 

 

 

 

 

 

 

Table l.
Decomposition Potential in Volts

. Conc. Cd . pH pH pH
mg/liter 1.22 2.85 6.70
449.6 -.65 -.65 -.64
228.8 -.65 -.69 -.66
114.4 -.66 -.69 -.66
57.2 -.68 -.68 -.66

Half-Wave Potential

1r Conc. Cd L pH A pH pH
mg/liter A 1.22 2.85 6.70
449.6 -.76 -.76 -.76
228.8 -.74 —.78 -.74
114.4 -.73 -.74 -.73
57.2 “072 “073 “072

 

 

 

 

 

Drop time:

Shunt Resistance:

3.2 seconds
50,000 and 22,222 ohms

Range: 0 to -5 volts

 

 

lO

 

Fig. 2

Stannous sulfate was next added to the nickel sulfate
solution at the rate of 475 mg of tin per liter. The curves
obtained as shown by Fig. 5 were not satisfactory. The
solution containing the stannous sulfate clearly showed
increasing amounts of precipitate upon standing. This
was also evident in the current-voltage curves since the
amount of stannous ion shown was much less than the 1:1
hdilution used.

The difficulty in the determination of stannous sulfate
in the nickel sulfate solution was overcome by the use of

an acid solution of nickel sulfate (pH 2.21). Again 473 mg

I
of tin per liter w are added as stannous chloride, using
the same method as before the runs were made. The current-
voltage curves Fig. 4 Show the improvement in the determina-
tion of tin and also well-defined decomposition potentials
on the curves. Tables 2 and 3 show the comparative results

in each case.

Table 2
Stannous sulfate in nickel sulfate (pH 4.83)

 

 

 

 

 

 

 

 

Tin mg Diffusion Half-wave Decomposition

per liter current potential potential
microamperes

473.0 069 -035 “.25
236.5 .31 -.36 -.28
118.2 008 “9:58 “.31

59.1 .04 -.45 -.40

Table 3

Stannous sulfate in nickel sulfate (pH 2.21)

 

473.0 1.30 -.44 -.29
236.5 .63 -.43 -.32
118.2 .28 -.59 -.31

59.1 .14 -.39 -.as

 

 

 

 

 

 

Drop time: 3.5 seconds
Shunt resistance 22,222 ohms
Range 0 to -3 volts

12

-._ ._ .__... -7 - —9
l

 

 

 

-_-_...._ 44.-

 

 

 

 

 

 

 

 

 

 

 

._4I.._...._ _..T_.-.__..-._

 

 

 

 

 

.-...II......-.. a. -
. .
. _. .
- if-..
.
. n.
I I-.- I..--..-.
. .
. _
- .

Tin 236.5 mg/liter curve 1
Tin 118.2 mg/liter curve 2

Fig. 4
.5 mg/liter curve 1

-tin 118.2 mg/liter curve 2

Tin 236

 

..._. .. - *._—._ -——___._.._.-__.___~_-_
I

I

 

I
.__._——_._._
|
. I
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-,_._.

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_ ___._ _ _ , _T-____+-_-_.--__... _ f..- ..

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_.____‘-._.._—.~— —
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I

:4...

I
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.
__._.—.. H‘s-*k.—- —

It

I

I

' I
.__.i - fi-

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r—r-a ~L....__~.

. .-_....__..._.._.__
l r .

COpper was also determined in nickel sulfate
solution. A known amount of cupric sulfate, .0499 grams
per 100 milliliters, was added to the nickel sulfate
solution. Again the conversion to mg of copper per liter
w as made.

The following table 4 shows the summary of results.
In each case it was necessary to run a blank determination
on the nickel sulfate solution due to the copper already
present in the solution. The amount of COpper as determined
in the blank was then subtracted in each case.

This use of blanks could be very useful. In cases
where the increase in the amount of copper present is
important, the increase'could be shown by polarographic
determinations.

