NBS

403

Microchemical

Analysis Section

SUMMARY OF ACTIVITIES

JULY 1965 TO JUNE 1966

Edited by John K. Taylor

«*i or coA ?

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*#*tM Of *

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(A Q

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

W'W^-M-MMM
THE NATIONAL BUREAU OF STANDARDS

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UNITED STATES DEPARTMENT OF COMMERCE • John T. Connor, Secretary

NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

NBS TECHNICAL NOTE 403

ISSUED SEPTEMBER 1, 1966

Microchemical

Analysis Section:

SUMMARY OF ACTIVITIES

JULY 1965 TO JUNE 1966

Edited by John K. Taylor

Microchemical Analysis Section

Analytical Chemistry Division

Institute for Materials Research

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

For sale by the Superintendent of Documents, Government Printing Office

Washington, D.C., 20402 - Price 50 cents
FOREWORD

The Analytical Chemistry Division was established as a

separate division at the National Bureau of Standards on

September 1, 1963* and became part of the Institute for

Materials Research in the February 1, 1964, reorganization.

It consists at present of nine sections and about 100 technical

personnel encompassing some 45 different analytical competences

from activation analysis and atomic absorption to vacuum fusion

and X-ray spectroscopy. These competences, and in turn the

sections which they comprise, are charged with research at the

forefront of analysis as well as awareness of the practical

sample, be it standard reference material or service analysis.

In addition it is their responsibility to inform others of

their efforts.

Formal publication in scientific periodicals is highly

important. In addition, however, it has been our experience

that informal, annual summaries of progress describing efforts

of the past year can be very valuable in disseminating information. At the National Bureau of Standards such publications

fit logically into the category of a Technical Note. In 1966

we plan to issue these summaries for all of our sections. The

following is the second annual report on progress of the Microchemical Analysis Section.

W. Wayne Meinke, Chief

Analytical Chemistry Division

ii
PREFACE

This report summarizes the program and activities of the

icrochemical Analysis Section of the Analytical Chemistry

ivision. This section is new in name only, since the

nalytical areas included in its program have been administraively linked for the past several years. Prior to April 1966

,

he section was known as the Analysis and Purification Section,

t that time, the purification programs were transferred to

he newly created Separations and Purification Section and the

ame of the section was officially changed to its present one

o more properly reflect its program emphasis.

The Microchemical Analysis Section has the primary mission

make contributions to the science and technology of analysis

jf small samples. Its program includes fundamental studies to

mprove precision, accuracy and sensitivity of analytical

ethods as well as the development of new and improved methods

f chemical analysis applicable to wide areas of materials

esearch. As a closely related activity, the section provides

nalytical measurements of high reliability to the various

•esearch programs of the Bureau and to the Standard Reference

[aterials program.

Research projects are active in the following analytical

ompetence areas: mass spectrometric gas analysis, polaro-

;raphy, coulometry, stoichiometry, classical microchemistry.

pn addition, the section has considerable analytical experience

ind investigates and develops methods incidental to specific

malytical problems in the following areas: gas chromatography,

mclear magnetic resonance spectrometry, infra-red spectrometry,

investigations in the area of microscopic analysis have just

been activated and will include the development of ultra-micro

techniques.

Activities during the reporting period are classified

Ander research or analytical development. The classification

iii
is often arbitrary since nearly all of the analytical applications have required more than incidental efforts of both

kinds. Investigations which would appear to have considerable

general applicability have been classified in the first group,

while those more closely related to specific materials have

been placed in the second category. In most cases, where

analytical methods have been described, it has been attempted

to describe the procedures used briefly, yet with sufficient

detail to make them understandable to the experienced analyst.

However, specific details could be made available to anyone

interested in such matters.

In order to specify adequately the procedures, it has

been necessary occasionally to identify commercial materials

and equipment in this report. In no case does such identification imply recommendation or endorsement by the National

Bureau of Standards, nor does it Imply that the material or

equipment is necessarily the best available for the purpose.

John K. Taylor, Chief

Microchemical Analysis Section

iv
TABLE OF CONTENTS

PAGE

I. MASS SPECTROMETRY GAS ANALYSIS 1

A. Introduction ..... 1

B. Facilities 1

C. Research Activities ... 1

1. High Pressure Mass Spectrometry 1

2. Standard Reference Materials , . . 7

D. Analytical Activities ..... 15

1. Sample Pretreatment Prior to Mass Spectrometric Analysis , 15

2. General Applications 17

2. POLAROGRAPHIC ANALYSIS 22

A. Introduction 22

B. Facilities 22

C. Research Activities 23

1. High Precision Polarography 23

2. High Sensitivity Polarography ....... 25

3. Ultra-Small Sample Analysis 27

D. Analytical Development Activities 28

1. Standard Reference Materials . 28

2. Research Materials 34

3. Identification of Metals . . . 39

3. COULOMETRIC ANALYSIS 4l

A. Introduction 4l

B. Facilities 4l

C. Research Activities 43

1. Coulometric Iodimetry , 43

2. High Precision Controlled Potential

Coulometry ..... 46

D. Analytical Activities 48

1. Analysis of Uranium Oxide 48

2. Iodide Content of Tracer Solutions 50

3. General Applications 53

•. STOICHIOMETRY 54

A. Introduction 54

B. Research and Development 55

1. Magnesium . 55

2. Lead 62
PAGE

5. CLASSICAL MICROCHEMICAL ANALYSIS 63

A. Introduction 63

B. Facilities 63

C. Research Activities 65

1. Elemental Analysis of Small Samples ... 65

2. Reversed-Phase Chromatography . 67

D. Analytical Activities 67

1. Alumina Boules 67

2. Linac Cooling Water System 68

3. Beryllium Carbide 69

4. Iodide in Photographic Fixing Baths ... 70

5. Standard Reference Materials 70

6. Miscellaneous Analyses ..... 71

6. INTERNATIONAL RESEARCH GRANTS PROGRAM 73

7. SUPPORTING SERVICES o . . . 74

8. PERSONNEL AND ACTIVITIES 75

A. Personnel Listing . «,.... 75

B. Publications . 75

C. Talks . . . . <, . . . . o . . . . 76

D Committee Activities 000.... 76

9. REFERENCES „ 79

vi
LIST OP FIGURES

FIGURE NOo PAGE

1. Effect of sample pressure on ion yield for

oxygen . . . ^ 5

2. Dead-weight piston gage 8

3. Gas-mixing manifold 9

4. Schematic diagram of gas-mixing manifold .... 10

5. Relationship between the (44)/(28) ratio and

the concentration of carbon dioxide . . . <> . 14

6. Apparatus for the rapid reduction of water

samples 17

7. Cathode-ray polarograph equipped with dual

electrode synchronizers . . 23

8. General lay-out of coulometric laboratory ... 42

9. Coulometric electronic equipment mounted on

relay racks . 43

10. Analysis of coulometric titration data for

bias 45

11. Teflon cell for use in amalgam stripping

coulometry 47

12. Polarographic calibration curve for reduction

of iodate 52

13* Individual desiccator for drying magnesium

sulfate samples . 57

14. Carbon-hydrogen-nitrogen analyzer ....... 64

15. Microscopic equipment 64

vii
LIST OF TABLES

TABLE NO, PAGE

1. Variation with pressure of ion yield for

carbon dioxide .... ....... 3

2. Detection of butane in air 4

3. Detection of benzene in air .......... 6

4. Analysis of carbon dioxide in nitrogen,

mixture 1 . 9

5. Analysis of carbon dioxide in nitrogen,

mixture 2 11

6. Analysis of carbon dioxide in nitrogen,

mixtures 3> ^» and 5 • • • • 12

7. Ratio of (44)/(28) for three mixtures

determined on two successive days 13

8. Summary of mass spectrometric gas analysis

services 18

9. Differential polarographic determination of

copper and zinc 24

10. Analysis of standard reference materials by

polarographic and other techniques ...... 3(3

11. Polarographic determination of tin 32

12. Direct polarographic determination of copper

and nickel in stainless steel . 33

13. Effect of sodium hydroxide concentration on

Cr-Pb peak potential . 36

l4„ Analysis of arsenic trioxide 46

15. Analysis of uranium oxide from several sources . 49

16. Conditions for evaporation of iodide solutions . 51

17. Analysis of iodide tracer solution , 53

18. Analysis of solutions containing known amounts

of magnesium ....... 58

viii
LIST OF TABLES (CONT'D)

TABLE NO. PAGE

19. Analysis of purified magnesium oxide 6l

20. Determination of carbon in f luorocarbons .... 66

21. Composition of a typical sample of beryllium

carbide . 69

22. Determination of iodide in photographic

fixing baths 70

ix
MICROCHEMICAL ANALYSIS SECTION: SUMMARY OF ACTIVITIES

JULY 1965 TO JUNE 1966

Edited by John K. Taylor

ABSTRACT

This report describes the scientific programs and research

activities of the Microchemlcal Analysis Section of the

Analytical Chemistry Division of the NBS Institute for Materials

Research during the period July 1965 to June 1966, General

activities are reported in the areas of gas analysis by mass

spectrometry, polarography, coulometry, stolchiometry, and

classical microchemlcal analysis. Research accomplishments

described in some detail include: Improvements in the

sensitivity of gas analysis using high-pressure mass spectrometry; analysis of deuterated compounds by mass spectrometry;

comparative polarographic analysis of high precision; polarographic methods for trace and ultra-trace determination of a

number of elements; highly accurate coulometric iodimetric

titration; a highly precise method for determination of

magnesium based on its final weighing as magnesium sulfate;

and a number of microchemical procedures for the analysis

of a variety of materials.

'
h

1. MASS SPECTROMETRY GAS ANALYSIS

k. Introduction

The primary gas analytical tool of this laboratory is a

•nass spectrometer. Many other techniques, however, are emloyed in instances wher'e the mass spectrometer alone would

ot suffice for the analysis or where treatment of the sample

s required before mass spectrometric analysis. The primary

oal of the research effort has been to develop mass spectroetric techniques which minimize the necessity for the use of

other techniques with the main purpose to increase the accuracy

and sensitivity of the mass spectrometer, particularly in the

ield of trace analysis.

Facilities

The instrumentation available in this laboratory is essentially that described in last year's report [ref. 1, p. 6].

In addition, a Consolidated Electrodynamic model 21-620 mass

.spectrometer was available. This instrument lacks some of the

features of the Consolidated 21-103C but was found to be quite

useful for several phases of the research activity.

The mass spectrometer gas analysis laboratory was moved

to the new Gaithersburg site in April 1966 . A three module

bay with darkroom facilities has been provided which, houses

the mass spectrometer, a nuclear magnetic resonance spectrometer and most other laboratory apparatus concerned with gas

analysis and with the preparation of gas mixtures.

C. Research Activities

1 High Pressure Mass Spectrometry

a. General Considerations . Early attempts to detect low concentrations of helium 4 (1-500 ppm) in helium 3

by utilizing inlet pressures as high as 10 mm suggested the

possibility of the application of high pressure mass spectrometry for the detection of trace constituents in other gas

mixtures. It was early recognized that the number of gaseous
systems which could be studied would be quite limited. The

method would of necessity be more or less limited to inorganic

systems or to systems in which the trace component was organic.

A recent publication [ 2] shows that the method is quite applicable for the determination of trace constituents in helium.

We have attempted to extend the method to other systems in

which helium is not the major component.

The inlet system to the mass spectrometer was modified by

the addition of a McLeod gage. The vacuum system exhausting

the analyzer tube was modified to the extent that two pumping

systems were provided to increase pumping speed. One system,

an ion pump, was not suitable alone for high pressure operation

particularly for the rare gases. A two stage mercury diffusion

pump in parallel with the ion pump proved a satisfactory combination. This system has been further modified in hopes of

further increasing the pumping speed but no results have as

yet been obtained.

Several preliminary experiments indicated that a maximum

inlet pressure exists for a given gas above which the total ion

yield decreases rapidly. This pressure, with the pumping system

used, was around 5 mm for such gases as nitrogen, carbon dioxide

and argon. The effect seems to depend somewhat on the rate at

which the gas can be pumped away. The reason for the maximum

is no doubt the increase in ion-molecule collisions in the

ionizing region and in the analyzer tube which would directly

reduce the number of ions reaching the collector.

b . Spectra of Carbon Dioxide at Various Pressures . An extensive study was made of the effect of pressure on the

mass spectral pattern of carbon dioxide. The results, shown

in table 1, indicate no large variation in pattern over a

pressure range from 0.5 to approximately 10 mm but some slight

changes do occur.

i
Table 1„ Variation with pressure of ion

yielda for carbon dioxide.

ressure m

illimeters

f Mercury

Ions

9.6

8.5

7.7

4.4

2.5

2.2

2.0

1.2

0.6

0.5

C

+

(12)

+

(l6) C02

++

(22) C0

+

(28) C0

2

+

(44)

16.3 13-7 1.63 12.2 100

13.6 12.6 1.65 11.3 10.0

13-0 12.2 I.65 11.2 100

10.6 11.3 1.79 10.8 100

9.8 10.9 1.79 10.7 100

9.8 11.0 1.81 10.7 100

9-7 11.0 1.82 10.9 100

9.2 10.6 1.89 10.5 100

9.2 10.8 1.85 10.9 100

9.2 10.8 1.86 10.8 100

Ion yields are expressed as the percentage of ion current

relative to that at (44).

The pattern is expressed as the percentage of ion current

it the lower masses relative to that at the parent ion mass

,44)*. The decrease in the relative amounts of the fragment

ons with decreasing pressure really represents an increase

n the amount of the parent ion with decreasing pressure,

his immediately suggests the possibility of increased thermal

gffects 5n the ionizing region resulting from the greater density of the gas at higher pressure. It is interesting to note

:hat the only ion which does not decrease with decreasing

)ressure is the (22) which is the doubly charged parent ion.

This further suggests that the added thermal energy at higher

pressures affects the production of the doubly charged parent

Ion to an even greater extent than the parent ion itself.

Mass numbers are expressed as the singly charged ion at the

mass number indicated, e.g. (X), If and when a doubly charged

ion is discussed, it will be so stated.
The next step was an attempt to determine approximately

the minimum detectable quantity of a substance that could be

directly determined using high inlet pressures. Mixtures

were prepared by successive dilution of concentrated mixtures

prepared in small (l liter) stainless steel pressure vessels.

