A FAST, SENSITWE, INSTRUMENTAL COMBUS’E‘IQN
METHOD FOR THE DETERMINATION OF TOTAL
PHOSPHO‘RUS

Ti'xesis for the Degree of M. S.
MICHIGAN STATE UNIVERSITY
PAUL R HANDY
1967 I

   
  

LI BRA 21’
Michigan hate
Univer; ry

 

 

 

«.n Mt}:- ’1 2002?}:

ABSTRACT

A FAST, SENSITIVE, INSTRUMENTAL COMBUSTION METHOD
FOR THE DETERMINATION OF TOTAL PHOSPHORUS

by Paul R. Handy

An apparatus is described for reduction of phosphorus
containing compounds to phosphine in a quartz tube

at 900 - lOOO°C in a stream of hydrogen. The phosphine
is separated from interferences of hydrogen chloride,
hydrogen sulfide, and light hydrocarbons by the use of

a short alumina column, followed by a 20-inch PorapakW Q
column, and measured by a sodium thermionic detector.
Both organic and inorganic phosphorus compounds yield
phosphine under the specified conditions. The method
routinely requires microgram-sized samples with
sensitivity capabilities to the nanogram level and requires

less than five minutes analysis time per sample.

A FAST, SENSITIVE, INSTRUMENTAL COMBUSTION METHOD

FOR THE DETERMINATION OF TOTAL PHOSPHORUS

Paul R. Handy

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Chemistry

1947

 

91/7/03
/’,q’/‘O-U7

ACKNOWLEDGMENTS

The acknowledgment of those whose aid, advice, and
encouragement was most important to the production of this
volume and the work it represents must surely be most
directly applied to the faculty advisor. Dr. MacDonald
must be commended for his outstanding effort especially
since work on this particular project precluded finishing
other work already in progress in which he had a more
personal interest. I thank him for listening to an idea
and thalfollowing through to see it to completion.
Needless to say, it has been most gratifying working
under his guidance. Recognition must also be paid to the
Michigan State University department of chemistry without
whose facilities and liberal financial support this work
could not have been accomplished. I should also like to
thank Mr. David Lewis for the samples of phosphine

which allowed the characterization of the detector apart

from the rest of the system.

I should like to extend a special note of gratitude to
Mr. Wendell Brewbaker of the Michigan Department of
Agriculture Laboratory for his two major personal
introductions. He is responsible for my introduction to
the chemistry and problems encountered in residue
analysis, including the use of the thermionic detector

as used in this work. His second introduction was to his

ii

ACKNOWLEDGMENTS (continued)

daughter, now my intended, who has given much moral
support and encouragement for the completion of this

work.

Table of Contents

Title Page
Acknowledgments
Table of Contents
List of Tables
List of Figures
List of Appendixes

Introduction

History
Classical methods - carbon and hydrogen
Instrumental methods - carbon and hydrogen
Instrumental methods - oxygen
Reduction methods - sulfur

Structure determination by reduction
Specific detectors — microcoulometric
Specific detectors - thermionic

Experimental
Purpose of apparatus
Flow control
Reduction tubes
Temperature
Separation of Products
Connection to chromatograph
Detector conversion and requirements
Measurement and recording
Sample injection
Chemicals

Results and Discussion
Comparison with microcoulometric system
Temperature operating range
Separation
Detector characteristics
Results

Conclusion

Bibliography

Page
ii
iii

iv

vi

H

oooooo \JU‘I-fi'WNI’UHl—J

List of Tables

Table 1 Response to Various 0.01 M Solutions Page 28

iv

List of Figures

 

Figure No. Title Page No.
I Apparatus for Elemental Analysis of
Phosphorus 9
II ll mm Reduction Tube Design ll
III Concentric Reduction Tube Design ll
IV Response vs. Reduction Temperature 20
V Reduction Profile at Various Temperatures2l
VI Chromatographic Separation of PH 23
VII Detector Response vs. Detector 3
Temperature 25
VIII Detector Response vs. Hydrogen
Pressure 25
IX O P Calibration Curve 27
X R>sponse to 0.01 Molar Solutions 29
XI Response to TBPO 50
XII Response Variation with Sample
Volume . 30
XIII Peak Profile Variations with Increased
Sample Volume 31

List of Appendixes

Operation Procedure Page 34

vi

Introduction

Phosphorus determinations have for many years been based

on colorimetric procedures which tend to be slow and
cumbersome as well as being difficult to apply to
submicrogram quantities. A new look at phosphorus analysis
has been taken with the idea of using a high temperature
reduction of phosphorus compounds to phosphine in a

quartz tube and handling the reduction products in a

closed continuous gas—flow system. The final measurement
is by means of a gas chromatographic detector sensitized

to phosphorus—containing compounds and is sensitive to

nanogram quantities.
History

Gas—chromatographic type elemental analysis systems have
evolved rapidly within the last eight years from variations
of older gas evolution and adsorption techniques to their
present sophisticated state. The most popular carbon-
hydrogen determination, the Pregl method (1), calls for the
oxidation of the sample at temperatures of 700 to 800°C

in a stream of oxygen over a catalyst, usually platinum,
specific absorption of the combustion gases and final
gravimetric determination. An inert carrier gas may be
used for the combustion of organic compounds when copper

oxide, cobaltic oxide, or silver permanganate is used as

l

the oxygen donor.

