Nat; yttfity fe-01 Admin. Bldg. NBS TECHNICAL NOTE 505

Microchemical

Analysis Section:

Summary of Activities

July 1968 to June 1969

U.S. DEPARTMENT OF COMMERCE

' -m': > mmmi
NATIONAL BUREAU OF STANDARDS

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UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director

NBS TECHNICAL NOTE 505

ISSUED OCTOBER 1969

Nat. Bur. Stand. (U.S.), Tech. Note 505,140 pages (Oct. 1969)

CODEN: NBTNA

Microchemical

Analysis Section:

•Summary of Activities

July 1968 to June 1969

Edited by John K. Taylor

Microchemical Analysis Section

Analytical Chemistry Division

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

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, U.S. Government Printing Office

Washington, D.C, 20402 - Price $1.25
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 57 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 a highly

important output of our laboratories. 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 about our programs. A word

is perhaps in order about the philosophy of these yearly

progress reports. In any research program a large amount of

information is obtained and techniques developed which never

find their way into the literature. This includes the

"negative results" which are so disappointing and unspectacular but which can often save others considerable work. Of

importance also are the numerous small items which are often

explored in a few days and which are not important enough to

warrant publication—yet can be of great interest and use to

specialists in a given area. Finally there are the experimental techniques and procedures, the designs and modifications

of equipment, etc., which often require months to perfect and

yet all too often must be covered in only a line or two of a journal article.

11
Thus our progress reports endeavor to present this information which we have struggled to obtain and which we feel

might be of some help to others. Certain areas which it

appears will not be treated fully in regular publications are

considered in some detail here. Other results which are

being written up for publication in the journal literature

are covered in a much more abbreviated form.

At the National Bureau of Standards publications such as

these fit logically into the category of a Technical Note.

In 1969 we plan to issue these summaries for all of our

sections . The following is the fifth annual report on progress of the Microchemical Analysis Section.

W. Wayne Meinke, Chief

Analytical Chemistry Division

iii
PREFACE

This report summarizes the current program and recent

activities of the Microchemical Analysis Section of the

Analytical Chemistry Division. This Section has the primary

mission to contribute to the science and technology of the

analysis of small samples and its program includes both fundamental studies to improve the precision, accuracy and sensitivity of analytical techniques, and developmental research

to provide new and improved methods applicable to wide areas

of materials characterization. As a closely related activity,

the Section provides analytical measurements for various

research programs of the Bureau and develops and characterizes

Standard Reference Materials

Research projects are active in the following competence

areas: gas analysis; polarography ; coulometry; potentiometry

microscopy; conventional microchemical analysis; nuclear track

technology; and ionic equilibria studies.

It has been found to be convenient to classify activities

in this report either as research or analytical developments.

Such classification must be considered to be arbitrary in many

cases in that developmental aspects have Deen involved in

virtually all work reported, resulting in improved procedures

and techniques. Space limitations have dictated only a brief

description of methods in most cases. It is hoped that such

descriptions will be understandable to an experienced analyst.

However, specific details of all work reported here will be

made available to anyone interested in such matters.

A major effort of the Section during the year has been

concerned with the analysis of standard reference materials.

No effort has been spared to characterize these materials to

a high degree of reliability. The use of such materials not

only establishes benchmarks for industrial control but also

provides a sound basis for inter-laboratory comparisons and

for the intercomparison measurement techniques and methodology.

iv
Such materials are regularly used in this laboratory to verify

the accuracy of analytical procedures . They are referred to

by an identification such as SRM #l60b, for example. A

catalog containing full descriptions of these materials may

be obtained from the Office of Standard Reference Materials,

National Bureau of Standards, Washington, D. C. 20234.

In order to describe 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
TABLE OP CONTENTS

PAGE

1. GAS ANALYSIS 1

A. Research Activities 1

1. Trace Oxygen Analyses 1

2. Atmospheric Argon 1

3. Atmospheric Carbon Dioxide 3

4

Oxygen in Air 7

B. Standard Reference Materials 9

1. Sulfur Dioxide in Air 9

2. Hydrocarbon in Air Standards 11

3- Carbon Dioxide in Air 12

C. Research Materials Service Analysis 12

1. General 12

2. Miscellaneous Analyses 15

2. POLAROGRAPHIC ANALYSIS 17

A. Introduction 17

B. Major Constituent Analysis 17

1. Analysis of Bis(l-phenyl-l,3-

butanediono) Copper(II) (SRM #1080a) . . 17

2. Copper and Lead in Microstandard

Particles 18

3. Copper and Nickel in Service Samples . . 20

4. EDTA (Disodium Salt, Dihydrate) 21

C. Minor Constituent Analysis 23

1. Meso-bilirubin 23

D. ' Small Sample Analysis 23

1. Antimony and Bismuth in Thin Film and

Source Material 23

E. Trace Analysis 24

1. Lead in Fish Protein Concentrate .... 24

2. Lead and Bismuth in Ductile Irons and

Stainless Steels 25

3. Lead, Bismuth and Tellurium in Special

Iron and Low-Alloy Steel Standards ... 26

4. Reagent Analysis 27

5. Trace Elements in Glass-Simulated Lunar

Standard Reference Materials 29

6. Analysis of Air Pollutants 34

3. COULOMETRIC ANALYSIS 37

A. Introduction 37

B. Research Activities 38

1. Verification of the Roller Equation ... 38

2. Recalculation of the Atomic Weight of

Potassium 47

vi
PAGE

3. Coulometric Determination of Microgram

Amounts of Chromium 49

4. Determination of Cr+6/Cr+3 Ratio .... 53

5. Couiometric Method for Determination

of Oxygen in Elemental Boron 57

C. Analysis of Standard Reference Materials . . 59

1. Analysis of Separated Boron Isotopes . . 59

2. Analysis of Potassium Dichromate .... 59

3. Calcium Carbonate 60

4. Analysis of Gold-Silver Alloys 61

5. Analysis of Potassium Chloride 64

6. Analysis of Sodium Chloride 65

7. Stainless Steel Analysis 67

8. Potassium Dihydrogen Citrate 68

D. Analysis of Research Materials 69

ELECTROANALYTICAL MEASUREMENTS 73

A. Introduction 73

B. Symposium on Ion-Selective Electrodes .... 73

C. Research Activities 76

1. Modification of a Silver Sulfide IonSelective Electrode for Microchemical

Analysis 76

2. Construction and Characteristics of a Fluoride Ion-Selective Microelectrode . . 79

D. Analysis of SRM Gold-Silver Metal Microprobe Wires 82

E. Analysis of Miscellaneous Materials 83

1. Determination of Fluoride in Dust

Samples 83

2. Determination of Fluoride in Acid

Mixtures 84

COMPLEX EQUILIBRIA STUDIES 85

A. Introduction 85

B. Research Activities 85

1. Aqueous Boric Acid-Borate-Mannitol

Equilibria 85

2. Lanthanide Metal-Nitrate Equilibria ... 98

MICROSCOPIC AND CLASSICAL MICROCHEMICAL ANALYSIS . 101

A. Introduction 101

B. Ultramicrochemical Standards 101

1. Water Content Measurements 102

2. Density Measurements 103

3. Capacity of the Hydrogen Form 104

4. Sulfur Determination 104

vi 1
PAGE

5. Handling Techniques 105

C. Clean Room 105

D. Applications of the Nuclear Track Technique

to Trace Analysis 110

1. Determining Elements by the (n, a)

Reaction 110

2. Determination of Elements by (y, f)

Reactions 112

E. The Quantimet-QTM 113

7. INTERNATIONAL RESEARCH GRANTS PROGRAM 115

A. Introduction 115

B. Mercury Coated Rotating Platinum Electrode

(MCRPE) 115

C. Electrolysis Cell for Medium Exchange .... ll6

8. PERSONNEL AND ACTIVITIES 117

A. Personnel Listing 117

B. Publications 117

C. Talks 118

D. Committee Activities 120

E. Standard Reference Materials Analyses .... 122

9 . REFERENCES 124

viii
LIST OP FIGURES

FIGURE NO. PAGE

1. Preparation of standard gas mixtures by

weighing 5

2. Analysis of "submicro" gas sample 16

3. Apparatus used for EDTA determination .... 22

4. Elements added to glass standard reference

materials 30

5. Effect of mannitol concentration on the

apparent ionization constant of boric acid

in 1M KC1 at 25 °C 4l

6. End points of titrations of 0.06 meq samples

of H~B0 Q at different apparent values of K .43 o j a

7. Assay of boric acid as a function of the

composition of electrolyte and the concentration of boric acid 44

8. Error encountered in coulometric titrations

of mannitoboric acid at different cK values

a du^ to the difference between potentiometric

inflection point and the equivalence point . . 46

9. Coulometric determination of chromium at

nanogram levels 50

10. Inverted silver sulfide membrane electrode . . 77

11. Silver sulfide electrode response to silver

activity (test solution vol. = 5 yl) 78

12. Fluoride microelectrode 80

13- Detail of fluoride microelectrode tip .... 8l

14. Microelectrode response to fluoride activity . 82

15. Proton magnetic resonance spectra in D

? of:

0.5M mannitol; 0.5M mannitol, 1.0M boric

acid; 0.5M mannitol, 1.0M sodium

me tab orate 87

IX
FIGURE NO. PAGE

16. pH of mannitol-borax solutions in which

mannitol concentration was varied, borax

concentration was held constant 87

17. Formation constants for BM~ calculated from

_2 changes in pH of a 10 M borax solution to

which small amounts of mannitol were added . . 88

18. pH of mannitol-boric acid solution in which

mannitol concentration was varied, boric

acid concentration was held constant 93

19. Infrared spectra of solids containing free

and complexed nitrate 99

20. Plan of the clean room facility 106

21. Anteroom, change room, and air shower . . . , . 107

22. Entrance from the air shower into the class

1000 area 108

23. Verticle laminar flow fume hood in class 100

area 108

24. Microscopy table in cleanest portion of the

room 109

25. Pass through, emergency exit and portion of

microscopy table , . . 109

26. Bismuth fission-track counting by the QTM . . . 114
LIST OF TABLES

TABLE NO. PAGE

1. Results of three determinations of

atmospheric argon 2

2. Typical weighings obtained at one step in

mixing procedure , . . . . 6

3. Weight of sample calculated from weights in

Table 2 6

4. Oxygen content of air obtained during the

cruise of the Oceanographer 8

5. Oxygen content of air obtained during the

cruise of the Eltanin 8

6. Summary of gas analytical services 12

7. Copper in SRM #1080a 18

8. Copper in microstandard particles 19

9. Lead in microstandard particles 19

10. Lead in isotopic microstandard particles ... 20

11. Analysis of EDTA (disodium salt, dihydrate) . . 22

12. Lead and bismuth in ductile irons and

stainless steels 25

13- Lead and bismuth in steels 26

14

.

Tellurium in steels 27

15. Lead in reagents 28

16

.

Iron and titanium in acids 29

17- Trace elements in glass 29

18. Iron in soda lime glass, SRM #80 32

19. Titanium in soda lime glass, SRM #80 32

20. Nickel recovery 33

21. Zinc recovery 33

xi
TABLE NO. PAGE

22. Analysis of particulates 36

23. Analysis of particulates 36

24. Analysis of K

2

Cr

2 solution, SRM #136b,

assay percent 99.977 54

25. Analysis of synthetic solutions with 9:1,

1:1, and 1:9 ratios of chromium(III) and

chromium (VI) 55

26. Determination of oxygen in boron 58

27. Results of analysis of K

2

Cr

2

Lot 3608 ... 59

28. Results of analysis of calcium carbonate ... 60

29. Effect of environment on the assay of

CaCO 61

30. Results of analysis of Ag-Au alloys 63

31. Mass balance for Au-Ag alloys 64

32. Results of analysis of SRM KC1 65

33. Results of analysis of SRM NaCl 66

34. Analysis of SRM stainless steel for chromium . 68

35. Analysis of KH citrate 69

36. Determination of chromium in ruby laser ... 70

37. Analysis of KC1 solutions for conductance

measurements 70

38. Analysis of H -loaded ion-exchange beads ... 71

39. Analysis of sea water standard P,- , 72

40. Values for gold 83

41. Titration of 100 ml 9-389 x 10~ 3 M borax with

1.000 x 10" 2

M mannitol 89

42. Formation constants of borate-mannitol

complexes 98

xii
TABLE NO. PAGE

43. Percent gain in weight from the dry state

at 30$ RH , 102

44. Percent gain in weight from the dry state at

varying relative humidities 103

xi 11
MICROCHEMICAL ANALYSIS SECTION: SUMMARY OF ACTIVITIES

JULY 1968 to JUNE 1969

Edited by John K. Taylor

ABSTRACT

This report describes the research activities and scientific programs of the Microchemical Analysis Section of the

Analytical Chemistry Division of the NBS Institute for

Materials Research during the period July 1968 to June 1969.

General activities are reported in the areas of gas analysis,

polarography , potentiometry , coulometry, chemical microscopy,

and classical microchemical analysis. Research activities described in some detail include; gravimetric preparation of

gas analysis standards; polarographic determination of trace

elements in glass; fabrication and performance of a microfluorine electrode; elucidation of the boric acid-boratemannitol system; investigation of the relation between the

equilibrium point and inflection point in acidimetric titrimetry; coulometric determination of trace quantities of

chromium; and determination of trace elements by nuclear track

measurements. A number of procedures which have been developed

for the analysis of a variety of materials, utilizing the

techniques mentioned above, are also included.

Key words: Chemical analysis, Coulometric analysis, Gas

analysis, Ionic equilibria, Ion-selective

electrodes, Microchemical analysis, Microscopic

analysis, Polarographic analysis.

xiv
1. GAS ANALYSIS

A. Research Activities

1. Trace Oxygen Analyses

Pour electrochemical cells based on a modification of a design previously described [1] were constructed and incorporated into a system for the analysis of trace oxygen concentrations at levels below one part per million (ppm) . The

modification consisted primarily of eliminating all possible

sources of leakage which might introduce minute quantities of

oxygen to the system. Electrical connections were made

through glass-to-tungsten joints and all gas connections are

vacuum-tight ground joints. The operation of the cells was

found to be superior to those previously used both in the

higher and lower concentration ranges . Extensive experiments

with the cells , however, merely indicated a cell theoretically

sensitive but deficient in actual practice. This deficiency

lies not within the cell, but rather can be attributed to the

associated hardware. It was found that commercial valves and

fittings, no matter how carefully used, were never entirely

leak-free in terms of the detection of traces of oxygen between 1 ppb (part per billion) and 1 ppm.

Reluctantly this effort was shelved until such time is

available to allow construction of a completely leak-free gas

handling system. Therefore, further work on gas standards

with very low concentrations of oxygen in nitrogen has been

deferred.

2

.

Atmospheric Argon

A method for the accurate determination of argon in air

was briefly described in a previous report [1]. More extensive

details and initial results have been presented [2]. Briefly,

these results indicate a value for the concentration of atmospheric argon lying closer to that of Shinya Oana [3] than

that of Moissan [4J. The method depends on the careful pre-
paration of weighed mixtures of argon and nitrogen which are

used to calibrate a mass spectrometer for subsequent

determinations of the ratio of argon to nitrogen in atmospheric air samples from which the oxygen has been removed.

Table 1 gives some of the results of the three investigations

Results are expressed as the mole percent of argon in the

argon-nitrogen portion of the atmosphere.

Table 1. Results of three determinations of

atmospheric argon.

Argon in Mole Percent

No. Moissan (1903)

1.183

Shiny a Oanu (19 49)

1.16

This

Investigation

(1968)

1 1.133

2 1.181 1.16 1.176

3 1.183 1.16 1.154

4 1.184 1.18 1.167

5 1.187 1.16 1.159

6 1.179 1.16 1.164

7 1.184 1.16 1.164

8 1.183 1.14 1.158

9 1.182 1.16

10 1.181 1.16

11 1.179 1.16

12 (1.201) 1.16

Avg. 1.182 1.16 1.159

s 0.002 0.01 0.013

These preliminary results, while lacking the precision of

Moisson's results, show a clear discrepancy. The method by

which the results were obtained will be modified in accordance

with the availability of new and better equipment for both

the preparation of standards and the mass spectrometric comparison of the standards with atmospheric air. It is hoped

that a minimum accuracy of about one part in 10,000 can
eventually be achieved. If this accuracy can be realized, a determination of the argon-to-nitrogen ratio of eighty atmospheric samples obtained from locations around the world will

be attempted.

3. Atmospheric Carbon Dioxide

The National Bureau of Standards issues as standard

reference materials three concentrations of carbon dioxide in

nitrogen and are identified as SRM #1601, 1602, and 1603,

respectively. These are intended to bracket atmospheric concentrations and to serve for the calibration of instruments

used to determine these levels of carbon dioxide. While the

accuracy of these standards (± 1 mole percent of the total

carbon dioxide) is adequate for most routine monitoring problems, there exists the need for at least one ultimate and

definitive sample with an accuracy of at least two orders of

magnitude better than 1% . A preliminary investigation of the

feasability of the preparation of such a mixture has been completed and the preparation of three primary standards has begun

Because of the cost, time, and degree of care necessary for

the production of these standards, they are not intended for

distribution but it is expected that not only will they serve

as the primary standard for atmospheric carbon dioxide concentrations but will also be used to recertify the currently

available standard reference materials to a value one order of

magnitude better than at present.

The new samples are being prepared by successive dilution

of higher concentrations of carbon dioxide in nitrogen.

Formerly such standards were prepared in a similar manner and

the final concentration was determined by calculations based

on measured pressures . Methods for measuring pressures in

the range through which the dilutions were made were adequate

for producing mixtures with an accuracy of 0.1$.

Other factors such as temperature and compressibility

added additional uncertainties which combined to result in an
overall accuracy of about 1% . Probably the largest and least

easily determined sources of error are the compressibilities

of the two gases involved and the unknown manner in which the

compressibility varies in the composition of the mixture.

Little or no data are available concerning the compressibility

of gas mixtures. The final degree of uncertainty in the concentration of gas mixtures prepared by measurement of volume

would necessarily remain high until such data are available.

An alternative method, and one which has just recently found

increased use in industry, is the preparation of gas mixtures

by weight. In principle, it should be simple to prepare

mixtures by such means but in practice numerous problems may

arise. The very low density of gases as compared to the usual

substances encountered in chemical gravimetry require large,

relatively heavy containers whose total weight far exceeds the

weight of the gases . Buoyancy corrections became quite

significant and in relation to this any changes in shape of

the gas container with changes of pressure must be known or be

predictable

The preparation of the carbon dioxide standards required

a balance capable of weighing to at least one part in ten

thousand. The total weight of the sample and the cylinder

containing it was about 8 kg. A balance meeting such requirements is shown in Figure 1. The volume of the container is

about 2£; the contained gas has a total volume of about 60

(S.T.P.) and weighs about 100 grams.

Buoyancy corrections were determined to be negligible

both under conditions of varying barometric pressure and

temperature when cylinders are weighed against a tare of

similar volume. Possible buoyancy changes due to the distortion of the cylinder under full working pressure (500 psi) are

considered negligible. It is impossible to measure changes

arising from this source, unlike changes arising from barometric pressure and ambient temperature which can be determined

by observing changes as these parameters change, and therefore

4
Figure 1. Preparation of standard gas mixtures by weighing.

it is necessary to measure the physical changes of a cylinder

under conditions when it is empty and full. A cylinder was

measured with a micrometer caliper at three points on its

circumference at three points along its length for a total of

nine points . The cylinder was then charged to full pressure

and remeasured. No change in dimension was observed under

these conditions, however, this single determination is not

considered definitive and a further investigation is planned.

In practice, cylinders to be used for mixtures are weighed

against two other cylinders which are carried through the

mixing process without change. The order in which cylinders

are weighed is such that abrupt shifts in the "zero" of the

balance are readily observed and gradual "zero" shifts are

compensated. At least ten separate weighings of each sample

are made and the standard deviation of the average of each

sample weight must be less than 1 part in 10,000. In Table 2

is an example of a single weighing in the process of making
a mixture. Cylinders 1 and 4 are references and remain

unchanged through the procedure. Cylinders 2 and 3 contain a mixture of carbon dioxide and nitrogen. The weights shown are

the differences between the weights of cylinder 1 through 4

and a tare consisting of a similar cylinder. The weight of

the sample shown in Table 3 is determined from the difference

in weight between cylinder 2 and 1 before and after filling

and cylinder 3 and 4 under similar conditions

Table 2. Typical weighings obtained at one step

in mixing procedure

Weight in Grams

No. Cylinder 1 Cylinder 2 Cylinder 3 Cylinder 4

1 57.747 155.832 149.957 36.838

2 57.746 155.831 149.956 36.838

3 57.744 155.830 149.956 36.840

4 57.745 155.832 149.956 36.838

5 57.744 155.833 149.958 36.839

6 57.749 155.835 149.961 36.841

7 57.740 155.833 149.958 36.839

8 57.746 155.832 149.957 36.839

9 57.745 155.832 149.956 36.838

10 57.745 155.832 149.957 36.839

Table 3. Weight of sample calculated from weights in

Table 2.

No. Cylinder 2 Cylinder 3

1 104.534 104.369

2 104.534 104.368

3 104.535 104.366

4 104.536 104.368

5 104.538 104.369

6 104.535 104.370

7 104.535 104.369

8 104.535 104.368

9 104.536 104.368

10 104.536 104.368

Avg. 104.536 104.368

s 0.001 0.001

The weight differences are measured with brass weights

and since no change in volume of the sample occurs the only

buoyancy correction that must be applied is that represented

6
by the differences in the air volume of the brass weight difference occurring between weighings. Barometric pressure and

temperature were noted at each weighing in order to allow this

calculation.

The gases used to compound these mixtures were prepared

and analyzed in such a way that the required accuracy could

be maintained throughout the mixing procedure. The carbon

dioxide was obtained from a cylinder of research grade material

which was cooled to dry ice temperature and "blown off". It

was subsequently blown off several times at room temperature.

Both the carbon dioxide and nitrogen were analyzed mass

spectrometrically . The nitrogen used in the dilution to the

final concentration must either be carbon dioxide free (< 30

ppb ) or the carbon dioxide content must be known with an

accuracy within ± 30 ppb. The method of analysis will probably

be an adaptation of the method described in section A. 3.,

"Atmospheric Carbon Dioxide".

4 . Oxygen in Air

Samples of atmospheric air were obtained during cruises

of the research vessels, U.S.N.S. Oceanographer and U.S.N.S.

Eltanin. The purpose of the sampling was to determine

possible variations in oxygen content in the atmosphere over

the oceans in areas of varying oxygen producing organisms

.

These samples, 46 from the Oceanographer and 32 from the

Eltanin, were analyzed for oxygen content by comparison with

NBS Standard Reference Material #1609, 20.95 mole percent

oxygen. The method is described in detail in a previous report [1]. The results are shown in Tables 4 and 5. The

limit shown on each value is the standard deviation of three

values. Each value represents ten instrument readings. It

is interesting to note that almost without exception the value

for the oxygen content is 20.946 mole percent. The few

exceptions are also those with the greatest standard deviations

suggesting an experimental error rather than an actual variation in atmospheric oxygen content

.