Some problems due to adsorption were encountered and to minimize these effects, dilutions were made by transferring the

higher-concentration mixtures to clean vessels followed by

dilution, rather than diluting the mixture directly in its own

vessel. While adsorption might still pose something of a

problem, these early experiments were not designed for high

accuracy but were more exploratory in nature.

The following observations were quite useful in defining

the sensitivity limitations of the system.

c. Butane in Air . Mixtures of butane were prepared

in both nitrogen and air. In order to prevent damage to the

larger analytical instrument, mixtures with high pressures of

air were analyzed on a Consolidated model 21-620 mass spectrometer where damage due to filament failure could be much more

easily remedied. On this instrument, the smallest detectable

quantity of butane, based on the (58) ion was 20 parts per

million at an inlet pressure of 10.2 mm. Agreement with the

data obtained mass spectrometrically and from the mixing data

is shown in table 2.

Table 2. Detection of butane in air.

Butane Added Butane Found

1.02 mole % 1.02 mole %

.10 mole % .10 mole %

.010 mole % .013 mole %

.002 mole % .002 mole %

Earlier results with argon had suggested that the

sensitivity* for the minor constituents followed changes in

*The sensitivity is defined as the ion current in scale divisions, or other arbitrary units, per unit of pressure in the

inlet system.
the sensitivity of the major constituent. Figure 1 shows the

total ion yield for argon-40 and argon-36 as a function of

pressure. While argon-36 is not a trace constituent , it is

present at concentrations below 0.5 mole percent.

40a + Ar

ARGON

ATOM ION CURRENT

AT HIGH PRESSURES

Figure 1

PRESSURE - MILLIMETERS Hg.

Effect of sample pressure on ion yield for argon.

From this data it was assumed that the sensitivity for

the minor constituent would follow that of the major constituent. A comparison of the ratio of ion yield at (32) to that

of (40), (43) and (58) in the air-butane system suggested that

the sensitivity for the minor constituent did not in fact

follow that of the major constituent but rather tended to increase relative to the major constituent as the pressure increased.

The low resolving power of the model 21-620 mass spectrometer made it difficult to measure the ions at mass 43 because

. of overlap both from atmospheric argon and carbon dioxide as
well as a large peak at (42) due to N^ . It was necessary,

therefore, to depend on the magnitude of the parent ion (58).

The sensitivity used to calculate the pressure of butane from

the parent ion was that determined at the \% mixture level.

d. Benzene in Air . A detectable peak at (78) was

found in the spectrum of a mixture of benzene in air calculated;

to have a benzene content of 2 ppm. The inlet pressure necessary to detect this concentration was 10. 5 mm. Results are

shown in table 3«

Table 3» Detection of benzene in air.

Benzene added Benzene found

130 ppm 140 ppm

13 ppm 15 ppm

2 ppm 3 ppm

e. Sulfur Dioxide in Air . At an inlet pressure of

13 mm, a detectable peak was found at (64) in a mixture whose

sulfur dioxide content was estimated to be 1.3 ppm. This

system illustrates one of the problems which arises in high

pressure mass spectrometry. The ion at (48) is quite unusual

and occurs in a very limited number of spectra, consequently

it is a valuable identifying ion. However, the ion molecule

reaction CU+0—0^ also has a mass of 48. This then could be

a source of unpredictable error in the interpretation of any

spectrum in which oxygen is a major component.

f

Propene in Carbon Dioxide . Another major problem

in high pressure mass spectrometry is the tremendous broadening

of peaks due to the major constituents. Thus far, no way has

been found to reduce the broadening without simultaneously

reducing the sensitivity. A brief study was made of the system

COp-propene using both the model 21-620 and the model 21-103

mass spectrometers. With the model 21-103* the lowest concentration of propene that could be detected was about 180 ppm.

Even this level of concentration was difficult to detect because the (42), CUHfi , appears only as a dimple on the side of

J

6
ne rapidly rising (44) . A situation such as this can be

emedied to some extent by the use of other peaks in the spectra,

or instance,, while the (42) was difficult to detect, the (39)

hich is prominent in propene was much easier to measure.

g. Oxygen in Nitrogen . The large number of requests

"or the determination of low concentrations of oxygen in nirogen and other gases prompted a brief study of the feasability

f high pressure mass spectrometry for this analysis. The

ajor peaks of both substances lie only 4 mass units apart and,

s could be predicted, overlapping of the (28) on the (32) was

he limiting factor. While mixtures of known concentration

ere not prepared, it was still possible to see a peak due to

xygen on the tail of the (28) at a pressure of 9 nim. This

uggests that it may be possible to determine oxygen at conentrations near 10 ppm directly in nitrogen.

h. Summary . While this work is not yet considered

omplete, the experience gained from the above and from work

one before the period covered by this report has made it

ossible to apply the knowledge gained to the solution of

everal difficult service analyses as well as to a rather ineresting problem concerning the preparation of a gaseous

ixture as a possible standard reference material. This work

s reported in the following section.

2 . Standard Reference Materials

a. Carbon Dioxide in Nitrogen . The increased

"interest in possible long-term variations in the carbon dioxide content of the atmosphere suggested the production of

, standard reference material consisting of a known concentraion of carbon dioxide in nitrogen at concentrations approxilately that of the atmosphere. Under normal operating conditions, the mass spectrometer would only be capable of deleting atmospheric concentrations of C02 (300 ppm) to an

.ccuracy of about 30$. Experience with high-pressure mass

pectrometry suggested that an accuracy of better than Vfo

.light be possible within the range of inlet pressures

7

-:.
previously used. Further, it suggested that a very rapid and

precise method might evolve which would lend itself admirably

to the production and analysis of such a gaseous standard

reference material. However, such a method would depend completely on the availability of several mixtures of accurately

known carbon dioxide content and it was felt that preparation

of these was the logical first step.

A gas mixing manifold was constructed consisting of four

pressure gages allowing pressures from to 2000 psia to be

measured with an accuracy greater than Vfo. The gages for use

above one atmosphere were calibrated over their entire ranges

with a dead weight piston gage (see figure 2). The gage for

pressures from to 1 atmosphere was calibrated against a

mercury manometer read with a cathetometer

The equipment is shown in figure 3« Figure 4 shows

schematically the arrangement of valves, gages and connections

Figure 2. Dead -weight piston gage.

8
Figure 3. Gas-mixing manifold.

An initial mixture of carbon dioxide of approximately 5

;tole percent was prepared from analyzed samples of nitrogen

nd carbon dioxide. This was analyzed by mass spectrometry,

y Orsat absorption analysis, and gravimetrically . The results

ogether with the value calculated from the measured mixing

ressures are shown in table 4.

Table 4. Analysis of carbon dioxide

in nitrogen, mixture 1,

Analytical Method

Mass Spectrometry

Orsat Analysis

Gravimetry

Calculated Value

, Standard deviation.

Estimate of the error involved in mixing.

COp in Mole Percent

5.52 ± 0.07 a

5.5 ± .2 a 5.49 ± 0.05*

5.60 + 0.06 b

9
0-2000 psio 0-1000 psio 0-200 psia 0-15 psia

VENT

CYLINDER CONNECTIONS

TO VACUUM PUMP

Figure 4. Schematic diagram of gas-mixing manifold.

This concentration region is ideal for accurate mass

spectrometric and gravimetric analyses. Accordingly, the

correct value for the mixture is taken as the average of these

two methods. Some interaction between carbon dioxide and

nitrogen has been reported at elevated pressures [3J« Since

no data was available at the pressure of CCU at which the abov'

mixture was compounded, only a crude approximation of the

magnitude of the effect was possible. This approximation

amounts to 1.25$ and reduced the calculated value from 5*67

to 5-60.

10
This mixture was then used to prepare a second mixture

with a calculated composition of O.63I mole percent. In this

concentration range, gravimetry is the only method capable of

the desired degree of analytical accuracy. The results are

shown In table 5.

Table 5. Analysis of carbon dioxide

in nitrogen, mixture 2.

a -14-4 1 Twr 4-i~ * C0o i- n Mole Percent Analytical Method 2

Gravimetry 0.628 + .004 a Calculated from

Measured Pressure 6u + ^

Mass Spectrometry O.63 _ .01

aStandard deviation

Estimate of the error involved in mixing.

The previously mentioned molecular interaction studied

by Haney and Bliss has no significant effect at this concentration of carbon dioxide and the only deviation from ideality

to be considered in the mixing data is the compressibility of

nitrogen. Values of the compressibility factors for both

nitrogen and carbon dioxide, accurate to better than 0.1$,

are available [4].

Gravimetry at this level is satisfactory but large volumes

of gas are necessary and unavoidable fluctuations in ambient

sea temperature and barometric pressure can constitute significant

sources of error. While these errors were minimized by careful

observation of ambient conditions, it was not possible to

;-•', eliminate the effect completely. For this reason, the concentration determined from the measured pressures is considered

more valid than the gravimetric value. Accordingly, the value

O.63I mole percent is considered to be the concentration of

carbon dioxide, in this mixture.

11
This latter mixture was next used to prepare 3 additional

mixtures whose concentrations were determined both by gravimetry

and by calculation from the measured mixing pressures. The

results are shown in table 6.

Table 6. Analysis of carbon dioxide in

nitrogen., mixtures ~5 >h , and 5.

o -, C0o in Mole Percent Sample 2

Calculated from

Gravimetry Measured Pressure

Mixture 3 0.0233 ± .0003a 0.0232 ± .0003 b

Mixture 4 0.0308 + .0010 a 0.0312 + .0003 b

Mixture 5 0.0341 + .0010 a 0.0344 + .0003^

a Standard deviation.

^Estimate of the error involved in mixing.

These latter three mixtures were those used to calibrate

the mass spectrometer over a concentration range from 200 to

350 ppm. The three mixtures were analyzed at inlet pressures

sufficiently high to allow the ion current at (44) due to

carbon dioxide to be read to better than 1%. The ion current

at (28) was measured under identical ionizing conditions to

avoid complication arising from attempts to reproducibly vary

the ionizing current. Consequently, it was necessary to replace the input resistor for the low sensitivity setting of

the preamplifier (5x10 ) with a resistor of lower value

(1x10^). This arrangement allowed both mass numbers of interest

to be recorded consecutively and rapidly at magnitudes so that

each could be read to better than \%.

A series of measurements were then made on two successive

days. The ratio of the ion current at (44) to that of (28)

was then calculated. The results are shown in table 7»

When the average of each set of ratios is plotted against

the concentration of carbon dioxide calculated from the measured

pressures, a straight line results as shown in figure 5«

12
Table 7. Ratio of j^U- for three mixtures

determined on two successive days.

Date Mixture No. 3 Mixture No. 4 Mixture No. 5

3/24 0.0131 O.OI76 O.OI96

.0132 .0175 .0196

.0129 .0177 .0195

.0130 .0176 .0194

.0131 .0177

.0174

.0176

.0177

o0195

Average 0.0131 O.OI76 0.0195

3/25 0.0131 0.0177 0.0197

.0132 .0177 • 0197

.0132 .0176 .0195

.0195

Average 0.0132 0.0177 0.0195

The linearity indicates that tne ratio of the ion current

at (44) to that of (28) is directly proportional to the concentration of carbon dioxide. The inlet pressures for all

samples reported in table 7 varied from 0.86 mm to 1.04 mm.

The variation of the measured ratios with pressure are random

and show no relation to the pressure, in the range of pressures

measured.

This method will allow rapid determination of large num-

, bers of samples of carbon dioxide in nitrogen on a routine

"1: basis. It will only be necessary to periodically affirm the

calibration factor of the spectrometer to be certain that the

ratio determined from the calibration standards has not changed,

b. Other Applications . The method for the determination of carbon dioxide in nitrogen described above is capable

of a high degree of accuracy because it is based on a comparison

of sample data with that obtained from standards of known

ii composition . The pressures necessary to determine carbon dioxide accurately by this method are only 1 mm. This pressure

13
could easily be increased from 5 to 10 times. Detection of ion

currents 100 to 200 times smaller could also be achieved. Thus

concentrations of carbon dioxide as much as one thousand times

less could be detected, although with diminished accuracy.

0.200

0.180

RATIO-

(44)

(28)

0.160

0.140

0.120

AVERAGE

RANGE

i

0.024 0.026 0.028 0.030 0.032 0.034 0.036 CARBON DIOXIDE CONCENTRATION IN MOLE PERCENT

Figure 5. Relationship between the (44)/(28) ratio

and the concentration of carbon dioxide.

14
Two gases presenting particularly difficult analytical

problems in the region from 1 to 1000 ppm are carbon monoxide

and oxygen. Carbon monoxide has a parent ion coincidental with

that of nitrogen. Oxygen is an ever present background ion

current in the mass spectrometer. Therefore, neither of these

can be easily analyzed directly by mass spectrometry in the low

concentration region. If, however, they were first converted

to carbon dioxide, the analysis could be carried out as easily

and as accurately as the previously described method.

Methods for the conversion of carbon monoxide and oxygen

are readily available and no great difficulty with an analysis

of this sort is anticipated.

D. Analytical Activities

1 . Sample Pretreatment Prior to Mass Spec trometric

Analysis

In many cases it is impossible to obtain quantitative

results on analysis of certain samples by direct mass spectrometry. Some technique must be available by which the sample

can be treated to alter its composition or nature In order to

perform accurate analysis. A good illustration of this problem

is a sample which contains deuterium and hydrogen in which

exchange between the deuterium and hydrogen in the sample and

that of water invariably present in the mass spectrometer can

occur. Typical of this type of material is heavy water. It

is impossible to directly measure the ratio of deuterium to

hydrogen in water containing high concentrations of deuterium

even with extensive pre-conditioning of the spectrometer.

The best method for this type of analysis is to first

reduce the water or other compound to hydrogen and deuterium

which can then be measured directly. Several methods have

been suggested for this reduction but, in all cases, they are

rather time consuming and do not lend themselves to the routine

analysis of large numbers of samples, particularly those containing high concentrations of deuterium.