The time consuming aspects of the gravimetric step were
attacked simultaneously by Duswalt and Brandt (2) and
Sundberg and Maresh (3),who converted the water of
combustion to acetylene by reaction with calcium carbide
and trapped the resulting carbon dioxide and acetylene

at liquid nitrogen temperatures. The combustion products
were volatilized, separated via gas-solid chromatography
(GSC) on silica gel, and determined with a thermal
conductivity detector. This determination was soon
extended to include determination of nitrogen as N2 by
both Nightengale and Walker (4) and Huyten and Rijnders (5).
Nightengale also eliminated the trapping step by using

an induction furnace for rapid sample combustion with
collection on a molecular sieve column and subsequent
programmed temperature elution. Meloan and co-workers
(5,7,8) used the trapping procedure not only to extend
the analysis to sulfur, carbon, chloride, and bromide but
also to improve the chromatographic separation for

simultaneous analysis. Van Hall 31 al. (9) have

 

determined carbon in aqueous solutions of organic
substances. The determination is done in an oxygen
stream at 950°C with a platinum catalyst and an infrared
analyzer as a specific detector for the carbon dioxide

produced.

\J~J

Oxygen determinations have been run by modifications of
the Unterzaucher carbon-reduction procedure in which the
organic oxygen is converted to carbon monoxide at
llOO°C. Harris, Smith, and Mitchel (1) used a stream of
helium and pyrolyzed the organic sample over carbon in a
closed system. The pyrolysis products, carbon monoxide
and hydrogen, were recirculated through the system to
assure complete conversion of all oxygen to carbon
monoxide and to remove the hydrogen by diffusion through
a heated palladium tube. A thermal conductivity cell in
the system monitored the course of the reaction and
measured the conductivity of the resulting helium-carbon
monoxide mixture versus helium. thz and Bober (10)
developed a flow system to convert oxygen to carbon
monoxide at ll20°C but dismissed the necessity of removing
the hydrogen formed in the combustion by using hydrogen
rather than an inert gas as the carrier. An activated
charcoal GSC column separated the carbon monoxide from
other combustion products so that no interference from

nitrogen, sulfur, or chlorine was observed.

Reduction techniques using hydrogen gas as a carrier have
been shown to be a successful route for the determination
of sulfur. Schulter, Parry, and Matsuyama (ll) converted
sulfur-containing compounds to hydrogen sulfide at l200°C
using a nickel catalyst. The hydrogen sulfide was

determined amperometrically with mercuric chloride or

1+
colorimetricallyzfiter absorption in dilute sodium hydroxide.
A gas-chromatographic sulfur determination was developed
by Okuno, Morris, and Haines (12), who used a hydrogen
carrier gas for reduction of the sample at 1000°C in a
quartz tube with a platinum gauze catalyst. The combustion
products (hydrogen sulfide and hydrocarbons other than
methane) were trapped at liquid nitrogen temperatures and
the methane was retained on a molecular sieve at carbon
dioxide temperatures. The separation of the trapped
combustion products was done sequentially on a tandem
gas-liquid-chromatographic (GLC) column consisting of
12—foot silicone plus a 6-foot tricresyl phosphate column.
It was observed that conversion of the organic matter to
methane was not complete but that an estimation of a
carbon to sulfur ratio could be made. A major source of
error in the chromatographic determination of hydrogen
sulfide or other reactive gases produced by hydrogenation
(e.g. hydrogen chloride or hydrogen bromide) is adsorption
losses in the separation column. Huyten and Rijnders (5)
improved the determination of hydrogen sulfide by splitting
the combustion stream, selectively removing the hydrogen
sulfide from one, and comparing the thermal conductivity
response of the two. This procedure reduced the errors

to about 2% relative to sulfur.

Hydrogenation gas chromatography techniques have been used

more extensively for structure determination than for

5

elemental analysis. Thompson gt al. (15 - 16) used a

 

catalyst of 0.5% palladium on alumina in a stream of
hydrogen to effect a low temperature (below 400°C)
replacement of sulfur, nitrogen, oxygen, or halogen in
organic molecules. The hydrogenation products, after
gas-chromatographic separation and identification, were
used to reconstruct the sample's structure. Beroza
(17,18) extended this work to include a rather comprehensive
list of compounds and their hydrogenation skeletons for
use as an analytical tool for identification of unknown
gas—chromatographic peaks. Mausha and Nishimiua (19)
used a similar combustion technique but eliminated the
trapping procedure used by Thompson and Beroza by direct
coupling of two chromatographs through a hydrogenation
unit. The first chromatograph was used for determination
of the sample volume delivered to the combustion unit.