7
Table 4. Oxygen content of air obtained during the

cruise of the Oceanographer

Sample No. Oxygen Content Sample No. Oxygen Co ntent

S-l 20.9^6 + .001 S-26 20.945 + .001

S-2 20.946 + .001 S-27 20.945 + .001

S-3 20.945 + .001 S-28 20.945 + .006

S-4 20.945 + .002 S-29 20.948 + .002

S-5 20.946 + .002 S-30 20.947 + .001

S-6 20.945 + .002 S-31 20.946 + .001

S-7 20.946 + .001 S-32 20.946 + .001

S-8 20.946 + .001 S-33 20.946 + .001

S-9 20.946 + .001 S-34 20.946 + .001

S-10 20.945 + .001 S-35 20.945 + .001

S-ll 20.946 + .001 S-36 20.946 + .001

S-12 20 .946 + .001 S-37 20.946 + .001

S-13 20.946 + .001 S-38 20.945 + .001

S-l4 20.946 + .001 S-39 20.946 + .001

S-15 20.946 + .001 S-40 20.945 + .001

S-16 20.946 + .001 S-41 20.949 + .006

S-17 20.946 + .001 S-42 20.949 + .004

S-18 20.946 + .001 S-43 _ _ S-19 20.946 + .001 S-44 20.945 + .003

S-20 20.946 + .001 S-45 _ S-21 20 .945 + .002 S-46 _ _ S-22 - - S-47 20.942 + .002

S-23 20.947 + .001 S-48 20.949 + .001

S-24 20.947 + .001 S-49 20.944 + .001

S-25 20.949 + .001 S-50 20.946 + .001

Table 5. Oxygen content of air obtained during the

cruise of the Eltanin.

Sample No. Oxygen Content

1 20.946 + .001

2 20.946 + .001

3 20.946 + .001

4 20.946 + .001

5 20.946 + .001

6 20.946 + .001

7 20.946 + .001

8 20.945 + .001

9 20.945 + .001

10 20.945 + .001

11 20.946 + .001

12 20.946 + .001

13 20.946 + .001

14 20.946 + .001

15 20.946 + .001

16 20.946 + .001

Sample No. Oxygen Content

17 20.944 + .001

18 20.947 + .002

19 20.942 + .003

20 20.946 + .001

21 20.943 + .002

22 20.953 + .008

23 20.947 + .002

24 20.945 + .001

25 20.945 + .001

26 20.946 + .001

27 20.941 + .004

28 20.943 + .002

29 20.947 + .002

30 20.947 + .001

31 20.945 + .001

32 20.946 + .001
B. Standard Reference Materials

1. Sulfur Dioxide In Air

It had previously been determined that ordinary mild

steel and stainless steel containers, while satisfactory for

high concentrations, were not suitable for storage of mixtures

of dilute concentrations of sulfur dioxide in air. Before a comprehensive investigation of other methods of preparing

sulfur dioxide mixtures was attempted, a single high

concentration (0.2 mole percent) was prepared in a large (1A)

cylinder. The mixture was then transferred to 20 small (2£)

cylinders

.

A mass spectrometric comparison was made between the gas

in the small cylinders and the gas in the large cylinder. The

comparison was made by admitting a sufficiently high pressure

of the mixture into the inlet system so that the mass 64 due to

S0„ was easily read to better than 1% . The ion current due

to nitrogen in air at mass 28 was brought within readable

limits by adjustment of the input resistor of the preamplifier

and by scanning the mass 28 at a lower sensitivity than for

the 64. Thus differences of 1 part in 40 thousand could be

easily determined. Using this method it was possible to obtain a comparison between the contents of the large cylinder

and the contents of the small cylinders with rapidity and ease

compared to other methods for determining sulfur dioxide in

this concentration range.

The results obtained in the above study and with a later

duplicate study using a new mixture indicates that little or no

reaction (less than 1%) occurs in the small cylinders after

transfer from the large cylinder. Analytical results obtained

after refilling cylinders previously exposed to 0.2 mole percent sulfur dioxide in air indicates that no residual sulfur

dioxide remains in the cylinders

.

The mass spectrometric method described above is adequate

for comparison of one concentration of sulfur dioxide with
another but is not considered to be sufficiently absolute for

certification of the final concentration. This value must

depend on careful analysis of the individual components

and accurate measurement of the pressures of each component.

The value obtained mass spectrometrically must agree within

limits with this value but will not be used in the final

certification.

Some preliminary work has been done on a method for

producing low concentrations of sulfur dioxide in an air

stream. The device is that described by O'Keefe et al. [5]

and depends on the effusion of sulfur dioxide at a fixed rate

from a porous plastic tube containing liquid sulfur dioxide.

A specimen tube was obtained and the constancy of the effusion

rate was ascertained by measurement of the weight loss versus

time. Subsequent use of such a tube would depend on the

constancy of this weight loss. In order to determine whether

an independent check of effusion rates might be possible a simple titrimetric procedure was evolved.

The tube was placed in a container filled with a dilute

hydrogen-peroxide solution. This was immersed in a thermostated water bath and the interval during which the tube was

immersed was measured. At the end of the interval the sulfuric

acid formed was titrated with dilute sodium hydroxide and the

total evolved sulfur dioxide could be calculated. The values

obtained by weighing and by titration of the sulfur dioxide

evolved by a single tube are as follows

0.069 mg/min by weight at 25 °C

O.O67 mg/min by titration at 25 °C

The agreement is quite good and the possibility of measuring

effusion by titration will be pursued. The advantages are

that the time interval between weighings can be much more

easily defined and errors in weighing are eliminated. Once

equipment is set up and solutions standardized, determinations

can be performed quite rapidly. Using suitable techniques it

10
is possible to obtain a good value of the effusion rate in

about 15 minutes after immersing the tube in solution.

2 . Hydrocarbon in Air Standards

A series of methane in air standards containing approximately 1, 10, 100 and 1000 ppm methane was prepared and

analyzed. Preparation of certificates of analysis is now in

progress. The analyses of the standards were performed by

using a flame ionization instrument to compare the response

from the standard to the response from two calibration

standards. The two calibration standards were prepared as

follows . A calibration standard in the hundred ppm range was

compounded by stepwise dilution of methane with air of known

low hydrocarbon content, concentrations being determined from

the weights of the components with a precision analytical

balance. With this standard and air containing no hydrocarbon, obtained by passing air through cupric oxide at

1050 °C, a calibration standard containing about 2 ppm hydrocarbon was analyzed accurately using the flame ionization

instrument?

The concentrations of the standard reference gases obtained from the pressures of the components during compounding

and the concentration determined with the flame ionization

instrument agree within 1%

.

Difficulty in finding a suitable prepared container was

experienced with mixtures containing 1 and 10 ppm hydrocarbon.

Certain containers using a resin sealant between the valve and

the body of the cylinder were found to contribute markedly to

the hydrocarbon content of a mixture therein. Cleaning the

sealant from these containers and resealing with teflon tape

alleviated the problem. However, each container of standard

reference gas at the 1 and 10 ppm levels of hydrocarbon has

been analyzed to make certain that the concentration is the

same as that in the bulk mixture.

11
3. Carbon Dioxide in Air

As mentioned earlier in this report, standard reference

materials consisting of carbon dioxide in nitrogen will

probably be recertified to a higher degree of absolute

accuracy. In addition, work has begun on a method for the

determination of atmospheric carbon monoxide and carbon

dioxide based on the catalytic conversion of these compounds

to methane with subsequent determination of the methane using

a flame ionization detector. The method was first described

by Stevens [5]

Preliminary results indicate that the method has promise

but many technical details must be evaluated. A promising

feature of the method is its applicability to the absolute

determination of low concentrations of carbon dioxide . Heretofore, these determinations could only be performed on

rather specialized infrared apparatus which is not available

in this laboratory. It is hoped, as previously mentioned, to

adapt the method for the determination of the "zero" level of

carbon dioxide in the gases used in the preparation of the

standard mixture of carbon dioxide.

C. Research Materials Service Analysis

1. General

Service analyses and compounding of gas mixtures are a

regular function of this laboratory. Mass spectrometry is

the most frequently used analytical technique, however electrochemical cells, gas chromatography, infrared, and other

methods are used when the need arises. Table 6 summarizes

analytical and mixture compounding services.

Table 6. Summary of gas analytical services.

A, Mass Spectrometric Analysis

Number of

Material Samples Sample Size Determined

Organic Materials

Gases evolved 3 10 ml CpClu

from plastics

Pyrolysis 3 small ampoules ^ 30 different organic

products and inorganic components in each sample

12
Table 6. (Continued)

Material

Number of

Samples Sample Size Determined

Inorganic Material s Air samples 82 11 STP °2

from various

geographic

locations

"Anomalous"

water

1 small

capillary 2

, C0

2

, H

2

Gas mixtures 3 ^ 200 ml STP H

2

Gas mixtures 3 cylinder H

2

Sample from

airplane cab in

1 1 gallon STP composition

NH

3

1 cylinder H

2

Reactor

products

1 500 ml flask N

2

, 2, NO, N

2 0, co2

Hydrogen 1 cylinder purity

Power plant

stack gas

3 * 200 ml STP H

20, N

2

, CO,

2

, co

2

, so

2

Ar,

Air sample 1 large yellow

cylinder

CC1

2

H

2

C1F, glass ampoule impurities

Combustion

products

Mixture of

organic and

inorganic

gases in Op

glass ampoule H" 2

, He, N

2

, NO, Ar, C0

2

cylinder approximate composition

13
Table 6, (Continued)

Number of

Material Samples Sample Size Determined

Mixture of

organic and

inorganic

gases in Np

Helium from

Reactor

Inorganic Materials (Continued)

cylinder approximate composition

1£ STP He , N

2

, 2, Ar, D

2

N

2

Isotopically Altered Materials

2

Helium-3 10

Oxygen evolved 6

from irradiated solids

15 15 14 15 large ampoules N^N^O, N^V^O,

N

l4

N

l4

Neon 3 cylinders

Gas mixtures 2 500 ml flask

Gas mixture 1 cylinder

Helium-3 2 30 ml ampoul

impurities and Neon

isotope composition

CH~D, CHjj, impurities

CH~D, CHj,, impurities

30 ml ampoules He J

3 He , H

2 0, N

2

,

2

, Ar, C0

2

-3 -4

30 ml ampoules He , He

small ampoules oxygen-18, oxygen-16

B. Compounding of Gas Mixtures

Mixture Concentration of Minor Component

0.102 mole %

90 ppm

215 ppm

14

CO in air

Co in air

S0

2

in air
Table 6. (Continued)

B. Compounding of Gas Mixtures (Continued)

Mixture Concentration of Minor Component

2

in N

2

21.508 mole %

2

in N

2

20.627 mole %

CHn in air 119.1 ppm

CHm in air 11.1 ppm

Hp in air (2 cylinders) 1.39 mole %

H

2

in He 2.15 mole %

C0

2

and

2

in He 1.09 mole % COp, 2.08 mole %

2

2

in He 5.18 mole %

C. Electrochemical Determination of Oxygen

Number of

Material Samples Sample Size Determined

Ar 1 cylinder

2

Mixture of 1 cylinder Op

organic and

inorganic

gases in N

2

2 . Mi see 1 lane ous Analy s e s In addition to the relatively routine analyses listed

in Table 6, the work of this laboratory often involves either

the modification of existing techniques or the origination of

new methods of treating or handling samples in order to

accomodate urgent or unusual conditions . Identification of

possible incendiary fluids, determination of unusual atmo15
Figure 2. Analysis of "submicro" gas sample.

spheric components, and determination of contamination in

ultraclean systems are but a few. The operation shown in

Figure 2 involved the analysis of a "microscopic" gas sample

contained in a short length (approx. 1 cm) of quartz tubing so

thin that it was almost invisible to the unaided eye. The

sample was of such small volume that the inlet system of the

mass spectrometer used for the analysis had to be completely

closed and the sample was contained in a small "L" attached to

the leak line. The sample was crushed by manipulating an internal magnet with an external magnet. By means of this technique it was possible to identify two components whose total

-10 -9 volumes at N.T.P. were only 1 x 10 and 2 x 10 liter.

(E. E. Hughes and J. M. Ives)

16
2. POLAROGRAPHIC ANALYSIS

A. Introduction

Experience gained in this laboratory over a period of

years and particularly in the last few years has established

polarography as a prime technique for both trace and major

constituent analysis. Accordingly, such measurements have

been utilized for solution of a number of important analytical

problems involving standard reference materials as well as material related to several areas of NBS research. During

the course of this work, a number of methods have been developed or modified to provide improved analytical utility.

Some of these developments during the past year are outlined

in the following sections.

B. Major Constituent Analysis

The improved precision obtained by the comparative polarographic method [6] has continued to be applicable to other

analytical problems during the past year, particularly those

concerned with SRMs . A few of tnese will be discussed below.

1. Analysis of Bis (1-phenyl-l ,3-butanediono) Copper(II)

(SRM #1080a)

The copper metallo-organic standard, which is used for

blending with lubricating oils to prepare standards for monitoring wear of engine parts, was checked for homogeneity and

analyzed by the following procedure:

After drying for 2 hrs at 110 °C, 0.6-g samples were

slowly ignited to destroy organic material. The residues were

dissolved in 20 ml of 50% nydrochloric acid (V/V) , 20 ml of

pyridine was added and the solutions were diluted to one liter.

Copper was then measured polarographically at about -0.4V vs.

a mercury pool anode in comparison with reference solutions

prepared in the same manner from melting point copper, SRM #45d.

Results for six samples taken from different parts of the same

lot are shown in Table 7 along with results obtained by the

NBS Activation Analysis Section.

17
Table 7. Copper in SRM noi30a.

gnation

Copp ar, percent

Sample desi Polarography A<2tiva tion analysis'

1 16.355 16.43

2 16.375 16.32

3 16.360

4 16.365

5 16.385

6

Avg.

16.360

16.367 16.37

s 0.011

aby S. S. Nargolwalla, Activation Analysis Section.

2 . Copper and Lead in Microstandard Particles

Comparative polarography has proved useful in the analysis

of microstandard ion-exchange beads [7], a new standard reference material being issued by NBS. Accuracies of 1% or better

are required and often the amount of sample available is

limited.

Two different lots of the copper microstandard were submitted for analysis. Copper was eluted from 0.15-g duplicate

samples of Sample 1-11-1 using concentrated hydrochloric acid.

The acidity was adjusted to be equivalent to 4 ml of 50% HC1

( V/V) , 4 ml of pyridine was added, the solutions were diluted

to 200 ml, and copper was measured polarographically at about

-0.4V vs. a mercury pool anode in comparison with reference

solutions prepared in the same manner from melting point

copper, SRM #45d.

For the determination of copper in Sample R17-0015,

duplicate 0.3-g samples were slowly ignited to about 700 °C.

The residues were dissolved in 10 ml of 50% HC1 (V/V), 10 ml

of pyridine was added, the solutions diluted to 500 ml and

18
measured poiarographically as described above. The results

are shown in Table 8. Sample 1-11-1 contained an appreciable

amount of sodium which accounts for its copper content being

lower than that of Sample R17-0015.

Table 8. Copper in microstandard particles.

Sample Copper, percent

1-11-1 (Cu) 11.96

11.9^

Avg. 11.95

R 17 0015 13.35

13.36

Avg. 13.36

The first attempts to determine lead after elution with

nitric acid were unsuccessful owing to the oxidation of the

ion-exchange resin to sulfate by nitric acid and consequent

precipitation of lead sulfate. Duplicate 0.2-g samples were

then eluted with warm dilute hydrochloric acid and diluted to

500 ml with approximately 3M hydrochloric acid. Lead was

measured poiarographically at about -0.5V vs. a mercury pool

anode using reference solutions prepared as before from melting point lead, SRM #49d. The results, as well as those obtained by atomic absorption on a sample of the same material,

are given in Table 9.

Table 9. Lead in microstandard particles.

Copper, percent

Sample Polarography Atomic Absorption

1-11-1 (Pb) 33.09

32.87

Avg 32.98 32.99

aBy T. C. Rains, Analytical Coordination Chemistry Section.

19
o n fc\ on p

Some isotopic lead (equal-atom, Pb- Pb ) mlcrostandard

particles were prepared in very limited amounts . Only about

300 mg total of material was available for analysis and for

issuance as a standard. There was no difficulty in determining the lead polarographically using duplicate 30-mg samples,

leaving sufficient material for issuance. The lead was eluted

and determined essentially as described above, except the dilution volume was 100 ml. As only 1 to 5 ml of this solution

is necessary for the final polarographic measurement, it is

seen that samples as small as 1 mg could be used without difficulty. The results, calculated on the basis of an average

atomic weight of lead in the samples as 207, are given in

Table 10.

Table 10. Lead in isotopic mlcrostandard particles.

Sample Designation Lead, percent

Run 16 34.47

34.73

Avg 34.60

The bead residues remaining after elution were examined

spectrochemically . No lead was detected. The limit of detection of about 20 ng confirms virtually complete elution of

lead under the experimental conditions

3 . Copper and Nickel in Service Samples

Methods similar to those described above have proved useful in the analysis of a number of samples received through

the NBS Service Analysis Program. For example, it was possible

to determine copper at the 12$ level in 25-mg samples of a

metal-organic compound in a similar pyridine-pyridinum chloride

supporting electrolyte after destruction of organic material

Results agreeing within 0.8% of the theoretical composition

were obtained by the single cell mode of operation.

20
A series of 8 Cu-Ni alloys ranging from less than 0.1 to

50$ Ni were also analyzed polarographically in a pyridinepyridinum chloride supporting electrolyte at about -0.9V vs.

a mercury pool anode. If necessary, copper could have been

determined simultaneously.

4. EDTA (Disodium Salt, Dihydrate)

Methods for the analysis of EDTA were investigated in

anticipation of its adoption as a standard reference material.

The use of an indirect polarographic method appeared most

feasible. For example, a known excess of a metal ion which

forms a complex with EDTA could be added and the excess

measured polarographically, allowing the concentration of the

EDTA to be determined. More accurate possibilities include

adding either a deficiency or an excess of the metal ion, then

titrating with a dilute solution of the metal ion or back titrating with a dilute solution of EDTA. In either case the

polarograph would be used as an end point detector. In the

first situation, the end point would be at the appearance of

a peak of the uncomplexed metal ion at high polarographic

sensitivity; in the second, the end point would be at the

disappearance of the peak of the metal ion.

Several systems were investigated. One of the most

favorable was the Cd-Cd EDTA complex in an ammonium hydroxideammonium chloride buffer solution. Both the metal ion titration and EDTA back titration were investigated. In the first

case, an accurately weighed amount of a commercial lot of

EDTA and a slightly deficient amount of high purity cadmium

in 50 ml of the buffer solution were titrated with a dilute

solution of the high purity cadmium to the appearance of a cadmium peak at about -0.7V vs. a mercury pool anode. The

apparatus used is shown in Figure 3. A 100 -ml beaker suffices

for a titration cell together with a one-ml beaker to contain

the mercury pool anode

.

21
Figure 3. Apparatus used for EDTA determination.

In the second case, a slight excess of cadmium was present in the same system as discussed and the solution was titrated with a dilute solution of EDTA to the disappearance of

the cadmium peak. The results are shown in Table 11 along

with those obtained by coulometry for the same material.

Further work on this procedure has been postponed until receipt of a lot of EDTA for use as an SRM. The precision and

accuracy of the method should be comparable to that obtained

by coulometry, provided larger samples and weight burets were

used.

Table 11. Analysis of EDTA (disodium salt, dihydrate).

Na

2

EDTA-2H 0, percent

Cd titration

100.05

EDTA back titration

100.00

Coulometry3- 100.036

By George Marinenko, Microchemical Analysis Section.

22
C. Minor Constituent Analysis

1. Meso-bilirubin

Work at NBS to issue bilirubin sufficiently pure for

use as a clinical standard led to the investigation of

polarographic determination of a possible impurity, namely

meso-bilirubin. Polarographic waves have been reported for

each of the materials in a sodium hydroxide supporting electrolyte [8]; however, the separation of half-wave potentials is

not sufficient to permit small amounts of meso-bilirubin to

be determined in the presence of an excess of bilirubin by

using direct polarographic procedures. Since both constituents

dissolve readily in dimethylsulfoxide , the use of this solvent

was investigated. Lithium chloride was added as a supporting

electrolyte. Bilirubin was reduced at about -1.1V and mesobilirubin at about -1.25V vs. a mercury pool anode. Both

peaks were drawn out and ill defined on the cathode-ray

polarograph so that slightly less than 30% of meso-bilirubin

could be detected in the presence of about 70% bilirubin.

By the use* of sufficiently pure meso- or bilirubin for calibration solutions in differential polarography , the determination of either would be no problem as the effect of an excess

of either one could be eliminated by adding a similar amount

to the supporting electrolyte in the second cell. The use of

another type of high sensitivity polarographic technique such

as pulse polarography, might lead to better peak resolution

and lower limits of detection. Also, it is possible that

other supporting electrolytes would provide better resolution

of the peaks.

D. Small Sample Analysis

1. Antimony and Bismuth in Thin Film and Source Material

The program started several years ago on the analysis of

very small quantities of thin films has continued with the

analysis of a number of antimony-bismuth films with total

weights of several hundred micrograms . The bismuth/antimony

23
ratios in the samples analyzed recently ranged from about 20/80

to 90/10. Antimony (III) is measured at about -0 . IV and bismuth

at about -0.2V vs. a mercury pool anode in a supporting electrolyte" of dilute sulfuric and hydrochloric acids

E. Trace Analysis

1. Lead in Fish Protein Concentrate

Samples of a fish protein concentrate produced by the

Bureau of Commercial Fisheries for use as a high protein

source were submitted for determination of lead. Similar

samples were analyzed here earlier [9] by an improved and

shortened procedure over the AOAC method. The present samples

were produced from fish from a different source and the possibility existed of the presence of large amounts of interfering metals; hence a separation seemed advisable.

The fish protein concentrates, which had been dry-ashed

by the Bureau of Commercial Fisheries were received in Vycor

crucibles. The samples were moistened with water and nitric

acid and evaporated and ignited over a Bunsen burner to oxidize residual organic material. The residues were dissolved

in one ml of hydrochloric acid and a few ml of water and again

taken to dryness at a low temperature. The residues were then

dissolved in 10 drops of hydrochloric acid and 15 ml of water

and iron was reduced by heating with a few mg of hydrazine dihydrochloride . The solutions were transferred to a separatory

funnel and lead was extracted with sodium diethyldithiocarbamate and chloroform. After evaporation and destruction of

organic material, the residues were dissolved in 0.1N hydrochloric acid and measured on the cathode-ray polarograph in

the subtractive mode of operation using a background blank

carried through the entire procedure. Solutions for the construction of a calibration curve were also carried through the

procedure. The peaks measured were extremely well defined and

the lead concentration found ranged from 0.5 to 0.7 ppm.

Bismuth could have been measured in the same solution if de24
sired. The procedure is more sensitive and quicker than the

AOAC spectrophotometric method and the peaks, being better

defined, may be measured with greater accuracy than by the

earlier polarographic procedure.