15
The system shown in figure 6 was found to work quite well

for the rapid reduction of water containing as much as 99$

deuterium. Liquid samples of less than 5M-1 volume are admitted

through a heated silicone rubber septum into the evacuated

system. The heated stainless steel septum holder is identical

to that described in last year's report [ref. 1, p. 2]. The

vaporized sample passes through the zinc column, heated to

about 450°C, and ultimately the gaseous reaction products are

collected in the small receiver (A) . Any minor amounts of

unreacted water are trapped in the small trap (B) . The small

size of the sample allows virtually complete reduction. Several

samples were reduced without using the cold trap and no excess

water was found in the reduced gases. Many samples can be

reduced and analyzed after only a short period of conditioning

with water of approximately the deuterium content as that of

the sample.

Some further work is planned with this apparatus on a

determination of the magnitude of the effect, if any, of preferential reduction of hydrogen especially as it may affect

samples having high deuterium content.

Other samples in which the deuterium was determined with

success were DC1 and DBr, both of which were reduced over copper

at 400°C. Deuteriated ammonium chloride was analyzed by

reducing a solution consisting of a weighed quantity of water

of known deuterium content in which had been dissolved a

weighed portion of the ND^Cl. The resulting solution was then

reduced with hot zinc and the change in deuterium concentration

was then used to calculate the deuterium content of the ND^Cl.

The method and operation described above has the advantage

that samples can be prepared for analysis with great rapidity

and that many samples can be analyzed in a short time. However,

it was found to lack precision. Results agreeing within \%

were possible but it is believed that isotope exchange effects

preclude better precision.

16
TO VACUUM

PUMP

SAMPLE

RECEIVER

(A)

512/30

STOPCOCKS

COMBUSTION TUBE FURNACE

HEATER

'*£»> // ////// //////////////////..£&%

GLASS WOOL ZINC

) SAMPLE INJECTED

^ HERE

STAINLESS STEEL

SEPTUM HOLDER

GLASS WOOL

KZJ

Figure 6. Apparatus for the rapid

reduction of water samples.

2 . General Applications

A large number of service analyses were performed, many

of which included other methods of analysis such as nuclear

magnetic resonance, gas-liquid chromatography, infra-red gas

analysis, gravimetry and adsorption gas analysis. Also included was the compounding of several gas mixtures.

While some of the analytical services are of a routine

nature, many presented a challenge due to lack of reference

data or due to lack of knowledge of the system involved. A

typical problem was that of developing a method for the determination of the presence of mixed boron halides resulting from

the reaction of mixtures of boron halides. This work was performed in cooperation with members of the Inorganic Chemistry

section of the Inorganic Chemistry Division.

The primary problem was the complete lack of reference

spectra of the mixed boron halides and the existence of only

a limited amount of information on the spectra of the boron

17
halides. In spite of this, a method of analysis was developed

which allowed not only the identification of the following

species but allowed a reliable estimation of their concentration:

BF

2

C1 BFC1, F

2

B BFC1 F

2

B BC1

2

FC1B BC1,

Other service analysis of some interest included the

development of a rapid method for the testing of calibrated

1 ft helium leaks, determination of enrichment of benzoic acid

used in determinations of several organic reaction mechanisms

analysis of high purity methane for use as a primary standard

by the gas industry, and the chromatographic purification of

cyanogen azide.

Table 8 gives a breakdown of typical service analysis

indicating the type of analysis and the number in each category.

Table 8. Summary of mass spectrometric

gas analysis services.

Number of

Material Sample3S Sample £Size Determined

Pure Chemic als

N

2

2 500 ml STP 2

, Ar

SF6

1 Cylinder Purity

CH4

2 Cylinder N

2

, 2, C02, CjpHg,

C

3

H

8

He 1 Cylinder N

2

, 2

CH,-CsCH 2 Cylinder Methyl ether, 1-Bu

N

2

1 Cylinder

2

, H

2

Morpholine 6 20 ml of each Purity

Nitromethane 3 20 ml of each Nitroethane,

Nitropropane

C

2

F

4

1 1 ml STP C 2 P

6

!

18
Table 8. (Continued)

Material

Number of

Samples Sample Size Determined

ethyl

jiethacrylate

benzoic acid

Jorpholine

Organic Substances

3 20 ml of each

3 0.05 g

2 20 ml

Comparison of mass

spectra

1 P) Amount of

enrichment

Compare mass spectra

Unknown Gas

fixtures

ixtures of

• 2

in N

2

Iixtures of

Fu in air

fixtures of

r2

, o

2

, co2

°roducts of

)etonation

Jnknown in

Sealed Cell

Jnknown Gas

lixture

laseous Products

of Reaction

Inorganic Substances

2 100 ml STP

5 Cylinder

12 100 ml STP

7 Cylinder

4 300 ml STP

4 20 ml STP

1 10 ml STP

2 10 ml STP

5 0.1 ml STP

N

2

, 2, CO, C02, H

2

°2

Total pressure of CF^

N

2

, 2, C02

Rate of helium passage

through various sized

leaks

N

2

, 2, C02, CO, H

2

Np with normal isotope

distribution

H

2 0, N2

, 2

, C02

, C

BF-, BF

2 C1, BFC12

, BClo, F

2BBFC1, F2

BBC1

2

, FClBBClp, BpFhj BpClh

19
Table 8. (Continued)

Material

Number of

Samples Sample Size Determined

Inorganic -Organic Mixt ur e

Polluted Air

Air .

Flue Gas

Products from

Teflon

Combustion

Products from

SiC Combustion

Gaseous Products

of Reaction

Gaseous Products

of Reaction

Gaseous Products

of Reaction

Gaseous Products

of Reaction

Gaseous Products

of Reaction

Gaseous Product

of Synthesis

Gaseous Product

of Synthesis

Gaseous Products

of Polymer

Combustion

2

12

2

6

4

4

6

Noncondensibles 1

from Reaction

Gaseous Products 2

from Reaction

1000 ml STP

10 to 300 ml

STP

500 ml STP

2 ml STP

0.5 ml STP

_7 3x10 moles

10 3 ml STP

0.01 ml STP

0.01 ml STP

_Q

5x10 mole

0.5 ml STP

0.5 ml STP

0.5 to 1.0

ml STP

10" 3 ml STP

10 3 ml STP

Chloroform, toluene

Possible hydrocarbon

pollution, COp and H

p

N

2

, Q2

, Ar, CO, C02

, N0

2

, S0

2

N

2

, 2

, C0

2

, CP4

, S02

F

2

, SiF4

C02

, OFk, SOpFp, SIFl

C

2F6* C 4F8' C

3

F8' C 2

F

N

2 0, CpHj-Cl, C 2H

5

0H,

CpHh, CpHp, HC1, COp,

Triethyl phosphate

Hp , CH^

Hydrocarbons, boron

compounds

Spectrum of compound

CqH^BC lr-,Ge

CgHj-OH, CJHg, CgRvCl,

Triethyl phosphate

Purity of C

2

F^H2

CoF^H2

, CoF^H-., C0

2

2F^, CoF-H-, CoFrHo,

cyclo-C^Fg

H

2

, Air, CH4

BF

3

, CH

3

BF

2

, (CH

3

) 2

BF,

20
Table 8. (Continued)

Material

,

h

: Br

petic Acid-dh

D4

2

CI

Number of

Sampl es Sample Size Determined

Deut erated Compounds

3 'Cylinder H/H+D ratio

1 Cylinder H/H+D ratio

1 30 ml H/H+D ratio

3 0.05 g.

crystal each

H/H+D ratio

1 10 ml H/H+D ratio

1 10 ml STP ^2 } ^2

(E. E. Hughes and W. D. Dorko)

21
2. POLAROGRAPHIC ANALYSIS

A

Introduction

The polarographic research program has a two-fold objective. One aspect is the development of methods of increased

precision and accuracy. The second is concerned with improvements in sensitivity in trace-level determinations. The use

of micro-sized samples is a further aim in both program areas.

Success has been achieved in both of these directions

during the past year. Considerable effort has been devoted to

studies of differential polarography. A cell-reversal technique

has been found to be highly advantageous in improvement of

precision and accuracy. In addition, a number of methods have

been developed for trace element determinations, particularly

in standard reference materials and research materials used in

investigations by other groups. The cathode-ray polarograph

shown in figure 7 was used for all the work described, except

for some determinations in the ultra-trace range. Anodic

stripping voltametry has proved especially useful at this

level of determination.

B. Facilities

The polarographic instrumentation is essentially the same

as was described in the summary report of last year [ref. 1, p .6 However, the new facilities at the Gaithersburg laboratories

permit a much more convenient arrangement of this equipment.

The measurements laboratory has been divided into sub-modules

by means of partial partitions allowing each type of instrument

to be housed in a separate compartment.

A second thermostated bath and electrode synchronization

device has been acquired for use with the cathode-ray polarograph. This makes it possible to use one electrode stand for

single cell or for subtractive double-cell measurements and to

keep a pair of well-matched capillaries in reserve, yet available for ready use for high-precision comparative measurements.

22
s

1

Figure 7. Cathode-ray polarograph equipped with

dual electrode synchronizers.

Research Activities

1 . High-Precision Polarography

Differential polarographic techniques have been developed

in this laboratory which permit the determination of major

constituents in brasses, alloys and other matrices with a

recision of as good as 1.6 parts in 10,000, These

techniques were described in a talk presented at the Pittsburgh

'Conference on Analytical Chemistry and Applied Spectroscopy,

"February 21, 1966. A paper describing the work is being subemitted for publication.

The precision of ordinary differential polarography is

greatly limited by the matching of the capillaries and general

electrode balance. The techniques developed here minimize this

effect. To eliminate the constant bias owing to slight differences in capillary characteristics, resevoir heights, and

.general electrode balance, the differential signal from the

23
sample is measured against that of an accurately known standard. The cells are then interchanged and the differential

signal is remeasured. The average gives a result with minimum

effect from electrode inequalities, since a positive unbalance

in one position leads to an equal negative unbalance in the

second position.

These techniques have been used for the determination of

cadmium in metal-organic compounds and in lithium-cadmium

alloys, copper and zinc in brass and manganese bronze, and

iodine at the 0.1 ppm level. The most precise results, obtained

for 10 determinations of cadmium in 1 N hydrochloric acid at

the 100-ppm level, showed an average deviation of 0.016$ of the

amount present.

Copper and zinc were determined together in a solution of

pyridine and pyridinium chloride. The metals were dissolved

in dilute nitric acid, evaporated to dryness, after which the

residues were dissolved in hydrochloric acid, pyridine and

water, so that the final solutions were 0.5 M in pyridine and

pyridinium chloride. Results for the analysis of standard

reference materials, 62d (a manganese bronze), 37e (a sheet

brass), and a copper-zinc solution are shown in table 9«

Table 9. Differential polarographic determination

of copper and zinc

Sample

Cu Present, Cu Pound,

%

Zn Present, Zn Pound,

Cu-Zn

Solution

49.79 49.80 50.21 50.20

Brass, 37e 69.61 69.71 27.85 27.75

Bronze, 62d 59.07 59.03 37.14 37.06

This technique has the advantage that highly accurate and

precise results are obtained on very small samples. The

measurements of table 9 were made on 5 ml. of solution containing from 90 to 200 ppm of copper and zinc. This would be

the equivalent of 90 to 200 micrograms of sample if a final

24

!,
Ivolume of 1 ml had been used. The method is equally applicable

to the determination of a number of other ions such as tin,

lead, nickel, uranium, and chromium, many of which can also be

determined when present together in the same solution.

Differential polarography may also be used to advantage

in homogeneity and specification testing merely by comparing

the unknown in one cell against a similar standard in another

cell

Certain anions may also be determined by this technique,

or example, a research project in another government agency

equired that solutions containing about 0.1 ppm of iodide be

analyzed with results accurate to within 2% of the true value.

Iodide gives a poorly-shaped wave with cathode-ray polarography;

however, the iodate wave is well-defined. The oxidation of

very small amounts of iodide to iodate has been reported to be

incomplete; therefore, it was necessary to investigate the

optimum conditions. It was found that by adjustment of the pH

to 3 > addition of bromine, and gentle heating at steam bath

temperatures to remove bromine, quantitative results could be

obtained. The iodate may then be measured polarographically

in a supporting electrolyte containing 10 g per liter each of

sodium carbonate and potassium chloride.

Results on standard iodate solutions showed an average

deviation of 5 parts in 1000 which is equivalent to an uncertainty of 0.5 ppb in the 0.1 ppm solution submitted for

analysis

2 . High Sensitivity Polarography . a. Determination of Tellurium in Selenium. A

•imethod developed in this laboratory [ 5] for the determination

of trace amounts or greater of tellurium in cartridge brass and

iwhite cast iron standard reference materials has been extended

to include its determination in intermediate purity selenium.

The method, as originally developed, is extremely sensitive

and selective and is applicable to the determination of nanogram

quantities of tellurium in almost any matrix. For determination

25
of tellurium in selenium, 2-g samples were dissolved in nitric

acid and evaporated to dryness. Sulfuric acid was then added,

the solutions were evaporated several times with nitric acid

to remove selenium, and evaporated to dryness. The resulting

residues were dissolved in 2 ml of 50$ phosphoric acid, the

solutions were diluted to 10 ml, and measured on a cathode ray

polarOgraph at -1.2V vs. a mercury pool anode. Values of 0.33

and 0.35 ppm of tellurium were obtained. A limit of detection

of 0.005 to .01 ppm in the final solution is possible. If a

final volume of 5 ml is used, this would correspond to about

0.01 to 0.02 ppm in the original material. Larger sample

weights would permit further lowering of the absolute detection

limit

The selenium also was examined for copper, cadmium, and

lead. Two-gram samples were dissolved in a mixture of dilute

nitric and hydrochloric acids and evaporated to dryness

several times with hydrobromic acid to volitalize selenium.

The residues were dissolved in 0.5 ml of o,l N hydrochloric

acid, followed by the addition of 2.0 ml of 0.2 M oxalic acid

and 2.0 ml of 0.06 M ammonium hydroxide, and examined polarographically. Polarographic examination of the resulting

solution showed copper, cadmium, and lead each to be below

the 0.5-PPm level.

d. AnoQic stripping Analysis . noun une riign-pui-j. oy

zinc and reagent-purification programs have necessitated investigation of the determination of ultra-trace amounts of

copper, cadmium, and lead. Extremely high instrumental

sensitivity may be obtained by preconcentration by electrolysis

(plating) onto a cathodic electrode for relatively short periods

of time, generally about 5 to 15 minutes. The drop is then

stripped anodically, and the enhanced peak current resulting

from the oxidation of the metal accumulated in the drop is

measured.