A heated calcium carbide column converted the inorganic
gases formed in the combustion to acetylene, which was
then separated from the basic hydrocarbon skeleton on the
second chromatographic column. The elemental analysis
had little utility at the reduction temperatures used
(230 - 250°C) due to excessive broadening and tailing of

the chromatographic peaks.

Combustion techniques have become quite sophisticated in
the development of specific detectors for gas chromatography.

Coulson and Cavanaugh (20) developed a microcoulometric

J\

titration system for chloride analysis of combustible
samples. The samples were ignited in a stream of oxygen
at 800°C, and the effluent fed into a titration cell
where the chloride was precipitated by silver ion. The
silver ion was generated coulometriCally and the current

used related to the halide concentration. Coulson gt al.

 

(21) adapted the microcoulometric titration system for
use with sulfur by changing the titration medium to iodide-

triiodide for the oxidation of sulfur dioxide to sulfate.

Burchfield 33 al. (22 - 24) used the hydrogenation

 

technique on chromatographic effluents to determine combined
chlorine and sulfur and extended the procedure to include
phosphorus. This was accomplished by the reduction of the
chromatographic effluent by the hydrogen carrier in an
empty quartz tube at temperatures of 925 - 1000°C. The
silver ion microcoulometric titration cell used gave
response only to hydrogen chloride, hydrogen sulfide, and
phosphine of the reduction products. It was found that the
addition of a silica gel GSC column would irreversibly
adsorb hydrogen chloride and separate hydrogen sulfide

from phosphine for the simultaneous determination of
relative phosphorus and sulfur composition of a single
chromatographic peak. The system could be made absolutely
specific for phosphorus by replacing the silica gel with

an alumina GSC column which would retain both hydrogen

chloride and hydrogen sulfide, yet allow passage of phosphine.

7

Karman and Guiffrida (25 — 27) reported that the inherently
sensitive hydrogen flame detector could be sensitized
specifically for halogen and phosphorus containing
compounds. The conventional hydrogen flame detector is
composed of a burner at which the column effluent is mixed
with hydrogen and combusted in a stream of air. A
conventional electrometer is used to measure the ion
current between the burner jet and a collector ring

above the flame held at several hundred volts potential
relative to the jet. This detector is characteristically
sensitive to the carbon content of organic molecules,
relatively flow insensitive,and has a good dynamic range.
The hydrogen flame detector was modified by the addition
of a sodium salt to the tip of the jet and produced a
six-hundred-fold increase in the response for a ten-
carbon phosphorus compound and a twenty-fold increase for
a hexachloro hydrocarbon relative to that observed with
the normal hydrogen flame detector (27). The large
response to phosphorus containing compounds indicates that
the “sodium thermionic” detector is essentially specific
for such compounds. The mechanism is not completely
understood but experiments by Karman (25) indicate that
the presence of a hot alkali metal salt is necessary.
Apparently, the ion current increase is due to the
increased rate of volatilization of this metal salt rather
than a lowering of the ionization potential of some flame

species.

Experimental

The experimental apparatus was designed to incorporate
the hydrogen reduction of organophosphates with the
sensitive and more readily available thermionic detector
into a single, continuous flow instrument. The apparatus
is presented in outline form in Figure I and has three
general components: the carrier gas supply and control,
reduction tube with its associated tube furnace, and a

basic laboratory hydrogen flame chromatograph.

The carrier gas used is dictated by the reaction to be
performed and the detector used for the determination.
This system requires hydrogen to be present in both the
reduction zone and the detector to support combustion of
the sample. The detector flame stability requires that a
diluent gas be present in approximately a 1:1 ratio with
the hydrogen; therefore, a hydrogen-nitrogen mixture was
used as carrier gas. The nitrogen (Matheson, prepurified),
hydrogen (H.S.U. stores), and compressed air (M.S.U.
stores) cylinders were fitted with two-stage regulators,
shutoff valves, and sensitive micrometer barrel needle
valves (Ideal V 52—3-1A). The hydrogen flow was further
regulated by inserting a resistance composed of a one-foot
length of one-quarter inch copper tubing filled with

80— - 200-mesh alumina between the regulator and needle

valve. The nitrogen flow was split so as to feed the

8

H

9

FIGURE I Apparatus for
Elemental Analysis of Phosphorus

 

 

 

 

 

 

 

 

 

 

   

I 9

R8 T

---- ------_-----------------’

H and carrier flow control
sample injection

quartz reduction tube

tube furnace

subtraction column
chromatograph injection port
separation column

thermionic detector
electrometer

data display

O\OOO\IJ\\J1-C'\Nf\)}—'

10
chromatograph carrier system as well as join the hydrogen
flow through the reduction tube, the needle valve controlling
the flow through the reduction zone. The compressed air
is fed directly to the chromatograph which due to the
high flow rate requires no further control. A Hoke toggle
valve allowed air to be supplied to the reduction tube,
with the hydrogen turned off, for the purpose of burning
out the hydrocarbon residue which accumulates in the
reduction tube. All tubing connections were made with
Swagelok fittings using either one-quarter inch copper
tubing or one-quarter o.d. by one-eighth inch i.d. Tygon”

tubing and each connection carefully checked for leaks.