Likewise by adding a known amount of cepper and noting
the increase due to the copper added, the amount of copper
originally present can be calculated. As starred on the
table, 7.93 mg of copper has a diffusion current of .44
microamperes. Then .60 microamperes, diffusion current
of the blank, would equal 10.80 mg. of copper per liter.
This is the amount originally present.

As shown by table 4 and in spite of the presence of
copper in the original solution, the amount of COpper can
be determined to 2 mg per liter. This is considerably
lower than in the case of cadmium.

Cadmium and COpper both have approximately the same
"current carrying" ability.but cadmium has the larger
atomic weight which is the determining factor. Table 5

and Fig. 5 show the comparative result for cadmium and

 

COpper in the same solution.

14

 

 

 

 

 

 

 

 

 

 

 

Table 4 Diffusion Current in Microamperes
0 Cu in s s s
Mg/liter 22,222 22,22 200,000 400,000
50,000
127.0 6.78 6.94
63.5 5.40 5.50
31.75 1.66 1.62
15.87 1.20 .78 .92 .89
9.95 .44* .43
3.96 .20 .21
1.98 .15 .10
.99 .01 .07
Blank .58 .64 .60 .59
Table 5
‘ Cu Mg/liter Microamperes Cadmium Microamperes
mg/liter 1+
127.00 6.74 224.80 7.06
68.50 5.14 112.40 3.53
51.75 1.47 56.20 1.57
15.87 .62 28.10 .81

 

 

 

 

 

 

Drop time:
Range:

8.0 seconds
0 to -5 volts.

Shunt resistance for table 6:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

.fojW-‘f A wrnTTj'

 

 

 

. Fig. 5
C0pper 127.8 mg/liter curve 1
Cadmium 224.8 mg/liter curve 2

Copper present alone in the nickel sulfate solution
was also determined by the oxidation reaction. The dropping
electrode was made the positive electrode and the range
of +1 to -2 vdlts was used.

The range for the determination of copper by this
method is very small. Large concentrations of copper
changed the current reading of the system so much,that at
the zero applied E.M.F. the current reading was outside the
range of the graph paper. Large external shunts had the
same effect on analysis of the dilute copper solutions.

The same solutions were used as in the determination

of copper by the reduction method. Again a blank was run

to determine the copper originally present and the the

correction made.

Table 6

16

 

Copper mg
per liter

Diffusion
Current in
Microamperes

Half-wave
potential

Decomposition
potential

 

31.75
:16.89
7.56

 

 

Blank

2.44

1.20
.542
.76*

 

4 .23
4 .23

+ .23

 

 

 

Drop time: 3.5
Shunt Resistance
Range: +1 to -2

seconds

: 22,222 ohms

volts.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I 1 I :5
‘11 l 7' {1 ii: : 'I I“
:in WM! NIMHQ‘
I gi"li II; 5' IEI IE.
HM; WW :1: i 1‘: H? H
. ' WWW“ ‘51"
L; Hi1 H1! Ml!
II: I. I ' l l ili"
':! Ilg
IL” :' x? l 1 WW
"‘ i' E 8”“ ‘ W *i i! ‘f in
will-W" I w»: m
”'1'? NW“? 'JHHiTIMH'
will 1011!: i ‘iiiiig‘iig
1 .r .. ,, _
!? Ii :1 ill‘ :Eif i'g; M; 'iii :1
H? '1 ! W:?;1H £Hiés:,'i. -i
‘m.7”“7" b3~ «'1 . git J
*-—---:1 _; ’3‘;

 

 

 

Fig. 6

Copper 16.89 mg/liter curve 1

Copper

7.56 mg/liter curve 2

17

By comparing table 6 with table 4, it is evident
that the same number of mg of copper by the oxidation method
results in a larger diffusion current. The constancy of
the amount of copper present can again be shown by the
calculation of the copper in the blank. By this method,
using the starred value in the table and the blank, the
amount of copper originally present will be 10.64 mg per
liter. This is in excellent agreement with.va1ue 10,80
mg as found by the reduction method and well within the
limit of accuracy of the electro-chemograph.