2 . Lead and Bismuth in Ductile Irons and Stainless

Steels

Polarography is very useful in the analysis of low

levels of lead and bismuth in a number of SRMs . Not only is

the sensitivity and selectivity greater than that obtained

by other techniques, but both elements in the ductile irons

can be determined simultaneously in a supporting electrolyte

containing nitric acid and sodium tartrate after separation of

the iron with isobutyl acetate and the lead and bismuth with

sodium diethyldithiocarbamate . For the stainless steels,

volitalization of the chromium as chromyl chloride is necessary. The results are shown in Table 12.

Table 12. Lead and bismuth in ductile irons

and stainless steels.

Lead, percent Bismuth, percent

SRM Number n Avg.

Ductile

s Iron

Avg. s

1140 3 0.0052 .0003 0.0015 0.0001

1140a 3 .0128 .0014 .0031 .0001

1141 4 .00092 .00003 .00008 .00001

1141a 4 .00035 .00001 .00006 .00001

1142 4 .00048 .00008 .00002 .00001

1142a 4 .00028

Stainless

.00001

Steel

.00002 .00001

160b 2 0.00097 .00001 < 0.0005 0.00005

1155 2 .00096 .00001 < .0005 .00005

25
A value of 0.001$ lead was obtained for SRM #l60a which

was carried through the procedure as a control. This agrees

with the certified value of lead; bismuth was not certified

in SRM #l60a.

3 . Lead, Bismuth and Tellurium in Special Iron and Low- Alloy Steel Standards

The polarographic methods described above for lead and

bismuth are applicable for analysis of a new series of

spectrographic iron and low-alloy steel standard reference

materials (SRM #1261-1265) . Since some of the levels are in

the sub-ppm range, the magnitude of the blank encountered is a problem, particularly for lead, as it is a common contaminant

of many reagents.

Work to the present time has been confined to acceptance

testing and has proved the utility of the method, but blanks

of more than 0.5 ug of lead were obtained. One-gram samples

were used for SRM #1265, which contained the least lead and

bismuth and the concentrations found were approximately 0.3

and 0.1 ppm, respectively. Spark Source Mass Spectrometry

(SSMS) found 0.3 ppm of lead, but no bismuth or tellurium was

detected. Larger samples will probably be used when the final

melts are submitted for certification analysis. Results obtained for the acceptance testing of SRM #126l and #1263 are

shown in Table 13 along with values obtained for SRM #1180

which is provisionally certified to contain 0.0043$ lead and

0.0025$ bismuth, respectively.

Table 13. Lead and bismuth in steels.

Polarc graphy SSMS a

Sample

1261

1263

1180

Pb, % < 0.0001

.002

.004

Bi, %

0.001

.001

.002

Pb,$ Bi, $

0.00001 0.0003

.001 .002

By C. W. Mueller and P. J. Paulsen, Spectrochemical Analysis

Section.

26
A method developed in this laboratory for the determination of tellurium in brasses and cast irons' [10] was applied

to its determination in SRM #126 1, 1263, and 126 5. The

method has proved to be extremely sensitive. Results are

shown in Table 14. SRM #1178 has not been certified for

tellurium but a value of 0.004% has been obtained by another

cooperating laboratory. One-gram samples were taken for SRM

#1265. For the certification analysis, larger samples will

probably be used and the bulk of the iron will be removed

prior to the tellurium separation.

Table 14. Tellurium in steels.

Tellurium, percent

Sample Polarography SSMSa

1261 0.0004 - 1263 .002 0.001

1265 < .0001 not detected

• 1178 .004

By C. W. Mueller and P. J. Paulsen, Spectrochemical Analysis

Section.

4 . Reagent Analysis

To evaluate blanks in a number of trace analyses, including some discussed above, it was necessary to analyze a number

of the reagents used. Whenever available, commercially prepared high-purity reagents or regular commercial reagents which

have been found to have low metal contents are used for all

trace determinations. In some cases the regular commercial

reagents were of sufficient purity and occasionally were even

better than the high-purity reagents

.

Prior to the analysis of SRM #1265, several reagents and

the distilled water used were checked for lead. At the same

time, beakers made of two different types of materials, pyrex

27
and quartz, were used. Both types had been subjected to

repeated cleanings and had been used exclusively for trace

lead determinations for a long period of time prior to this

experiment

One-hundred ml samples of the reagents in question were

evaporated to dryness in the respective beakers. The residues

were dissolved in . IN hydrochloric acid and lead was measured

subtractively with the cathode-ray polarograph at about -0.5V

vs . a mercury pool anode . No difference was found in the lead

that could be attributed to beaker composition. The results

are given in Table 15.

Table 15. Lead in reagents.

Lead found, ppb (W/W)

Sample Evap. in Pyrex Evap . in Quartz

HC1, commercially 22 20

purified, bottle A 18 20

18

HC1, commercially 18

purified, bottle B

HNCU, commercially 1 1

purified

HC1, commercial grade 2

Distilled H ? 0.1

.1

An unexpected high concentration of lead was found in

the purified hydrochloric acid. Accordingly, a second sample

was taken from bottle B to eliminate the possibility of an

accidental contamination of bottle A, which might have accounted for its high value

Several different commercially purified acids were also

analyzed for iron and titanium to determine their suitability

for use in analysis of some new standard reference glasses

28
(section E.5.). One-hundred ml samples were evaporated to

dryness at a low temperature in teflon beakers. The residues

were dissolved in . IN hydrochloric acid and solutions of

oxalic acid and ammonium hydroxide were added. Iron and titanium were then measured subtractively with the cathode-ray

polarograph at about -0.2V and -0.5V vs. a mercury pool anode,

respectively. The results are shown in Table 16

.

Table 16. Iron and titanium in acids.

Sample

HC1, commercially purified

HN0~,j commercially purified

HP, commercially purified

PPb (W/W)

Iron Titanium

11 6

6 < 1

9 2

5 . Trace Elements in Glass-Simulated Lunar Standard

Reference Materials

As a result of wide-spread need for new glass and rocktype standard reference materials certified for a number of

elements in trace concentrations, NBS is now concerned with

the issuance of 5 new glass standards, designated as simulated

lunar materials. The melts for the standards were prepared at

Corning Glass Works and the aim composition is shown in Table

17.

Table 17. Trace elements in glass.

Glass designation

95GCA

95GCC

95GCD

95GCE

95GCG

Composition

Base glass

Base glass + 0.02 ppm of 61 elements

Base glass + 1 ppm of 6l elements

Base glass + 50 ppm of 6l elements

Base glass + 500 ppm of 6l elements

29
The soda-lime base glass has the approximate composition

72 55 SiO 12J8 CaO, lk% Na

2 0, and 2% A12

. This was chosen as

the base partially because it can dissolve a wide concentration range of many elements. The 6l different elements added

are shown in Figure 4 by the crosshatched portions of the

periodic table.

In the preparation of the glass, each melt was withdrawn

from the crucible as rods in 6-foot lengths and each length

numbered consecutively. It was necessary first to establish

the homogeneity of a given lot. The homogeneity checking and

analyses of these materials obviously present new problems

for many analytical methods. Cathode-ray polarography is a very advantageous technique to use for many of these determinations because of its sensitivity and resolution, however in

the presence of the large number of possible interferences,

some separations will be necessary for certain elements.

IA MA VIA VIIA

U Np Pu Am Cm Bk Cf Es I Fm Md i No U

Figure 4. Elements added to glass standard

reference materials.

30
The 500-ppm glass was the first to be ready for analysis.

The development of polarographic methods and the determination

of Fe , Ti, Ni, and Zn was requested as well as homogeneity

testing for nickel at 8 different portions along the glass

rods . It was first necessary to find the optimum supporting

electrolytes. It seemed probable that both iron and titanium

could be determined simultaneously, as an EDTA-sodium acetate

supporting electrolyte had been used previously here with good

results for titanium and tables of half wave potentials showed

the iron reduction peak to be far enough away from titanium

to allow both to be measured with the cathode-ray polarograph

.

A similar separation of reduction peaks was reported for a

sodium pyrophosphate-sulfuric acid supporting electrolyte.

Standard curves for the 1-10 ppm concentration range

showed the EDTA media to have better linearity than the pyrophosphate; however either are suitable for this concentration

range. Interferences in the doped glasses can be removed by

ammonium hydroxide and cupferron separations

.

The methods were tested by determination of iron and

titanium in SRM #80, a soda lime glass which is presently out

of stock. The results are shown in Table 18. Procedure A

used the EDTA supporting electrolyte and B, pyrophosphate.

The results, particularly for A, show good agreement with the

recommended value. This glass was issued in 1927. The

earlier certified value for iron was found to be high owing

to an inaccurate iron blank correction in the gravimetric procedure used.

The results for titanium in SRM #80 which were obtained

at the same time as those for iron are shown in Table 19.

Here, also, the results show good agreement for Ti with either

supporting electrolyte. Although the Ti0

2 value had only been

certified to one significant figure, the values reported by

cooperating analysts had been rounded off and actually were

31
known to two significant figures from which an average of

0.023% Ti0

2

or 0.014% Ti could be computed.

Table 18. Iron in soda lime glass, SRM #80.

Iron, percent

Recommended value Procedure A Procedure B

0.056% Fe

2 0^

(0.039% Fe) a

0.0378

.0382

.0382

.0382

0.0367

.0367

.0360

.0366

Average 0.0381 0.0365

s = .0002 .0003

aRevised 8/30/57 from earlier value of 0.065% Fe

2

^ (- oZ| 5% Pe)

Table 19. Titanium in soda lime glass, SRM #80.

Titanium, percent

Certified value Procedure A Procedure B

0.02% Ti0

2

0.0140 0.0141

.0136 .0139

(0.014% Ti) .0138 .0137

.0140 .0133

Average 0.0138 0.0138

s = .0002 .0003

Methods were then developed for the determination of

nickel and zinc in these glasses. Previous experience with

nickel has shown it to be best determined in pyridine and

either pyridinium chloride or pyridinium sulfate supporting

electrolyte, with few interferences. Zinc also gives a very

well defined peak in these supporting electrolytes, but is

subject to more interferences. In an ammonium oxalate supporting electrolyte, zinc also gives a well defined peak with

no interference from Ni, Co, or Mn. Aluminum and a number of

other ions present, however, form a colloidal hydroxide precipitate under some of these conditions, possibly occluding

some Ni and Zn, making separations from the glass advisable

for most accurate results.

32
Dimethylglyoxime appears to be the most suitable extractant for nickel, and dithlzone for zinc. The extraction procedure was checked by spiking 1-g portions of SRM #80 with

to 500-ug portions of nickel and zinc. The unspiked glass

was used as a blank in the second cell when the final polarographic measurement was made and was also measured against a

reagent blank on the second cell and subtracted from the spiked

values. Solutions containing to 500 yg of nickel and zinc

alone were also taken through the extraction procedure and

the results are shown in Table 20.

Ni added,

50

100

200

500

Table

yg

20. Nickel recovery.

Ni recovered, yg

Ni alone

48.5

100.6

202.9

512.2

Ni + SRM glass

49.8

101.0

201.1

505.6

The nickel recovery from the spiked soda lime glass was

calculated by subtraction of that found in the soda lime glass

which had not been spiked. The average error in the nickel

recovery from the glasses is about a percent which is within

the measuring error of direct polarography

.

The zinc recovery from the spiked glass was calculated

in the same manner as that for nickel. With the exception of

the 100-yg spike sample, the recoveries were also within the

expected measurement error. The results for zinc are shown

in Table 21.

Table 21. Zinc recovery.

Zn found, yg

Zn added, yg Zn alone Zn + SRM #80

50 49.8 49.4

100 sample lost 96.4

200 197.2 199.0

500 503.6 498.2

33
The 500-ppm glasses were analyzed for nickel homogeneity

using the above method. The glass rods which were 1/2 in. in

diameter were cut with a silicon carbide wheel into wafers

weighing about 0.7 to 1 g. The use of an entire wafer for

analysis provided results representative of the entire cross

section.

Samples were taken through the procedure in 6 different

sets with 3 to 7 separate determinations being made for each

sample position. No differences between different portions

of the rods were found greater than that found between sets,

thus indicating nickel homogeneity. A total average of 450

ppm of nickel was obtained with a standard deviation of 7 ppm.

This uncertainty is about 1.6$ of the amount present and is

well within the measurement error expected from a direct

cathode-ray polarographic measurement.

Preliminary results for zinc show a similar precision.

Work now in progress for the determination of iron and titanium

in the 500-ppm samples indicates an equally favorable

performance.

The methods described should also be applicable to the

remaining standards; however, preliminary work on iron and

titanium in the blank and 0.02-ppm glass has shown the precision to be much lower and that blank corrections are a

major problem.

6. Analysis of Air Pollutants

Among the increasing problems accompanying atmospheric

pollution studies has been the lack of reliable and sensitive

methods for determination of many of the particulate contaminants. Although the newer polarographic techniques now

available should be especially useful for these problems, they

do not seem to have been utilized significantly.

In order to check the applicability of polarographic

techniques to some of these problems, as well as to obtain

information on possible atmospheric contributions to blanks

34
encountered in trace analyses, a number of air particulate

samples were collected and analyzed polarographically . This

work was done in collaboration with R. A. Paulson, also of

the Microchemical Analysis Section.

An open-type metallic filter holder was used for all

samples except for several collected with a glass filter

holder ordinarily used for liquids. The latter was used to

eliminate the question of contamination from the metal filter

holder. Although the glass filter can be cleaned more rigorously, it is not convenient to assemble for air sampling.

It was necessary also to check the blank arising from the

filter materials used to collect the sample. A number of

types of filters were analyzed and were found to contain appreciable amounts of several elements particularly iron and

copper. By simply washing the filters prior to use, however,

the blank could be lowered considerably.

A number of samples were taken, both in the laboratory

and in two outdoor sampling locations using acid-washed, 47

mm, 0.8- membrane filters.

For the samples taken in the laboratory, the house vacuum

line was connected to the sampler and a 10 1/min limiting

orifice was placed in the outlet connector of the filter holder.

The sampler was placed about 2 feet above the laboratory bench

and the amount of air sampled varied from 28 to 80 cubic

meters. The samples were then ashed in a low temperature

asher, dissolved in hydrochloric acid and measured in an

oxalic acid-ammonium hydroxide supporting electrolyte. Iron,

copper, lead, and cadmium can all be measured concurrently.

Cadmium was not looked for in the first samples as it was

assumed that the amounts present would be too low to be detected without resorting to prolonged preconcentration and

anodic stripping. It was found, however, that a ten-second

pre-electrolysis time was sufficient to obtain a measurable

cadmium peak by the stripping technique. The results are

shown in Table 22.

35
Table 22. Analysis of particulates.

yg/m3

Fe Cu Pb Cd

0.22

.15

0.019

.036

0.35

.45

0.002

_a

Room.B309, avg

Room B325, avg

aNot determined.

For the outside sampling, a pump was used which provided

an average flow of about 25 1/min which was checked by attaching a rotometer flow meter to the filter holder. Flow measure-:

ments were taken at the beginning and end of a run and an

average value was used for calculations. The Station I sampling location is in a suburban residential section, Silver

Spring, Md., where all homes are heated with gas. The Station

II sampling location is in a heavily wooded country area in

Potomac, Md., approximately 5 miles from the nearest town and

on a dead end road. The heating in this area is by fuel oil,

gas, and electricity. The samples collected were ashed,

treated and measured polarographically in the same manner as

those just described. The results are shown in Table 23.

Table 23. Analysis of particulates.

yg/m3

Fe Cu Pb Cd

Station I, avg 1.17 0.040 0.75 0.002

Station II, avg 0.65 .006 .51 .0003

The results represent the average of about 12 determinations of samples collected during the period of November 1968

to February 1969. They are generally in keeping with those

obtained for similar sites in different localities showing

that polarography is very suitable for determination of certain metallic contaminants of the atmosphere.

(E. J. Maienthal)

36
3. COULOMETRIC ANALYSIS

A. Introduction

The coulometric analysis laboratory has been engaged in

several closely related activities. The major portion of the

research effort was devoted to a continuing study and development of precise and accurate methods for major constituent

analysis. In general, this effort is dovetailed with the

anticipated needs of the Standard Reference Material program.

The output of this phase of research (the resulting methods)

serves as the basis for evaluation and certification of chemical properties (stoichiometry , oxidizing power, hydrogen ion

content, chloride content, etc.) of a large number of SRMs

which are disseminated throughout the United States and abroad.

It is significant to stress that the evaluation of materials

by coulometric methods is conducted on the absolute basis.

Thus, the use of coulometry for assay purposes unifies the

measured properties through a common set of standards (volt,

ohm, gram and second) , directly traceable to the four fundamental units, which in turn form the basis of the International

System of Units (SI)

.

To meet the existing need for precise determination of

chromium in laser materials a significant effort was devoted

to the development of a micro method, which enables determination of total chromium in the material as well as the Cr /Cr

ratio.

As an outcome of NBS research it was possible to recalculate the atomic weight of potassium using a combining weight

ratio, which has not been previously used for this purpose.

On the basis of extensive research in the area of analytical chemistry of boric acid, described in a previous report

[1] it was possible to verify experimentally the validity of

the Roller equation, which predicts the difference between the

inflection point and the equivalence point of acid-base titrations .

37
Through the combined effort of this laboratory and the

Mass Spectrometry Section, the atomic weight of naturally

occurring boron was redetermined. Also, a number of SRMs and

other research materials were characterized coulometrically in

the course of the year.

Details of some of the more significant aspects of these

activities are given in the following sections.

B - Research Activities

!• Verification of the Roller Equation

It has been known for many years that as acids become

progressively weaker, the hydrolysis of their salts is more

pronounced and the inflection point of a potentiometric acidbase titration curve occurs prior to the stoichiometric equivalence point. The subject has been treated theoretically in

great detail in the early part of this century. However,

very little attention has been given to this potential source

of significant systematic error in practical analyses This

indifference to a source of error was not an oversight on the

part of eminent experimentalists but rather the error was insignificant for their purposes. Moreover, most of the work

in chemistry was done by comparative methods in which systematic sources of error are totally or to a large extent compensated, provided an accurately known appropriate standard is

used. This characteristic of comparative methods is in fact their forte. On the other hand, the necessity of "an accurately known appropriate" standard is perhaps their weak point.

In the case of absolute methods of analysis such as

coulometry, no compensation is encountered and as a result all

sources of systematic error (such as equivalence point error) must be evaluated and appropriate corrections need to be applied

To this end, it was necessary to establish experimentally the magnitude of this source of error.

According to Roller [11] the difference between the pH at the equivalence point (ep) and the pH at the inflection point

38
(ip) can be represented by the following equation

( PH)

ep

- ( PH) lp

= 0.65 A^iT

-14

where K is the ion-product constant for water (K = 10 at

w w

25 °C) , c is the concentration of the salt of the weak acid

at the equivalence point (moles/liter) and K is the dissociaa tion constant of the weak acid. It is apparent from this

equation that (pH) - (pH) . in an "unsymmetrical" titration

ep ip

of weak acid with strong base becomes larger as the concentration of salt at the equivalence point is decreased and as the

acid becomes weaker.

Converting the above equation to reflect the error in the

titer as a function of cK , Roller arrived at essentially the

a

following relationship:

A = -3xl0~ 12 (cK ) _1

a

where A is the percentage error in the titer due to the

[(pH) - (pH) . 1 difference. Several methods have been used ^ ep ^ ip

to study, experimentally 3 the dependence of the inflection

point * on cK . a

Valik, in collaboration with Maclnnes, conducted differential potentiometric titrations of the dibasic aspartic acid, in

-4 -1 which K = 1.5x10 and K = 2.5x10 . However, these ina

1

a

2

vestigators did not find any difference between the titer to

the first inflection point and that from the first to the

second inflection point . Maclnnes pointed out that the difference between the stoichiometric and potentiometric end

points increased as the acid or base became weaker, but the

difficulty of locating the end point also increased. He stated

that "it may be safely concluded that within the accuracy to

which the potentiometric end point of a titration can be

established, it is identical with the stoichiometric end point"

[12].

39
Bates and Wichers [13], in their precise intercomparison

of acids by differential potentiometric titration with a hydrogen electrode, were also concerned about the difference between the inflection point and the equivalence point. They

pointed out that a study of the course of titration curves

adjacent to and on both sides of the inflection point was made

by Bates and Canham. In every case, the inflection point determined experimentally appeared at a pH lower than the

equivalence point computed from the dissociation constant of

the acid and the ion-product constant for water. Moreover,

the differences were somewhat greater than the uncertainties

in the calculations and larger than those estimated by the

Roller equation.

In the course of a coulometric investigation of the boric

acid-mannitol system in our laboratory, pK of boric acid was

a

measured in media containing different amounts of mannitol.

The results of this study indicate that by merely varying the

concentration of mannitol one can have a whole spectrum of

acids, varying smoothly in pK . The continuum of acids thus

a

produced offers a unique possibility for the study of the relationship between the inflection point and the equivalence

point

a. Experimental . The measurements were conducted

using previously-described instrumentation and apparatus [14].

Since, in coulometric acidimetry, it is advantageous to employ

1M KC1 as the supporting electrolyte, all measurements reported here were made in aqueous 1M KC1 at 25 °C. No attempt

was made to control the temperature but on the basis of other

measurements in this laboratory, it is known that the temperature of the environment does not ordinarily differ from 25 °C

by more than a degree.

In the determination of pK of boric acid as a function

a

of mannitol concentration, two concentrations of boric acid

solutions were us.ed. They were prepared by weighing appropriate

40
amounts of borax (NBS pH standard, SRM #l87a) , addition of a

precalculated weight of mannitol to produce the desired final

concentration of mannitol, and dilution to volume with 1M KC1.

Nitrogen was passed through the solutions to remove COp , after

which the pH was measured.

Since this borax is very close to stoichiometric

NapBjjO «10H 0, or in the resulting solution [H

2

B0"]/[H BO.]

is close to 1, the value of the pH measured, was considered

to be equal to pK , where pK is the apparent dissociation

a a

constant of the boric acid.

A plot of the dependence of pK of boric acid in media

a containing different amounts of mannitol is shown in Figure

5. The effect of mannitol on the ionic equilibria of

i.o

u.O

<

.05

.03

.02

.01

.005

.003

.002\

I.I0"2 M _ POTASSIUM

- ACID - PHTHALATE

(PK 2 )

BORIC ACIDO 5xlO"3 M

• 3x I0" 2 M

PHOSPHATE BUFFER X

-O* 1 -£•—

I

9

pK

Figure 5. Effect of mannitol concentration on the

apparent ionization constant of boric

acid in 1M KC1 at 25 °C.

41
phthalate and phosphate buffers was also measured. These two

buffers were used in the role of controls and the appropriate

curves for them are also plotted on the same figure.

The values of pK (or pH) plotted on the abscissa axis

a were obtained by measurements of the same parameters in the

absence of mannitol and the horizontal arrows indicate the

apparent change of these parameters caused by the presence of

1M KC1.