The basic reduction tube design is shown in Figure II.
This design has the hydrogen-nitrogen carrier entering
through a 3-mm i.d. side arm into a 5-mm joint connecting
the reduction zone on one side and the injection septum

on the other. The early reduction tubes were constructed
using a Pyrex“- to quartz-graded seal for connection of the
Pyrex inlet tube and septum socket to the quartz-reduction
zone. Because no special provisions were made for heating
the injection port to volatilize the injected liquid
sample, the furnace was moved as close as possible to the
injection area. This construction was found to be
undesirable since the graded seal was subjected to a
higher temperature than it was designed for. Furthermore,

it was observed when repairing one broken seal that the

11

FIGURE II 11 mm Reduction Tube Design

 

é—a ; 1+

5 l 115'

\JJ

st

 

 

 

white silicone injection septum
2 mm i.d. quartz inlet tube

11 mm i.d. quartz tube

female spherical joint, quartz
male spherical joint, Pyrex

11 mm i.d. Pyrex tube

brown silicone septum

0.092 inch needle stock

OO'\IJ‘\\J‘l-P\Nf\)}—‘
0

FIGURE III Concentric Reduction Tube Design

1 I

 

 

 

 

 

 

1. white silicone injection septum

2. 5 mm i.d. quartz tube

3. 2 mm i.d. quartz tube

4. 2 mm i.d. quartz inlet tube

). female quartz spherical joint, quartz

12

walls were much thinner after use, indicating that the
tube in the injection area is involved in the reaction.
Therefore, all quartz construction was used in subsequent
tubes to eliminate the weakness of the graded seal and
allow injection of the sample directly into the reduction
zone. Burchfield (24) reported that the optimum size and
length of the reduction tube was 2 mm i.d. by 45 cm in
length, which seemed to indicate that we should favor
smaller reduction tubes. A second reduction tube was
constructed of 5-mm i.d. quartz tube compared to the
original ll—mm i.d. tube. The response was not appreciably
increased; and furthermore, it was observed that when
samples in excess of one microliter were injected, the
expansion of the solution caused a back flash of the

vapor down the inlet tube thus losing a portion of a
slightly volatile sample. A laboratory fabricated check
valve placed in the inlet stream just before the inlet
tube failed to remedy the problem. A new reduction tube
was designed to eliminate the problem of sample back flash
by using two concentric tubes as in Figure III. The inner
tube of this new reduction apparatus was of 2-mm i.d.
quartz tube; and it was observed that although the back
flow problem was apparently corrected, the inner tube
quickly became coated with combustion residue causing an

increased noise level and decreased reduction efficiency.

According to Burchfield, the temperature requirement for

15

reduction of phosphates to phosphine in a quartz tube is

in the temperature range of 900 to 1000°C. The most
frustrating portion of the eXperimental work has been
concerned with achieving a constant temperature within

this range. Initially, a Sargent $436400 microcombustion
furnace was used but was found to be totally incapable

of operating consistently above a temperature of 850°C.

An older Sargent tube furnace, Model No. 49090, incorporating
ceramic—backed elements, was obtained along with a supply

of spare elements which produced temperatures within the

desired range if steady maintenance was supplied.

Once the reduction products are formed, the problem becomes
one of detector response to the various products and the
necessary separation of interferences. The sodium thermionic
detector, basically still a hydrogen flame detector, gives
a definite response to hydrocarbons; this constitutes the
major interference. The other two major interferences
would be hydrogen halides and hydrogen sulfide. Separation
of the phosphine from hydrogen chloride and hydrogen
sulfide was achieved using a short GSC column of either
silica gel or activated alumina. Burchfield (24) found
that silica gel will irreversibly adsorb hydrogen chloride
and separate hydrogen sulfide from phosphine, while
activated alumina will adsorb both hydrogen chloride and
sulfide. The adsorbent (2 to 4 centimeters of alumina) was

held in a 4.5—inch Pyrex subtraction tube joined to the

14

quartz reduction tube via a spherical joint connection.
This spherical joint was responsible for much of the

early irreproducibility observed between one series of
reductions and another. The joint became quite warm due
to its proximity to the tube furnace as well as the linear
heat conducting properties of quartz. It was observed that
channeling of the silicone vacuum grease used to seal the
joint acted as a variable relief valve so that the flow
through the system would change from series to series as
well as within a particular series itself. The problem
was rectified by shielding the joint from the furnace with
a transite-aluminum foil heat reflector and using Apiezon

W wax instead of silicone grease.

