I!

A UNITED STATES DEPARTMENT OF COMMERCE

PUBLICATION

Ssof"

MMM B^ of WJJ*

NBS TECHNICAL NOTE 504

OCT

A969

Analytical Coordination Chemistry

Section:

Summary of Activities

July 1968 to June 1969

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards ' was established by an act of Congress March 3, 1901 . Today,

in addition to serving as the Nation's central measurement laboratory, the Bureau is a principal

focal point in the Federal Government for assuring maximum application of the physical and

engineering sciences to the advancement of technology in industry and commerce. To this end

the Bureau conducts research and provides central national services in four broad program

areas. These are: (1) basic measurements and standards, (2) materials measurements and

standards, (3) technological measurements and standards, and (4) transfer of technology.

The Bureau comprises the Institute for Basic Standards, the Institute for Materials Research, the

Institute for Applied Technology, the Center for Radiation Research, the Center for Computer

Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system with measurement systems of other nations; and furnishes essential services leading to accurate and

uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of an Office of Measurement Services and the following technical

divisions:Applied Mathematics—Electricity—Metrology—Mechanics—Heat—Atomic and Molecular Physics—Radio Physics - —Radio Engineering -—Time and Frequency - —Astrophysics '-' —Cryogenics.

-

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to im- proved methods of measurement standards, and data on the properties of well-characterized

materials needed by industry, commerce, educational institutions, and Government; develops,

produces, and distributes standard reference materials; relates the physical and chemical properties of materials to their behavior and their interaction with their environments; and provides

advisory and research services to other Government agencies. The Institute consists of an Office of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations in the development of technological

standards, and test methodologies; and provides advisory and research services for Federal, state, and local government agencies. The Institute consists of the following technical divisions and

offices: Engineering Standards—Weights and Measures — Invention and Innovation — Vehicle Systems Research—Product Evaluation—Building Research—Instrument Shops—Measurement Engineering—Electronic Technology—Technical Analysis.

THE CENTER FOR RADIATION RESEARCH engages in research, measurement, and application of radiation tp the solution of Bureau mission problems and the problems of other agencies and institutions. The Center consists of the following divisions: Reactor Radiation—Linac Radiation—Nuclear Radiation—Applied Radiation. THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and

provides technical services designed to aid Government agencies in the selection, acquisition,

and effective use of automatic data processing equipment; and serves as the principal focus

for the development of Federal standards for automatic data processing equipment, techniques,

and computer languages. The Center consists of the following offices and divisions: Information Processing Standards—Computer Information — Computer Services — Sys- tems Development—Information Processing Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal government; promotes the development of the National Standard Reference Data System and a system of information analysis centers dealing with the broader aspects of the National Measure- ment System, and provides appropriate services to ensure that the NBS staff has optimum accessibility to the scientific information of the world. The Office consists of the following

organizational units:

Office of Standard Reference Data—Clearinghouse for Federal Scientific and Technical Information ' —Office of Technical Information and Publications—Library—Office of Public Information—Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg. Maryland, unless otherwise noted; mailing address Washing-ton, DC. 20234.

- Located at Boulder. Colorado 80302.

3 Located at 5285 Port Royal Road, Springfield, Virginia 22151.
UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director

NBS TECHNICAL NOTE 504

ISSUED OCTOBER 1969

Nat. Bur. Stand. (U.S.), Tech. Note 504, 120 pages (Oct. 1969)

CODEN: NBTNA

Analytical Coordination Chemistry

Section:

Summary of Activities

July 1968 to June 1969

Edited by Oscar Menis

Analytical Coordination Chemistry 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
FOREWORD

The Analyticct-L 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, 196*J, 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.

li
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 Analytical Coordination Chemistry Section.

W. Wayne Meinke a Chief

Analytical Chemistry Division

111
PREFACE

The strong interaction during the past year between

research and development and the analysis of Standard

Reference Materials is again reflected in the work of this

section. Particular emphasis has been placed on the development of new or improved methods and the modification of

instruments to provide greater precision, accuracy ana

sensitivity as demonstrated in the analysis of a variety of

Standard Reference Materials. Areas of research have

included flame emission and atomic absorption, spectrophotometry and spectrofluorometry , thermal analysis and the

determination of gases in metals.