Several types of electrodes may be used including graphite, platinum, mercury-plated platinum, or a hanging mercury

26
drop. The latter , the type that is commonly called a Kemula

electrode, was used for the work described here. The electrode

size is controlled by extrusion of a mercury drop through a

glass capillary attached to a micrometer syringe.

There are many factors effecting the reproducibility of

measurements with such an electrode, including temperature,

plating potential, reproducibility of stirring rate during the

preconcentration electrolysis, variation in drop size, completeness of oxygen removal, and capillary and cell positioning.

Other problems, common to trace analysis in general, include

^adsorption on container walls and atmospheric and reagent

contamination

Since high-purity reagents are required for the analysis

of high-purity zinc, several fractions of hydrochloric acid,

purified and/or distilled by the Separation and Purification

Section were submitted for evaluation of the effectiveness of

the purification process. These were checked for copper,

'cadmium, and lead by the anodic stripping technique. The

unpurified acid was found to contain about 3 ppb- of cadmium,

13 ppb of lead, and 21 ppb of copper. Cadmium was not detected

in any of the distillation fractions. In this particular case,

the limit of detection was about 1 ppb; however, greater

sensitivity could be obtained by such means as increasing the

! plating time and the electrode size. In the third fraction,

the lead content was decreased to about 3 ppb and copper to

; about 4 ppb.

3. Ultra-Small Sample Analysis

As a result of studies by the Harry Diamond Laboratories

j on the vacuum-deposition of multi-component thin films which

'• may be used In resistance circuits, analyses of microgram

I

samples of nickel-chromium-copper-aluminum (75-20-2.5-2.5)

films were required. Owing to the very small amounts of film

: usually involved, few analytical measurements of composition

had been made by other workers in the thin-film field. The

sensitivity and selectivity of the cathode ray polarograph

27
appeared to offer a possible means of solution to the problem.

The films, weighing as little as 300 micrograms, had been

deposited on glass plates weighing approximately 5 to 10 g.

Obviously, the weighing errors for such samples are large.

Fortunately the nickel-chromium-copper-aluminum ratios, and

in some cases the nickel-chromium-copper ratios, give the

required information. For convenience, the methods developed

are based on the use of three separate aliquots from a solution

of the film which has been stripped from the plate with aqua

regia. However, if increased sensitivity is desired, as would

be required for much smaller samples, all three may be done on

the entire solution by making suitable separations. Chromium

was determined in 1 M sodium hydroxide after oxidation with

hydrogen peroxide. For the determination of copper and nickel,

chromium was first reduced with sulfur dioxide, after which

copper and nickel were measured in a pyridine-pyridinium sulfate supporting electrolyte. Aluminum was determined as the

Solochrome Violet RS complex as described earlier [ref. 1, p. 13

after removal of copper and nickel by extraction with sodium

diethyldithiocarbamate and extraction of the aluminum with

cupferron. The precision of the results was generally about

± 2%. This can be improved, whenever more accurate results

are required, by the use of differential polarography.

Other thin films submitted by Harry Diamond Laboratories

were of nickel-chromium, which were analyzed as described above,

and of antimony-bismuth, which were measured as described

earlier [ref. 1, p. 13].

D. Analytical Development Activities

1 . Standard Reference Materials

Many of the methods used for the analysis of standard

reference materials, while very accurate, are time-consuming,

tedious, and/or often require large sample weights. Polarography has been applied in this laboratory to many of these

materials in an attempt to improve the methods, for confirmatory

28
an.alysis, and to provide results by more than one technique

to evaluate reliability of analytical results. During the

past year, procedures have been developed for the polarographic

determination of 6 elements in various standard reference

materials and for the determination of about 12 other elements

in a variety of matrices. Values obtained by polarography on

standard reference materials are shown in table 10 and are

n compared with those obtained by other analysts using different

techniques

a. Stainless Steels . Polarographic procedures were

investigated for the determination of aluminum, lead, and tin

in stainless steel spectrographic standards 1152 and 1154.

Aluminum was determined in 1152 on 0.2-g samples which were

dissolved in aqua regia. Most of the copper, iron, nickel,

cobalt, manganese, vanadium, and titanium was extracted as

diethyldithiocarbamate complexes with chloroform. Aluminum

was then extracted with cupferron and chloroform at a pH of

-;.;. 4.5., followed by destruction of the organic material by fuming

to dryness with nitric acid and perchloric acid. To remove

residual amounts of iron and titanium, an additional acid

cupferron extraction was made. Aluminum was then separated

from residual amounts of chromium by extraction of the cupferrate complex at a pH of 4.5. The organic material was

destroyed as above, the residue was dissolved in 1 ml of 5 M

M perchloric acid, 5 ml of 2 M sodium acetate, and 2 ml of 0.05

percent Solochrome Violet RS, diluted to 50 ml, and heated 5

minutes at 55-70°C to form the aluminum-dye complex. The

complex was measured polarographically at -0.7 V vs. a mercury

pool anode.

Samples of 1154 weighing 0.5 g were dissolved in 50 percent

hydrochloric acid, diluted, filtered, and the residue ignited

at 800°C. After evaporation to dryness with sulfuric acid and

hydrofluoric acid, the residue was fused with 0.20 g sodium

carbonate and added to the original filtrate which was then

diluted to 50 ml. Aluminum was then determined as described

29
•H co

rJ a)

01 3

4-1 cr

cd •H 2 c

X!

co CJ u co c H 0)

J-l

M

co cu

'4-1

x

0) J_> OS O

T3 X) H c

CO CO T3C u

cd •r-l 4J x CO a

cO

4-1

u o ooo

co rJ H cO

ro .—1 >> o

r-l CM

crj 5 ^ <c X XCO H

a

CD ^ •r-l CD cO u-i d c •H .—

•H 4-) CO fa

co o >o

faw

C)o

CQ I /"NI O Cjl rn J-J •Hi CQ cO XI 2 .—

a o cO Qj u ^ MJ

4->l

col si

CD —I | W|

h <r

m cm en in

O vO r^ r-^ o o o r-l CN CO 00 <J- <f -< CN o o o o o o O CN O CN o

cO

X cOX cd en <* <r o C^ o o r-l CN en o o o o o

rl col cd cO

C/) CO 1 col en <t

CQ

X

X I o o O QJ o o ~ H CI

cO cO cO <f o a-N r-i m m o o o o o

CN|

H

oom

O CN

-a a) r- r-l O CN

CJ

r-l 00

00 <f O CN

CJ00<r

CN

XC rH

cu CO < 2 in

oi i—

an

—

X

G r-l Pm c/) < 3 -H U 2 O

en

CJCNo

CJm

CMo

CJ <f r-l O CN o m m o o CN

<t o O CM < H

in

x

CNo

r-i <jm CM en <t cm

m r~ oo 00 o o o r-l CN en oo -j- <f o CN o o o o o o O CM O CN oXCN

00

aF

CO

co00 CO

r-l

m

as

•* cO

CJ CO •HU OO

4-1 CO

m e

•H *. > CJ

CO •r-l

i-> S-i 00 4-1 o CO u S

4-1 o o 4-) CO o

r-l

X

w CM

a> M-l

aa

CO

COoo oI—

M o o

•H •r-l u r-l 4-1 4-1 CO CO e e o •H

4-1 > o CO X r! CU O

CJ T3 Xa o

cO •r-l u u

00 4-> o CO u e

4J •H o S-i CO 4-> ex, •H CO H cO X

30
jibove, using 10 -ml aliquots.

Lead was determined polarographically in stainless steel

standards 1152 and 1154 after making some separations. The

samples, weighing from 0.2 to 0.5 g* were dissolved in dilute

p,qua regia and evaporated to dryness. The resulting residues

•iere dissolved in 2 ml of 50$ hydrochloric acid, and evaporated

a

'

;o dryness again. Iron was extracted with isobutyl acetate from

hydrochloric acid solution of the residue. Chromium was

volatilized as chromyl chloride by fuming to dryness with

perchloric and hydrochloric acids. Residual iron was reduced

ith ascorbic acid and lead was extracted as the sodium

diethylidithiocarbamate complex with chloroform from an ammonia-

:al solution containing potassium cyanide and sodium tartrate.

After destruction of the organic material, lead was measured

olarographically in a sodium tartrate-nitric acid supporting

lectrolyte at -0.7 V vs. a mercury pool anode. Spectrographic

tandard 444 was used as a reference standard and duplicate

alues of 0.0038$ of lead were obtained. The standard is

certified to contain 0.0037$ of lead, based on chemical and

spectrographic analyses.

Tin was determined in sample 1152 by two methods using

1-g samples. In one set, the samples were dissolved in 30$

hydrochloric acid, oxidized with nitric acid, heated to boiling,

gassed with hydrogen sulfide, and filtered. After oxidation of

sulfide and organic material, tin was precipitated with ammonium

hydroxide using aluminum as a carrier. The precipitates were

dissolved in hydrochloric acid and diluted to 25 ml in a

supporting electrolyte whose final concentration was 1 M in

hydrochloric acid and 4 M in ammonium chloride. Tin was

measured on the cathode-ray polarograph at about -0.45 V vs.

a mercury pool anode. In the second set, tin was extracted as

the thiocyanate complex from a hydrochloric acid solution.

After oxidation of the thiocyanate and organic material, tin

was precipitated with ammonium hydroxide using iron as a

carrier and finished as described above.

3l
Tin was determined using 0.5-g samples of 1154 by thiocyanate extraction -ammonia precipitation using iron as a

carrier, and finished as for 1152. Individual results are

given in table 11.

Table 11. Polarographic determination of tin.

1152 1154 Method Percent

Hydrogen sulfide precipitation 0.0041

.0045

Thiocyanate extraction .0043 0.0238

.0042 .0245

.0045 .0224

A value of 0.021$ of tin was found for reference standard lOle,

which is certified to contain 0.020$ tin and 0.015$ for reference standard 444 which is certified to contain 0.014$ of this

element.

The thiocyanate separation would seem to be quicker and

more convenient than the hydrogen sulfide precipitation.

Both methods, however, offer considerable advantages over the

traditional method consisting of hydrogen sulfide separation,

ammonium hydroxide precipitation, reduction of tin ( IV) to

tin(ll) by prolonged boiling with lead, and maintenence of an

oxygen-free atmosphere during the subsequent titration with

standardized iodate. A value of 0.020$ of tin in a 10-g

sample of lOle was obtained earlier by the author using this

latter method.

For the certification of stainless steel 73c, attempts to

determine both copper and nickel in the same ammonium hydroxide

ammonium chloride supporting electrolyte with no prior separations gave reasonably good results. However, for the more

accurate work needed for the certification of a standard

reference material, copper and nickel were determined together

in 0.2-g samples in pyridine-pyridinium sulfate media after

extraction of iron with isobutyl acetate and volatalization of

chromium as chromyl chloride. Values of 0.129$ of copper and

32
"-

w

.199$ of nickel were obtained on the reference standard 73b

hich is certified to contain 0.125 and 0.197$ respectively.

'Copper was also checked by another direct determination in the

following manner. The iron was reduced with hydrazine hydrochloride and copper measured in a starch-sodium formate supporting electrolyte (pH 2-3) at -0.25 V vs. a mercury pool

janode. Nickel was not determined in this media; however, lead

could be measured at about -0.5 volts in the same solution. A

Value of 0.124$ of copper was obtained for 73b by this procedure

The direct determination of copper and nickel in ammonium

hydroxide -ammonium chloride media should be adequate for many

Purposes. It is quite rapid, requiring only the sample disolution, neutralization, dilution to volume, and polarographic

measurement. The results would generally be slightly low,

owing to adsorption on the bulky hydroxide precipitate. Ascorbic acid is unsuitable as a reductant for iron in this case,

because the copper may be partially reduced to the metal.

Results obtained by this direct method are shown in table 12.

Table 12. Direct polarographic determination

of Cu and Ni in stainless steel.

Copper found, Nickel found,

Sample Percent Percent

73b 0.119 O.195

73c .084 .230

.085 .237

.085 .221

.083 .225

b. Maraging Steel . Polarographic determinations of

aluminum and titanium in maraging steel, standard reference

f

n aterial H56, were also investigated. The procedure for

luminum utilized the method described above. Titanium was

letermined in a sodium acetate-EDTA supporting electrolyte

after cupferron and ammonium hydroxide separations. Sample

weights of 0.2 g were used in both determinations. Standard

reference material 170a was used as a reference standard in

33
both determinations. A value of 0.277$ was obtained for

titanium, whereas the certified value is 0.28l$. The polarographic result, however, may be compared with a value of

0.278$ titanium obtained earlier by the author using the conventional hydrogen peroxide-photometric method, after separation

of all interferences. At the same time, a value of 0.282$

was obtained by a gravimetric procedure using a 5-g sample.

The polarographic determination yielded a value of 0.043$

for aluminum in 170a, which is certified to contain 0.046$.

However, an earlier determination by the author gave the value

0.042$ using the conventional ASTM sodium bicarbonate-sodium

hydroxide -aluminum oxide method, with a 10-g sample.

c. Nickel-Chromium Cast Iron . Titanium was determined in nickel-chromium cast iron 82b with 0.5-g samples by

essentially the same procedure as used for 1156, with the

exception that the ammonium hydroxide separation was omitted.

A value of 0.047$ was obtained on reference standard 82, which

is certified to contain 0.048$ titanium.

2 . Research Materials

The versatility of polarography has made it very useful

in the analysis of a wide variety of research materials, as well

as in many "trouble shooting" situations in which chemical

analyses have been needed. A few of the more interesting

problems and the methods developed for their analysis by cathode

ray polarography are described in the following sections.

a. Lubricating Oils . Three lubricating oils

containing 1, 50, and 500 ppm respectively of each of copper,

iron, aluminum, lead, chromium, nickel, tin, silver, and

magnesium were prepared by another NBS group as standards to

monitor engine xvear and predict possible engine failure.