The exit end of the subtraction tube was a septum socket
holding a silicone septum pierced by a 1.5-inch length of
0.092—inch o.d. stainless steel needle stock. The needle
stock is used to connect the reduction apparatus to the
injection port of the F and M 700 chromatograph through
two septums to insure against development of leaks at the

injection port.

The F and M 700 is a dual-column hydrogen flame instrument
incorporating its own flow control for both carrier and
detector gases, an oven capable of being used for temperature
programming, and a battery-powered electrometer for

measurement of the detector output. The instrument was

l5
initially operated with only an empty glass capillary
crossover column for connecting the injection port to the
detector. An additional separation procedure was sought
since no separation of phosphine from the light hydrocarbons
was evident. The low pressure limit, using the adsorbents
in the su btraction tube, was dictated by the spherical
joint connection eliminating the use of the long GLC columns
normally used. A new column packing, a porous polymer bead
(Porapak? Waters Associates), introduced by O. L. Hollis
(28) has been used for room temperature separation of light
hydrocarbons and inorganic gases. A twenty-inch column of
Porapakb Q performed complete separation of phosphine from
small amounts of light hydrocarbons with minimum peak tailing.
The greatest problem encountered using glass columns
occurred when fitting them into the instrument using Swagelok
fittings to seal the system. Manufacturer’s instructions
indicated that three siliconerubber O-rings should be used
between the nut and back ferrule to form the gas—tight seal.
Several broken columns later, it was apparent that this
system puts a little too much strain on the glass. Another
method (29), using only a back ferrule in reverse with only
one O-ring replacing the front ferrule, has provided a

tight seal with minimal strain on the glass.

The separated gases pass from the column to the detector
where the hydrogen used for the combustion of the column

effluent is usually added; however, with hydrogen composing

16
the greater part of the carrier, this is unnecessary and
the chromatograph hydrogen supply is turned off since the
carrier alone will support combustion. The air necessary
to support combustion of the effluent is introduced in the
normal manner around the base of the detector jet. The
conversion of the detector from hydrogen flame to sodium
thermionic is accomplished by crowning the jet with a
platinum spiral that has sodium sulfate fused to it. The
platinum spiral is made by taking 22-gauge platinum wire
and winding four turns around the threads of a 4/40 screw
then bringing the excess down and wrapping it around a
one—eighth inch copper tube so that the spiral winding sets
flat over the end of the tube. The wire is then trimmed,
cleaned, dipped into a saturated sodium sulfate solution,
and fused in a Bunsen flame. After several applications
of the salt solution and subsequent fusion, the inside of
the spiral portion is uniformly coated with the salt and
the spiral is then placed over the jet (30). The flame
obtained has the yellow-orange color characteristic of
the sodium flame test rather than the almost invisible

hydrogen flame.

The ion current across the flame was measured by the
chromatograph electrometer and displayed on a Sargent MR
recorder. The recorder was equipped with a disc integrator
but most of the peak areas were determined by a polar

compensating planimeter, K and E No. 620000.

17
The samples used were 0.01 molar solutions in water for
sodiumdihydrogen phosphate and in benzene for the
organophosphorus compounds. These solutions were
injected using a lO-microliter Hamilton No. 701 N syringe
with sample sizes varying from 0.4 to 2 microliters. The
injection technique employed was to flush the syringe
several times with solvent. A 0.3- to 0.5-microliter
slug of solvent is drawn in, followed by a l- to 2-
microliter air space before the sample is drawn completely
into the barrel for reading. Benzene was the organic
solvent of choice as it combusted to minimal amounts of
methane and ethane. The use of hexane as a solvent with
organophosphate at concentrations less than 0.01 molar
produced an ethane peak which began to swamp the phosphine
peak. The samples were obtained from the following sources:
sodiumdihydrogen phosphate, Baker reagent; tributyl
phosphate, Eastman white label; triphenyl phosphine,
Carlisle Chemical Works, Inc., (recrystallized from 95%
ethanol, m.p. 81°C); malathion and ronnel, American

Cyanamid and Dow Chemical Companies respectively.

Results and Discussion

The experimental device just described has been used
successfully to effect the reduction of phosphorus containing
compounds to phosphine for measurement of total phosphorus

content. The system rudimentarily resembles that of

l8
Burchfield (25) but differs in several basic ways. First,
his samples were all volatile therefore would be easily
swept into and through the heated reduction zone for
reaction. Our extension of this method to solutions of
compounds with low vapor pressures is sure to extend the

utility of the method.