Iron was determined in the nickel sulfate solution
in the form of the ferric ion. In order to prevent the
precipitation of ferric ion as ferric Indroxide, the
nickel sulfate solution was made strongly acid (pH 0.8)
with C.P. sulfuric acid. To this acid solution 0.1 g
of anhydrous ferric sulfate per 100 mls was added. The
current-voltage curves were obtained in the usual manner.
However 1:1 dilution was not used. The results are
tabulated.

The maximum that is very marked for this ion was not
suppressed by glue. The maximum is more pronounced with
increasing concentration of the reducible ion.(l)Current
voltage curves Fig. 7 show this effect. Heyrovsky attributes

the maxima to an adsorption of the electroreducible ion

on the drops of mercury.

Table 7.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Iron mg per Diffusion current -
liter Microamperes
S S S
10,526 22,222 200,000
279.50 8.76 8.60
159.65 4.52 4.54
46.55 1.54 1.50
54.91 1.20 1.11
27.95 .86 .85
I._I_,_____I_I_II I
.l H I
1 WI‘ ‘
I III. ' L
IIIL 1L9“:
1 I f
l I
I r 3
! I
.I II r"‘“dd
W _ .
iii ' .
I:I ...!|-
I '— ,
1 III .I ”L I ,
Ilfi. 1.“.I» 7 w. win]
Fig. 7

Iron 279.5 mg/liter curve 1
Iron 159.6 mg/liter curve 2

18

19

DETERMINATION OF VITAMIN B COMPLEXES

The determination of vitamins is of the utmost
importance. This undoubtedly resulted in Lingane's
determination of the vitamin B complexes. Lingane found
that riboflavin gave good polarographic waves and that
its diffusion current was directly proportional to its
concentration.(b)The current¢voltage curves that were
made by the writer are similar to those of Lingane. The
various modifications are Specifically mentioned as such.

The vitamin B complexes used are the controlled
products of Parke Davis Co. Thiamine hydrochloride was
determined in 0.1 N potassium chloride. Weighed samples
of 1 mg each were dissolved in a known amount of the
indifferent salt solution. These sample weights were then
converted into parts per million (ppm). This procedure
was follow ed for each complex. Also dilution was 1:1.

The current—voltage curve Fig. 8 depicts the results
.for 200 and 100 ppm of thiamine hydrochloride. The following
curve Fig. 9 shows the simultaneous determination of
thiamine hydrochloride and riboflavin.

The reduction of the nicotinic acid when dissolved
directly in 0.1 N potassium chloride did not appear on the
current-voltage curve. waever by the use of 0.1N sodium
bicarbonate fairly good waves were obtained. The sodium
bicarbonate solution neutralizes the nicotinic acid and also
acts as a buffer. Linganef6)by first neutralizing the
nicotinic acid with sodium hydroxide, was able t0 obtain

well-defined curves in 0.1N potassium chloride. By the

20

use of the bicarbonate, the nicotinic acid can be
determined directly. These results are quantitative as
shown by the current voltage curves Fig. 10 and by the
Table 9.

Pyridoxine was found to be quite difficult to work
with and obtain satisfactory results. Various supporting
electrolytes were tried. The best results were obtained
using potassium thiocyanate as the indifferent salt. In
this solution, pyridoxine produced curves with pronounced
maxima, Fig. 11. No satisfactory method for the suppression
of the maxima was found. Methyl red was the best of the
suppressors used. Glue was found to interfere with the
diffusion current in the case of the vitamins and could
not be used.