Because of difficulties in preparation and mixing of the

sample, homogeneity and possible segregation on standing were

of major interest. Samples, taken under a planned program,

were submitted for analysis. Polarography was found to be

34
.31

especially convenient for the determination of copper, nickel,

tLead, iron, and aluminum by the methods described below.

In all cases, it was necessary to ash the samples, which

had been prepared from relatively non-volatile metal-organic

ftandard reference materials as described in an NT3S Monograph

6]» Samples weighing f^rom 1 to 18 g were very slowly dryashed to a temperature of 500°C and the residues dissolved.

bopper and nickel were measured polarographically in pyridineJpyridlnlurn sulfate supporting electrolyte.

The method used for the determination of iron depended

upon the amount present. At the 1-ppm level, iron was extracted

kith cupferron from an acid solution and determined by the

polarographic reduction of the Solochrome Violet RS complex.

In the 50- and 500-ppm samples, iron was determined directly

on a solution of the residue in a sodium acetate-EDTA supporting

electrolyte . Aluminum was reduced polarographically as the

Solochrome Violet RS complex after its extraction as aluminum

cupferrate. Lead was measured in 1 M sodium hydroxide. The

determination of chromium was investigated concurrently with

that of lead. It appeared possible to determine .both in the

same sodium hydroxide solution, although other workers had

found merging lead-chromium peaks at the sodium hydroxide

concentrations used. Solutions containing 100 and 200 micrograms each of lead and chromium were evaporated to dryness,

"after which the residues were dissolved in 3 drops of hydrochloric acid and 10 ml of water. Two ml of 30$ hydrogen perjoxide was added, followed by sufficient 10 M sodium hydroxide

to give final alkali concentrations of 0.1, 0.2, 0.5 and 0.8 M

respectively. The solutions were boiled 10 minutes to oxidize

^chromium and diluted to 50.0 ml, before measuring lead and

chromium polarographically. The solutions which were 0.5 and

lD.8 M in sodium hydroxide gave peaks which were poorly resolved.

In the remaining two solutions, the peaks were well-defined and

sufficiently separated for Individual measurement. The results

are shown in table 13.

35

11

le
Table 15. Effect of sodium hydroxide concentration

on Cr-Pb peak potential.

En

- E„. (volts) Cr Pb v ' Sample 0.1M 0.2M O.^M 0.8M

2 ppm -0.22 -0.17 -0.15 -0.10

4 ppm - „27 - .19 - .16 - .14

Thus it appears that lead and chromium may both be

determined in a supporting electrolyte which is not more than

0.2M in sodium hydroxide.

b. Chromium in Various Matrices . The determination

of chromium as a minor constituent is illustrated by the following examples for a non-metallic and metallic matrix, respectively.

A synthetic sapphire, also containing about Vfo of yttria,

was pulverized, after which 0.5-g portions were dissolved by

heating with 10 ml of hydrochloric acid in a sealed tube at

270°C[7]. The resulting solution was diluted to 100 ml and

portions equivalent to 10 mg of sample were aliquoted. The

chromium was then oxidized with hydrogen peroxide in 1M sodium

hydroxide and measured polarographically. Replicate values of

0.661, 0.668 and 0.664;$ of chromium illustrate the precision

of the method.

Two nickel-chromium powders containing about 93 and 97$

of the former were analyzed for their chromium content.

Pifty-mg samples were used and the solutions for the calibration

curve were prepared to contain the same amount of nickel as the

samples to correct for possible adsorption losses on the nickel

precipitate. Chromium was determined as described above and

duplicate values of 2.96 and 2.95$ were obtained for one sample

and 4.67 and 4.72$ for the other. The time required for each

determination is approximately 20 minutes.

c. Lithium-Cadmium Alloys . The differential polarographic techniques discussed earlier were used to good

36
advantage in the case of two lithium-cadmium alloys, received

'rom the Alloy Physics Section, containing about 90 and 95$

;admium respectively. Since these alloys react rapidly with

pir, it is necessary to keep then in an inert atmosphere.

Accordingly, the rod-shaped samples, which had been stored in

)il, were transferred to. a glove bag containing an atmosphere

Df helium. Samples weighing 0,7 to 1.5 g were prepared in

;he following manner. The rods were cut with diagonal cutters,

cleaned in benzene, dried, weighed, removed from the glove bag,

and dissolved in hydrochloric acid and water. After dilution

o 500 or 1000 ml, 10-ml aliquots were diluted to 100 ml with

N HC1. These were then measured comparatively with reference

to standard cadmium solutions of similar composition and

esults of 9^.10 and 92.45$ of cadmium, respectively, were

btained for the two specimens. The values of lithium by

ifference were then 5*90 and 7»55$« In order to determine

he extent of oxidation, and also for an independent measurement

f the lithium content, aliquots of the original solutions were

iven to the Analytical Coordination Chemistry Section for

iie termination by atomic absorption. Values of 5*88 and 7.^5$

f lithium were obtained which show excellent agreement with

those obtained by difference.

d. Indium-Thallium Alloys . Other samples received

from the Alloy Physics Section were six indium-thallium alloys,

ranging in composition from about 5 to 70$ indium, for the

letermination of either constituent. The suitability of several

supporting electrolytes was investigated. A sulfuric acidPotassium chloride medium had previously been used very successfully in this laboratory for the determination of indium,

iowever, for the present samples, the reduction of thallium

as found to be too close to that of indium for good peak

esolution. A 2 M acetic acid-2 M ammonium acetate mixture was

tried and two well-defined peaks were obtained, that for

bhallium occurring at approximately -0.7 volts and for indii.urn

37
at -0.9 volts. The calibration curve for indium was linear

for both anodic and cathodic scan in the region of concentration

checked (40-200 ppm). For thallium, the calibration curve

was linear by cathodic scan between 60 and 180 ppm, but not at

300 ppm. It seems probable that the region of linearity would

be extended by a more thorough investigation of the polarographi

conditions.

The method developed for the determination of indium was

as follows: Samples, weighing from 0.1 to 0.2 g, were dissolved

in dilute nitric acid and diluted to 100 ml. Ten-ml aliquots

were taken and 5»5 ml of acetic acid and 3.9 g of ammonium

acetate were added. The pH at this stage was about 4.6 to 4.8.

The solutions were diluted to 50 ml and measured polarographically at -0.9 V as indicated above.

e. Bismuth in Bismuth-Tin Alloys . As a result of

some phase-diagram studies by the Metallurgy Division, analyses

of a large number of binary alloys of bismuth and tin were

required, ranging in composition from to 100$ bismuth. In

order to remove tin, the samples were dissolved and evaporated

with a hydrobromic acid-bromine mixture, as described earlier

for aluminum-tin alloys [ ref . 1, p. 13]. Although evaporations

to dryness were done at approximately 100°C, some loss of

bismuth in standard solutions occurred. The addition of sulfuric acid before subsequent evaporation to sulfuric acid

fumes was found to eliminate this loss.

Several supporting electrolytes were investigated, including nitric acid-sodium tartrate at a pH of 4.5 and a sulfurichydrochloric acid mixture. The latter gave better defined

peaks in the concentration ranges covered, although the calibration curve was somewhat non-linear. In some cases, relatively large amounts of sample were used in order to minimize the

effect of Inhomogeneities. However, aliquots were chosen so

that the final bismuth concentration was approximately 2 to

10 mg per 100 ml. Results on standard solutions of bismuth

showed an average recovery of 99.8 t 1.3$»

38
f . Metal Organic Complexes . Polarography has been

very useful in the determination of copper , nickel, and zinc

in a variety of metal organic complexes which have been of

interest in connection with EPR studies of their structures

„

These compounds are of a relatively rare type, the copper ions

in the lattice being very close together and reacting strongly

in a magnetic field.

For the determination of zinc in crystals of zinc-doped

copper complexes, 0.1-g samples were measured polarographically

in a pyridine-pyridinium chloride supporting electrolyte after

dissolving in dilute hydrochloric acid. A typical determination

gave results of 0.21$ for the zinc content of the crystals.

Nickel was determined directly on a one-mg sample of a

;nickel complex after dissolution in 0.1 ml of 50$ perchloric

acid, addition of water, 0.1 ml of pyridine and dilution to

5 ml. The nickel content of this material was found to be

14.5$.

Zinc and copper were determined in 10-mg samples of a

zinc-copper phenanthroline complex after destruction of the

organic material by treatment with sulfuric and nitric acids,

evaporation to dryness, dissolution of the residue in 0.2 ml

of 50$ perchloric acid, addition of 0.2 ml of pyridine, and

dilution to 10 ml. Zinc was found to be 17.6$ and copper 0.17$,

which illustrates the nature of the analytical problem.

Other samples of this nature were nickel- or zinc-doped

copper complexes. Four to 9 rng samples were wet-ashed, then

ignited, and dissolved in 1 ml of 50$ hydrochloric acido One

ml of pyridine was added, the solutions diluted to 10 ml and

measured polarographically. Copper in the copper-nickel mixture

was found to be 24.8$ and nickel 0.53$. Copper in the copperzinc mixture was found to be 24.5$ and zinc to be less than

0.1$.

3. Identification of Metals . This laboratory has been called upon occasionally to make

qualitative or semiquantitative examinations of small amounts

39
of samples, especially of metals. For example, a water filter

housing, suspected to be brass, was quickly identified as such

by cathode ray polarography . Minute scrapings taken from the

interior were measured in a supporting electrolyte containing

0.4 ml of 5°^ hydrochloric acid, 0.4 ml of pyridine and 4 ml

of water. The scrapings were found to contain approximately

65^ of copper and 35^ of zinc. Such a determination requires

about 5 minutes and provides positive identification of the

alloy used.

A fragment from the radiator of an antique aircraft,

suspected of being either copper or brass was treated in a

similar manner and found to contain about 6Vfo copper and YJ%

zinc .

(E. J. Maienthal)

40
3. COULOMETRIC ANALYSIS

f\. Introduction

The program in coulometric analysis was Initiated nine

/ears ago at the National Bureau of Standards. Its primary

pbjective was to develop absolute methods of analysis based

apon physical standards, rather than upon standards of chemical

purity. The program has been very successful In that it has

provided methods for the assay of standard reference materials

that are reliable to a few parts in one hundred thousand and

are accordingly the most precise and accurate primary standardization procedures available.

During the past year, coulometry has been extended by the

ievelopment of an iodometric method of precision comparable to

the earlier methods. This has been used to establish the

reductimetric equivalency of arsenious oxide intended as a

chemical primary standard. Coulometric methods already developed have been used In the analysis of several research

materials as described in a following section. In addition,

preliminary work has been initiated on precise methods of controlled-potential coulometry.

B. Facilities

The general facilities and equipment for coulometric

analysis were described in detail in the previous report

[ref. 1, p. 14] . In brief, they consist of a power supply

capable of maintaining a selected level of current within a

[few parts in a million over a period of 8 hours. A quartz - crystal controlled time-interval meter permits the duration of

electrolysis to be determined within a part in a million.

The move to the new laboratories in Gaithersburg, Maryland

rovided the opportunity to rearrange the laboratory equipment

in what appears to be a very satisfactory layout, shown in

figure 8. The electrical measurement equipment is located in

one module, while chemical operations are carried out in a

separate room. The laboratory furniture, consisting of a

41
combination of tables and benches, is arranged in a P shape,

the vertical portion of which is parallel to one of the walls

of the room on which the services are located. This arrangement

provides 28 linear feet of bench-front perimeter with nine

directions of approach so that considerable flexibility in the

placement of equipment is possible.

Figure 8. General lay-out of coulometric laboratory.

Two standard relay racks on casters are used to mount the

equipment employed in constant current coulometry and controlled

potential coulometry, respectively, as shown in figure 9» The

mobility thus provided, together with the flexibility resulting

from the arrangement already described, should greatly facilitate:

both the research and analytical aspects of the coulometric

laboratory.

42
L

Figure 9. Coulometric electronic equipment

mounted on relay racks.

Z . Research Activities

1. Coulometric Iodimetry

a. Efficiency of Generation of Iodine . A prime

requirement for accurate constant-current coulometry is the

establishment of conditions to insure efficient electrode

"reactions. The electrolytic oxidation of iodide to produce

odine has been studied as early as I89O, independently by

erroun [8] and by Kreider [9]* However, their investigations

s well as those of subsequent workers have not been of sufficient accuracy to establish conditions for reagent generation

within the requirements of the present program (0.001$ or better)

43
Accordingly, an intensive study of the electro-oxidation of

iodide was undertaken.

A series of precise measurements was made over a wide rang

of two varying parameters, namely current density and concentra

tion of iodide in the electrolyte. The complete results will b

described in a forthcoming publication. In brief, it was established that in a phosphate buffer at pH 7, when the iodide

concentration is 0.1 molar, the current efficiency is 100.0000

o percent for current densities between 1.2 and 3*0 mA/cm . For

a current density of 3.8 mA/cm in this electrolyte, the curren'

efficiency falls to 99.9998 percent, while for 5.0 mA/cm2 it

becomes 99«9985 percent. Since the composition of the electrolyte does not change significantly during a titration, these

values based on electrochemical measurements represent the titration efficiency that can be expected under the conditions

specified.

b. Summary of Procedure. On the basis of the measurt

ments described above, a supporting electrolyte composed of a

0.1 M solution of potassium iodide in a pH 7 phosphate buffer

(0.05 M KH2 P0

2|

-0.05 M Na2HP0^) was chosen. The current density

used was 2.5 mA/cm^. An amperometric end-point system was used

consisting of two platinum indicator electrodes with areas of

2

1 cm with 150 mV impressed between them. The electrolysis

cell was of the design developed in this laboratory. Current

and time measurements were made in the manner described in

earlier publications from this laboratory.

c. Iodimetric Analysis of As2 0~. Portions of

arsenious oxide, KBS Standard Sample 83c, varying in size from

about 2 to 15 meq were titrated. The differences between the

number of microequivalents calculated to be present and that

found by titration were plotted with respect to size of sample

and the result is shown in figure 10.

kk
ANALYSIS FOR BIAS

2

I

5 10

SAMPLE SIZE,meq

15

Figure 10. Analysis of coulometric

titration data for bias.