The presentation of this material has been arranged to

facilitate the use of this information by the reader as it

applies to his specific needs or interests. For this reason

the topics dealing with the research aspects of the specific

competences and the area of Standard Reference Materials are

reported separately. In presenting the latter separately,

we are able to emphasize the complex nature of the materials

and to give proper perspective to the section's contribution

to the NBS efforts in chemical characterization. The descriptive information associated with the Standard Reference

Materials should assist the reader in making better use of

these materials. Even more important, however, we hope it

will encourage the reader to communicate with the division

to point out the current needs which may have been heretofore neglected and thus be of help in developing a more

meaningful program by the Analytical Chemistry Division.

Problems related to clinical chemistry have not been

discussed in this report; however, a broad program is being

initiated involving spectrophotometry, spectrofluorometry

,

and flame spectroscopy for use in preparing suitable Standard

Reference Materials for the clinical chemist. The initial

stages concerned the recruitment of appropriate personnel,

iv
the acquisition of special equipment and material, and the

development of a program essential in this study. For this

reason a full program report will be forthcoming in succeeding

reports. While some of the work reported may appear fragmentary and lack detail, it is anticipated that much of it will

appear later in its entirety in journal articles or NBS

Miscellaneous Publication 260.

In order to adequately describe experimental procedures,

it is occasionally necessary to identify commercial products

and equipment by the manufacturer's name or label. In no

instances does such identification imply recommendation or

endorsement by the National Bureau of Standards, nor does it

imply that the particular product or equipment is necessarily

the best available for that purpose.

The assistance of Mrs. Rosemary Maddock is gratefully

acknowledged. Also, we acknowledge the invaluable assistance

of Mrs. Mary Pantazis, Section Secretary, who performs a wide

variety of duties essential to the work in this section, and

for her tireless efforts in typing this report.

Oscar Menis, Chief

Analytical Coordination Chemistry

James I. Shultz, Assistant Chief

Analytical Coordination Chemistry

v
TABLE OF CONTENTS

PAGI

FLAME EMISSION AND ATOMIC ABSORPTION SPECTROMETRY. 1

A. Introduction 1

B. Source of Monochromatic Radiation 1

1. Electrodeless Discharge Lamps 1

C. Derivative Flame Emission Spectrometry .... 2

1. Experimental Setup 2

2. Experimental Procedure 4

3. Results and Discussion 5

D. Evaluation of the Atomic Absorption Method for

Arsenic 9

1. Corrections for Physical Interferences . . 9

2. Effect of Band Width on Absorption .... 10

E. Analytical Application to Standard Reference

Materials 11

1. Determination of Copper in Basic Oxygen

Furnace Steel and Chrome-Moly Steel - NBS-SRM 178 and 36b 11

2. Determination of Magnesium in Nodular Iron - NBS-SRM 3^2a 13

3. Determination of Trace Impurities in

Calcium Carbonate - NBS-SRM 380 13

F. Service Analyses 13

SPECTROPHOTOMETRY AND SPECTROFLUOROMETRY 15

A. Introduction 15

B. Research Activities 16

1. Development of a Method for the Simultaneous

Spectrophotometric Determination of

Cobalt j Nickel and Copper 16

a. Procedure 16

b. Discussion and Results 18

2. Development of New Solvent Extraction

Systems Designed Especially for High

Sensitivity SpectrophotometrySpectrofluorometry 27

a. Experimental 27

b. Discussion and Results 28

3. Spectrophotometric Determination of Vanadium

and Iron with $-Isopropyltropolone ... 31

a. Experimental 32

b. Procedures 33

c. Results and Discussion 35

4. Direct Spectrofluorometric Determination

of Rare Earth Elements in Synthetic

Glasses 38

a. Preparation of the Borate Glasses. . . 38

b. Placement of the Solid Sample in the

Light Beam 39

vi
TABLE OF CONTENTS (CONT'D)