A number of different sized samples of virtually stoichiometric boric acid were titrated coulometrically to a differential potentiometric inflection point in 1M KC1 containing

various amounts of mannitol. Figure 6 shows data for two such

titrations . Both the upper and the lower curves show titration

of approximately the same size sample of boric acid. The upper

titration (A) was carried out in 1M KC1 while the lower curve

(B) corresponds to a titration carried out in 1M KC1 and 0.25M

mannitol. The parameters calculated for the systems are shown

in the legend of the figure. The presentation of these titration curves is somewhat unconventional and for that reason it

merits some explanation, It is well known that a relatively

smooth potentiometric titration curve, when plotted as a first

derivative, may show a significantly large amount of scatter.

Accordingly, while the potentiometric curve itself may appear

to be very precisely reproduced under a given set of conditions,

the random scatter of points in the differential plot would impair precise determination of the inflection point. When the

acid is as strong as B, in the lower part of Figure 6, the pH

difference measured for a reaction increment is sufficiently

large that the uncertainty of the measurement itself does not

affect significantly the differential titration curve. On

the other hand, for boric acid titrated in noncomplexed form

in 1M KC1, shown in the upper part of Figure 6, the pH differences measured per microequivalent of hydrogen ion reduced

the amount to only a few hundredths of a pH unit and therefore

the random errors of measurement affect significantly the

42
differential plot. For this reason, the multiple retitration

method was used in order to identify more precisely, the pH

of the inflection point. After the sample is titrated beyond

the inflection point, a few hundredths of a ml of strong acid

such as hydrochloric acid are delivered into the titration

cell thus regenerating some of the boric acid, after which a differential potentiometric titration is carried out. The

composite curve resulting from 3 such repetitive titrations

is shown as A of Figure 6. It is seen that for titration A,

-13 where the cK value is 7.27*10 , the potentiometric infleca tion point occurs approximately 3% prior to the calculated

i -9 equivalence point, whereas for cK value of 2.4 •10 in B, it

a

is practically coincident with the equivalence point.

PH

9.U

9.0

8.6

8.2

7.8

7.4

7.0

0.050 0.031 0.052 0.8 0.9 1.0 II ApH/A/ieq FRACTION TITRATED

0.0 0.4 0.8 1.2 1.6 ApH/A>2.eq0.98 1.00 1.02 FRACTION TITRATED

Figure 6. End points of titrations of 0.06 meq samples

of H_B0_, at different apparent values of K .

B.

3 3

,-4,

A. C = 6.32 x 10 "M H

3

B0 33

K = 1.5 x 10~9

: cK = 7.27 x 10" 13

C = 6.02 x 10

_i4

M H

3

B0

3

; K = 3.98 x 10~6

; cK = 2.40 x 10"9

a ' a

43
The calculated values of the fraction titrated are based

on the assumption that assay of the same material in an electrolyte containing higher concentrations of mannitol and boric

acid ig accurate. The validity of this assumption is substantiated by titration of a number of large samples in three

relatively high concentrations of mannitol. These data are

summarized in Figure 7.

<

100.01

100.00 -

99.99

COMPOSITION OF SUPPORTING ELECTROLYTE

O IMKCI-0.25M MANNITOL

9 IMKCI-0.75M MANNITOL • IM KCI - I.05M MANNITOL

1 I 0.2 0.4 0.6 OS 10

CONCENTRATION OF H^Oj, mole • I

1.2 1.4

Figure 7. Assay of boric acid as a function of the

composition of electrolyte and the

concentration of boric acid.

b . Results and discussion . On the basis of data

shown in Figure 7, it is evident that in the mannitol concen-

_2 tration range from 2x10 to IM, pK of boric acid is a linear

a

function of the log C , where C designates the molar concen- ° m

' m ° tration of mannitol. In this range

dpK

dpC

= 2.

m

44
Since neither the phthalate nor phosphate hydrolytic

equilibria are affected by the concentrations of mannitol used

in this investigation, as evidenced by the constancy of pH of

these two buffers on such addition, it seems reasonable to

conclude that the changes in pK of boric acid result from the

a

mannitol-borate interaction (complexation) . The elucidation

of the hydrolytic equilibria in this system is under investigation in our laboratories and will be described elsewhere.

The data obtained in titrations of boric acid for several

values of cK are summarized in Figure 8. In the figure,

a

experimental points for the error in the assay of boric acid

titrated in different media are plotted against the appropriate

_q

cK . For cK = 2.5x10 , the point on the graph represents

a a

an average value since some of the individual titration

results were greater than 100$ and the error function for

these results could not be represented on the log graph. The

experimental value of the error of this point is 0.002 ± 0.010

absolute percent, where the uncertainty represents the standard

deviation of the mean based on 6 degrees of freedom. The

solid line represents the titration error predicted by the

Roller equation. It can be seen that the errors encountered

due to the difference between the inflection point and the

equivalence point, determined in these titrations, are in

excellent agreement with the errors predicted by the Roller

equation over 5 orders of magnitude of the cK values

.

a

The use of mannitoboric acid in media of different

mannitol concentrations has provided the first test of the

Roller equation under conditions where both parameters, c and

K , can be varied for a single acid of known stoichiometry

.

Moreover, the applicability of the Roller equation to hydrolytic

equilibria involving a complex acid in a medium which is not

simply water has been verified, a fact which was not known

until the present investigation.

45
= I I I M ll l

| 1 I I lllll| 1 ! I lllllj I I I 1 1 1 1 1| I I I III".

10 ml i i i mill i i i mill i i I i\ I Hill,

10 10 10 cK„ Figure 8. Error encountered in coulometric titrations of

mannitoboric acid at different cK values due

a

to the difference between potentiometric inflection point and the equivalence point.

Titrations conducted in:

1M KC1 (K = 1.2 x 10~9

) a

8 1M KCl + 0.0 47M mannitol (K = 2.4 x 10" 7

)

• 1M KCl + 0.25M mannitol (K = 4.0 x 10"6

) Solid line represents the error calculated by

Roller equation.

The study of pK of boric acid in media of different

a

mannitol concentrations opens up an interesting possibility

of producing variable pH buffers. In examining Figure 8 one

can see that the pH of a borax buffer can be changed 5 pH

units (from 9 to 4) by varying the mannitol concentration from

to 1M. In the lower mannitol concentration region it would

be difficult to accurately prepare buffers because the pH is

a log function of mannitol concentration. However, at the two

46
extremes (0 concentration of raannitol and in the 0.15-1.0M

mannitol range) the pH of a buffer can be adjusted with a high

degree of precision. The pH of such buffers of a given borax

concentration will be a function of mannitol concentration and

can be changed by varying the buffer but they would have the

same buffer capacity.

2 . Recalculation of the Atomic Weight of Potassium

Absolute analytical methods (such as coulometry or absolute

gravimetry) may now be carried out with precision comparable and

sometimes better (0.001%) than the uncertainty in the atomic

weights j so that accurate knowledge of the latter is a prime

requisite

.

For many years chemical methods for determination of

combining weight ratios have been used with reasonable success

for the evaluation of atomic weights. Recently, there has

been a tendency to determine atomic weights through the use

of mass spectrometric measurements of the isotopic abundances

and values of nuclidic masses [15]. Denying the mass spectrometric metheds no due credit, it should be kept in mind that

reliable values of atomic weights can still be obtained by

other methods, including accurate analytical methods. It is,

therefore, surprising that when one examines the 19 6l report

of the International Commission on Atomic Weights [16], one

discovers that the atomic weight of potassium was apparently

based on a single set of measurements of the abundance of

5QJV 40 4l K, K, and K isotopes by Nier [17] and the values of the

nuclidic masses from the table of Everling, Konig, Mattauch,

and Wapstra [18]. (No changes in the atomic weight of K have

been made since that time.) The atomic weight value for

potassium thus arrived at is 39.102 which is significantly

different from 39.098, the value obtained by converting the

1959 chemical atomic weight value (.0 = 16) 39.100 to the 12

C

unified atomic weight scale.

47
Nier's measurements were made on the relative basis since

the mass spectrometer was not calibrated on the "absolute"

basis with isotope mixtures prepared from the separated isotopes «of the element in question. Instead, the mass spectrometer was calibrated with argon. Since argon and potassium

have significantly different physical properties it appears

that the accuracy of such measurements is contingent on the

proof that volatilization of potassium does not alter the

isotopic ratios. Such proof was not offered. Nier's

41 40 39 measurements show the abundances of K, K, and K to be

6.91 ± 0.04, 0.0119 ± 0.0001 and 93.08 ± 0.04 percent,

respectively. The combined uncertainties of the isotopic

abundances represent an overall uncertainty of 0.002 AMU in the

atomic weight of potassium.

Data obtained in earlier work at the National Bureau of

Standards in differential potentiometric titrations of acids

by Bates and Wichers [13] may be used for the evaluation of

the atomic weight of potassium. Their comparison of the

single crystal benzoic acid and potassium hydrogen phthalate

to the same lot of Na-CO,. produced the following ratios

C

7 H.0 9

N^

°C q

= 2.304075 ± 0.00051

CnHO.K

N

° l = 3.853045 ± 0.000031

where the uncertainties represent standard deviations . Using

these values, one can readily arrive at the ratio of potassium

acid phthalate to benzoic acid

° u°

= 1.672274 ± 0.000050

C

7

H6°2

The atomic weight of potassium, then, may be expressed in

terms of the atomic weights of C , H and as follows:

4b
K = 3.7059l8[C]+5.033644[H]-0.655452[O]

where symbols in the brackets represent atomic weights of the

indicated elements. Using 12.01115, 1.00797, and 15.9994, for

the atomic weights of C, H, and 0, respectively, one arrives

at 39.099 (± 0.001) as the value for the atomic weight of

potassium.

It can be seen that this value is in much closer agreement

with 39.098, the atomic weight of potassium adopted in 1959

12 (normalized to C scale), than with the presently accepted

value. Since the discrepancy between the presently accepted

value and those obtained by other techniques can not be reconciled with the uncertainties ascribed to each, it is hoped

that more work will be stimulated to verify the accuracy of

the atomic weight of potassium by other independent means

.

3 . Coulometric Determination of Microgram Amounts of

Chromium

Research programs elsewhere at NBS required data on the

total amount of chromium in ruby laser material. The concentration of chromium in ruby is approximately at the 0.03%

level. The material available for analysis is often in limited

amount. In the present instance, a 30-mg sample appeared to

be the maximum amount available for analysis. Thus it was

necessary to develop a precise and accurate method for determination of 10 ug of Cr with precision and accuracy of a

few tenths of a relative percent. In other words it became

necessary to develop a method which would enable the determination of 300 ppm of Cr within a few ppm.

A further objective was to develop a method sensitive

enough to establish the Cr /Cr ratio. Such a determination

is based on the determination of hexavalent chromium originally

present in the sample, followed by an oxidation procedure and

the determination of total chromium. Small differences

encountered in such indirect analyses require precise analytical

methods at the submicrogram level.

49
Earlier studies [19] showed that coulometric generation

of ferrous ion at the Pt-cathode can be achieved with one

hundred percent current efficiency from an electrolyte two

tenths molar or more with respect to ferric ion in two molar

sulfuric acid, provided the current density never exceeded

four milliamps per square centimeter. The end point in this

investigation was determined amperometrically using a polarized

Pt-indicator anode and a saturated calomel electrode as the

nonpolarizable reference cathode.

A special coulometric titration cell assembly was designed

for this determination and is shown in Figure 9. The cell

consists of three separate compartments each with a maximum

volume of 10 cm , separated horizontally by intermediate

compartments, in which two fine porosity sintered glass frits

are sealed. The two intermediate compartments have stopcocks

Figure 9. Coulometric determination of chromium at

nanogram levels.

50
sealed to the top to allow application of suction or pressure

to fill or empty the compartments . The cathode compartment

has two 1-cm2 platinum electrodes sealed in each side of the

compartment. The two electrodes serve as the generator cathode

and the indicator electrode. Such a cell construction has

several advantages: 1) increases the sensitivity of the detection system, 2) eliminates losses of sample into liquid

junction by diffusion, 3) minimizes IR drop across the indicator circuit, and 4) allows indicator currents to be measured

concurrently with generation.

The separation of the titration cell compartment (cathode)

from the reference electrode and the auxiliary anode with

small intermediate compartments is essential to eliminate

loss of sample into the liquid junction by diffusion. The

small amount of sample which diffuses into the two intermediate

compartments can be returned to the titration cell by applying

nitrogen pressure or vacuum as needed through the stopcocks

that are sealed to the top. The auxiliary Pt anode and the

SCE reference electrode are further separated from the titration cell with porous vycor rods. This separation minimizes

the interference effects which one would encounter if the

species formed at the auxiliary anode or the KC1 at the SCE

electrode were able to diffuse into the small intermediate

compartments and later forced into the titration cell. The

technique was evaluated with standard hexavalent chromium

solutions prepared from SRM #136b Potassium Dichromate. The

preparation sample was weighed to the nearest 0.003 mg in a platinum boat using the substitution method.

When required, the persulfate oxidation process was used

to oxidize chromium to the hexavalent state. The weights of all

solutions were determined by the substitution method.

Two procedures were used to obtain a satisfactory end

point. The first technique, applicable to sample sizes of 1

microgram or more is as follows

.

51
A small amount of chromium(VI) is added to the supporting

electrolyte in the cell containing 0.5M ferric ion in 2M

sulfuric acid. This amount is required in order to oxidize

any reducing impurities in the electrolyte and to establish

a pretitration curve. Along the linear portion (poised with

ferrous ion) of the amperometric curve, the diffusion current

is extrapolated to zero current to determine the excess ferrous

ion which is formed in pretitration.

Subsequently about 95% of the precalculated amount of

ferrous ion is generated, and the weighed hexavalent chromium

solution is delivered into the cell. The remaining portion

of hexavalent chromium is used to establish a titration curve

which has a slope identical to the pretitration curve. The

sensitivity (slope) for both curves is about 40 uamp/yeq Pe

It is apparent that in view of comparable slopes, reliable

zero current intercepts for the pretitration and the titration

curves can be established to make possible precise and accurate

titrations. This procedure of extrapolation to a fixed current

value (zero) is essential for samples in the microgram range

because the uncertainty in establishing the residual current

(0.01 ueq Cr) approaches the working sample size (0.05 ueq or

1 yg Cr) . An investigation of the Cr(vT) -Pe(II) amperometric

titration curve shows that this uncertainty is primarily due

to the reaction rate of the system and to the instability of

the indicator currents in the region of the equivalence point.

The second technique (direct reading amperometry) employs

a measurement of the change in indicator current along the

coulometrically calibrated amperometric curve after the addition of the unknown Cr sample. It is used for determining

from 200 ng down to 10 ng of chromium. The pretitration is

conducted until the indicator current becomes a linear function

of [Pe ]. Subsequently the indicator current is displaced

down scale and then expanded to the maximum sensitivity of the

polarograph. Then in this sensitive region the amperometric

52
curve is calibrated by coulometric generation of small amounts

of ferrous ion. The weighed sample is delivered to the titration cell and the indicator current decrease is observed after

the reaction is completed. The linear change in iron(II) concentration is evaluated graphically along a normalized indicator current and its intercept is taken as the end point.

Sample solutions (prepared from SRM #136b Potassium

Dichromate) ranging in size from approximately 15 nanograms to

30 micrograms of chromium were titrated by the above-described

method and the results were studied for precision and accuracy.

A summary of the results is shown in Table 24. The average

assay value and the standard deviation are given for each

sample size. Within the experimental uncertainty, the assay

value for any sample size is in good agreement with the certified oxidizing power (9.9.977 percent). The accuracy of the

results for any sample size set is determined by the random

errors of measurement. Examination of data shows that this

random uncertainty represents virtually a constant amount of

chromium, independent of sample size. This error is really

the random error of the titration system (i.e., end point

sensitivity, volume of electrolyte, stirring rate, etc.).

Further improvement is anticipated by appropriate changes

of these parameters.

4. Determination of Cr /Cr _ Ratio

Future characterization of laser materials will require

an accurate knowledge of Cr /Cr ratio. To this end an investigation of the feasibility of determination of Cr /Cr

ratio was conducted at the microgram sample size level.

Three standard solutions containing known amounts of Cr

+3 and Cr at approximate ratios of 9:1, 1:1, and 1:9 were prepared from K

? Cr„07

, SRM #136b , the same material as used in

the previous section.

Aliquots of these solutions were titrated directly to determine the concentration of Cr . Subsequently a procedure

53
was developed for aliquoting the samples, conducting micro-

+ 3 +6

scale oxidations of Cr to Cr with persulfate and delivering

the resulting oxidized samples into the titration cell without

any significant loss.

Table 24. Analysis of K„Cr

2 solution, SRM #136b,

assay percent 99.977-

Sample No. yeq calc yeq found % assay

1. Sample size approximately 30 yg of Cr

1 1.1447 1.1443 99.97

2 1.3678 1.3671 99.95

3 1.4252 1.4245 99.95

4 1.7361 1.7351 99.94

Average 99.95

s = 0.02

II. Sample size approximately 2 yg of Cr

1 0.13005 0.12940 99.50

2 .11219 .1117 99.56

3 .11216 .1119 99.77

4 .11997 .1204 100.36

5 .11095 .11070 99.77

6 .1255 .1253 99.84

Average 99.80

s = 0.3

1

III. Sample size approximately 150 ng of Cr

1 0.00949 0.00950 100.1

2 .00944 .00952 100.9

3 .00940 .0092 97.9

4 .00692 .0070 101.2

Average 100.0

s = 1.5

IV. Sample size approximately 15 ng of Cr

1 0.00089 0.00095 107

2 .00094 .00087 93

3 .00120 .00110 93

4 .00072 .00076 105

Average 99

s = 7

54
Additional aliquots of the above three solutions were

analyzed by this new technique. The results of analysis of

the above three solutions for Cr and total chromium are shown

in Table 25.

Table 25. Analysis of synthetic solutions with 9:1, 1:1,

and 1:9 ratios of chromium(III) and chromium(VI)

.

Solution 1. [9:1 ratio of Cr(III) and Cr(VI)]

Sample No. yeq Cr(VI) calc yeq Cr(VI) found % Recovery

1 0.1109 0.1108 99.9

2 .1255 .1253 99.8

3 .1200 .1204 100.3

4 .1122 .1119 99.7

5 .1122 .1117 99.6

Average 99.9

s = 0.3

yeq yeq

Sample Cr(VI) Cr(III) yeq Cr yeq %

No. calc calc found Cr(III) Recovery

1 0.1292 1.1262 1.2550 1.1258 99.97

2 .1195 1.0408 1.1598 1.0403 99.96

3 .1233 1.0736 1.1968 1.0735 99.99

4 *.l466 1.2763 1.4223 1.2757 99.96

Average 0.1297 1.1292 I.2585 1.1288 99.97

s = 0.02

Average ratio jwvi)^ = 8 - 7 ° 62

calc

Cr(III) R

Cr(Vl) . _ " 8 ' 7032

found

Solution 2. [1:1 ratio of Cr(III) and Cr(VI)]

Sample No. yeq Cr(vT) calc yeq Cr(VI) found % Recovery

1 1.0830 1.0826 99.96

2 1.0497 1.0496 99.99

3 1.1203 1.1198 99.96

4 1.0400 1.0397 99.97

Average 99.9 7

s = 0.02

55
Table 25. (Continued)

Solution 2. (Continued)

yeq yeq

Sample Cr(VI) Cr(III) yeq Cr yeq %

No. * calc calc found Cr(III) Recovery

1 1.1231 1.1440 2.2664 1.1433 99-97

2 0.6626 0.6751 1.3376 0.6750 99.99

3 .8792 .8957 1.7743 .8951 99-96

4 1.0906 1.1110 2.2010 1.1104 99.97

Average 0.9389 0.9565 1.8949 0.9560 99-97

s = 0.02

. , . Cr(III) -, nn or. Average ratio ~

(yt)— = 1- 01 °< r calc

Cr(III) _ , 0l82

Cr(VI) - - " 1 - 01BZ

v ' found

Solution 3. [1:9 ratio Cr(III) and Cr(VI)]

Sample No. yeq Cr(VI) calc yeq Cr(VI) found % Recovery

1 1.3432 1.3430 99.98

2 1.5442 1.5436 99.96

3 1.2692 1.2690 99.98

4 1.6833 1.6827 99.96

Average 99.97

s = 0.02

yeq yeq

Sample Cr(VI) Cr(III) yeq Cr yeq %

No. calc calc found Cr(III) Recovery

1 1.2339 0.1336 1.3671 0.1332 99.97

2 1.2857 .1392 1.4245 .1388 99.97

3 1.5661 .1696 1.7350 .1689 99.95

4 1.6832 .1823 1.8653 .1821 99.99

Average 1.4422 0.1562 1.5980 0.1558 99-97

s = 0.02

Average ratio jwyj)^ = 0.10 83

calc

Cr(III) _ n inft1

Cr(Vl) . . " °- 1081

found

56
It is evident that the precision of titrations of these

solutions is comparable to the precision of pure dichromate

samples of corresponding size. Thus it is possible to determine Cr /Cr ratio by an indirect method based on the determination of Cr followed by oxidation with persulfate and

subsequent determination of total chromium as Cr . The amount

of Cr can then be calculated as the difference between the

latter and the former titrations.

5 . Coulometric Method for Determination of Oxygen in

Elemental Boron

In conjunction with other research activities of the

National Bureau of Standards, two samples of elemental boron,

one sintered in a furnace in the presence of oxygen and the

other unsintered powder, were submitted for oxygen determination

It occurred to us that B

? 0_ could be easily converted to boric

acid and titrated coulometrically in the presence of mannitol

as already described [lj. Each mole of titrated H„BO_ would

correspond to 0.75 moles of oxygen in the original oxide.

The submitted samples were analyzed by vacuum fusion as

well as coulometrically. In the coulometric method, samples

were crushed in a steel mortar and delivered into the solution

containing mannitol (1M KC1-0.75M mannitol). The results of

analysis for the two materials are summarized in Table 26.

It is interesting to note that the results obtained by

titration are about a factor of 2-H lower than those obtained

by vacuum fusion.

Several possibilities exist for this apparent discrepancy.

In view of the precision of the measurements one has to rule

out the possibility of random errors . One must therefore consider possible differences in the two distinctly different

measurements

.

Vacuum fusion measures the oxygen in the total volume of

sample. On the other hand, in the coulometric procedure,

though the sample is very finely crushed (i.e., large surface

57
to volume ratio) there still exists a considerable amount of

the sample which is not exposed to the solution. Thus a possibility exists that one measures only the surface oxide

by titration. One would however expect that significant

leaching of B

? 0_ from the interior would occur and thus the

precision of measurement would be greatly affected by the

leaching time. This was not indicated by the coulometric

measurements

It is also clear that oxygen in boron in any other form

than BO. (such as iterstitial oxygen, adsorbed, combined with

other elements as oxide) would not be detected coulometrically

yet would be found in the vacuum fusion determination.

Further work is in progress to elucidate the causes of this

difference since they can, perhaps, be utilized to an advantage

of discrimination between oxygen in the form of B 0_ and other

possible forms

Table 26. Determination of oxygen in boron.