Such a plot is a convenient and sensitive means to indicate

any analytical bias which is evidenced by an intercept for a

sample size of zero. The deviation of the material from either

stoichiometry or absolute purity is reflected in the slope of

such a curve. In the present case it can be seen that the

intercept corresponds to approximately 0.04 \ieq which is in

good agreement with the intercept. Independent determinations

of the blank correction on the same amount of reagents as used

in the sample preparation gave a value of 0.05 u.eq.

The assay of two lots of arsenious oxide, using 0.5 g

(samples, is given in table 14. The standard deviation of this

determination was found to be 32 ppm. This oxide was also

assayed by titration with iodine purified by sublimation from

a KI-Iq mixture, and a result of 99. 987 percent was obtained

, (K. Sappenf ield, private communication) . The excellent agreement

^5
of these two results confirms the electrochemical conclusion

that the coulometric method is both accurate and precise.

Table 14 . Analysis of arsenic trioxide.

Number Assay, percent

1 99.9859

2 99.9834

3 99.9844

4 99.9896

5 99.983o

6 99.9904

Average 99.9861 S = 0.0032

2. High Precision Controlled-Potential Coulometry

a. Amalgam Stripping Coulometry . A new method for

the coulometric analysis of metals which form amalgams is being

investigated. A weighed sample of the metal is dissolved in

mercury and subsequently stripped from it coulometrically under

controlled-potential conditions whereby only the desired constituent will be anodically dissolved into the electrolyte.

The current-time function is integrated by converting the resulting voltage drop across a standard resistor in series with

the coulometric cell to frequency, by means of a voltage-tofrequency converter, using a scaler for read-out.

Amalgam stripping offers several advantages over conventional coulometry. The time of analysis is decreased because

diffusion coefficients of metals are significantly larger in

amalgams than those of the corresponding metal ions in solution.

Mechanically, the amalgam method does not require careful handling of solutions nor is there the danger of loss of sample

into the auxiliary electrode compartment. Indeed, the fact that

the sample is confined in a separate phase eliminates the need

for separation of the electrode compartments, since the phase

46
loundary provides the separation of reactants and products of

he electrode reaction.

b. Cell Design and Construction. A cell has been

iesigned and constructed for use in controlled-potential

ptripping-coulometry, which incorporates the following features

?he cell, shown in figure 11, is constructed of Teflon to take

Edvantage of its hydrophobic properties. It may be completely

isassembled for cleaning. The anode compartment is located

centrally, thus providing a uniform electrical field distribution with a consequent more uniform current density distriDution.

Figure 11. Teflon cell for use in

amalgam-stripping coulometry.

47
The contact with the mercury anode is inserted through a

hole drilled in the Teflon body of the cell. It may be a rod

of platinum or other suitable metal. However, pyrolytic graph! v

l is prefereed since it is not wetted by mercury and thus will not"

trap portions of the amalgam under analysis. The cell top is

made of Lucite to permit viewing of the cell interior during

assembly and also during the electrolysis.

c . Evaluation of Performance . Preliminary studies

for the evaluation of the method and equipment are presently

in progress. Samples of Melting Point Zinc, Standard Sample

43gj weighing 7 to 8 mg have been analyzed with a precision

of about 0.01 percent. This precision is within the limit

attributable to weighing errors and other uncertainties of the

experiments. Further refinements in technique are planned to

exploit the full potentialities of this new method. Studies

are also planned to apply this procedure to the assay of lead,

cadmium and other amalgam-forming metals. Modification of

technique to permit successive stripping of metallic constituent

should also make possible the analysis of metallic mixtures.

D. Analytical Activities

1. Analysis of Uranium Oxide . The highly precise coulometric method for the determination

of uranium developed earlier in this laboratory [ref. 1, p. l6,l<

has been used for analyses related to the uranium isotopic

standards program. Oxides of several isotopic compositions

were subjected to thermal treatment, converted to uranyl sulfate

and titrated coulometrically with electro-generated titanous

sulfate as previously described.

The results of analyses of these oxides are summarized in

table 15. All oxides were prepared by the same thermal treatment, consisting of ignition in air, followed by ignition in

oxygen. This work was done by L. A. Machlan (Section 310.04)

and is described in the Annual Report of the Analytical

Coordination Chemistry Section [10]. Sample 950a is of normal

48

-
••:

':

ranlum and is issued by NBS as a chemical standard for the

alysis of uranium. The other materials are for use in the

reparation or calibration of uranium isotopic standards. The

erms "depleted" and "enriched" refer to the U235 isotopic

ontent. The atomic weights were calculated from the isotopic

ibundances of all of the uranium atoms in the various samples.

ill materials were "pure" in that the total metallic impurities

ire believed to be less than 100 ppm.

Table 15. Analysis of uranium oxide from several sources.

Atomic Weight

Material Assay, percent

950a 99.923

)epleted Secondary 99-929

depleted Primary 99*921

enriched Primary 99.922

s& of U in Sample

0.023 238.03

0.027 238.050

0.009 238.051

0.006 235.047

lit I

a Standard deviation for a single determination,

The average assay values of these materials are in close

agreement with each other. It may therefore be concluded that

the thermal treatment was reproducible and leads to the same

[J/UoOo ratio, independent of the isotopic composition of the

samples. In order to establish an uncertainty limit for the"

compliance with U^Oq stoichiometry, all of the analytical

results were pooled to provide an average assay value of

|99.924 i 0.011 percent, where the uncertainty figure represents

|the 95 percent confidence interval for the mean, based on 11

degrees of freedom. This is in excellent agreement with a

value of 99.925 - 0.013 percent, based on 16 degrees of freedom,

found in some earlier assays in this laboratory for sample 950a

subjected to the same thermal treatment.

Previous work in this laboratory has involved extensive

assay of uranium metal "dingot", for which a value of 99*977 i

0.004 percent was obtained. Samples of this metal were converted to oxide by the thermal treatment described. The UoOg

49
so prepared gave an assay value of 99*906 percent. When this

is corrected to reflect the uranium content of the original

metal, the U-dOq assay value is calculated to be 99*928 percent

which is in close agreement with the composition obtained for

the other four oxides.

In summary, it may be concluded that the thermal treatment

used in these experiments produces an oxide which is within

99*928 percent of theoretical stoichiometry. The empirical

stoichiometry may be considered to be U-Oo qo^B*

2, Iodide Content of Tracer Solutions . Two independent methods of analysis were required to insure

an accurate, unbiased analysis of the iodide content of a trace]

solution containing about 17 mg I/ml. Three samples of the

solution were provided for analysis, each containing about 1 mg

of iodine. One of the methods chosen for this purpose was the

conversion of iodide to iodate by oxidation with bromine water,

followed by polarographic measurement of the diffusion current

resulting from the reduction of Iodate. The second method

involved coulometric titration of iodide with electrogenerated

silver ion.

In coulometric analysis, to minimize dilution effects, it

was necessary to evaporate all solutions prior to analysis.

Accordingly, a study was made of conditions of evaporation.

Eight 2 -ml aliquots of a solution of potassium iodide, each

containing 2,845 jieq of iodide, together with additional

materials in several cases, were evaporated to dryness at 100°C | in an oven and analyzed coulometrlcally. The results obtained

are given in table 16.

It is evident that significant losses occur on evaporation

of neutral potassium iodide solutions with or without addition

of bisulfite (samples 1, 2, 4 and 5). This is attributed to

air oxidation. Addition of sodium carbonate minimizes such

losses. Accordingly, all evaporations were made under this

condition.

50
m

Table l6 Conditions for evaporation of iodide solutions.

Recovery,

... h ample percent

1 2 ml KI soln 98.4

2 2 ml KI soln 96.7

3 2 ml KI soln + 250 mg Na2 C0~ 99.^

4 2 ml KI soln + 5 mg K^CV 87.7

5 2 ml KI soln + 5 mg KgSgOj- 62.6

6 2 ml KI soln + 5 mg K^O^ + 25 mg Na2 C0~ 99.1

7 2 ml KI soln + 5 mg K^CV + 25 mg Na2C0~ 101.9

8 2 ml KI soln + 5 mg KgSgO^ + 250 mg NagCO- 99.2

The oxidation of Iodide to iodate was verified for

solutions approximating the composition of the tracer solution.

Solutions of KI were oxidized with bromine water and the

excess bromine was expelled by boiling. The solutions were

diluted with supporting electrolyte (final concentration 10

mg/ml Na^Oo; 0.1 N KC1; 0.001$ Triton X-100) and determined

polarographically. For comparison, Iodate solutions were

prepared, from the reagent grade KI0~, aliquoted, diluted to

volume with supporting electrolyte and measured polarographically,

The results presented in figure 12 show good agreement

between the two types of calibration and consequently verify

the conditions for oxidation of iodide. The comparison of the

results of the analysis of the solution by the two methods is

given in table 17.

The agreement of the results obtained is very satisfactory,

when it is considered that some determinations were made on

samples as dilute as 6 ppm. The independence of the two methods

provides considerable confidence in the accuracy of the results.

The polarographic method is not subject to interference from

other halogens or elements titratable by silver. On the other

51
3.0

2.0

»-z

O

g

U.Q

• SOLUTIONS PREPARED FROM KI03

O SOLUTIONS PREPARED BY OXIDATION

OFKI

6

/xglVml

8 10

,

Figure 12. Polarographic calibration curve

for reduction of iodate.

52
land, these are the only elements that would interfere in the

20ulometric procedure under the conditions of the analysis.

Table 17. Analysis of iodide tracer solution*

Polarographic

Flask No.

j mg I /ml

1 17.42

2 17.42

3

Average

17.20

17.35 i

Coulometric

Flask No. mg I/ml

1 17.36

2 17.02

3

Average

17.30

17.23 :

— + n 1 1 mrr T /ml &

a

s represents standard deviation of individual .measurement

3. General Applications

The method developed in this laboratory for precise

argentimetric analysis of halides has been used on several

occasions to verify the compositions of solutions used in

other research programs. In all cases, a reliability of 0.01

percent or better was required. Primary standardizations of

alkaline earth chloride solutions have been made in conjunction

with the isopiestic research project. Accurate determinations

of chloride have also been made for the program concerned with

the establishment of the pD scale.

(G. Marinenko)

53
4. STOICHIOMETRY

A. Introduction

Deviations from ideal composition, nonstoichlometry, occu

in many chemical compounds. In many cases these deviations ar

too small to be detected chemically but in many other cases

they are large enough to be detected by precise and accurate

chemical analysis. Because of this possibility of departure

from the law of constant proportions, stoichiometric considera

tions are necessary whenever highly precise chemical analyses

are undertaken. For example, in gravimetric analysis in which

a precipitated compound of an element Is ignited or converted

to a weighable compound, the stoichiometry of the compound

weighed is of the utmost importance. Whenever a compound is

used as a standard for an element, the stoichiometry of the

compound is again of prime importance.

Most of the classical methods of analysis have not been

proven better than 0.1$. Only a few methods have been reportec

with a proven precision and accuracy of 0.01$ or better. Work

in this laboratory has been concerned with the development of

methods of this precision and accuracy so that the stoichiometr

of a compound can be verified to 0.01$.

Emphasis has been given to the Division's program for the

mass spectrometric determination of atomic weights in which it j is necessary to quantitatively blend the separated Isotopes of

an element with a precision of about 0.01 percent. Since the

amounts of separated isotopes available for this use ordinarily

are relatively small, the methods developed for their determina

tion should require only small samples. This small sample

requirement is also consistant with the mission of this sectionthat is, obtaining the largest amount of information from the

smallest possible sample.

Precise and accurate methods of analysis have previously

been described for chlorine, bromine, copper, and chromium in

last year's "Summary of Activities" [ref. 1, p. 26]. Using thes

54
tt

;ra

thods, it should be possible to prove the stoichiometry of

mpounds of these elements to about 0.01$.

It is anticipated that future work will be focused on

oichiometric problems arising from the program for the mass

ectrometric determinatipn of atomic weights, but attention

11 also be given to stoichiometric problems elsewhere within

e Bureau.

Research and Development

•- 1. Magnesium

a. Non-Stoichiometry of MgO . Attempts to prepare

oichiometric magnesium oxide from magnesium metal were not

iccessful. The MgO/Mg ratios so obtained were at least 0.2$

.gher than theoretical. This high ratio is probably due

.ther to occlusion of gases by magnesium oxide, the amount of

lich depends in a large degree upon the method and throughness

1 ignition, or to a higher oxygen content than theoretical.

nee oxides of many metals are known to exhibit both phenomena,

I was decided to abandon the attempts to prepare stoichiometric

SO.

b. Stoichiometry of Magnesium Sulfate . An investigaLon of the stoichiometry of magnesium sulfate showed that it

possible to prepare stoichiometric magnesium sulfate. This

s shown by converting pure magnesium metal crystals, shown

d contain less than 20 ppm of detected metallic impurities by

Dectrographic analysis, to magnesium sulfate by dissolution in

-trifled sulfuric acid and evaporation of the resulting solution

followed by ignition at 600°C. The MgSO^/Mg ratio was found to

b 4.9514 which is in good agreement with the calculated ratio

g 1962 atomic weights of 4.9512.

Because of the hygroscopic nature of magnesium sulfate,

was necessary to resort to a special weighing technique to

btain valid results. The platinum crucible which contained

he magnesium sulfate was covered with a small piece of

latinurn foil before the final ignition at 600°C, After the

55

t
furnace had cooled to 500°C, the crucible was transferred to a

special individual desiccator which was kept in an oven at

150°C to lessen the thermal shock on transfer. The individual

desiccator was constructed by sealing a small glass drying bulb

to a 70 ml glass weighing bottle, as shown in figure 13. The

drying bulb was packed with Po°r and closed with a rubber stoppe

when cool. The desiccator containing the crucible was transferred from the oven, cooled, stoppered, and allowed to stand

at room temperature for about four hours to attain thermal

equilibrium. The covered crucible was then weighed against

time on a micro-balance. Weighings were recorded each minute

for five minutes. The weight at "zero time" was determined

from a weight vs. time plot. The weight of the magnesium sulfate was determined from this weight less the weight of the

crucible and cover.

c . Concentration of Magnesium Solutions . A method

has been developed for the precise assay of magnesium solutions

(as nitrate, chloride, or sulfate) based on weighing the magnesi

sulfate produced on evaporation of weighed portions of the

solution and conversion to magnesium sulfate by repeated evapora

tion after the addition of purified sulfuric acid. The precision and accuracy of this method has been determined by

applying the method to solutions containing known amounts of

magnesium. Pour solutions prepared from the high purity

magnesium metal crystals were assayed by withdrawing four

weighed portions from each solution and determining the magnesiu

as described. The results of these determinations are shown in

table 18.