PAGE

c. Discussion and Results 39

C. Analysis of Standard Reference Materials

(SRM's) and Related Samples 43

1. Precise and Accurate Determination of

Cobalt in Aluminum Neutron Flux

Wire (NBS-SRM 953) 43

2. Simultaneous and Differential Spectrophotometry Determinations of Molybdenum

and Tungsten in Mo-W Compact with

Tiron (4,5-dihydroxy-m-benzene

disulfonic acid) 46

a. Preparation of Samples 46

b. Dissolution. . . 46

c. Analysis 47

d. Results and Discussion 48

3. Spectrofluorometric Determination of AirBorne Beryllium 49

4. Spectrophotometric Determination of

Iron and Copper in High Purity Gold. 49

5. Service Analyses 52

3. DIFFERENTIAL THERMAL ANALYSIS 53

A. Modification of Instrument 53

B. Experimental 54

1. Modification of Commerical DTA - Thermocouple Wiring 54

a. Changes in Thermocouple Arrangement 55

b. Recorder Changes 57

c. Lower Scanning Rates ....... 57

d. Automatic Voltage Divider for Bucking

Voltage Source 58

C. Temperature Calibration 6l

1. Thermocouple Changes 6l

2. Calibration Procedure 62

3. Sample Cups 62

4. Results 63

4. GASES IN METALS 69

A. Introduction 69

B. A New Inert-Gas-Fusion Apparatus for the

Determination of Oxygen and Nitrogen in

Metals 69

C. The Testing of a Maraging Steel for Use as

a Low Oxygen Content Standard Reference

Material 71

D. The Determination of Nitrogen in Ferrous

Materials 73

vii
TABLE OF CONTENTS (CONT'D)

PAGE

5. ANALYSIS OF STANDARD REFERENCE MATERIALS 74

A. Introduction 74

B. SRM Information and Summary 76

1. Steel (2 Cr-1 Mo) - SRM 36b 77

2. High Silicon Steel (3 Si) - SRM 125b. . . 78

3. Low Carbon (<0.002 C) Steel - SRM 131b. . 79

4. Stainless Steel (19 Cr-12 Ni-3 Mo) - SRM 160b 80

5. Carbon Steel (0.4 C) - SRM 178 8l

6. Ingot Iron and Valve Steel - SRM 1090,

1093 82

7. Cast Steels Spectrographic - SRM 1138-

1139 83

8. Spectrographic Standards 1261-1265 (Iron

and Steels) 84

9. Standard Cast Iron - SRM 122e 86

10. Standard Nodular Iron - SRM 342a .... 86

11. Standard Ferrosilicon - SRM 59a 88

a. Silicon 88

b. Manganese 90

c. Chromium 91

d. Iron 91

12. Metal-Organic Materials 9 4 13. Clay Standards 97a and 98a 95

a. Gravimetric Methods for Si02 96

b. Gravimetric Methods for AI2O3 .... 97

C. ASTM Activities 98

6. REFERENCES 10

7. PERSONNAL AND ACTIVITIES 103

LIST OF TABLES

TABLE NO.

1. Detection limits by flame emission spectrometry

for ac scan 7

2. Detection limits by flame emission spectrometry

with ac scanning in the presence of matrixions 8

3. Effect of copper and iron on the absorption of

arsenic at 1937 A 9

4. Role of spectral band Q width on the absorption

of arsenic at 1937 A 11

5. Summary of NBS-SRM analyses by flame emission

and atomic absorption spectrometry 12

viii
TABLE OF CONTENTS (CONT'D)

TABLE NO . PAGE

6. Analysis of synthetic solutions of cobalt,

nickel and copper 25

7. Analysis of NBS Standard Reference Materials

(SRM's) 26

8. Rate of formation of the colored complex V(V)-

IPT in chloroform 35

9. Additive properties of vanadium and iron IPT

complexes 37

10. Relative fluorescence R/P of various concentrations of europium in borate glass; excitation

at 255 nm 42

11. Relative fluorescence R/P of gadolinium in

borate glass 42

12. Relative fluorescence R/F of gadolinium as a function of concentration in glass containing

equal amounts of Gd(III) and Sm(III). ... 43

13. Spectrophotometric determination of cobalt in

aluminum neutron flux wire with 2, 3-quinoxalinedithiol 45

14. Simultaneous differential spectrophotometric

analysis of Mo-W Compact 48

15. Spectrophotometric determination of iron and

copper in high purity gold 51

16.. Spectrophotometric-spectrofluorometric service

analysis 52

17. DTA transition point measurements 66

18. Oxygen homogeneity in maraging steel 72

19. Determination of nitrogen ferrous alloys. ... 73

20. SRM's analyzed by Analytical Coordination

Chemistry Section 74

21. Composition data for SRM 36b 77

22. Composition data for SRM 125b 78

23. Composition data for SRM l60b 80

24. Composition data for SRM 178 81

25. Nitrogen data for SRM 1090 „ 83

26. Nitrogen data for SRM 1093 83

IX
TABLE OF CONTENTS (CONT'D)

TABLE NO. PAGE

27. Composition data for SRM's 1138 and 1139 .... 84

28. Composition data for SRM's 1261, 1262 and 1265 . 85

29. Composition data for SRM 342a 87

30. Percent silicon obtained on bulk material ... 88

31. Certified metallo-organic compounds 94

LIST OF FIGURES

FIGURE NO.