Coulometrically

determined

Material oxygen, wt %

a Vacuum fusion

Unprocessed boron

Sample 1 0.005

2 .003

3

Average

.002

0.004 0.01g#

s = .002

Sintered boron

Sample 1 0.306

.281

Average

.292

0.298 0.4 %

s = .020

Vacuum fusion analyses were performed by J. T. Sterlini

Analytical Coordination Chemistry Section.

58
C . Analysis of Standard Reference Materials

In the course of the past year a number of standard

reference materials were analyzed for the purpose of selection,

acceptance, and certification. The highlights of this work

are presented in the following sections

.

1. Analysis of Separated Boron Isotopes

The method described in a previous report [1] was successfully used for standardization of separated boron isotope

solutions which were subsequently used by the Analytical Mass

Spectrometry Section to prepare known B /B ratio blends for

calibration of mass spectrometer bias. On the basis of this

work, the atomic weight of the reference boric acid sample was

calculated (SRM #951, at. wt . 10.811756 ± 0.000053). The

same work led to the certification of isotopic composition of

SRM #952 Boric Acid. The atomic weight of this material is

10.063267 ±0.000029.

2

.

Analysis of Potassium Dichromate

A new lot of potassium dichromate was selected on the

basis of coulometric titration of hexavalent chromium with

electrogenerated ferrous ion. The material will be reissued

as SRM K„Cr

2 7 oxidimetric standard.

The method employed for the evaluation of this material

was developed a few years ago in this laboratory [19]. The

results of analysis of triplicate samples from three randomly

selected bottles are shown in Table 27.

Table 27. Re suits of smaly sis of K

2

Cr

p 7

, Lot 3608.

Sample

No.

Assay, %

(3608-1)

99.973

Assay, %

(3608-12)

99.975

Assay, %

(3608-26)

1 99.980

2 99.976 99.975 99.977

3 99.980 99.981 99.978

Avera ge

s = 99.977

0.003

59
3 . Calcium Carbonate

The most expedient evaluation of SRM #915, CaCO appeared

to be via acidimetric reaction. An excess of coulometrically

standardized HC1 was added to a preweighed sample of CaCO...

The resulting solution was permitted to sit until reaction was

complete. Subsequently the contents of the reaction flask were

quantitatively transferred into a coulometric cell and the excess acid was back-titrated. The results of analysis of the

material "as received" are shown in Table 28.

Table 28. Results of analysis of calcium carbonate.

Sample

No. Assay, %

1 100.000

2 99.993

3 99 .984

99.992

The purpose of the second stage of investigation was to

determine the effect of the environment on the assay of CaCO...

Can CaCO.-., when exposed to high humidities, be returned to

the original state by some physical treatment?

One portion of the material was exposed to 90$ relative

humidity for one week, then placed in a drying oven at 210 °C

for 6 hrs , followed by storage in a desiccator over Pp^s u^il

weighing and coulometrically analyzed after each step. A

second portion was placed in a 75% RH environment for one week

(with occasional stirring of the crystals). A third portion

was placed in a 90% RH environment for one week. In each case,

five hundred-milligram samples were weighed out, reacted with

excess coulometrically standardized HC1, and the excess of HC1

was back-titrated coulometrically. The results are summarized

in Table 29.

60
Table 29. Effect of environment on the assay of CaCO

Sample

3'

No. Treatment

90$ humidity;

Assay

1 99.993

2 210 °C for 6 hrs 100.000

3 P o r desiccat or

Average

99.996

99.996

4 75$ RH 99.986

5 75$ RH 99.992

6 75$ RH

Average

99.990

99.989

7 90$ RH 99.979

8 90$ RH 99.981

Average 99.980

The value reported for the material "as received" was

99.992$. Since the humidity in the laboratory was about 30$,

this value of humidity can be assigned to the assay on an "as

received" basis.

It is apparent that the material is only slightly susceptible to moisture (0.02$ at 90$ RH ; perhaps via physical

adsorption) and can be returned to the virtually stoichiometric

state by placing it in a drying oven.

4. Analysis of Gold-Silver Alloys

In the course of issuance of SRM gold-silver alloys for

microprobe standards, it became necessary to have an accurate

evaluation of the compositions of these alloys. Coulometry

was called upon to do the determination of silver. However,

it was found that alloys containing more than 40 percent gold

gave difficulties due to problems of solution and required

gravimetric determination. The results of both procedures

are summarized in the following.

61
Preliminary studies have shown that an 80% Ag alloy can

be parted by successively higher concentrations of nitric acid

(starting with 1:4 = HNO

:H

2 ° and finishing with essentially

concentrated nitric). Similar parting of 60% Ag was not complete as evidenced by the formation of AgCl precipitate when

the residual gold is dissolved in aqua regia. Alloys containing higher concentrations of gold (40% Ag-60% Au and 20% Ag80% Au) could not be parted in nitric acid, nor could they be

dissolved in aqua regia, because of encapsulation in the AgCl

precipitate. Since the object of these determinations was Ag,

the inquartation method was obviously discarded because it

would require addition of several times the amount of the

element in question. Au-Ag alloys containing less than 10%

Ag can be easily dissolved in aqua regia.

The unfortunate situation is that the aqua regia dissolution product (AgCl) is not easily applicable to coulometric

analysis

Thus, the 80% Ag alloy was parted in nitric acid, a small

excess of coulometrically standardized NaCl solution was added

and the excess NaCl was back-titrated coulometrically with

electrogenerated Ag . The two results obtained by this method

are represented by samples Nos . 1 and 2 in Table 30 under Alloy

1707. The same alloy was also analyzed gravimetrically by

parting it in nitric as above, then adding HC1 to form aqua

regia (thus dissolution of gold and precipitation of AgCl takes

place), filtering and weighing AgCl. The results of this

determination are shown as sample Nos. 3 and 4 under the same

alloy. It is clear that the agreement of the two results is

unbiased. The fifth sample was analyzed by first alloying

the weighed sample with a sufficient amount of high purity gold

to make it an approximately 10 Ag-90 Au alloy, dissolution of

this alloy in aqua regia and gravimetric determination of AgCl.

This was necessary to establish the accuracy of analysis when

fusion of alloy with more gold is performed. Since result

62
No. 5 is concordant with the other four, the third method is

demonstrated to be bias free. Accordingly, all results can

be combined into one set and the data treated as homogeneous

Table 30. Results of analysis of Ag-Au alloys.

Sample No. Ag, wt %

Alloy 1707 1 77.583

2 77.52

2

3 77.52

?

4 77.58 1

5

Average

77.58

4

77.55

9

s = 0.03

2

Alloy 1706 1 59.95 2

2

Average

59.96

Q

59.95 6

• s = o.oo

6

Alloy 1705 1 39.98

3

2

Average

39.98

8

39. 98

5

s = 0.00,-

Alloy 1704 1 19.90

3

2

Average

19.9« 8

19.92

6

s = 0.02,

The other three alloys (60, 40 and 20$ Ag) were additionally alloyed with high purity gold to reduce Ag concentration

below 10$, dissolved in aqua regia and the resulting AgCl was

63
determined gravimetrically . The above coulometrically analyzed

80% Ag Alloy, appropriately alloyed with Au was used as the

control. Thus, the analysis of the three higher Au alloys are

direct»ly compared to the coulometric assay. The results of

analysis are summarized in Table 31.

Table 31. Mass balance for Au-Ag alloys.

20 Au-80 Ag

Ag determined in this lab 77 . 56%

Au (mean of 3 labs) 22.43

Total 99.99%

40 Au-60 Ag

Ag determined in this lab 59.96%

Au (mean of 3 labs) 40.03%

Total 99.99%

60 Au-40 Ag

Ag determined in this lab 39.98%

Au (mean of 3 labs) 60.05%

Total 100.03%

80 Au-20 Ag

\g determined in this lab 19.93%

Au (mean of 3 labs) 80.05%

Total 99.98%

5 . Analysis of Potassium Chloride

A preliminary screening of various lots of KC1 to permit

the selection of the most suitable material for issuance as a

SRM was accomplished by coulometric assay. The material will

be issued as a halide composition standard as well as a standard

for preparation of solutions for conductivity measurements

Analyses of halides are now conducted in our laboratory

by titration with electrogenerated mercurous ion. This appears

64
to be preferable to argentimetry in the precipitation of chloride since the solubility product of the former is about 8

orders of magnitude lower than that of AgCl. Thus the precipitation reaction is more complete.

The preliminary analysis of two composites from the selected lot under varying pretreatment conditions are shown in

Table 32. The results show that a drying procedure is necessary to obtain material of satisfactory assay. Drying at 130 °C

removes most of the water but the higher temperature of 200 °C

is required to remove water presumed to be in interstices of

the polycrystalline material.

Table 32. Results of analysis of SRM KC1.

Sample set % Assay Average Remarks

Comp Dsite 1-6

I 1 99.915

2 99.901 99.908

II 1 99.980

2 99.981 99.980

5

III 1 99.997

2 99.996 99.996

5

Composite 7-12

IV 1 99.912 99.912

V 1 99.982

2 99.975 99.978

5

VI 1 99.994

8

2

99.995-l 99.995

6. Analysis of Sodium Chloride

As received

Crushed and dried

at 130 °C for 18

hrs

.

Crushed and dried

at 200 °C for 18

hrs

.

As received

Crushed and dried

at 130 °C for 18

hrs . Crushed and dri.ed

at 200 °C for 18

hrs

.

Selection of a desirable lot of NaCl to be issued as a SRM presented similar problems as noted in the case of potassium

chloride

.

65
Two lots of sodium chloride (one fine and one coarse)

were analyzed for their chloride ion content by titration with

coulometrically generated mercury(I) . The end point was determined potentiometrically with a mercury-mercurous chloride

indicating electrode and a glass reference electrode. All

samples were weighed by the substitution method and their

masses were corrected for the effects of air buoyancy.

Both lots were analyzed on the "as received" basis and

after drying at 130 °C for 18 hrs . Analyses were also carried

out on samples from the coarse lot which were ground in an

agate mortar and then oven dried at 200 °C for 18 hrs. The

results of analysis are summarized in Table 33.

Table 33. Results of analysis of SRM NaCl.

Sample set % Assay Average Remarks

Fine material

I 1 99.957 99.957 As received

II 1 99.998 v Dried at 130

for 18 hrs. 7

2 100.004

1

3 99.998

5

100. 000^

Coarse material

III 1 99.929 As received

2 99.919 99.924

IV 1 99.942 Dried at 130 °C

2 99.933 99.938

for l8 hrs -

V 1 99.996^ Crushed and dried

2 99.998

Q 99.997, £a f

00 ° C for l8

It is apparent from sample sets I and III that both lots

of "as received" material have a significant amount of moisture

The results for sample set II indicate that drying at 130 °C

for 18 hrs is sufficient to remove all the moisture from the

66
fine lot of NaCl. The results for sample set IV show that

the above treatment is not effective in removing all the moisture from coarse NaCl. For example, a comparison of the assay

values for sample sets III and IV shows only about 0.01$ loss

in moisture. However, when this sample is crushed and dried

(130 °C for 18 hrs) the assay value indicates that the material

is virtually stoichiometric.

Both lots of NaCl appear to be of high purity; but the

fine lot can be made stoichiometric somewhat easier than the

coarse because it requires no crushing. However, it is evident

that both of these materials would require a specification for

drying if they are to meet the requirements for primary standard

reference materials

.

7. Stainless Steel Analysis

The coulometric determination of chromium in stainless

steel is very advantageous since the method does not require

the additional load of carrying control samples or preparation

of standard solutions.

Six bottles of SRM stainless steel samples were received

for chromium determination: SRM #l60b - 2, SRM #l60b - 12, SRM

#l60b - 15A, SRM #l60b - 25, SRM #l60b - 28, and SRM #1155.

The samples were weighed, dissolved and oxidized using

the same procedure as described earlier for the analysis of

chromium in SRM stainless steels #10 IP and #101G. The

chromium(VI) was titrated coulometrically with electrogenerated

iron (II) . The results of analysis for 500 mg samples are

summarized in Table 34. No correction was made for vanadium

which was also titrated as chromium. Therefore, in the final

calculations, a correction factor corresponding to %V x 0.3^

must be subtracted from the weight percent obtained for

chromium, based on an independent vanadium determination.

The uncertainty for the analytical process is on the order

of 0.03$.

67
Table 34. Analysis of SRM stainless steel for chromium.

Preparation No.

1

2

1

2

1

2

1

2

3

Bottle No. Wt % , Crd

160b - 2 18.430

160b - 2 18.463

160b - 12 18.486

160b - 12 18.430

160b - 15A 18.473

160b - 1-5 A 18.442

160b - 25 l8.484b

l8.504b

160b - 25

Average

18.504

18.461

s 0.028

1155 18.492

1155 18.460

1155

Average

18.442

18.465

s 0.026

,Uncorrected for vanadium

Results for same preparation

8. Potassium Dihydrogen Citrate

Assays of several lots of potassium dihydrogen citrate

have been made in studies of feasibility as a pH standard.

The laboratory scale purification of this material, done at

NBS , was very gratifying. The resulting material, analyzed

coulometrically , appeared to be virtually stoichiometric.

Coulometric acidimetric evaluation of commercial preparations to serve the same purpose have thus far been discouraging.

Two commercial preparations of KH~ citrate appear to be highly

nonstoichiometric. The results of analysis of these two lots

of commercial material are shown in Table 35.

68
Table 35. Analysis of KH" 2

citrate.

Sample No. Titration No. Assay, %

7124 1 100.141

2 100.135

Average 100.138

7125 1 100.358

2 100.364

Average 100.361

It appears that these preparations are contaminated with

some acid of lower equivalent weight than potassium dihydrogen

citrate. Further investigation of possible SRM candidates is

in progress

.

D. Analysis of Research Materials

In addition to conducting research and analyzing standard

reference materials, the coulometry laboratory analyzes at

special request various research materials related to other

NBS programs which require accurate assay (0.01% or better).

A few typical examples which illustrate the nature of this

phase of our work are cited.

The titration method described in section 3.B.4. has been

successfully used to determine chromium in ruby laser. The

results of analysis are summarized in Table 36. The weight

percent, calculated as CrpO_ is 0.0346. The standard deviation of the mean, 0.0001 wt % 3 is somewhat larger than the

precision of the method tested with solutions of pure dichromate. Analytical manipulations including dissolution of the

material in a pressure bomb, subsequent handling, dilution

to volume, aliquoting and oxidation all contribute to the

overall error. It is therefore not surprising that the precision of the results with real samples is about a factor of

three lower.

69
Table 36. Determination of chromium in ruby laser.

Sample size - 30 milligrams

Sample No. 2 3

1 0.0348

2 .0344

3 .0345

4 .0348

Average 0.0345

The laboratory continues to study HC1-HF mixtures, resulting from calorimetric experiments, involving combination

of halogenated hydrocarbons. The analyses entail determination of hydrogen ion concentration and chloride concentration.

Acidimetric analyses of DC1 solutions which are needed in conjunction with the establishment of pD scale have also been

continued.

Research in the area of conductance standards requires

accurate analysis of potassium chloride solutions . A sample

set of results in this area is illustrated by the following.

Two KC1 solutions (labelled #9 and #10) were aliquoted by

weight, corrected to true mass and the Cl~ in each aliquot

was titrated with electrogenerated Hg(I) . The end point of

titrations was determined potentiometrically . These analyses

are summarized in Table 37. On the basis of these analyses,

the #9/#10 ratio is 1.0004l

Q

. Table 37. Analysis of KC1 solutions for

conductance measurements.

Sol'n No. Mas s of sample, g meq X~ found meq/g

9 a

9 b

9 c

12.10168

10.08243

20.14008

1.205019

1.003805

2.005180

Average

0.0995745

.0995598

.0995617

0.0995654

10 a

10 b

10 c

10.56794

8.71284

11.58117

1.051805

0.867100

1.152630

Average

0.0995-279

.0995198

.0995260

0.0995246

The standard deviation of each mean (based on pooled standard

deviation) is 0.0000038 meq/g (or 0.004 relative %) . 70
Occasional analyses were performed on hydrogen-loaded

ion exchange beads. The set of data cited below was taken in

order to determine the effect of the duration of drying on

the loading factor. Two of the samples were dried in a

vacuum oven for 20 hrs at a temperature of 105 °C 3 and the

other two were dried for 188 hrs under the same conditions.

The samples were delivered into a coulometric cell with 1M

KC1 at pH = 7.00, and the liberated H was reduced at a Pt

cathode by passage of constant current to pH = 7.00. The

results are given in Table 38.

Table 38. Analysis of H -loaded ion-exchange beads.

Dried 20 hrs

Sample No. Weight meq H found meq H /g of bead

15-1 0.2546 g 1.1938 4.689

15-2 .2633 g 1.2338 4.686

25-1 0.2663 g 1.2556

25-2 .1973 g 0.9295

Average 4.688

4.715

4.711

Average 4.713

Occasionally there is the opportunity to compare coulometric results with those of other laboratories. This was

the case with a synthetic sea water, Standard Sea Water P50,

issued by the I. A. P.O. Standard Sea Water Service, Charlottenlund Slot, Denmark. Our mercurimetric determinations of

halides in this standard are summarized in Table 39. The

ampoule value is based on conventional titrimetry. It is

gratifying to see such excellent agreement between two independent measurements.

71
Table 39. Analysis of sea water standard P^ n . 5U

meq X~/g sol'n

Aliquot No. (corrected to vacuum)

1 0.546474

2 .5^6569

3 .546520

0.546521

Recalculated as "chlorinity"

the results became 19.3757 °/oo

as compared with 19.375 °/oo, the value appearing on the

ampoule

(G. Marinenko and C. E. Champion)

72
4. ELECTROANALYTICAL MEASUREMENTS

A. Introduction

The electroanalytical measurements program has become

strongly oriented along the lines of ion-selective electrodes

and their microanalytical applications. Although the major

portion of this year's time has been used in organizing the

Symposium on Ion-Selective Electrodes and in editing the proceedings of that meeting, some limited research and service

analyses were undertaken and completed.

B. Symposium on Ion-Selective Electrodes

The Symposium on Ion-Selective Electrodes held at the

National Bureau of Standards in Gaithersburg, Maryland, on

January 30-31, 1969 was attended by approximately 450 physical

and biomedical scientists. The widely divergent disciplines

represented were matched by an equally broad spectrum of

topics reviewing the state of the art of these electrochemical

sensors

.

Ten hour-long invited papers were presented by some of

the foremost authorities on various aspects of this subject.

In addition to the formal presentation of papers, several

hours of discussion time were scheduled in order to provide a forum for the active exchange of information on novel applications, instrumentation, and experimental problems and techniques . Lectures on the first day were concerned primarily with

principles, characteristics, basic thermodynamic studies, and

reference electrodes while the second day was devoted to interdisciplinary applications ranging from biomedical research and

clinical applications to industrial analysis and control.

The first paper by George Eisenman (Univ. of Chicago)

entitled "Theory of Membrane Electrode Potentials" dealt with

an examination of the parameters determining the selectivity

of solid and liquid ion exchangers and of neutral sequestering

agents such as cyclic antibiotics and polyethers which offer

73
the possibility that the exquisite selectivities characteristic

of living cells can be duplicated in an artificial electrode.

The similarities and differences among the mechanisms of the

three types of electrodes were discussed as well as their

particular advantages and limitations.

The next paper by James W. Ross (Orion Research) summarized

the work directed toward developing useful new ion-selective

electrodes of the solid-state and liquid membrane types . In

addition, he discussed the general characteristics of these

electrodes and the future development of new electrodes of

various types . This paper was followed by a similar presentation on heterogeneous membrane electrodes of the precipitateimpregnated type by Arthur K. Covington (Univ. of Newcastle

upon Tyne , England). He also discussed the very important

topic of reference electrodes. It was pointed out that, although interest is usually directed toward the indicator electrode, the function of the reference electrode should also be

thoroughly understood. Liquid junction potentials and essential features, designs, and methods of utilization of reference electrodes were discussed.

James N. Butler (Tyco Laboratories) reviewed the use of

solid-state and liquid ion exchange membrane electrodes in

studies of the thermodynamics of solutions. Studies of this

type range from the measurement of activity coefficients to

studies of multiple equilibria in constant ionic media.

Roger G. Bates' (NBS) presentation on activity standards

and standardization pointed out that problems arise because

there is no unique way of defining the activity of a single

ionic species but showed how the pH convention could be extended to yield standards for electrodes reversible to other

cations and anions

The paper by Edward W. Moore (Lemuel Shattuck Hospital)

was concerned with studies in biological fluids using the

calcium ion exchange electrode. Applications to biomedical

74
research and clinical medicine were presented in connection

with studies of hyperparathyroidism, cirrhosis, and hypercalcemia of malignancy.

Raja N. Khuri (American Univ. of Beirut, Lebanon) reviewed

the uses of both the glass and non-glass ion-selective electrodes in biomedical research. Problems associated with potentiometric measurements in biological systems both in vitro

and in vivo were discussed.

A review of the uses of these sensors in physicochemical

studies was given by Garry A. Rechnitz (State Univ. of New

York at Buffalo) . While devoted primarily to kinetics and

complex ion studies, he also described some of the interesting

problems raised regarding the method of operation of these

sensors

.

Truman S. Light (Foxboro Company) discussed industrial

analysis and control using ion-selective electrodes in various

modes of operation such as monitoring flowing streams by

single or multiple electrodes, observation of a sample stream

following reagent injection, and the use of ion-selective

electrodes as end-point detectors in automatic process titrators . Richard A. Durst (NBS) reviewed direct potentiometric

techniques, potentiometric titrations, and the analytical

applications of ion-selective electrodes to various problems

including oceanographic , pollution, and agricultural studies.

The formal report of these proceedings will be published

in book form. This, approximately 500-page volume, will include the complete texts of the invited lectures plus a transcription of selected segments of the recorded discussions. This NBS Special Publication [20] should be of considerable value in advancing the state of the art by providing

a thorough evaluation of the subject and a comprehensive

review

.

75
C . Research Activities

1. Modification of a Silver Sulfide Ion-Selective

Electrode for Microchemical Analysis

Previously, a fluoride electrode was modified for microchemical analysis by inverting the electrode, encircling the

membrane with a sleeve, and placing the sample solution into

this microcell [21,22]. In the case of the silver sulfide

electrode, sample microcells may be formed by drilling depressions directly into the silver sulfide membrane. This soft,

polycrystalline material is easily drilled with little tendency

to fracture or cleave

A cross-sectional view of the final electrode configuration

is shown in Figure 10 with the drilled 5- and 10-ul depressions

A teflon cap is milled to fit snugly over the end of the electrode body and a 1 mm hole is drilled through this cap to accommodate the reference electrode probe. The purpose of the

cap is to reduce evaporation of the small volumes of sample

and to facilitate alignment of the reference probe and sample

cell.

The 0.1N AgNO internal reference solution of the silver

sulfide electrode is not gelled with agar as used with the

fluoride electrode [21], since the agar reacts with silver.

Instead, the electrode is completely filled with the reference

solution to eliminate problems from entrapped air bubbles. A

silica gelled internal reference solution was also used with

good results, but entails considerably more work to prepare.