Secondly, his use of a chromatographic column for the
separation of sample components and solvent caused problems
in column losses for the solutes. These column losses
obviously differ between compounds and thus contributed

to the qualitative response he obtained for phosphorus
compounds. However, the GLC column provided separation of
the organophosphate from the solvent which was vented
around the reduction zone while using direct injection

we are forced to contend with a large volume of solvent
vapor in the reduction zone. Indeed this has caused
difficulty with the smaller reduction tubes as the
expansion of the solvent did cause some observable losses.
However this seemed to be of minor importance in the

larger sized reduction tubes.

The third and most obvious difference is the use of the
sodium thermionic detector instead of the microcoulometric
detection system. The microcoulometric detection system
approaches the sensitivity of the flame ionization detector

and is somewhat more selective as it is insensitive to

l9
hydrocarbons. However it does lack in availability and
operating convenience. A more generally useful method
of phosphorus determination would result using the more
commonly available hydrogen flame detector which is easily

adapted to phosphorus detection as described previously.

The temperatures required for reduction of phosphorus
compounds seems to fall into the region of 600 to 1000°C

as shown in Figure IV. Although reduction does apparently
occur at lower temperatures, it is indicated that the
reproducibility tends to suffer below 900°C. At the

highest temperatures attained, the production of light hydro-
carbons is increased as shown in Figure V. An attempt was
made to correlate the methane peak height with sample

volume injected, but it was found that the methane peak

was extremely temperature dependent. The light hydrocarbon
production diminishes with temperature until only the

sample injection spike, due to sample expansion, and
phosphine peak remain. Phosphine formation was noted for
aqueous inorganic compounds such as sodiumdihydrogen
phosphate, diammoniumhydrogen phosphate, sodium pyrophosphate,
and phosphine gas, as well as, organophosphates including
triphenyl phosphine (¢3P), tributyl phosphate (TBPOQ),

ronnel, and malathion.

The reaction products were separated as stated earlier

by the use of two columns. Of the GSC adsorbents used to

20

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22
remove the hydrogen halides, silica gel especially tended
to broaden the phosphine peak and increase tailing. The
Porapakysection is effective in separating the phosphine
from the lower hydrocarbons as well as completely retaining
the solvent at near room temperatures. Benzene was found
to have a retention time of about two minutes at a column
temperature of 160°C in the twenty-inch column used. When
water is used as the solvent, it does tend to bleed off
the adsorbent and although the hydrogen-type flame is not
responsive to water, it does cause a decrease in the flame
temperature and thus change the sensitivity of the detector.
The characteristics of the Porapakdcolumn are such that
peaks are almost perfectly symmmetrical as in Figure VI
while the reduction peaks are characteristic as in Figure

V. An authentic sample of PH was injected and gave the

3

typical reduction peak shape with its characteristic

retention time.

Response seems to be a greater function of the detector
rather than reduction efficiency once a sufficient hydrogen
flow rate is established in the reduction zone. Flow

rates were measured from the cold detector with a soap

film flow meter and stopwatch. The flows were determined
individually and were found to vary from trial to trial.
However the hydrogen flow was in the range of 130 to 150 ml
per minute and total nitrogen flow a composite of 70 to

100 ml per minute through the reduction tube plus 50 to 50 ml

FIGURE VI Chromatographic Separation of PH3

column temp. 30°
20-inch Porapakw Q

1 pl PH3 solution

 

 

 

 

 

 

 

 

.1 ~4f“\J ‘_. ,_.r'-~__J - e‘=‘__~

T 1600 detector temp. 1. 250° detector temp.

I . . attenuation x 2 attenuation x 5
njection

24

per minute added at the injection port. The air flow rate
was set at 40 psi gauge pressure and was not directly
measurable. The flow through the reduction zone depends
upon the pressure drop created by adsorbents in the
subtraction tube and column packing. Leaky joints between
the subtraction and reduction tubes also caused changes

in flow rates before the heat shielding and wax sealing

of the joint. The procurement of the phosphine solution
allowed the study of the characteristics of the detector
apart from the reduction system. The chromatographic

mode was used and the effects of detector temperature and
hydrogen flow rate were determined. Figure VII shows

the response to phosphine with detector temperature which
increases until something greater than 500°C beyond which
the response drops to zero. This is most likely due to
decomposition within the detector block. The detector

was routinely operated near 270°C but was set at 255°C as
a temperature rise of about 15 degrees was observed within
fortyéfive minutes after ignition of the flames. The
presence of an optimum hydrogen flow is obvious from
FigureVHI which shows response versus gauge pressure of
hydrogen. Detector response to variations in nitrogen
pressure seemed to be more important as far as flame
stability and noise level are concerned rather than direct
changes in response. The detector itself was found to
lose sensitivity with time; and if used daily, the platinum

wire adapter would have to be removed, cleaned, and

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26

recoated with sodium sulfate weekly.

The reference compound chosen for most of the work was
triphenyl phosphine as it was readily available, easily
purified by crystallization, and easily weighed. A
standard curve was made with a series of solutions varying
from 10 to 0.2 milligrams per ml of OBP. The curve shown
in FigureIX was obtained and, though not exactly linear
over the entire range, the curve is still analytically
useful if the unknown is compared to a standard of near

the same response. Another standard curve using

0.010 molar solutions gave a linear response over this
range of sample sizes as shown in Figure X and Table l.