1. Location of quartz plate within the optical

system 3

2. Flame emission spectrum of barium 4

3. Effect of calcium on barium in flame emission

with ac scanning and second derivative

measurement 6

o 4. Spectrum of copper in the region of 3274 A . . . 6

5. Lithium calibration results by flame emission

with ac scanning and second derivative

measurement 8

6. Spectrum of arsenic over the wavelength region of

1880 A to 2005 & 10

7. Absorption spectra of the copper, nickel and

cobalt complexes and of the reagent 19

8. Reduction of copper(II) to copper(I) by 2,3-

quinoxalinedithiol 20

9. Absorbances of the colored complexes at various

acidities 21

10. Absorbance spectrum of the vanadium(V) - 3-isopropyltropolone complex 36

11. Optimum angular placement of glass sample for in

situ fluorescence analysis 39

12. Excitation spectrum of europium(III) ; fluorescence

measured at 617 nm 40

13. Fluorescence spectrum of europium(III)

;

excitation at 395 nm with xenon source .... 40

14. Fluorescence spectrum of europium(III) ; 255 nm

excitation with mercury arc 4l

15. Apparatus for dissolution - extraction of iron in

high purity gold 50

x
TABLE OF CONTENTS (CONT'D)

FIGURE NO. PAGE

16. Thermocouple wiring 56

17. Model B programmer motor speed vs rate dial

setting 57

18. Automatic voltage divider 59

19. Differential thermal curves - NBS Standard

Reference Materials 64

20. Differential thermal curves - NBS FreezingPoint Standards 65

21. Homogeneity data on proposed SRM quartz ... 67

22. Homogeneity data on proposed SRM potassium

nitrate 68

XI
ABSTRACT

Research developments are described in flame emission

and atomic absorption spectrometry, spectrophotometry,

spectrof luorometry , differential thermal analysis and the

analysis and certification of Standard Reference Materials.

The application of ac wavelength scanning and second derivative measurements of spectral line intensities serve to

overcome broad-band and continuum interferences of matrices

in flame emission analysis. It also provides for the

analysis of samples as small as 50 ul. In atomic absorption

studies of arsenic, basic corrections for spectral interferences are given.

New spectrophotometric methods have been developed for

the analysis of multicomponent systems. These include the

simultaneous determinations of cobalt, nickel and copper

with 2 ,3-quinoxalinedithiol and of vanadium and iron with

3-isopropyltropolone . The extraction of ternary ion

association complexes initially containing non-colored or

non-fluorescent organic cations, followed by displacement of

these groups by highly colored or highly fluorescent dye

cations directly in the organic phase, has provided a means

of simultaneously improving sensitivity and selectivity in

absorption and fluorescence spectrophotometry. The determinations of gold and uranium are described to illustrate the

approach. Spectrofluorometric studies of the determination

of rare earth elements in synthetic borate glass are also

presented.

Instrument modifications and temperature measurement

techniques now provide a tenfold increase in the precision of

measurements of phase transition temperatures of quartz and

potassium nitrate on differential thermal analysis standards.

Procedures, analytical data and background information

are presented for Standard Reference Materials of steels,

cast and nodular irons, ferrosilicon, high-purity materials,

xii
neutron flux monitor wire, organo-metallic compounds, glasses,

and clays. These descriptions include atomic absorption

methods for copper in steel, magnesium in nodular iron,

impurities in calcium carbonate, high precision spectrophotometric methods for cobalt in aluminum wire, molybdenum

and tungsten in microprobe standard, traces of iron and

copper in high purity gold and methods for the determination

of silica and aluminum in clays.

xiii

1. FLAME EMISSION AND ATOMIC ABSORPTION SPECTROMETRY

A. Introduction

The state of the art has grown at a spectacular rate

during the past year as Indicated by the 300 papers and

4 books that were published during this period. This

expanding interest is reflected at NBS by the number of

invited lectures, the many requests for assistance and

consultation and short courses given on the subjects.

In a continuing effort to improve our competence in

flame emission and atomic absorption spectrometry, new

instrument designs and techniques were evaluated. These

include new sources of monochromatic radiation, nebulizerburners, gas systems, optical arrangement, electronics and

analytical techniques. The technique of ac repetitive

scanning of narrow wavelength regions reported previously [1]

for atomic absorption has been extended to flame emission.