Comparable results were obtained with both the 5- and

10-yl sample compartments. Figure 11 illustrates the response

of the electrode (5-ul cell) to varying activities of silver in

both buffered (with respect to silver) and unbuffered solutions

In the case of unbuffered silver nitrate solutions, the elec-

_7 trode response is Nernstian down to almost 10 'M (point #6).

However, for solutions buffered by the presence of various insoluble silver salts, the response is Nernstian (solid line)

76
-25

down to the lowest level studied, approximately 10 M. Apparent deviations from Nernst response are more likely due to

errors in calculating the silver activity than to non-Nernstian

behavior of the electrode. These results suggest that the

electrode must, at some point, begin to respond to some complex

form of silver, since at the lowest silver activities, there

are theoretically no free silver ions in the solution. In

fact, at point #13 on the curve, the electrode is apparently

responding to 1 millionth of an atom of silver (again assuming

it is responding only to free, hydrated silver ions)! Certainly, further studies are needed to elucidate this rather

anomalous electrode behavior.

Figure 10. Inverted silver sulfide membrane electrode.

(a) internal reference electrode compartment; (b)

polycrystalline silver sulfide membrane; (c) and (d)

sample solution cells: 5 and 10 ul, respectively; (e)

teflon cap to prevent sample evaporation; (f) 1-mm

diameter hole in cap for insertion of external reference electrode salt bridge; (g) reference electrode

salt bridge containing M% agar gel of saturated KNO3*

77
600

400

200

-200

400

-600

-800

Figure 11. Silver sulfide electrode response to silver

activity (test solution vol. = 5 yl)

(Solid line: 59.2 mV/pAg)

Point Solution C'omp)osition

^ pAg

( calc) E(mV)

1. 10

-1

M AgNO 1.1 + 550

2. 10~ 3 Mi. 3 + 438

3. 10 M 4 + 385

4. 10" 5 M 5 + 32 3

5. 10 M 6 + 260

6. 10" 7 M

10"8 M

7 + 225

7. 8 + 213

8. Sat T d Agl

• 6 M1 ,

8.2 + 150

9. Sat'd Agl + 10" Kl 10.3 + 21

10. Sat'd Agl + 10" 4M Kl 12.3 - 91

11. Sat'd AgCl 4 1M Na

2

S

p 0^ 14.2 - 256

12. Sat'd AgCl -f 0. 1M Kl 15.5 - 298

13. 0.1M Na

2

S + 1M NaOH 24.9 - 872

78
2 . Construction and Characteristics of a Fluoride IonSelective Microelectrode

The feasibility of constructing a fluoride microelectrode

suitable for studies in microliter volumes of sample solutions

has been demonstrated. This basically simple and straightforward technique illustrates the potentiality of such ionselective electrodes in studies similar to those in which

glass microelectrodes are currently used. Although still about

two orders of magnitude larger than the smallest glass microelectrode [23], the characteristics of this first fluoride

microelectrode are encouraging enough to. prompt further work

in the miniaturizing of this and other ion-selective electrodes.

Previously, small volumes (5 to 50 ul) could be studied

with the conventional ion-selective electrodes using the inverted electrode technique, such as was demonstrated with the

fluoride electrode [21,22], or the drilled-well electrode, as • described above for the silver sulfide electrode. Although

these systems allow measurements on small volumes of solution,

these electrodes cannot be used for measurements in situ but,

rather, the sample has to be placed in the microelectrode cell.

In contrast, while this fluoride microelectrode is still too

large for most in vivo measurements, it would be applicable to

certain in situ studies where the solution volume is a limitation or in conjunction with other microelectrodes, where

simultaneous measurements must be made on a limited volume of

sample or on a continuous basis. In such cases, the inverted

microelectrodes would not suffice.

The microelectrode (Figure 12) is constructed from a section of polyethylene tubing drawn out to a 2-mm (o.d.) neck

at the lower end. A small, cone-shaped piece of lanthanum

fluoride is inserted into this narrow end of the tube and heat

sealed into place. In the first design, the microelectrode

was used in this form, but was later refined as shown in the

enlargement of the tip (Figure 13). In this latter design, the

tip was painted with polystyrene coil dope which, after drying,

79
was scraped away to expose a small, well-defined area of the

crystal tip.

In addition, the first form of the electrode employed a mercury contact to the inner surface of the lanthanum fluoride

membrane. This type of contact proved unsuccessful, and the

internal reference electrode system was used. This consisted

of an internal . 1M NaF-O.lM KC1 solution into which dipped

the silver-silver chloride reference electrode. The electrode

was connected to the meter by shielded cable.

The final form of the microelectrode tip (Figure 13) was

an exposed conical portion of the LaP^ crystal of approximately

1.5 ul volume. This small area electrode had a relatively low

resistance of 900 Kfi.

Figure 12. Fluoride microelectrode.

(a) Microelectrode tip (see enlargement - Figure 13)

(b) Silver-silver chloride internal reference

electrode

(c) 0.1M NaF-O.lM KC1 solution.

(d) Shielded lead to pH-millivolt meter.

80
Figure 13. Detail of fluoride microelectrode tip.

(a) lanthanum fluoride tip (uncoated), volume ^ 1.5 ul;

(b) LaFo crystal body [insulated with (c) polystyrene coil

dope]; (d) polyethylene tube (electrode body); (e) silversilver chloride internal reference electrode; (f) NaF-KCl

(each . 1M) reference solution.

With respect to the original form of the microelectrode,

i.e., mercury internal contact and uncoated (fully exposed)

membrane tip, the principal problem was poor long-term

stability. Although the slopes of individual calibration

curves, run within one hour's time, were approximately Nernstian

(average slope: 57.7 mV/pF), the variation in the E° of this

electrode was on the order of ± 20 mV from day to day.

The depth of immersion of this uncoated electrode tip had

little effect on the potential. The emf shifted about 2 mV

negative over the 1-mm length of the exposed crystal. This is

not too surprising, however, since even when just a small

portion of the tip enters the solution, it is very likely that

a film of the solution coats the entire crystal. The small

variations in emf that do occur are probably due to fluoride

activity variations within the thin solution film.

81
Ix 10" 1x10" |x 10" |x 10"

i 1 1

1

i i i i i 1 1

1

I i i i i 1 1

- 300

6.8xl0"7 6.8xl0"6 6.3xl0"5 5.8x10 4 9.5xlO"3

FLUORIDE ACTIVITY (moles /liter) Figure 14 . Microelectrode response to fluoride activity.

Curve A - Original design electrode (mercury internal

contact and uncoated membrane tip)

Curve B - Improved electrode design (Ag-AgCl internal

reference and partially coated tip)

Using the "improved" version of this electrode, i.e.,

Ag-AgCl internal reference and coated tip, the response to

fluoride activity shown in Figure 14 was obtained. Although

deviating noticeably from Nernstian response in the micromolar range, the slope in the more concentrated solutions

is improved (59.5 mV/pF) . The coated electrode showed no

depth of immersion effect, and the long-term E° variations were

improved by a factor of ten to ± 2 mV (possibly due to room

temperature variations; measurement cell not thermostated)

All of the measurements were made on macro volumes of

stirred solutions (approx. 25 ml) against a normal-size saturated calomel electrode. Using a micro capillary reference

electrode in conjunction with this micro fluoride electrode,

measurements could be made on 2-ul sample volumes . Further

miniaturization is possible along similar construction lines

which could lead to intracellular fluoride determinations

D. Analysis of SRM Gold-Silver Metal Microprobe Wires

The composition of four Au-Ag alloys (20 mil wire form),

intended for use as electron microprobe standard reference

82
materials, was determined by a gravimetric procedure in which

preferential dissolution of one of the constituents was

affected prior to analysis . Due to the uncertainties in the

previously reported values [1], redeterminations of the gold

content of the alloys were performed using a slightly modified

procedure. The low silver alloys were again inquartated with

enough high-purity silver to increase the silver content to

between 70 and 80%. At this level, all of the alloys can be

easily dissolved in 1:1 nitric acid. The gold residue is

filtered and ignited. Instead of weighing at this point as

before, the gold is dissolved in aqua regia, and a small

quantity of residual material (presumably AgCl from undissolved

silver occluded by the gold and silicate material from the inquartation crucible) is removed by filtration. The gold is

then reprecipitated with sulfurous acid, filtered, ignited,

and weighed.

The results are given in Table 40 and supercede all

previously reported data. There appears to be no difference,

within the precision of the results, between the composition

of the lead and trail ends of the alloys

.

Nominal

Table 40. Values for gold.

Au, % - Ag, % Found: Au, %

20 80 22.46

40 60 40.06

60 40 60.04

80 20 80.13

E . Analysis of Miscellaneous Materials

1 . Determination of Fluoride in Dust Samples

The versatility of the fluoride ion-selective electrode

to unusual analytical problems is illustrated by its application to the determination of fluoride in a sample of dust.

The analysis of fluoride in this sample was performed using

combustion in an oxygen flask and determination with the

fluoride ion-selective electrode. Three determinations were

made using 0.2-0.3g samples. The results were

63 ppm

122 ppm

78 ppm

Mean 88 ppm.

83
Washed laboratory sand and dust from the NBS grounds were

also analyzed. No fluoride was detected within the sensitivity

of the method which is approximately 2 ppm with this size

sample. The variation in the results of the sample could be

caused by inhomogeneity of the sample or incomplete combustion

of the fluorine compounds in the sample.

The oxygen flask method was used (by R. A. Paulson) for

the combustion using a polycarbonate flask. Fifty yl of diethylene glycol was added to the sample as a combustion aid.

Ten ml of . 1M potassium nitrate solution was used as the

absorbant. The same solution was used to wash out the flask

and the final volume was 25 ml. A fluoride ion-selective

electrode and a plastic silver-silver chloride reference

electrode in an all plastic system were used for the direct

potentiometric determination of the fluoride. The electrode

system was calibrated with standard fluoride solutions in the

range from 10"3m to 10"5m.

2 . Determination of Fluoride in Acid Mixtures

In support of NBS calorimetry research, analyses were

performed on aqueous mixtures of hydrofluoric acid and (a)

HC1 and (b) HN0

3

. In the first case, the fluoride determinations in the

HF-HC1 mixtures were performed by the potentiometric titration

with a standard LaCl^ titrant using a fluoride ion-selective

indicator electrode. The analyses were carried out on 0.5-0.9g

aliquots of the four fluoride sample solutions resulting from

the reaction of ClFc, and NF3O with mixtures of H2 and O2 • Results ranged from 0.5 to 0.8 meq F~/g soln.

Fluoride was determined by direct potentiometry in HF-HNO3

mixtures produced by the thermal decomposition of fluorinated,

substituted triazines . Approximately 2-ml samples of the mixtures were weighed, neutralized, and diluted to 25 ml prior to

direct potentiometric measurement with a fluoride electrode.

The analysis results ranged from 2.4 to 7.7 x 10" 2 mmole F~/g

solution for 12 separate samples, and agreed well with the

theoretically calculated fluoride contents

(R. A. Durst)

84
5 . COMPLEX EQUILIBRIA STUDIES

A. Introduction

Frequently analytical procedures involve complex equilibria which are not well understood. Knowledge of the chemistry

involved in such systems is of interest from a purely theoretical standpoint, in that the methods do not have to be accepted

empirically, and from a practical standpoint, in that improved

methods are possible only when existing methods are understood.

During the past year the boric acid-borate-mannitol system [24]

and several lanthanide-nitrate systems have been investigated.

B. Research Activities

1. Aqueous Boric Acid-Borate-Mannitol Equilibria

The stoichiometry and equilibria of the boric acid-boratemannitol system have been the subjects of extensive studies.

It is generally thought that mannitol reacts with borate to

yield complexes of the borospiran structure with mannitol-toboron ratios of 1:1 and 2:1. While Tung and Chang [25],

Boeseken and Vermaas [26,27], Deutsch and Osoling [28], Ross

and Catotti [29], and Torssell [30] agree that both 1:1 and

2:1 complexes are formed, they report widely divergent formation constants. Antikainen [31] reports that, over the range

of mannitol solubility, the 2:1 complex is incompletely formed

and the ratio of complexed mannitol to complexed boron does

not exceed 1.8. Very recently Nickerson [32] has reported

that only a 1:1 species is formed and proposes the previous

workers have been in error since they presupposed a 2:1 complex and interpreted the data to fit that model. While results

from this laboratory do not support the conclusions of

Nickerson, his criticism does, at least in some cases, have

merit

.

The boric acid-borate-mannitol system has therefore been

reinvestigated to establish unequivocally the stoichiometry

of the system and tc obtain reliable values for the equilibrium

85
constants involved. In those cases where the experimental

data seemed reliable, the data of previous workers were reevaluated according to the stoichiometry found in this work.

Reassessment of these data has revealed a number of misinterpretations which, once resolved, yield consistent results.

Several instances of such data reassessment are discussed

below

a. Experimental . Commercially available boric acid,

sodium metaborate, sodium tetraborate (borax), mannitol, and

deuterated solvents were used.

A 60 MHz nuclear magnetic resonance spectrometer was used

to obtain the proton magnetic resonance spectra of a 0.5M

mannitol solution and 0.5M mannitol solutions containing excess borate and boric acid. The spectrum of an additional

mannitol-boric acid sample containing DC1 to repress the

ionization of boric acid was obtained. All spectra (Figure 15)

were obtained in D

? and the chemical shifts measured relative

to acetone internal standard.

All pH measurements were obtained using an expanded scale

pH meter and a glass-reference combination electrode. The pH

meter was calibrated using pH 4, 7, and 10 buffers. All

measurements were at 25.0 ± 0.5°.

For experiments with large amounts of mannitol present,

a boric acid or borax solution of twice the desired concentration was prepared and 50 -ml aliquots were delivered to 100-ml

volumetric flasks. The desired amount of mannitol was weighed,

dissolved in the minimum amount of distilled water and transferred quantitatively to the volumetric flask. The solution

was diluted to volume, mixed thoroughly, and the pH of the

resulting solution was measured. Plots of pH vs. log mannitol

concentration were obtained in this manner for borax concentrations of 1.000 x 10~3M to 5.000 x 10~ 2

M. Typical examples

of these plots are shown in Figure 16 . A similar plot for a 0.200M boric acid solution is shown in Figure 17

86
I 1

2.0 1.5 1.0 ppm VS ACETONE

Figure 15. Proton magnetic resonance spectra in D

?

of:

A) 0.5M mannitol; B) 0.5M mannitol, l.QM boric acid;

C) 0.5M mannitol, 1.0M sodium met ab orate. Addition of

DC1 to B returned spectrum to A.

ph

• 5.00 X 10' M BORAX

_L I I I I I I I I I I I

Figure 16

.

0.02 Q04 0.06 0.08 0.10 0.20 0.40 OfiO 0.80 1.00 TOTAL MANNITOL CONCENTRATION, motes/liter pH of mannitol^borax solutions in which mannitol

concentration was yaried, borax concentration

was held constant.

87
PH

0.02 0D4 0.06 0.08 OKI 020 0.40 TOTAL MANNITOL CONCENTRATION, moles /liter

0.60 O80 1.00

Figure 17. Formation constants for BM calculated from

_2 changes in pH of a 10 M borax solution to

which small amounts of mannitol were added.

See Table 4l.

For experiments with small amounts of mannitol present,

_2

a 1.000 x 10 M mannitol solution was delivered in small

increments to 100.00 ml of the appropriate boric acid-borate

solution from a 5 -ml buret. Measurements of pH were taken to

the nearest 0.001 pH unit after each addition of mannitol.

Data from a typical titration of this kind are shown in Table

41.

b. Results and discussion . The proton magnetic

resonance spectrum of 0.5M mannitol in D

2 is shown in Figure

15 j curve A. The eight non-alcoholic protons of mannitol are

so similar that only a single resonance appeared in the

spectrum at about 1.5 ppm vs. acetone. In the presence of

1.0M borate, curve C, the singlet was considerably broadened.

If mannitol forms a borate complex, this broadening would be

expected due to a small change in the chemical shift of

protons on the carbons carrying boron bonded oxygen as well

as coupling of these protons to boron. In the presence of 1.0M

boric acid, curve B, the mannitol singlet was only slightly

88
broadened, presumably due to complexation of the small

equilibrium concentration of borate. In the presence of boric

acid and enough DC1 to repress its ionization, the spectrum

was the same as that of mannitol alone, indicating no complex

formation. Mannitol was therefore considered to react only

with the borate anion and not with boric acid.

Table 4l. Titration of 100 ml 9.389 x 10" 3 M borax

with 1.000 x 10" 2M mannitol.

ml.

Titrant pH

cm

xlO 3 mol/1

(BM ) 4 xlO mol/1

(M)

xlO 5 mol/1 log K

]_ 9.110 9.389 - - - 0.50 9.108 9.299 0.43

Q

0.68 2.83

1.00 9.106 9.210 0.85

5

1.35 2.84

1.50 9.104 9.123 1.27 2.11 2.82

2.00 9.102 9.036 1.69 2.71 2.84

2.50 9.100 8.951 2.09 3.49 2.83

3.00 9.098 8.867 2.49 4.23 2.81

4.00 9.094 8.700 3.28 5.66 2.82

5.00 9.090 8.540 4.02 7.60 2.79

6.00 9.087 8.400 4.58 10.80 2.70

7.00 9.084 8.265 5.10 14.42 2.63

(HB) ft (HB) lnlt . al = (Borax) = (B") lnltlal

(B-) =

< HB > K

a

(H

+

) (BM") = (B") lnitlal - (B-)

(M) " (M) total " (BM_)

K

l

(BM )

(B~) (M)

89
Cl ) Determination of the maximum mannitol to

boron ratio and the formation constant of the highest complex

Having established that mannitol (M) reacts only with borate

(B~) the increase in acidity of a boric acid (HB) solution

upon adding mannitol was considered to occur in two steps.

The dissociation (hydrolysis) of boric acid,

B(OH) + H

2 = BCOH)^" + H

+

which may be written more conveniently as

HB = B~ + H

+ K

a followed, upon the addition of mannitol, by formation of some

complex(es)

B~ + nM = BM K

n n

The overall reaction which was followed by monitoring pH was

therefore

HB + nM = BM " + H

+ K = K K

n o a n

Previous investigators have studied this reaction by

monitoring the pH of a boric acid solution upon addition of

mannitol in increments. As will be seen, this has led to a variety of interpretations and errone ois conclusions due largely

to the fact that extremely small initial borate concentrations

are present. In this work, borax was used instead of boric

acid, hence (HB) = (B~) initially. The pH of solutions of

constant borax concentrations was measured after adding various

amounts of mannitol. Typical plots of pH vs. log total mannitol concentration are shown in Figure 16

For the overall reaction above,

(BM ") (H +

) K = (HB) (M)

n

solving for pH,

90
pH = - n log CM) - log K - lor

CBM

n

")

At high mannitol concentrations, (M) was approximately equal

to the total mannitol concentration, C . It can be seen from

Figure 16 that the minimum pH's obtained experimentally were

on the order of 5. The source of hydrogen ion must have been

the dissociation of boric acid and, since hydrogen ion concentrations of 10 M were negligible to within a percent or better

compared to the initial concentration of boric acid, (HB) was

considered to be the initial boric acid concentration and

borate from the dissociation of boric acid was considered to

to be negligible. Finally, if the formation constant of the

complex was large, all of the borate could be considered to.

be in the form BM '"' at high mannitol concentrations.

n

to When these three approximations are valid, the previous

equation simplifies to

pH*

= - n logto C - log K

m

to o

and the plot of pH vs. log C has slope - n and intercept - log

K . In Figure 16 it can be seen that the approximations hold

for 0.005M and 0.01M borax. The linear portions with a slope

of -2 indicate a 2:1 mannitol-to-boron ratio for the complex.

(The maximum C ' s are approaching the solubility limit of

mannitol so that 2:1 represents the complex of maximum ratio).

At high borax concentration, 0.05M, the curve approached but

did not quite reach a linear portion of slope -2. Presumably,

the assumption that all borate was present as BM ~ did not

hold.

The intercept of the 0.01M and 0.005M borax curves with

the pH axis at log C =0, were found to be 4 . 16 and 4.08,

respectively. The pH values at C =0 showed a slight change

in the initial pH of boric acid with concentration. Measurements of pH of borax solutions at C =0 were, in fact, m ' ' measurements of pK . The small changes in pK with borax cona a

91
centrations were expected and were found to be in good agreement with those predicted from theory [33]. Therefore, K , being a product of K Cin this case K„) and K should also

have varied slightly with borax concentration.

From the values of pK and pK , taken from Figure 16

log K

?

was calculated. From four determinations of log K with

borax concentrations between Q.001 and 0.01M, values of 4.96,

4.98, 4.99, and 4.99 were found (average = 4.98).

(2) Determination of the formation constant of

the 1:1 complex . Formation constants for the 1:1 mannitolborate complex were determined by adding small amounts of mannitol solution from a buret to 100 ml of a boric acid-sodium

borate solution. Table 4l shows part of the data for a typical

titration of this kind. The initial concentrations of mannitol,

boric acid, and borate were corrected for dilution and the pH

measured after the addition of each increment of mannitol solution. Since changes in hydrogen ion concentration were of the

-12 order of 10 M when mannitol was added and since the source

of hydrogen ion was boric acid, the concentration changes of

-12

the latter were of the order of 10 M or negligible compared

to the total boric acid concentration. Therefore, (HB) was

taken as equal to the initial borax concentration. Using K

a

(from initial pH) and the measured pH, the concentration of

free borate (B~) was calculated. Negligible amounts of borate

were formed from boric acid and the original borate concentration equaled the sum of free borate plus complexed borate.

Thus the concentration of complex (BM~) was obtained by subtracting (B"") from the initial borate concentration. Finally,

the concentration of free mannitol was obtained by subtracting

the concentration of complex from the initial mannitol concentration and values for K.. were calculated.

Values for K are given in the last column of Table 4l.

They are essentially constant at low mannitol concentrations

and begin to decrease as mannitol concentrations increase.

92
This relationship is seen graphically in Figure 18 and is just

the effect that would be predicted if the formation of a higher

complex becomes important at appreciable mannitol concentrations

The agreement of calculated K, values at low mannitol concentration can be interpreted as proof of the existence of the 1:1

complex. The value of the formation constant of the 1:1

mannitol-b orate complex was taken to be the limit as mannitol

approaches zero, in Figure 18 this value corresponds to a

log K-, of 2.83. For other boric acid-borate concentrations

and ratios, values of 2.70, 2.75, and 2.89 were obtained, the

average being 2.79.

Since K„ is the product of the first and second successive

formation constants, 3-, and 3p, of the mannitol-b orate complex

and K is 3, , the successive constants were calculated.

B~ + M = BMM

BM~ + M = BM,

h ' K

l

K,

; $o =

log 3 1

= 2.79; log 6 2 = 2.19

2.90 1 1

" - O O

1 1 1

3 O

1 1 1 1

-

2.80

U

O

l

2.70 - o\

o\

-

2.60 \o

2.50

1 1

"

1 1 1 1 1 \° -

2.0 4.0 6.0 8.0 TOTAL MANNITOL CONCENTRATION , moles /liter x I04

10.0

Figure 18. pH of mannitol-b oric acid solution in which

mannitol concentration was varied, boric

acid concentration was held constant.