Comparison of the known and found concentrations showed

that: (a) the determined concentration of magnesium agreed to

about 0.01$ with the calculated magnesium concentration, (b)

systematic errors were negligible, and (c) the analysis of the

four solutions were of equal (within limits) precision.

56
::

i

»ppft

Figure 13. Individual desiccator for drying

magnesium sulfate samples.

Statistical analysis of the data resulting from these

lalysis and from the analysis of solutions prepared from

;parated magnesium isotopes showed that the standard deviation

an individual determination of the concentration of a

agnesium solution Is 0.0001334 millimole (mM) Mg/g sol with

p degrees of freedom. The standard error of the average of

}ur determinations is .0001 334

or 0c OOOO667 mM Mg/g sol. The

acertainty of the concentration at the 95$ confidence is

.HOXO.OOOO667 or 0,000142 mM Mg/g sol. This corresponds to

I uncertainty of 0.02$ for solutions containing 0.7 mM Mg/g

Dl.

57
Table 18. Analysis of solutions containing

known amounts of magnesium.

Sol'n Wt Sol'n Mg Found Cone. Sol'r.

No. g mM mM Mg/g Sol'

A 6.61027 4.368086 0.660803

6.49334 4.292734 0.661098

6.61881 4.376424 0.661210

6 .66686 4.408895

Avg.

Calc

O.O661315

0.661107

O.66IO56

B 7.51133 5.471140 0.728385

7.49563 5.460829 0.728535

7.11456 5.182303 0.728408

6.93171 5.048420

Avg.

Calc .

O.728308

0.728409

0.728410

C 7.31937 5.OOOI83 0.683144

7.26266 4.961524 0.683155

7.15365 4.887438 O.683209

7.52151 5.138688

Avg.

Calc .

0.683199

0.683177

O.683072

D 6.79383 4.148876 6.610683

6.98897 4.265132 0.610266

6.20624 3.790209 0.610709

6.69536 4.088852

Avg.

Calc

0.610699

0.610589

0.610559

58
This method for the determination of the concentration of

nagnesium solution was adopted after deciding that none of

\p conventional methods for magnesium were capable of yielding

ecise results. It is a valid method so long as the purity

; the magnesium sulfate Is known since magnesium sulfate has

ready been shown to be a stoichiometric compound. The

gnesium sulfate should be examined by emission spectrography

other techniques to determine the cationic impurity concen-

,ation and a correction made if necessary. The repeated

eatments with sulfuric acid would remove most of the common

ionic impurities such as chloride, bromide, or nitrate with

e exception of phosphate which would cause erroneous results.

d Purification of Magnesium Compounds . A procedure

;s been developed for the purification of water soluble

„gnesium compounds. This method which is based on the prepitation of the magnesium salt of (ethylenedinitrilo)

:tracetic acid (EDTA) has proven effective In reducing most

^purities to the low parts-per-million level or less.

The magnesium salt is dissolved in water, an .excess of

i amnionic al solution of EDTA is added, and the pH is adjusted

d 4.0. After about 2 days, the precipitation of the Mg-EDTA

3 substantially complete (better than 9$%) . Magnesium is the

nly known element to form a relatively insoluble precipitate

Lth EDTA. After recovering the Mg-EDTA by filtration through

orous glass, the salt was dissolved in dilute NH,.0H and reirecipitated by adjusting the pH to 4.0. The Mg-EDTA was then

gnited to MgO . The MgO can be dissolved in the appropriate

oid (nitric, hydrochloric, etc.) to produce the desired solution

salt.

The effectiveness of this method was shown by adding 50

jlements at the 0.1$ level to a solution of magnesium and

recipitating the magnesium by this method. The purified MgO

as then examined by qualtitative emission spectrography. The

59
results of this analysis are shown in table 19. With the

exceptions of tungsten, molybdenum, palladium and rhodium,

elements which do not form complexes with EDTA, the impurity

elements were either eliminated or reduced to the low partsper-million level. Since W, Mo, Pd, and Rh and not likely

impurities in magnesium compounds, the purity of most magnesiu:

compounds can be greatly increased by this method.

e . Preparation of Calibration Mixtures for the Mass

Spectrometrlc Determination of the Atomic Weight of Magnesium . The previously described work has been applied to the preparation of calibration mixtures of separated magnesium isotopes

for the mass spectrometrlc determination of the atomic weight

of magnesium. Separated magnesium isotopes in the form of

Mg2 and Mg containing about 0.2^ Cu and up to 0.05^ of

several other elements were purified by the EDTA method.

24 26 Samples of this purified Mg and Mg were analyzed by

quantitative emission spectrography. The results of this

24 26 analysis showed that the Mg and the Mg contained about

25 ppm and 17 ppm total detected cationic impurities,

respectively.

The purified oxides were taken into solution with dilute

nitric acid and solutions of each of the separated isotopes

were prepared. The magnesium content of each separated isotope

solution was determined by converting weighed portions to the

sulfate as described. The calibration mixtures were then

prepared by mixing weighed portions of each separated isotope

solution. These were then used as standards by the Analytical

Mass Spectrometry Section to obtain the absolute abundance

ratios of magnesium and the atomic weight was calculated.

60
Table 19. Analysis of purified magnesium oxide.

Concentration Range

>ment a Percentage Element Percentage

Concentration Range

Percentage Element

- Mn

j Mo

- Na

- Nb

- Ni

- 0s

0.0001-0.001 P

- Pb

0.0001-0.001 Pd

- Pt

- Rh

- Ru

< 0.0001 Sb

- Si

0.0001-0.001 Sn

0.0001-0.001 Sr

- Ta

- Te

- Th

- Ti

- U

- V

- W

- Zn

_ Zr

Ag

Al

As

Au

B

,Ba

Be

Bi

Ca

Cd

i Ce

Co

Cr

Cs Si 0.0001-0.001

| Cu

Pe

Ga

Ge

Hf

>, Hg

In

Ir

- K

La

Li

' The initial concentration of each element before purification

was 0.1$.

Itfote: - not detected

< less than

61
2 . Lead

A search of the chemical literature has shown that ther«j

is a need for a high precision-high accuracy method for lead j Initial work on the development of such a method based on the!

precipitation of lead chromate with a small excess of potass:

dichromate and determination of the excess chromate has been

encouraging. This method takes advantage of the precise

analysis of standard reference material 136b, potassium

dichromate, which has been shown to be 99-977 - 0.003$ [11]

A weighed amount of this KpCrpO^ is reacted with less than

the stoichiometric amount of lead and the excess chromate is

determined spectrophotometrically . Preliminary results

indicate that a precision and accuracy of 0.01$ should be

possible with this method.

(T. J. Murphy-)

62
la

5. CLASSICAL MICROCHEMICAL ANALYSIS

Introduction

Activities of this laboratory are for the most part, conerned with the elemental analysis of small samples. Mlcrohemical methods are economical of sample, a necessity when

amounts of materials available are very small. Frequently they

are relatively rapid to perform compared with macro determina-

:ions. The aim is to obtain more and more information from

smaller and smaller samples through more sensitive methods and

oy determining more than one element in a single sample. For

Drganic analysis which is still the largest part of the work,

this means using instrumental methods instead of the traditional

Pregl gravimetric and volumetric methods.

B. Facilities

Most of the equipment in this laboratory was described in

'the report of last year [ref. 1, p. 20]. In addition, an F and

;M Carbon-Hydrogen-Nitrogen Analyzer, shown in figure 14, has

been obtained. With this Instrument, carbon, hydrogen and

nitrogen are determined simultaneously through gas chromatographic separation and thermal conductivity detection of the

combustion products. The weight of sample used is approximately

0.6 mg.

The newly established microscopical laboratory is equipped

with a binocular polarizing microscope, shown in figure 15.

' It is equipped to view samples with either transmitted or

incident light, and photographs may be made with a 35 nun camera

attachment. The low power micromanipulators are available for

microchemical work.

This equipment is presently installed in a small laboratory

module used exclusively for this purpose. Such an arrangement

is suitable for many purposes. However, for work with extremely

small particles, a clean-bench facility will be set up to

minimize contamination from the laboratory atmosphere.

63
Figure 14, Carbon-hydrogen-nitrogen analyzer.

Figure 15 . Microscopic equipment

64
The microchemical laboratory in the new NBS facilities at

Jalthersburg, Md., consists of two adjoining modules with an

Interconnecting balance room at the rear. One module contains

nost of the larger equipment, such as the carbon, hydrogen and

nitrogen combustion equipment. The other module is used for

:hemical operations and contains such equipment as a pH meter,

2hloride titrator, Kjeldahl apparatus, oxygen flask combustion

apparatus, microburettes, oven, furnace, etc. Each module has

a four-foot fume hood and a desk, as well as storage space under

the lab benches.

The balance room has two microchemical balances and a

semimicro balance mounted on a marble slab supported on concrete

piers. An electrobalance is also available for certain weighing

operations.

C. Research Activities

Two research problems have been under investigation

during the past year. Since both are still in progress, it

is only possible to summarize the results obtained up to the

'present time.

1 . Elemental Analysis of Small Samples

A study has been made of the use of the C-H-N Analyzer

for small samples. The usual size of samples for this instrument is 0.5 to 0.7 mg. because the peak height linearity is

best in this range. However, the instrument has a considerable

reserve of sensitivity and samples of 0.1 mg. can be used if

samples having about the same amounts of nitrogen, carbon and

hydrogen are used for calibration. The limiting factors are

the magnitude of the blanks and the weighing of sample; but

it would appear that the carbon, hydrogen and nitrogen could

be determined within 1% absolute with a sample of this size.

The determination of carbon in highly fluorinated

f luorocarbons with the C-H-N Analyzer was studied. Samples of

copolymers of CpPh and C-F-H- with fluorine contents of

to 75$ were used. The normal combustion tube packings of

65
copper oxide and copper metal were used. These samples were

also analyzed with a conventional combustion train with a

special packing of magnesium oxide to remove fluorine. This

has been used here for many years. Table 20 gives the results

obtained.

Table 20. Determination of carbon in f luorocarbons

Sample By Conventional Combustion By C-H-N Analyzer

A

B

D

E

F

Carbon, percent Carbon, percent

30.78 30.70

31.16

28.90 28.80

28.65

25.33 25.48

25.31

30.23 30.28

30.50

32.45 32.43

32.16

34.71 34.50

34.35

The results agree within the acceptable limits of microchemical analysis. The advantage of the C-H-N Analyzer is tha

is requires about 10 minutes for a determination using a 0.6

mg. sample. The conventional combustion furnace requires an

hour using a 4 to 5 nig. sample. If hydrogen is to be determined also, the copper reduction tube in the C-H-N Analyzer

must be repacked each day since a peak, probably from HF,

begins to form just before the water peak, affecting the heigh

of the latter. Also, the C-H-N Analyzer should be calibrated

with standards every five or six runs to check the correction

constants.

66
2. Reversed Phase Chromatography

Some work was performed on the separation of traces of

ron from high purity zinc by reversed phase chromatography,

this method, a solution of the zinc in 5 ml of 8 M hydrotiloric acid is passed through a small column containing 7 cmJ

f Teflon-6 powder coated with 2-octanone. The iron is retained

n the column while the zinc is eluted with 6 M hydrochloric

- cid. Four 3-ml washings is sufficient to remove all the zinc,

he iron and the 2-octanone are stripped from the column with

ethyl alcohol and ethyl ether after which the iron is deterined spectrophotometrically with o-phenanthroline reagent,

y this method, a sample of reagent grade mossy zinc was found

o contain 3^- ppm of iron, while a sample of high purity zinc

ras found to contain 1 ppm of iron. The limiting factor is

•he magnitude of the blanks obtained. With a partial cleanip of reagents and the column resin, the blank amounted to 1 u.g.

Fith this small column it was possible to separate as much as

).4 mg of iron from a gram of zinc.

A program which is just starting involves the examination

md identification of particulate matter in the size range of

. to 10 ^ig. Identification will be made by microscopical study

)f the morphological and optical properties of the material,

and also, where feasible, by ultra microchemlcal tests.

-0. Analytical Activities

The analytical activities include determinations on a

ide variety of materials received from other NBS research

rojects, from the NBS Standard Reference Material program,

d also from other government agencies. Samples were received

from seven other government agencies during the past year,

he samples are often "problem" materials which require special

treatment or the development of methods or the modification of

xisting methods. Some of these are described below.

1 . Alumina Boules

Samples of alumina boules containing about 0.1$ each of

yttrium and thorium and Vfo chromium were analyzed. Solution

67

Jr

«
of this material was very difficult and required five days

of digestion in concentrated hydrochloric acid at 270°C in a

sealed glass tube [7] to complete the solution of 0.5 g samples

Chromium was determined polarographically (see p. 36 of this

report), yttrium was determined by flame photometry (section

310.04) and thorium was determined spectrophotometrically on

an aliquot of the solution using thoron reagent. It was found

that the presence of 25 mg of aluminum increased the apparent

thorium color by approximately 15$* so it was necessary to add

a like amount of aluminum to the thorium standards. The

results on three separate samples were 0.133* 0.116 and 0.122$

thorium.

2 . Linac Cooling Water System

The appearance of a brown sludge on a plastic sight tower

and the apparent corrosion of a filter holder led to an investigation of a recirculatory cooling water system in the NBS

Linac facility. The system contained fiber filters and a

demineralizer to remove particles and metal salts from the

water as they might form. Analyses were made for metals in the;

water, filters and demineralizer resin using micro electrodeposition for copper and lead in the resin, spectrophotometry

for Iron, copper and nickel in the water and filters, and

spectrochemistry for other metals on the resin. The brown

sludge apparently was iron from the make up water, and the

filter holder which was brass had lost a thin nickel plating

allowing a tarnish to appear. Although the water was quite

pure, a number of metals had been retained by the demineralizer

Copper was present in the largest amount due to solubility of

the copper pipes. After analyzing several layers of resin, it

was calculated that 5.5 grams of copper had dissolved but this

is negligable compared to the large amount of copper metal In

the system. Also found were lead and tin from soldered joints,

nickel and zinc from the filter holder and alkaline earth

metals from the make up water.