A new design in the optical and electrical components with

the ac scan and synchronous detection, provided a versatile

analytical tool. The interferences due to a continuum or

unresolved band structures are minimized, thus permitting

increased detection limits in the presence of relatively high

concentrations of matrix ions. Since many analyses required

only 50 yl of sample, this technique affords the analyst a

unique method for trace analysis in bioclinical and pollution

studies

.

The successful application of the ac scanning derivative

technique to the problem associated with the analysis of

Standard Reference Materials and special service analyses

attests to its wide utility.

B. Source of Monochromatic Radiation

1. Electrodeless Discharge Lamps

In the two earlier reports [1, 2], our experiences with

the electrodeless discharge lamp (EDL) were discussed. To

overcome the instability of the EDL, several new approaches

1
were investigated. The air flow for cooling the cavity was

preheated by passing it through a tube furnace. Controlling

the temperature of the air increased the radiant intensity

and the stability of the EDL. The intensity of lamps containing neon as a filler gas was greater than the argonfilled lamps.

For the first time, a multi-element EDL was prepared.

Lamps were prepared containing Pb , Zn and Cd as well as Li,

Na and K. The multi-element lamps performed as well as the

single element lamps.

Two RF power generators for these lamps with power outputs of 0-lOOw and 20-200w operating at 2450 MHz were also

tested. The stability and radiant intensity of the EDL were

similar for both generators. Three new cavities (one - 1/4

wave and two - 3/4 wave) are presently being evaluated.

C . Derivative Flame Emission Spectrometry

The measurement of an atomic line which appears in or

on a bandhead due to the concomitants or flame gases, is of

interest and concern to flame emission spectroscopists . In

an earlier report [1], an ac scanning technique with a continuous source was discussed for atomic absorption

spectrometry. The ac scanning of part of the continuum was

accomplished by vibrating a mirror within the optical path

mounted on the movement of a milliammeter . While the

optical arrangement demonstrated the feasibility of the ac

scan in atomic absorption work, there were certain limitations due to the development of an improved system which

utilizes an oscillating quartz plate and provides an

apparatus which is stable and easy to operate. The new

optical and electronic arrangement was tested in the flame

emission and atomic absorption modes.

1. Experimental Setup

The instrumental system used in this study consists of

(a) Czerny-Turner 0.75m monochromator , f/6.5 aperture,
curved slits, exchangeable grating blazed for 3000 and

o 7500 A with ll80 grooves /mm , (b) quartz plate mounted on a

rotating mechanical oscillator and (c) associated electronic

controls. The quartz plate (12x14x2 mm) is mounted on a

rotating mechanical oscillator possessing a variable

amplitude of up to 6° peak to peak, behind the entrance

slit, as shown in figure 1.

QUARTZ

PLATE

ENTRANCE

SLIT

I EXIT SLIT

Figure 1. Location of quartz plate within the

optical system.

The lateral displacement of the image is proportional to

the thickness of the quartz plate and to the angle of

rotation. Under the experimental conditions, the displaceo ment of the line was 1 A. A larger displacement can be

obtained by using a thicker quartz plate and by increasing

the angle of rotation. Since the image is defocused at the

exit slit, because of a change in optical path length, the

quartz plate was ground to a slight convex curvature corresponding to a 12m focal length.
The mechanical oscillator and the associated electronics were designed and built by the Measurement Engineering

Division of the National Bureau of Standards.

2. Experimental Procedure

o The 5536 A barium resonance line was scanned using an

oxygen-hydrogen flame. The light signal was chopped at

87 Hz using a mechanical disc chopper. The spectrum

obtained is shown in figure 2A.

Bo, 5536 %-

Figure 2. Flame emission spectrum of barium.

The mechanical disc chopper was removed from the

system and the quartz plate was placed behind the entrance

slit within the optical path. A current was applied to the

drive coil which produced an oscillation of the quartz plate

The synchronous lock-in amplifier was tuned to the frequency

of the vibrating quartz plate. A wavelength scan of the
o 5536 A barium resonance line was repeated. The resulting

spectrum was the first derivative with the peak corresponding

to the zero crossing of the X axis. This is shown in

figure 2B. While the first derivative has been used in

spectroscopy [3] for identifying overlapping band structures,

scanning of the wavelength region is required. This offers

no advantage in flame emission over the mechanical disc

chopper. The experiment was repeated, but the lock-in

amplifier was tuned to twice the frequency of the vibrating

quartz plate. The spectrum obtained (figure 2C) was the

second derivative and is proportional to the analyte concentration.