93
Since the second successive formation constant is very

nearly as large as the first, the formation of the second complex becomes important as soon as an appreciable amount of the

first complex is formed. It is evident, therefore, that values

of K, must be obtained in the limit of zero mannitol concentration especially when boric acid, and hence a very low borate

concentration, is used initially. Failure to recognize the

possibility of very similar successive constants has led

previous investigators to erroneous conclusions

Deutsch and Osoling [28] reported values of 2.5 and 4.7

for log K, and log K respectively. However, their calculation of these constants was based on the assumption that at

(HB)>>(M) only a 1:1 complex is formed. The formation constants

were calculated by these authors using a rather complex algebraic relationship in which K was calculated from pH measurements of a boric acid solution to which small amounts of mannitol were added. The calculation of K_ required prior knowledge

of K, . The values of K and K

p

reported by Deutsch and Osoling

have been questioned by later workers [29,32]. It appears that

the reported value of K_ is in error since, under the experimental conditions used, the mannitol concentration was significantly greater than the borate concentration and the 2:1 complex was formed. Data in the Deutsch and Osoling work are

further confused by the fact that the initial boric acid solution contained a small amount of some alkaline impurity and

the pH of the initial solution was higher than predicted from

V

The value of K-. obtained by Deutsch and Osoling is therefore in error (but fortuitously close to the correct value)

4 6

By assuming only a 2:1 complex, a value of K„ = 10 can be

calculated from the data used by these authors for calculating

K, . Applying an approximate correction .for the alkali error,

calculated from K. and the initial pH, brought the K value to

5

a

lCr * in excellent agreement with the value obtained in this

laboratory

94
Values of K

? reported by Deutsch and Osoling show considerable scatter (mean deviation, 39/0_ , the scatter being introduced by an incorrect value of K . Recalculation of K

2

using the original data, a correct value for K,, and an approximate correction for the alkali error gives K

? very close to

io 5 - Similarly, values of K„ in excellent agreement with those

obtained in this laboratory can be calculated from the data of

Boeseken and Vermaas [27] and Ross and Catotti [29]. These

-4 2 -4 workers reported K (K = K K ) to be 10 " and 10 ' , o o d. a

' respectively. Using appropriate values of K , K was calculated

a t— and log Kp values of 5.0 and 5.2 were obtained. No measurements

of K were obtained by these authors.

Torssell [303 reported values of log K, = 2.75 and log Kp = 5.06 for the formation of mannitol-borate complexes in excellent

agreement with the 2.79 and 4.9 8 obtained in this laboratory.

Torssell' s method, also using additions of mannitol to boric

acid and measurement of pR, involved extrapolating to zero

mannitol to obtain K, and thus precluded the assumption that

only a 1:1 complex is formed at any given concentrations.

Nickerson [32] has recently reported a number of arguments

to support the conclusion that mannitol reacts with boric acid

in a one-to-one ratio only. This conclusion, based on the

argument that only one mole of product, HBM, was formed per

mole of B reacting rather than two moles of product, H and

BM~ (or BMp~) , is weakened by the fact that it was later

assumed that HBM is a strong acid and dissociates to give in

fact two moles of product. Furthermore, treating the data as

though only one mole of product were formed resulted in the

questionable conclusion that the boric acid in solution must

exist as a dimer. While boric acid polymerization is knov/n,

it is well established that at concentrations of boric acid

>0.025M, only monomer and borate ion are present while at

higher concentrations the predominant polymeric species is a

95
cyclic trimer composed of two boric acids and one borate

[34-36].

A number of plots of pH vs. log mannitol concentration

for various amounts of mannitol added to boric acid, the concentration of the latter being held constant, were reported by

Nickerson [32]. Experiments of this type have been repeated

in this laboratory. A typical example is shown in Figure 17.

The results of these experiments are in excellent agreement

with those of Nickerson. The pH vs. log mannitol concentration

plots obtained in this manner have a slope of -1. However, the

conclusion of the previous author, that the slope of -1 implies

a 1:1 complex, is incorrect.

Since the starting material in these experiments was boric

acid, the borate concentration was always very low and, at high

mannitol concentrations, the formation of the highest complex

(of 2:1 mannitol to boron ratio) was expected. The observed

changes in pH were the result of dissociation of boric acid and

the formation of an equivalent amount of mannitol-b orate complex. Although an objection to equating the concentration of

liberated hydrogen ion with the concentration of complex has

been raised [32], the large concentration of mannitol relative

to borate allowed this assumption. (It has been previously

shown that the assumption that hydrogen ion concentration and

complex concentration are equal was not required when the

starting material was borax.)

The overall reaction following the addition of mannitol

to boric acid was as before;

and

HB + nM = BM + H

+

: K = K K

n ' o a n

(BM ") (H+

) K = CHB) (M)

n

Solving for pH

96
pH = - log K

q - log CHB) - n log CM) + log (BM

n

")

Since

CBM

n

") = (H

+

)

(log K + log [HB])

* 2 2 s m

when the total mannitol concentration, C is large compared to

the concentration of complex.

Plots of pH vs. log total mannitol concentration at constant boric acid concentration have a limiting slope -1. As

can be seen from the previous equation, this slope is consistent with a 2:1 mannitol-to-borate complex. Furtheremore , extrapolation of the curves reported by Nickerson and those obtained in this laboratory (Figure 17) to log mannitol equal

followed by multiplication of the intercept by -2, and subtraction of log (HB) and log K gave values for log K the

a t- formation constant for (BMp~) . The average value 5.00 is in

agreement with the 4.98 calculated from data obtained in this

laboratory and previously discussed.

By a similar treatment, the additional equilibrium data

of Nickerson can be shown to agree with those obtained in the

present work. Thermochemical data reported by Nickerson [32]

to indicate only a 1:1 combining ratio are inconclusive as

these were obtained at concentrations were one would not expect complete formation of a 2:1 complex.

Table 42 summarizes values of formation constants reported

by various authors and recalculated values obtained from their

data. The apparent anomalous behavior of the boric acidborate-mannitol system can be seen to result from misinterpretation of the experimental data rather than the nature of

system.

97
Table 42. Formation constants of borate-mannitol complexes.

This work

Deutsch and

Osoling [28]

Torssell [30]

Nickerson [32]

Ross and

Catotti [29]

Boeseken and

Vermaas [27]

Previously Reported

log Kls log K

2

2.5 , 4.7

2.75, 5.06

log K

c = - 1.92

log K = - 4.0 d

o log K = - 4.2 d

Recalculated

log K^ log K

2

2.79, 4.98

a

, 5.0

b

i ...

, 5.00

, 5.2

, 5.0

lValues of K, are unobtainable from data in this work.

'Reported values are in agreement with those obtained in this

laboratory and therefore not recalculated.

K is equilibrium constant for the reaction 1/2 H^B^M = HBM

K = K K . o a 2

2 . Lanthanide Metal-Nitrate Equilibria

Ion exchange, solvent extraction, and conductivity data

obtained for aqueous lanthanide nitrate solutions have frequently been interpreted in terms of a metal-nitrate interaction. Although nitrate salts are usually classified as

strong electrolytes, such interactions are not unreasonable for

highly charged metal ions such as the lanthanides . Infrared

spectroscopic and ion-selective electrode data obtained for

a number of lanthanide nitrate systems [notably La(III) and

Ce(IV)] suggest complexation rather than ion pair formation.

These results, which are of a preliminary nature, are discussed

below. The systems are currently being studied in detail with

the goal of explaining 1) lanthanide "catalyzed" nitrate reduction at the DME [37], 2) the behavior of the Ce (IV)-Ce (III)

electrochemical couple in nitrate solution, and 3) the mechanism of Ce(IV) oxidations of organic compounds (electron

transfer via bridging nitrates).

98
When nitrate is bound to a metal ion, the symmetry of

the nitrate is lowered from D_, to C~ and a corresponding

increase in the number of infrared active vibrations should

occur. Figure 19 illustrates the infrared spectra of solids

containing free nitrate and complexed nitrate. The existence

of the hexanitratocerate(IV) anion has been demonstrated by

x-ray crystallography [38]. In addition the loss of degeneracy (i.e., frequency separation) of the assymetric stretching

frequencies of bound nitrate are a measure of the dissimilarity of the nitrate oxygens and, therefore, a crude measure

of metal-oxygen covalency. In lanthanum nitrate solutions,

for example, the frequency separation is much larger than in

calcium nitrate solutions where ion pairing is believed to

occur [39 9 ^0]. The lanthanum nitrate bond therefore contains

some covalent character - hence complex formation rather than

ion pairing.

J l L J I L

(NH4 )2 Ce(N03 )6

J I I I I L 1800 1600 1400 1200 1000 800 600

cm

Figure 19. Infrared spectra of solids containing free

and complexed nitrate.

99
Nitrate ion selective electrode measurements are consistent with 1:1 and higher lanthanide-nitrate complexes. The

equilibria involved in the formation of these complexes is

currently under study.

(J. w. Knoeck)

100
6. MICROSCOPIC AND CLASSICAL MICROCHEMICAL ANALYSIS

A. Introduction

The demands of modern science and technology have outmoded many of the established microchemical techniques. As

a consequence, new procedures, possibly definable as ultramicrotechniques, have arisen to make possible the analysis of

smaller and smaller samples. The program here has oeen mainly

concerned with the detection and identification of micro amounts

of materials and the development and preparation of ultramicrochemical standards. Of interest also is the determination of

trace elements in various materials and the microchemical

analysis of organic and inorganic materials.

B. Ultramicrochemical Standards

During the past two years we have cooperated with the

Separation and Purification Section in the development of

microstandard ion-exchange beads. These standards are metal

ion-loaded ion-exchange beads from 5y to 25u in diameter. In

this size range the weight of metal ion present will vary from

a few pg to a few ng. Merely having a concentrated source of

material in this range can be useful for a number of tests,

such as limit of detection, but with proper characterization

the amount of material present can be stated within 10$ or

better.

Microbead standards differ from the usual standards in

several ways

:

1) The weight of metal ion present in an individual bead

is found from an optical measurement of its size.

2) These beads do not have the inherent stability usually

associated with standards. They are especially sensitive to

the water vapor present in air and in absorbing water they

increase in size.

3) It is very difficult to make standardization analyses

on individual beads.

101
However, if the metal ion content, water content and density

of a fairly large batch of beads is known the relationship of

the metal ion content to the bead diameter can be stated with

a certainty of a few percent. This laboratory helped in this

characterization in several ways which will be described in

the following sections

1. Water Content Measurements

Drying loaded ion exchange beads of this size (5-25y) at

120 °C under vacuum for 16 hours will remove practically all

the water from them. However, larger sized beads (^ lOOy) may

require several days to come to constant weight. Dry ionexchange beads absorb water rather rapidly so that it is much

simpler to handle individual beads in a controlled atmosphere

in the 20-40$ relative humidity range. Studies have been made

of the rate of absorption of water by loaded beads exposed to

30$ relative humidity. One-gram samples of beads, dried 16

hours at 120 ° under vacuum were placed in a humidity chamber

containing a saturated solution of calcium chloride at 23 °C.

Weight measurements were made at intervals . Results are given

in Tables 43 and 44. All had reached constant weight after

nine days

Table 43. Percent gain in weight from the dry state

at 30% RH.

Time

Cation on beads 5.5 hours 24 hours 3 days 9 days

Sodium 3.2 10.4 14.9 15.9

Calcium/sodium 3.4 11.8 16.8 17.7

Copper/sodium 3.4 13.1 22.0 23.3

Lead/sodium 3.2 9.1 10.9 11.3

Calcium 3.2 10.8 14.8 15.3

Copper 3.3 11.9 17.6 18.3

Lithium 3.5 12.2 17.5 18.2

102
Table 44. Percent gain in weight from the dry state

at varying relative humidities.

Relative humidity

Cation on beads

Sodium

Calcium/sodium

Copper/sodium

Lead/sodium

Calcium

Copper

Lithium

2 . Density Measurements

The density of dry beads has been determined using the

pycnometer method for solids. In order to have the beads as dry as possible, approximately 1 gram was dried and weighed in

the bulb of a 10 -ml pycnometer. Dry cyclohexane was used as

the liquid to keep the beads as dry as possible. The densities

of four metal-ion loaded ion exchange beads which are possible

standard reference materials were determined by this method

and found to be as follows

:

30 % 50 % 70 %

15.9 18.3 28.7

17.7 19.8 29.0

23.3 26.1 37.4

11.3 12.4 17.8

15.3 16.8 25.3

18.3 20.5 30.4

18.2 21.1 34.7

Calcium 1.500

Sodium 1.504

Copper 1.633

Lead 2.097

The range of densities present in a sample of loaded ion

exchange beads is of special interest because it is an indication of the uniformity of loading the beads. The density

gradient column is very convenient for determining the density

of small objects. The beads here are too small to be seen

individually but 25 mg will form a cloud where the density of

each bead matches that of the liquid. The columns were prepared using the method of Oster and Yamamoto [41]. The liquids

used were mixtures of methylene chloride, chloroform, carbon

103
tetrachloride, and methylene iodide. They were so chosen that

the liquids in the top and bottom bulbs of the gradient tube

differed by approximately 0.1 density units. The tube was

allowed to stand at least 2k hours before the beads were added.

The dried beads were mixed with a small amount of the upper

liquid before adding to the column. After equilibrium had been

reached the height of the band of beads was measured. Samples

of the liquid were taken 2 cm above and 2 cm below the band

and the density determined with a small pycnometer. By

assuming a linear gradient between the two points it is possible to calculate the density of the top and bottom of the bead

band and also the average density of the beads. Floats of

known density will be used in future experiments to prove that

there is a linear gradient present. In the case of the calcium

loaded beads (SRM #1800) the density range was found to be

0.005 density units.

Other tests have been made to aid in characterizing the

microbead standards. Two of these are the capacity determination and the sulfur determination.

3. Capacity of the Hydrogen Form

The capacity of the hydrogen form of the ion exchange

beads is determined by titration with 0.05N sodium hydroxide

solution after the addition of sodium chloride. An excess of

the base is added until the pH is about 11. When equilibrium

has been reached as shown by a constant pH, the excess sodium

hydroxide is titrated slowly with 0.05N hydrochloric acid to

a pH of 7. From these titrations the number of equivalents

of exchangable hydrogen ions can be calculated. The beads are

then filtered on a porcelain filter, dried and weighed. The

capacity is reported as milliequivalents per gram of dry

sodium resin. This latter step is necessitated because the

hydrogen form is very difficult to dry.

4. Sulfur Determination

The percentage of sulfur in the beads when compared to

104
the percentage of metal is an indication of the efficiency of

loading. There should be an equivalent of metal for each

equivalent of sulfur in fully loaded beads. It has been found

that the Carius combustion with fuming nitric acid at 250 °C

will destroy the beads completely. Sulfur is then precipitated

and weighed as barium sulfate using the conventional microgravimetric method.

5 . Handling Techniques

The metal-loaded ion exchange beads are cast on a clean

microscope slide for ease in handling and shipping. The beads

initially are dispersed in dry cyclohexane in a concentration

of 1 mg/ml. Twenty-five microliters of this slurry, spread on

a microscope slide, will usually give a well dispersed sample

of about 500 beads.

In use, the slide is examined under a microscope and

isolated beads of the desired size are selected and measured

using a filar micrometer. A bead so selected can be transferred by hand (40x magnification) using a needle with a very

fine point. Needles are usually made of tungsten wire or

glass. As Walter C. McCrone has many times pointed out, such

transfers are more easily made if the operator practices clean

living and makes use of all possible supports.

C. Clean Room

The horizontal laminar flow Class 100 clean room which

has been in the planning and construction stages for some time

has now been completed. A general description was given in a

previous report [1]. The layout is repeated in Figure 20.

This clean room is divided into two sections by a perforated aluminum wall. The HEPA filter bank is on the left and

the air flow is from left to right. The microscope tables are

located in the cleanest part of the Class 100 room. The Class

1000 room is so marked to indicate that it is for work which

does not require as high a level of cleanliness. However most

of the time, and especially if the Class 100 area is not

occupied, this area will meet Class 100 standards

.

105
CORRIDOR

Figure 20. Plan of the clean room facility.

A forward light-scattering airborne particle counter is

used to monitor the clean room. It is located in the anteroom

with the sensor in the clean room.

Each section of the room has a vertical laminar flow fume

hood. The air for the hood enters through HEPA filters in the

top. A portion of the air exits through a slot in the forward

part of the hood floor forming an air curtain. Only a small

amount of air enters the hood from the clean room. These hoods

are intended for handling volatile solvents, for light chemical

procedures and for handling samples which could contaminate the

clean room. The hoods were not planned for chemical work

requiring large amounts of acids.

Views of the clean room complex are given in Figures 21,

22, 23, 24, and 25.

Figure 21 shows the anteroom in the foreground, the change

room and the air shower. The change room contains the wash

106
basin and hand drier. The pass-through is also in the change

room.

Figure 22 shows the entrance from the air shower into the

Class 1000 area. A high speed centrifuge is on the right.

Figure 23 shows the fume hood in the Class 100 area. The

baffle wall separating the two areas of the room is on the

right

.

Figure 24 shows a portion of the microscopy table in the

cleanest portion of the room.

Figure 25 shows another part of the microscope table. It

also shows the emergency exit to the anteroom and the passthrough to the change room.

Figure 21. Anteroom, change room, and air shower. The

change room is equipped with wash basin and

hand drier. The pass^through is also located

in the change room.

107
Figure 22. Entrance from the air shower into the class

1000 area.

f 1

**~ t i

t^^mk

ii

HJ mm jm

Figure 23. Verticle laminar flow fume hood in Class 100

area. The baffle wall separating the two

areas is on the right.

108
Figure 24. Microscopy table in cleanest portion of the

room.

Figure 25. Pass through, emergency exit and portion of

microscopy table.

109
D. Applications of the Nuclear Track Technique to Trace

Analysis

The successful application of the nuclear track technique

[42-45] to the determination of traces of uranium in biological material [1] has prompted an investigation of its extension to the determination of other trace-level elements. A

search is in progress to identify candidate elements capable

of producing tracks either by emitting a charged particle or a fission fragment after a nuclear reaction. In addition, studies

are being made of detectors and detection conditions in order

to increase selectivity.

Elements being considered at this time produce tracks in

plastic through two types of nuclear reactions . The first of

these is the (n, a) reaction which produces shallow alpha

tracks in cellulose acetate (CA) or cellulose butyrate (CAB)

as a result of bombardment of the target element with thermal

neutrons. Lighter elements such as lithium and boron undergo

this reaction. The other reaction type (y , f) produces fission

tracks in Lexan (a polycarbonate) when the target elements are

bombarded with a high energy bremsstrahlung beam. In this case

the target nuclei are heavier elements such as thallium, lead,

bismuth, thorium, and uranium.

1 . Determining Elements by the (n, a) Reaction

In order to determine elements by tracks produced from

(n, a) reactions, the track-registration characteristics must

be known for the materials being considered as detectors.

Fleischer and co-workers found that the requirement for a charged particle to produce a track in a material was based on

the mass of the charged particle entering the detector. Their

work further showed CA and CAB to have the proper requirements

for recording alpha tracks, but ruled out Lexan, mica, and

Mylar as detecting materials [46-48].

The etching conditions suggested by Fleischer and coworkers [46,48] and by Loveridge and Mclnnes [49] for CA

and CAB have been studied but found to be unsuccessful. The

conditions for CA, consisting of etching times of 3 hours at

25 °C produced slides which were very foggy. Additional experiments indicated that the etching temperature was the critical

factor in obtaining properly etched slides. CAB required short

110
times of 8 minutes at 70 °C to obtain an optimum etched slide.

But at these high temperatures the time appeared to be critical

factor in obtaining slides and tracks that were not over etched.

Further experiments with both materials proved that CAB was the

more favorable plastic to be used as detecting material, if

etched at 50 °C for 45 minutes in a 6.5N NaOH solution.

a. Detection of boron . The detection of boron by

this technique is based primarily on the presence of boron-10

in the material. The alpha tracks are produced from the

l^B(n 3 a)7Li with a neutron cross section of 3840 barns.

(1) Experimental . Known amounts of the boron

containing material were placed on the CAB slides in solution

form, evaporated and covered with transparent tape. The slides

(25 mm x 40 mm x 0.25 mm) were irradiated in the NBS reactor

for 60 seconds at a neutron flux of 2.4 x lO^n* cm-^s" 1

. The

slides are then etched in NaOH by the procedure described above

and counted by using the Quantimet QTM [50], the procedure of

which will be discussed in section C. The net number of tracks

observed were compared with the net number of tracks obtained

from simultaneously irradiated standards.

(2) Results . Irradiation of known quantities

of boron shows that a linear relationship exists with the

amount of boron present and the number of tracks formed. The

detection limit for boron with a total integrated flux of 1.44

x 10l5n»cm~ 2 was found to be 4.3 x 10~1 2 grams per track.

b. Determination of lithium . The detection of

lithium is also isotopic and is based primarily on alpha

tracks produced from the °Li(n, a)^H reaction which has a thermal neutron cross section of 950 barns. The apriori

assumption that the number of tracks formed is directly related to the total amount of the element present has to be

made for lithium or any other element if quantitative results

are desired.

(1) Experimental . The same experimental procedure outlined in the boron discussion is used for lithium

detection.

(2) Results . Lithium also demonstrates a

linear relationship between the amount present and the number

111
of tracks formed. The detection limits for lithium under the

same conditions as cited for boron is 1.72 x 10~H grams per

track.

2 . Determination of Elements by (y, f) Reactions

The nuclear track technique has been limited previously

to nuclear reactions induced by thermal neutron irradiations

[45, 50-5^]. These reactions have been of interest because of

their large neutron cross sections which aid in their detection

sensitivities. Currently, investigations are underway to study

the radiation induced trails or tracks produced from the high

energy bremsstrahlung beam of a linear accelerator (LINAC)

The elements that produce fission tracks from the (y, f) reactions have comparatively smaller cross sections and, consequently, their sensitivities will be smaller than the fission

tracks produced from thermal neutrons

Fission tracks have been produced in Lexan polycarbonate

from thalium, lead, bismuth, thorium, and uranium by 35 MeV

photon activation. However, a five-minute irradiation for a

one-microgram sample indicated that only the latter three

elements appear to be promising for quantitative measurements.