A standard curve from 0.010 molar TBPO,+ is shown in Figure XI
with its deviation from ideal response shown in Figure XII
as response area per unit of TBPO1+ injected versus the
total volume injected, sample plus flush solvent. Note the
changes in the peak shape as the sample size is increased
as in Figure XII. These plots indicate the advisability

of injecting samples of similar concentration to the
standard being used. The detectability limit of the

method has been ascertained to be on the order of 2 times

10-10 moles of CBP.

Response variation from compound to compound has been
noted as in Table l. Ronnel almost invariably gives a

slightly higher response than does OBP, malathion, or TBPoq.

157

 

27

FIGURE IX ¢3P Calibration Curve

 

o
I
I,
136' , o
I
l
I
I
110 I 8
l
OI
’5 I
I
O
H 90- ’l
>< I
N I
B I
3 /
70' I
33 P
8 I
<‘ I
I
J z
50 I
I
a!
30 #7
I
9 960 - 970°C
31, 9! 11 mm i.d. reduction tube
I
I
r r _—_v r ' fi‘
1 3 5 7 9 11

micrograms 03p

28

TABLE 1 Response to Various 0.01 M Solutions

+

 

 

 

945° - 5
pl Injected Sample (0.01 M) Area x 100 in2

1.01 03? 97
1.0 Malathion 95.5
0.95 0BR 101
1.02 Ronnel 114
1.0 03? 98

975
1.0 gjp 68
2.0 03? 110
2.73 03? 152
0.45 ¢3P 43.5
0.95 ¢3P 62.5
1.0 g P 68.5

29

FIGURE X Response to 0.01 M Solutions

150‘

140q

120!

x 100)

 

2

100

Area (in

80

    
 
 

o 0.01 M ¢5P
u 0.01 M Ronnel
6O “ .
(3 0.01 g Malathlon
1 mm i.d. reduction tube

  

4O
0 l 2 5

Sample Size (pl)

50

FIGURE XI Response to TBPO

 

 

 

 

h,
250‘
[A 200-
o
O
H
x
m 150
c
H
m
(D
Q 100 11 mm reduction tube
945°C
0
50 T . r-
1 2 3
pl of Sample
FIGURE XII Response Variation with Sample Volume
110
8
o
H
x
m 90
c
H
l1-
8
m 70
B
in
g 0
o 5
C: 11 mm i.d. reduct n tube
3 945°C 0
a
<12 30 7 .
I ’1 I
O 2 4 6

Total Injected Volume
(pl)

51

omdm

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kw
I\)

Also, aqueous inorganic phosphates give a larger response
than equimolar organic phosphate compounds in organic
solvents. Whether this is a solvent effect or more

efficient reduction has not yet been ascertained.

Conclusion

The method as described has shown itself to be useful for
the analysisfor elemental phosphorus in a wide variety

of phosphorus compounds in several different oxidation
states. The procedure is straightforward and rapid and
the analysis time per sample, using the disc integrator
for peak area measurement, is well under 5 minutes.
Although the full analytical range has not been determined,
the range equivalent to l to 10 micrograms of triphenyl
phosphine per sample puts the method routinely at the
sensitivity limit of classical methods, with sensitivity
capabilities down to the nanogram level. Assuming a
one-microliter sample size, the present limit of accuracy
is I 10% for the lO-microliter syringe used for this

work. Improvement of sample introduction, combined

with speed, sensitivity, and versatility already attained,

should give the method rapid acceptance for phosphorus

analysis.

Bibliography

1. Harris, Smith, and Mitchel, Anal. Chem., 22, 1297

 

(1950).

2. Duswalt and Brandt, Anal. Chem., 52, 272 (1950).

 

5. Sundberg and Maresh, Anal. Chem., 52, 274 (1960).

 

4. Nightengale and Walker, Anal. Chem., 53, 1435 (1962).

 

5. Huyten and Rijnders,ZAnal. Chem., 205, 244 (1964).

 

6. Beuerman and Meloan, Anal. Chem., 54, 1571 (1962).

 

7. Beuerman and Meloan, Anal. Chem., 4, 519 (1962).

 

8. Mamaril and Meloan, 2; _£ Chromatog., 22, 25 (1965).

 

9. Van Hall, Safranko, and Stenger, Anal. Chem., 5,

 

315 (1963).

10. Gdtz and Bober, 2; Anal. Chem., 181, 92 (1961).

 

11. Schulter, Parry, and Matsuyama, Anal. Chem., 52,

 

413 (1960).

12. Okuno, Morris, and Haines, Anal. Chem., 53, 1427

 

(1962).