The results for the determination of pyridoxine are

tabulated, Table 10.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 8 Thiamine Hydrochloride
Half Wave Decomposition
ppm Microamperes Potential Potential
S S S S S S
22,222 50,000 22,222 50,000 22,222 50,000
200 5.78 5.83 —l.54 -l.55 -l.19 -l.l5
Table 9 Nicotinic Acid
Half Wave Decomposition
ppm Microamperes Potential Potential
200,000 50,000 200,000 50,000 200,000 50,000
100 .53 .49 ‘1075 “1074 ‘1067 -1068
50 .24 .18 -l.74 -l.76 -l.67 -l.71
Table 10 Pyridoxine
ppm Microamperes Half Wave Decompotential
Potential Potential
50,000 10,526 50,000 10,526 50,000 10,52
181 4.02 5.64 -l.58 -l.56 -l.l6 -l.25
95 2.06 1.76 -l.56 -l.55 -l.15 -l.27

 

 

 

 

 

 

 

 

 

 

 

 

 

22

 

 

 

 

 

 

‘ _ ._ .. _-r.i-.__.__._.-.. --.

 

 

 

 

 

l .
I 1 ' '
—--~L—--~—»+— -.—--—--=
' ‘ E l’,/
-~ F-i ! l .
7. I '
l _ __ f
‘ ’W“ I
I I I 1 I I I I

 

Thiamine Hydrochloride 200 ppm, S 22,222, curve 1
Thiamine Hydrochloride 100 ppm, 8 50,000, curve 2

E * L _ + ,__‘__._ ,_.i _ -4» _‘ ._ W «. .. N ’-
_ ‘ i i- 1.1 KL-
1 l
I I L‘\.\’
_ .li_._-- -——I _ _._ . _ ,__ ._.... .. ‘f‘

n
-1 '
..
..v—-i .— . -U.A__A ..._k . .7 - - ~ . --.- _,_.—l7 --..__.... -—o- _
I . “I , l
n ’ '

 

Fig. 9
Riboflavin A
and
Thiamine isdrochloride B

 

 

 

 

 

23

Fig. 11

I I

 

‘ E 3 f
.
- .4..- _- -1... ._,___..-. law, .1,
.
; I . I . .
‘ I

 

 

 

 

 

’—.._. «Hm—-—v————~»‘;~-~_

 

meel:
Pyridoxine 181 ppm

Curve 2:
' 95 ppm

idoxine

Pyr

 

 

 

 

 

 

 

 

 

 

Nicotinic Acid 200 ppm curve 1
Nicotinic Acid 100 ppm curve 2

 

 

 

 

 

 

 

 

 

 

 

 

 

.1—

'—V—"-_'*—

I
l
‘ I I
I I
‘ l l 1
l ' I
g .
.

A ‘- ._ _._....—_. ._._._

UTI:
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I

, .
Q I . I
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SUMMARY

Cadmium, stannous, cupric, and ferric ions may be
determined in nickel sulfate solution. Cadmium may be
quantitatively determined at various pH's. The stannous
and ferric ions must be determined in an acid solution.
The cupric ion may be determined either by oxidation or
by cathodic reduction. The latter is the more practical.

The vitamin B complexes can be determined polaro-
graphically. Thiamine hydrochloride and riboflavin can be
determined separately or together in 0.1 N potassium
chloride. Nicotinic acid can be determined directly in
0.1 N sodium bicarbonate. Pyridoxine can be determined.
directly in 0.1 N potassium thiocyanate. The simultaneous

determination of these four complexes was not accomplished.

(l)
(2)
(15)
(4)
(5)

(6)
('7)

(8)

LITERATURE

Kolthoff and Lingane; Chemical Reviews, 23, l (1959)

Borcherdt; J. Am. Chem. Soc., 59, 2171 (1957)

Muller; Chemical Reviews, 23, 95 (1959)

Adkins and Cox; J. Am. Chem. 800., pg, 1151 (1958)

Lingane and
Edition,

Lingane and

Lingane and
Edition,

Lingane, J.

Kerlinger; Ind.and Eng. Chem. Analytical
.12., 750 (1940) -

Davis; J. Biol. Chem., 157, 567 (1941)

Kerlinger; Ind. and Eng. Chem. Analytical
15, 77 (1941)

Am. Chem. 800., 61, 2099 (1959)

     
   
   
  
     

  

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