68
11

:

'.".::

3. Beryllium Carbide

A special sample of beryllium carbide was analyzed for

le NBS Heat Measurements Section who must know the composition

J? their materials very exactly in order that their measurements

f specific heats may be, interpreted properly. The beryllium

arbide, total beryllium., total carbon, uncombined carbon and

itrogen were determined by methods described in an earlier

eport [ref. 1, p. 24], In addition, beryllium oxide and

ater were determined directly. Beryllium oxide was determined

y heating a 100 mg sample in a stream of dry hydrogen chloride

t 700°C. The residue was ignited in air to remove free carbon

eaving a residue of beryllium oxide which was weighed or

etermined spectropho tome trie ally.

Beryllium metal was determined by collecting all the gases

ormed when a 10 mg sample was dissolved in a potassium hyroxide solution. These gases were analyzed in the mass

pectrometer and beryllium metal was calculated from the

ydrogen. The water present was determined by heating a 100

i.g sample in a stream of oxygen in a combustion train. The

ater reacts with the beryllium carbide to form methane which

s oxidized to form an equivalent amount of water which is

,bs orbed and weighed. The results of a typical analysis are

iven in table 21.

Table 21. Composition of a typical

sample of beryllium carbide.

Component Percent

Beryllium carbide 92.6

Beryllium oxide 2.0

Beryllium metal 2.6

Free carbon 2.8

Water 0.4

Beryllium nitride 0.02

Total beryllium 59.6

Total carbon 39.8

69
4. Iodide in Photographic Fixing Baths

The concentration of iodide present in used photographic

solutions, and especially in fixing baths, is of interest

today because of its possible relation to the stability of

microfilms. The analysis is complicated by silver and by the

large amounts of sodium thiosulfate and other sulfur compounds

present. In the method of analysis used, the fixing baths are

made strongly alkaline with sodium hydroxide, after which the

silver is precipitated as silver sulfide with sodium sulfide

solution. After filtration, an aliquot is treated with 30^

hydrogen peroxide to oxidize sulfur compounds. The iodide Is

oxidized to iodate with bromine in acetic acid and then titrated

with 0.01 N sodium thiosulfate.

The method was checked by adding weighed amounts of silver j iodide to new and used fixing baths. The results are shown In

table 22.

Table 22. Determination of iodide in

photographic fixing baths.

Iodide added (mg Kl/ml) Iodide Recovered (mg Kl/ml)

2.072 2.088

I.568 1.516

0.904 0.888

0.084 O.O83

O.O58 O.O53

5. Standard Reference Materials

Standard reference materials analyzed included the

acetanilide microchemical standard No. l4lb which is a standard

for carbon, hydrogen and nitrogen and was checked for those

elements. A number of organic fluorine compounds, of possible

use as reference materials, were analyzed for carbon and

hydrogen. Sodium nitroprusside crystals which are used as a

Mossbauer spectroscopy standard were analyzed for carbon,

70
Idrogen and nitrogen with the C-H-N Analyzer and for iron by

,'tration with potassium dichromate.

Intermediate purity selenium was analyzed for trace

nmts of chloride and sulfur. For chloride, a two-gram

iple was dissolved in nitric acid in the presence of silver

trate. After coagulating overnight, the silver chloride

,s collected on a Selas filter. It was dissolved in a few

. of ammonium hydroxide and reprecipitated in a Nessler tube

.th nitric acid. The chloride was determined nephlometrically

• comparison with known solutions. One ppm and three ppm of

iloride were found in two samples of selenium. The sensitivity

' ' the test, as outlined, is one ppm chloride.

For the determination of sulfur, two-gram samples of

: Senium were dissolved In nitric acid and the selenium com-

.etely vaporized by repeated evaporations as selenium bromide

.th hydrobromic acid. This step was necessary since earlier

ests had shown that selenium inhibited the precipitation of

arium sulfate. The sulfur was precipitated as barium sulfate

i a Nessler tube and determined nephlometrically by comparison

Lth standard solutions. Ten ppm of sulfur were found. A good

ecovery of sulfur added to selenium was obtained.

In addition, carbon, sulfur and phosphorus have been

etermined in a large number of iron base standard reference

aterials.

6. Miscellaneous Analyses

A brief mention is given of a number of analyses performed

o show the variety which is encountered. A chromium-osmium

Hoy, which was of special interest because of its unusual

lectrical properties at low temperatures, was received from

he Dental Research Section. A 100 mg sample of this alloy

as fused with sodium peroxide in .a nickel crucible and then

issolved in nitric acid. The osmium was volatilized as

smium tetroxide by boiling. The chromium was reduced with

ulfurous acid, reoxidized to chromate with ammonium persulfate

nd titrated potentiometrically with ferrous iron solution

71
which had been previously standardized with dichromate.

A method of analysis of fluoboric acid was evaluated for

the Harry Diamond Laboratories of the Department of Defense by

analyzing known mixtures of fluoboric acid and boric acid.

Analyses performed on the electrolyte in small capacitors from'

NASA showed that changes took place during environmental testiij

Six samples of graphite and diamond dust from the Naval Researc

Laboratory were checked for purity by microcombustion methods.

A referee microanalysis for bromine and sulfur was made on a

purine compound for the National Institutes of Health by the

oxygen flask combustion method.

Scandium oxide and boric oxide were determined in materia]

used in phase diagram studies by the High Temperature Chemistry:

Section. Samples of 30 to 100 mg were dissolved by sealed tube;

method. Boric oxide was then determined in the same solution

by titration with sodium hydroxide in the presence of mannitol.

(R. A. Paulson, J. R. Baldwin, and W. P. Schmidt)

72
':.:

:,

6. INTERNATIONAL RESEARCH GRANTS PROGRAM

The National Bureau of Standards awarded a grant to the

'khni on -Re search and Development Foundation, Haifa, Israel,

December 1, 1965* to investigate "Trace Analysis by Anodic

ripping Voltammetry" . Professor Magda Ariel, Chemistry

Dartment, Technion, Israel Institute of Technology, is

1 incipal investigator. Dr. John K. Taylor, Section 310.05,

the NBS project monitor.

Professor Ariel and her students will investigate anodic

tipping voltammetry including its application to media conning varying proportions of organic solvents. Problems

: --sed by adsorbtion, solution resistance, and the effect of

'-ectrodes, permitting the analysis of non-amalgam forming

tals will be given special consideration. The knowledge

tained from this work will be applied to practical analytical

tuations

The determination of trace amounts of zinc in silicates

'd other insoluble substances of a kindred nature has been

litially investigated. An analytical method has been developed

!ich is sensitive and unaffected by interferences resulting

om varying sample composition.

In the method, which has been submitted for publication

.2], the sample of rock is fused in a boric acid-lithium

h uoride flux or decomposed by direct acid attack, as required,

i either case, a final acid solution is passed through an

lion exchange column under conditions to retain zinc while iron,

-Ckel, vanadium, titanium, manganese, etc., pass through. Zinc

3 eluted with de-ionized water, directly into the electrolysis

ell where it is determined by anodic stripping polarography

The method has been applied to the analysis of three stand-

?d samples, ranging in zinc content from 47 to 500 parts per

Lllion with standard deviations of 5 to 10 relative percent.

(J. K. Taylor)

73
7. SUPPORTING SERVICES

The section does a limited amount of work in the areas

of gas chromatography, nuclear magnetic resonance, infrared

spectroscopy, and fluorescence measurements. Activities have

been confined largely to the use of these techniques for the

analysis or identification of certain research materials.

Several of the above techniques find considerable use in

connection with other analytical competences. In particular,

gas chromatography has been used as an adjunct to mass

spectrometry, both as a preseparation or preconcentration

technique and for confirmatory analyses. Infrared spectrometr;

has been used in the identification of gas chromatographic

fractions. Nuclear magnetic resonance spectra are furnished a

an analytical service to other research projects.

The section is responsible for the maintenance of the

equipment mentioned above and makes It available to qualified

users in other sections of the Bureau. This arrangement is

advantageous to those chemists who have only occasional need

for specialized equipment. In a similar situation, the sectioi

also provides occasional chemical services to non-chemical

groups at NBS, such as preparation of unusual solutions or

handling of materials under special conditions, for example.

(J. K. Taylor)

74
8. PERSONNEL AND ACTIVITIES

Personnel Listing

John K. Taylor, Section Chief

Carolyn ,E. Smith, Secretary

iss Spectrometric Gas Analysis --

>larography --

. )ulometry —

" ;oichiometry —

Ernest E. Hughes

William D. Dorko

E. June Maienthal

George Marinenko

Robert A. Martin

Thomas J. Murphy

.assical Microchemistry -- Rolf A. Paulson

John R. Baldwin

William P. Schmidt

ioii Publications

1. E. J. Maienthal and J. K. Taylor, Determination of

sllurium by Cathode Ray Polarography, Anal. Chem. _37, 1516

1965).

2. J. K. Taylor, E. J. Maienthal and G. Marinenko,

lectrochemical Methods, Trace Analysis , Interscience, N.Y.,

1965).

3. G. Marinenko and J. K. Taylor, Coulometric Calibration

f Mlcrovolumetric Apparatus, J„ Research NBS, 70£, 1 (1966).

4. R. A. Durst and J. K. Taylor, Photopolarographic

ehavior of Inorganic Depolarizers, J. Research NBS, 69A , 517

965).

5. J. K. Taylor, Density and Specific Gravity, Encyclopedia

f Industrial Analysis, Vol. 1, Interscience, N.Y., (1965).

75
C. Talks

1. J. K. Taylor, "The Science of Measurement" North

Bethesda Junior High School, Bethesda, Maryland, September

1965.

M n 2. J. K. Taylor, Panel Discussion of Preparation,

Preservation, and Use of Ultra-Pure Materials", 19^5 Eastern

Analytical Symposium, New York, N. Y., November 1965.

3. J. K. Taylor, "The Science of Measurement", Dunbar

High School, Washington, D. C, December 1965.

4. E. J. Maienthal and J. K. Taylor, "improvement of

Precision of Comparative Polarography", American Chemical

Society, Winter Meeting, Phoenix, Arizona, January 1966.

5. G, Marinenko and J. K. Taylor, "High-Precision

Coulometric Iodimetry", American Chemical Society, Winter

Meeting, Phoenix, Arizona, January 1966.

6. E. J. Maienthal and J. K. Taylor, "Applications of

Differential Polarography", Pittsburgh Conference on Analytic a Chemistry and Applied Spectroscopy, Pittsburgh, Pennsylvania,

February 1966.

7. J; K. Taylor, "Careers in Chemistry", Walter Johnson

High School, Bethesda, Maryland, March 1966.

8. J. Ko Taylor, "Modern Chemical Analysis", Georgetown

University, Washington, D. C, April 1966.

9. J. K. Taylor, "Careers in Chemistry", Crossland High

School, Camp Springs, Maryland, April 1966.

D. Committee Activities

J. K. Taylor

Service Analysis Coordinator, Analytical Chemistry Division

Member, Analytical Standards Committee

Chairman, Panel on Chemistry, Civil Service Board of Examiners

Vice-Chairman, Civil Service Board of Examiners

76
fiber, Review Board, Science Book List, American Association

'or the Advancement of Science

?sident, Washington Academy of Sciences (WAS)

airman, Committee on Science Education, WAS

fiber, Joint Board on Science Education

Director of Science Projects

footed member, Council of the American Chemical Society (ACS)

airman, Canvassing Committee for the ACS Award in Pure Chemistry

airman-Elect, ACS Division of Analytical Chemistry

nber, Board of Managers, Chemical Society of Washington

inber, Professional Relations Committee, Chemical Society of

Washington

sslon Chairman, 19^5 Eastern Analytical Symposium

airman, Arrangements Committee, IMR Symposium on Trace

Characterization

f ety Officer, Analytical Chemistry Division

s

June Maienthal

Reporter for Capital Chemist, Chemical Society of Washington

siaected member, Board of Managers, Chemical Society of

Washington

J. Murphy

mber, Civil Service Board of Examiners

mber, Committee on Meeting Arrangements, Chemical Society of

Washington

mber, Arrangements Committee, IMR Symposium on Trace

Characterization

mber, Committee on Annual Report of Atomic Weights, American

Chemical Society.

A. Paulson

mber, Service Analysis Committee, Analytical Chemistry

Division

'llaborator, Committee for Study of Microchemical Methods,

Association of Official Agricultural Chemists

77
Member, Arrangements Committee, IMR Symposium on Trace

Characterization

W. D. Dorko

Member, Arrangements Committee, IMR Symposium on Trace

Characterization

78
9 . REFERENCES

J. K. Taylor, Editor, NBS Technical Note 273, October 1,

1965.

E. T. Suttle, D. E. Emerson, B. W. Burfield, Anal. Chem.

38, 51 (1966).

R. E. D. Haney, H. Bliss, Ind. Eng. Chem. 36, 985 (19^4).

J. Hilsenrath et al, Tables of Thermal Properties of

Gases, NBS Circular 564, November 1, 1965.

E. J. Maienthal, J. K. Taylor, Anal. Chem. 37, 1516 (1965).

H. S. Isbell et al, Analytical Standards for Trace Elements in Petroleum Products, NBS Monograph ^K , October 1962.

C. L. Gordon, ¥. G. Schlecht, E. Wichers, J. Research

NBS 33, 451 (19^).

D. A. Kreider, Am. J. Sci. [4] 20, 1 (1905).

E. F. Herroun, Phil. Mag. [5] 40, 91 (1895).

0. Menis, Editor, NBS Technical Note 402 (1966)

G. Marinenko, J. K. Taylor, J. Research NBS 67A, 453

(1963).

G. Koster, U. Eisner, M. Ariel, J. Electroanalytical

Chem. (in press)

U.S. GOVERNMENT PRINTING OFFICE: 1966-251-019/25

79
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