15. Thompson, Coleman, Ward, and Rall, Anal. Chem., 22,

 

424 (1960).
14. Thompson, Coleman, Hopkins, Ward, and Ball, Anal.

Chem., 52, 1762 (1960).

 

15. Thompson, Coleman, Ward, and Rall, Anal. Chem., 5fiJ

 

151 (1962).

16. Thompson, Coleman, Ward, and Rall, Anal. Chem., 53,

 

154 (1962).

17. Beroza, Anal. Chem., 54, 1801 (1962).

 

18. Beroza and Sarmiento, Anal. Chem., 5?, 1555 (1965).

 

33

19.

20.

21.

22.

25.

24.

28.
29.

50.

Bibliography (continued)

Mausha and Mishimiua, Bunseki Kagaku, 4 (8),

 

732 (1965).

Coulson and Cavanaugh, Anal. Chem., 52, 1245 (1960).

 

Coulson, Cavanaugh, Devries, and Walter, i; Agr.

Food Chem., §, 399 (1960).

 

Burchfield, Johnson, Rhoades, and Wheeler, 2; 2:

Gas Chromatog., 5, 28 (1965).

 

Burchfield, Rhoades, and Wheeler, Abstracts, 148th
National Meeting, A.C.S., Chicago, September, 1964.

Burchfield, Rhoades, and Wheeler, 22 Agr. Food Chem.,

 

$2, 511 (1965).

Karman, Anal. Chem. 55, 1416 (1964).

 

Karman and Guiffrida, Nature, 201, 1204 (1964).

 

Guiffrida, 2; Assoc. Offic. Agr. Chemists, 47, 295

 

 

(1964).

Hollis, 0. L., Anal. Chem. 5g, 509 (1966).

 

Applied Science Catalog No. 10, p. 41 (Spring, 1966).

Brewbaker, W., personal communication.

54

Appendix I

Operation Procedure
I. Detector Conversion as described in the Experimental
Section
II. Reduction — subtraction tube preparation
A. Reduction tube
1. Clean the reduction tube in HBSOQ—dichromate
solution; rinse and dry.
2. Insert a l/2-inch pledget of quartz wool
in the center of the reduction tube.
5. Insert white silicone septum in injection
port.

B. Subtraction tube

1. Insert brown silicone septum in septum socket.

2. Insert needle stock connector.

5. Insert glass wool plug.

4. Add 2 - 4 cm of alumina.

5. Vibrate adsorbent and plug with glass wool.

C. Junction of reduction and subtraction tubes

1. Warm both halves of the spherical joint in
Bunsen flame.

2. Touch male portion to stick of black wax,
join to female, and rotate. Check for even
seal.

5. Attach screw clamp and snug down.

4. Let cool.

35

III.

IV.

Appendix I
(continued)

Attachment into Instrument

1.

Height of furnace is adjusted so reduction tube
is in line with injection port.

The reduction-subtraction tube assembly is placed
in position.

Needle stock connector is pushed through double
septums in the chromatograph injection port.
Heat shields are attached between furnace and
spherical joint.

Entire assembly is clamped securely into
position.

Carrier gas inlet line is connected to the
inlet tube and securely wired.

Chromatograph temperature settings: injection

port, 100°C; column, off; and detector, 255°C.

Operation CAUTION-Beware of hazardous hydrogen leaks.

A.

Initial

1. The furnace turned on for one hour warm-up
for temperature stabilization.

2. Carrier gas (nitrogen) turned on and set at
50 psi gauge pressure and 0.5 needle valve
setting.

5. The chromatograph hydrogen and air supply are

turned on 28emd40 psi respectively.

36

10.

11.

12.

Appendix I
(continued)

Detector flames ignited.

The reduction hydrogen supply is turned on,
40 psi gauge pressure and 1.5 needle valve
setting.

When hydrogen through reduction system will
support combustion, turn off chromatograph
supply to Column A.

Adjust the sodium flame using chromatograph
carrier flow controller until it burns
smoothly and extends 5/8 to 1/2 inch above
the adapter.

Allow 45 minute detector warm-up.

Turn on electrometer and recorder for 15 minutes
warm-up.

Balance the electrometer.

Set range setting at 10° and attenuation at
1, note stability of base line.

If base line is stable, set ath2 x 50.

Sample introduction

1.

Fill syringe several times with solvent and
flush.

Draw in about 1 ul of air ahead of plunger
then 0.4 ul solvent, another microliter of

air then the sample solution.

37

Appendix I
(continued)

Draw the sample completely into the barrel

for volume determination.

Inject through white silicone septum into the
reduction tube.

Note size of peak and make necessary adjustments

of range and attenuation.

Shutting down

1.

Turn off hydrogen gas at tank, let excess burn
off.

Turn off electrometer and recorder.

Turn off furnace.

Turn off chromatograph hydrogen and air
supply.

Reduce nitrogen pressure and turn on oven

to about 200°C to flush out solvent adsorbed

on column.

38

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