Since trace determination of bismuth by neutron activation

analysis is limited, bismuth appeared to be especially interesting for focusing analytical attention. However, the sensitivity or detection limit for bismuth, 3.13 x 10"? grams per

track, was found to be less than those for thorium and uranium,

4.17 x 10~9 grams per track and 1.72 x 10~9 grams per track,

respectively. Since the uranium and thorium sensitivities were

greater than that of bismuth, a pre-irradiation separation had

to be performed on the material to be analyzed.

a. Experimental procedure . The bismuth containing

material was dissolved in dilute HNOo. Then the solution was

mixed with 10 ml of a complexing mixture, containing 50 grams

of Na2 EDTA and 50 grams of NaCN dissolved in 1 liter of 1.5N

NHjjOH. Next, 1 ml of a 2% solution of sodium diethyldithiocarbamate was added. The bismuth was then extracted with 10

ml of CCI4 [55]. After addition of 1 ml of dilute HNO3 to the

CCI4 layer, the mixture was heated until all of the CCl^ was

driven off. Droplets of 100 microliters of the resulting

dilute HNOo solution were placed on Lexan slides that were

112
10 mm wide x 25 mm long x 0.25 mm thick in size. The slides

were then evaporated, covered, and irradiated for a minimum

of 5 minutes at a maximum bremsst rah lung energy of 35 MeV.

After irradiation the slides were etched in 6.5N NaOH at 50

± 2 °C for 45 minutes. The tracks were then counted and the

values were compared with values obtained from standards

irradiated simultaneously.

b. Conclusion . Analysis of both fractions of the

solvent extraction layers showed by the nuclear track technique

that all the uranium remained in the aqueous phase, while

tracer experiments with 20 ?Bi and the nuclear track technique

showed that 95% of the bismuth was extracted by the CCI4.

Therefore, the results demonstrate that trace quantities of

bismuth and uranium can be analyzed in the same matrix.

E. The Quant imet-QTM

Nuclear tracks that have been produced in the plastic

detectors have to be counted by some means. Normally this has

been done by counting each track in a microscopic field of

view by eye. This laboratory's procedure has been facilitated

by utilizing the Quantimet QTM, an image analyzing computer

microscope. The QTM consists of a microscope that is attached

to a closed circuit television camera together with a small

analog computer in line with a television monitor. The image

being analyzed is displayed on the monitor and the measurements

can be obtained from the monitor. Measurements that can be

made by the QTM include area measurement, projection lengths,

and image counting. In the case of track counting each track

that is being counted in a field of view is marked by a flag

or a line and the total number is given on the meter, as

illustrated in Figure 26

.

The use of the QTM as a tool for track counting is

feasible provided the tracks are randomly orientated throughout the field of view. If the tracks are not randomly orientated but begin to overlap or form a cluster, the instrument

will not be capable of detecting each track in the overlap or

cluster. For instance, the QTM will give higher count values

113
Figure 26. Bismuth fission-track counting by the QTM.

for a cluster of tracks than the actual number of tracks

present. These higher values are obtained even though the

acceptance angle is set at the minimum point at which two

features lying in close proximity to one another can still be

detected individually. Additional work will be needed to reduce the high track counting values of cluster but, even so,

the QTM reduces both the time element and the eye fatigue

involved in track counting.

(R. A. Paulson, B. S. Carpenter, and W. P. Schmidt)

114
7. INTERNATIONAL RESEARCH GRANTS PROGRAM

A. Introduction

The National Bureau of Standards awarded a grant to the

Technion Research and Development Foundation on September 5,

1968, to apply anodic stripping voltammetry to trace analyses

in Standard Reference Materials. The project is an extension

of the work initiated in December 1965 and is under the supervision of Prof. Magda Ariel.

B. Mercury Coated Rotating Platinum Electrode (MCRPE)

Studies of the mercury coated rotating platin un electrode

(MCRPE) have been continued and reported in a recent publication [56]. Various methods of coating the platinum with

mercury have been studied. A method using a mercury drop of

known weight was used whenever thick films (exceeding 15

uM) were desired, while the method recommended by Barendrecht

[573 was used for thin films. When no cathodic potential is

imposed on the electrode, the mercury film tends to coalesce

into droplets with resulting electrode failure. Addition of

surface active agents such as Triton X-100 has a retarding

effect but often decreases sensitivity. Certain media (e.g.,

nitrates) seem to hasten electrode failure while others (acetate

buffer, ammonia buffer, etc.) improve keeping qualities. Infrequently, electrodes may be regenerated by cathodisation,

but for the stringent demands of trace analysis, complete

dissolution of the film, cleaning of the platinum, and recoating are required.

Good results were obtained by electrodepositing a thin

film of nickel on the RPE which was then coated by dipping in

mercury. Excess mercury was removed by suction to leave a

film 2-3 uM in thickness. Such electrodes had superior keeping

qualities but should not be left exposed to the atmosphere.

The pre-electrolysis step for the MCRPE is similar to that

for the hanging drop electrode. A slightly improved sensitivity

115
_7

and resolution is found with stirred solutions down to 10 M.

7 ft In the 10" 'M to 10" M range, quiescent solutions are advisable.

Due to its rigid construction, the MCRPE is very convenient to transfer from solution to solution which is another

advantage of this electrode. Experimental studies have shown

good reproducibility and linearity of response for lead and

copper down to a concentration range of 10 M. These results

are encouraging for further work to overcome problems of

stability and reconditioning of electrodes

C . Electrolysis Cell for Medium Exchange

A number of anodic stripping volt amine trie (a.s.v.) determinations would be facilitated by carrying out the stripping

process in a medium different from that in which the preelectrolysis is performed. On the other hand, the transfer

of the electrode from one medium to another offers the danger

of loss of deposited metal by air oxidation or otherwise. Also

there is the possibility of contamination by carry-over of the

mother liquor to the stripping medium.

A system has been designed and constructed that facilitates

the medium exchange process. It consists of the electrolysis

cell proper and reservoirs to hold the sample solution and

medium exchange solution, respectively. A pumpimg system is

provided to interchange the solutions when desired. The system

will be described in detail in a forthcoming publication.

The usefulness of the apparatus has been demonstrated by

application to the determination of trace metals (Zn, Cd, Pb

Cu) in iron base samples. While a.s.v. combined with conventional medium exchange could serve for the determination of

copper in these samples [56], all four trace metals can now

easily be determined, simultaneously, in a single sample

aliquot

CM. Ariel and co-workers)

116
8. PERSONNEL AND ACTIVITIES

A. Personnel Listing

John K. Taylor, Section Chief

Carolyn E. Smith, Secretary

Gas Analysis —

Ernest E. Hughes

Julian M. Ives

Polarography —

E. June Maienthal

Coulometry —

George Marinenko

Charles E. Champion

Electroanalytical Measurements —

Richard A. Durst

John W. Knoeck

Microscopy and Microchemistry —

Rolf A. Paulson

B. Stephen Carpenter

William P. Schmidt

B. Publications

1. R. A. Durst and J. W. Ross, "Electrochemical Generation of Fluoride Ion by Solid-State Transference", Anal. Chem.

40_, 1343 (1968) . 2. G. Marinenko and J. K. Taylor, "Electrochemical

Equivalents of Benzoic and Oxalic Acid", Anal. Chem. 40_, 1645

(1968).

3. E. E. Hughes, Book review: Gas Effluent Analysis , William Lodding, Ed., J. Am. Ceramic Soc. 5, 260 (1968).

4. J. M. Ives,- E. E. Hughes, and J. K. Taylor, "Absolute

Determination of Low Concentrations of Oxygen in Inert Gases

by Means of Galvanic Cells", Anal. Chem. 40_, 1853 (1968).

5. J. K. Taylor, "Modern Electrochemistry", Indus. Res.

October 1968 , p. 68.

6. J. K. Taylor, Editor, NBS Technical Note 455, "Microchemical Analysis Section: Summary of Activities, July 1967 to

June 1968", U. S. Government Printing Office, October 1968.

117
7. R. A. Durst "Determination of Fluoride by Analate

Additions Potentiometry", Mikrochem. Acta 3, 611 (1969).

8. C. E. Champion and G. Marinenko, "Errors in Coulometric Chloride Determinations Due to Photodecomposition of

Silver Chloride", Anal. Chem. 4l, 205 (1969).

C. Talks

1. R. A. Durst, "Specific-Ion Microanalysis by Linear

Null-Point Potentiometry", Microchemical Workshop, American

Microchemical Society, Pennsylvania State University,

University Park, Pennsylvania, July 1968.

2. J. W. Knoeck and H. Diehl, "High Precision Constant

Current Coulometric Assay of Primary Oxidizing Agents", 156th

National Meeting, American Chemical Society, Atlantic City,

New Jersey, September 1968.

3. C. E. Champion , G. Marinenko, and J. K. Taylor,

"Coulometric Determination of Micrograms of Chromium", 156th

National Meeting, American Chemical Society, Atlantic City,

New Jersey, September 1968.

4. G . Marinenko and C. E. Champion, "High Precision

Coulometric Analysis of Boric Acid", 156th National Meeting,

American Chemical Society, Atlantic City, New Jersey,

September 1968.

5. B. S. Carpenter, "Determination of Trace Quantities

of Uranium in Biological Materials by the Nuclear Track

Technique", 1968 International Conference on Modern Trends in

Activation Analysis, National Bureau of Standards, October

1968.

6. J. W. Knoeck, "Nitrate Complexes of Cerium IV",

Midwest Universities Analytical Chemistry Conference, Northern

Illinois University, DeKalb, Illinois, November 1968.

7- J. K. Taylor, "What is Chemistry?", Col. E. Brook

Lee Junior High School, Silver Spring, Maryland, November

1968.

118
8. J. K. Taylor, "Electrochemical Methods for Environmental Analysis", University of Michigan, Ann Arbor, Michigan,

December 1968.

9. J. K. Taylor, "Electrochemical Methods in Trace

Analysis", Set on Hall University, South Orange, New Jersey,

December 1968.

10. R. A. Durst, "Careers in Chemistry", Earle B. Wood

Junior High School, Rockville., Maryland, December 1968.

11. R. A. Durst, "Analytical Applications of Ion-Selective

Electrodes", Symposium on Ion-Selective Electrodes, National

Bureau of Standards, January 1969.

12. J. W. Knoeck and J. K. Taylor, "The Boric AcidBorate-Mannitol System", 4th Middle Atlantic Regional Meeting,

American Chemical Society, February 1969.

13. J. K. Taylor, "What is Chemistry?", Joyce Kilmer

Junior High School, Vienna, Virginia, February 1969.

14. J. K. Taylor, "Relations of Electricity and Chemistry",

Joyce Kilmer Junior High School, Vienna, Virginia, February

1969.

15. G. Marinenko and C. E. Champion, "Coulometric

Titrations of EDTA", 4th Middle Atlantic Regional Meeting,

American Chemical Society, Washington, D. C, February 1969.

16. E. J. Maienthal and J. R. Baldwin, "Analysis of

Standard Reference Glasses by Cathode Ray Polarography "

, 4th

Middle Atlantic Regional Meeting, American Chemical Society,

Washington, D. C, February 1969.

17. B. S. Carpenter and C. Cheek, "Determination of

Uranium in Biological Materials by Fission Track Counting",

4th Middle Atlantic Regional Meeting, American Chemical

Society, Washington, D. C, February 1969 . 18. E. E. Hughes, "A Mass Spectrometric Technique for

the Accurate Determination of the Argon Content of the

Atmosphere", 4th Middle Atlantic Regional Meeting, American

Chemical Society, Washington, D. C, February 1969.

119
19. C. E. Champion, "Cyclic Volt amme trie Study for the

Exchange Rate of Cadmium with Calcium EDTA Complex", George

Washington University, Washington, D. C, March 1969.

20. J. K. Taylor, "Careers in Chemistry", Good Counsel

High School, Wheaton, Maryland, March 1969.

21. J. W. Knoeck, "Complex Formation and Ion Pairing in

Metal Nitrate Solutions", University of Arizona, Tucson,

Arizona, April 1969 . 22. J. W. Knoeck and J. K. Taylor, "Nitrate Complexes of

Lanthaanide and Actinide Metals - A Mechanism for Catalytic

Nitrate Waves", 157th National Meeting, American Chemical

Society, Minneapolis, Minnesota, April 1969.

23. J. W. Knoeck and J. K. Taylor, "Borate-Polyalcohol

Complexes", 157th National Meeting, American Chemical Society,

Minneapolis, Minnesota, April 1969.

2k. E. J. Maienthal , R. A. Paulson, and J. K. Taylor,

"Applications of Polarography to the Analysis of Air

Pollutants", 157th National Meeting, American Chemical Society,

Minneapolis, Minnesota, April 1969.

25. J. K. Taylor, "Wnat is Chemistry?", St. Ann Junior

High School, Arlington, Virginia, April 1969.

26. J. K. Taylor, "High Precision Electrochemical

Analysis", University of Maryland, College Park, Maryland,

May 1969

27. J. W. Knoeck, "Complex Formation and Ion Pairing in

Metal Nitrate Solutions", North Dakota State University,

Fargo, North Dakota, May 1969.

28. J. K. Taylor, "Electrochemical Methods for Elemental

Analysis", 10th Summer Symposium, ACS Division of Analytical

Chemistry, University of Georgia, Athens, Georgia, June 1969*.

D. Committee Activities

J. K. Taylor

Service Analysis Coordinator, Analytical Chemistry Division

Member, Review Board, Science Book List, American Association

120
for the Advancement of Science

Member, Board of Managers, Washington Academy of Sciences (WAS)

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

Member, Council Committee on Chemical Education, American

Chemical Society

Member, Panel on Chemistry, Civil Service Board of Examiners

Member, Board of Managers, Chemical Society of Washington

Member of Council, The Polarographic Society of London

Member, Advisory Committee, Laboratory Guide, American Chemical

Society

Chairman, Chemical Education Topical Group, Chemical Society

of Washington

Member, ISO/TC 48 Laboratory Glassware and Related Apparatus

Chairman, Program Committee, Alpha Chi Sigma

R. A. Durst

Treasurer (to 9/68), The Capital Chemist, Chemical Society of

Washington

Member, Member Services Committee, Chemical Society of

Washington

Safety Representative, Microchemical Analysis Section

Chairman, Symposium on Ion-Selective Electrodes, National

Bureau of Standards

Chairman, Symposium on Electroanalytical Measurements, 4th

Middle Atlantic Regional Meeting, American Chemical

Society

Elected member, Board of Managers, Chemical Society of

Washington

Member, Education Committee, Chemical Society of Washington

Faculty member, Stonecrest Study Center

Member, Colloquium Committee, Analytical Chemistry Division,

National Bureau of Standards

E. June Maienthal

NBS Reporter for Capital Chemist, Chemical Society of

Washington

121
Editor, Analytical Chemistry Division Newsletter, NBS

Division Representative for NBS Standard

G. Marinenko

Member, Ad Hoc Committee on Electronic Data Systems, Division

of Analytical Chemistry, NBS

Chairman, Refreshment Committee, Alpha Chi Sigma

R. A. Paulson

Member, Services Analysis Committee, Analytical Chemistry

Division, NBS

Collaborator, Committee for Study of Microchemical Methods,

Association of Official Agricultural Chemists

E. Standard Reference Materials Analyses

Material Analyst Determination Technique

Stainless Steel l60b, GM & CEC Cr C

1155 EJM Bi, Pb P

RAP Mo, Ni G

Ductile Iron 1140, EJM Bi, Pb P

1140a, 1141, ll4la,

1142, 1142a

Special Steels 1261, EJM Bi, Pb, Ti P

1265

Copper Organic 1080a EJM Cu P

Calcium Carbonate WPS Acceptance Testing G, M

GM & CEC Assay C

Au-Ag Microprobe 481 RAD Au, Ag Pot

GM Ag C, G

Plastic and Flint RAP C, H, Moisture G, M

Clays 97a, 98a

Boric Acid GM & CEC Assay C

Potassium Dichromate WPS Acceptance Testing G, M

GM & CEC Assay C

122
E. (Continued)

Material

Potassium Chloride

Sodium Chloride

KH

2

Citrate

Sodium Oxalate

Analyst

WPS

GM & CEC

WPS

GM & CEC

GM & CEC

WPS

Microstandard

Particles 1800, 1801, WPS

1802, 1803 RAP & wps

GM, RAP, WPS

EJM

Standard Glasses for

Trace Elements

Bilirubin

Glucose

Uric Acid

Creatinine

EJM

Determination Technique

Acceptance Testing G, M

Assay C

Acceptance Testing G, M

Assay C

Assay C

Acceptance Testing G, M

Stability G

S, C, H, Density G, M

Capacity C, Pot

Elemental Analysis P

Ni p

EJM Mesobilirubin P

WPS Ash, Moisture,

Insolubles

G

WPS C, H, N, Ash,

Insolubles

G, M

WPS C, H, N, Ash, G, M

Insolubles

Key to Analyst

CEC - Charles E. Champion

RAD - Richard A. Durst

EJM - E. June Maienthal

GM - George Marinenko

RAP - Rolf A. Paulson

WPS - William P. Schmidt

Key to Technique

C - Coulometry

G - Gravimetry

M - Microchemical

P - Polarographic

Pot - Potentiometric

123
9 . REFERENCES

[1] J. K. Taylor, Editor, NBS Technical Note 455, October

1968.

[2] E. E. Hughes, "A Mass Spectrometric Technique for the

Accurate Determination of the Argon Content of the

Atmosphere", 4th Middle Atlantic Meeting of the ACS,

February 12-13, Washington, D. C.

[3] Shinya Oana, J. Earth Sci . , Nayoga Univ. 5, 103-24

(1957).

[4] H. Moissan, Paris, C. R. Acad. Sci. 137 , 600 (1903).

[5] R. K. Stevens, A. E. O'Keaffe and G. C. Ortmon, Environ

Sci. and Tech., in press.

[6] E. J. Maienthal and J. K. Taylor, Mikrochim. Acta 1967 , 939.

[7] D. H. Freeman and R. A. Paulson, Nature 218, 563 (1968)

[8] B. Tvaroha, Naturwiss. 4_8 ? 99 (196l) . [9] J. K. Taylor, Editor, NBS Technical Note 425, October

1967.

[10] E.J. Maienthal and J. K. Taylor, Anal. Chem . 37, 1516

(1965).

[11] P. S. Roller, J. Amer. Chem. Soc . 5£, 1 (1928).

[12] D. A. Maclnnes , The Principles of Electrochemistry , Reinhold Publishing Corp., 1939, pp. 307-312.

[13] R. G. Bates and E. Wichers, J. Res. NBS 59., 9 (1957).

[14] G. Marinenko and J. K. Taylor, Anal. Chem. 40_, 1645

(1968).

[15] International Union of Pure and Applied Chemistry,

Comptes Rendus XXIV Conference, Prague, 4-10 Sept. 1967

pp. 130-141.

[16] A. E. Cameron and E. Wichers, J. Amer. Chem. Soc. 84 , 4175 (1962)

[17] A. 0. C. Nier, Phys . Rev. 77, 789 (1950).

[18] F. Everling, L. A. Konig, S. H. E. Mattauch, and A. H.

Wapstra, Nuclear Physics 1_8, 529 (.I960).

124
G. Marinenko and J. K. Taylor, J. Res. NBS 67A, 453

(1963).

R. A. Durst, Editor, Ion-Selective Electrodes , NBS

Special Publication 314, 1969.

R. A. Durst and J. K. Taylor, Anal. Chem. 39, 1483

(1967).

R. A. Durst, Anal. Chem. 40_, 931 (1968).

R. N. Khuri, in Ion-Selective Electrodes , R. A. Durst,

Editor, NBS Special Publication 314, 1969, Chapter 8.

J. Knoeck and J. K. Taylor, "Aqueous Boric Acid-BorateMannitol Equilibria", Anal. Chem. (in press).

Jo-Yun Tung and Hok-Ling Chang, J. Chinese Chem. Soc.

9, 125 (1942).

J. Boeseken and N. Vermaas , J. Phys . Chem. 35. > 1477

(1931).

J. Boeseken and N. Vermaas, Rec. trav. chim. 5_4, 853

(1935).

A. Deutsch and S. Osoling, J. Am. Chem. Soc. 71 a 1637

(1949).

S. Ross and A. J. Catotti, J. Am. Chem. Soc. 71, 3563

(1949).

K. Torssell, Arkiv Kemi 3, 571 (1952).

P. J. Antikainen, Acta Chem. Scand. 9, 1008 (1955).

R. P. Nickerson, J. Inorg. Nucl. Chem. 10, 1447 (1968).

R. G. Bates, in Determination of pH, Theory, and Practice , Wiley, New York, 1964, p. 84.

J. 0. Edwards, J. Am. Chem. Soc. 75_, 6154 (1953).

P. J. Antikainen, Suomen Kemi B_3p_, 74 (1957).

N. Ingri, G. Lagerstrom, M. Frydman, and L. G. Sillen,

Acta Chem. Scand. 11, 1034 (1952).

J. W. Collat and J. J. Lingane, J. Amer. Chem. Soc. 7_6,

4214 (1954).

T. A. Beineke and J. DelGaudio, Inorg. Chem. 7, 715 (1968)

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125
[40] D. E. Irish and G. E. Walrafen, J. Chem. Phys . 46_, 378

(1967).

G. Oster and M. Yamamoto, Chem. Rev. 63, 257 (1963).

R. L. Fleischer and P. B. Price, Phys. Rev. !L33, B63

(1964).

[41]

[42]

[43]

[44]

P. B. Price and R. M. Walker, Nature 196_, 732 (1962).

P. B. Price and R. M. Walker, J. Geophys . Res. 68_, 4847

(1963).

[45] B. S. Carpenter and C. Cheek, "Trace Determination of

Uranium in Biological Material by Fission Track Counting",;

Anal. Chem. (in press).

[46] R. L. Fleischer, P. B. Price and R. M. Walker, Annual

Review of Nuclear Science 15_, 1 (1965).

[47] R. L. Fleischer, P. B. Price, R. M. Walker, and E. L.

Hubbard, Phys. Rev. 133A , 1443 (1964).

[48] R. L. Fleischer, P. B. Price, and R. M. Walker, Science

149 , 383 (1965).

[49] B. A. Loveridge and C. A. Mclnnes , The Microscope l6_,

105 (1968)

[50] C. Fisher and M. Cole, The Microscope l6_, 8l (1968).

[51] R. L. Fleischer and P. B. Price, Geochimica et

Cosmochimica Acta 28_, 1704 (1964).

[52] R. L. Fleischer and P. B. Price, J. Appl. Phys. 34_, 2903

(1963).

[53] R. L. Fleischer and P. B. Price, Science 140_, 1221

(1963).

[5^] R. M. Walker, P. B. Price and R. L. Fleischer, Appl.

Phys. Letters 3, 28 (1963).

[55] E. B. Sandell, Colorimetric Determination of Traces of

Metals , Interscience .Publisher, Inc., New York, 1959,

p. 338.

[56] G. Koster and M. Ariel, Israel J. of Chem. 7, 21 (.1969).

[57] E. Barendrecht, "Stripping Voltammetry" in Electro - analytical Chemistry , Alan Bard, Editor, Vol. II,

Marcel Dekker, Inc., New York, 1967.

126
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scientific and technical activities. National Standard Reference Data Series.

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and chemical properties of materials, compiled from

the world's literature and critically evaluated. Product Standards. Provide requirements for sizes, types, quality and methods for testing various industrial products. These standards are developed cooperatively with interested Government and industry groups

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Technical Notes. This series consists of communications and reports (covering both other agency and

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adopted and promulgated under the Public Law

89-306, and Bureau of the Budget Circular A-86

entitled, Standardization of Data Elements and Codes

in Data Systems.

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