3. Results and Discussion

Since the CaOH band system over the region of 5520 to

o 5570 A interferes in the determination of barium [4, 5, 6,

7], the ac scanning with the second derivative was investigated as a means of reducing this interference. A sample

containing equal concentrations of calcium and barium was

tested and the calcium did not interfere with the barium.

Using the ac scan and taking the second derivative, no

continuum or unresolved band structure was detected. By

setting on the peak of the barium resonance line and taking

the second derivative rather than mechanically scanning the

wavelength region, barium can be determined with an airacetylene flame in the presence of a hundred-fold concentration of calcium, as shown in figure 3. Flames of higher

temperatures, such as oxygen-hydrogen or nitrous oxideacetylene with appropriate burners, permitted the

determination of barium in calcium in the ratio of 1:1000.

o The resonance lines of copper at 3247 and 3274 A are

located in a region of relatively strong OH emission. The

o strongest copper line at 3247 A coincides with a sharp OH

o bandhead at 3247 A and the ac scan did not improve the

detection limits. However, as shown in figure 4, there

o are two unresolved OH band-peaks at 3274 A. With an

5
_*lm »'* ,*~ *1 J--"-'**

Ba, *g/ml 5 10 5 10 5 10

Ca, eg/ml 100 100 1000 1000

Ca blank

Figure 3. Effect of calcium on barium in flame

emission with ac scanning and second

derivative measurement*

Figure 4. Spectrum of copper in the region of 327^ A,

6
o amplitude scan of 1 A or less, the unresolved OH band peak

is used as a base line. The detection limits measured with

the ac scan and second derivative signal for copper and

several other elements are given in table 1.

Table 1. Detection limits by flame emission spectrometry

for ac scan.

Oxidant and fuel—-oxygen-hydrogen

Burner total consumption

Phototube EMI 9558AQ

o a Element Wavelength, A Detection limits, y g/ml

Li 6708 0.00002

K 7665 0.0001

Mg 2852 0.1

Ca 4227 0.001

Cu 3247 0.1 (0.1)?

3274 0.03 (0.2)°

Detection limit is defined as 2a of background.

Values obtained with mechanical disc chopper.

The detection limits normally reported for flame

emission spectrometry are generally obtained with pure

water solutions. These values may be very misleading if

applied to samples containing certain cations. The detection limits obtained using the ac scan for lithium,

potassium and calcium in the presence of 1000 y g/ml of

various matrix elements are given in table 2. The values

are as low as those reported in the literature using pure

water solutions in flame emission spectrometry work.

Another unique feature of this technique is the size of

sample required for an analysis. In normal flame emission

spectrometry, three to five ml of solution are required for

making a scan of the wavelength region of interest. By

setting on the peak of a line and using the ac scan, only

a small portion of the solution is required. For example,

using a total consumption burner and a small bore capillary,
Table 2. Detection limits by flame emission spectrometry

with ac scanning in the presence of matrix-ions.

Oxidant and fuel oxygen-hydrogen

Burner total consumption

Sample size 0.25 ml

Matrix, element

1 mg/ml

Li

Na

K

Rb

Mg

Ca

Fe

Detect ion limit, ang

Li K Ca

— 0.2 3.0

0.02 0.08 0.5

0.02

iTob 3.0

0.02 3.0

0.02 0.1 (c)

0.02 0.03 - 0.02 0.2 3.0

ng = 10

-9

grams

Detection limit is defined as 2a of background.

Rubidium free of potassium not available.

'Magnesium free of calcium not available.

lithium was determined in a sodium matrix with only 50 ul of

solution as shown in figure 5. The reproducibility of the

Figure 5. Lithium calibration results by flame

emission with ac scanning and second

derivative measurement.

8
peak height was better than 2 percent of full scale. The

speed of the recorder pen was the limiting factor for the

required volume of solution.

D. Evaluation of the Atomic Absorption Method for Arsenic

1. Corrections for Physical Interferences

In a continuing effort to improve the precision and

accuracy, reported previously [1], of the determination of

arsenic by atomic absorption spectrometry, several new

parameters were investigated. The absorption of arsenic

o at the 1937 A resonance line varied with different cations

present. While spectral interferences in atomic absorption

are reported in the literature [6], physical interferences

are often present and are associated with the chemical

composition of the matrix. Scattered light which appears

as molecular absorption may be due to high solids or large

droplets produced by the nebulizer. The effects of copper,

o and iron on arsenic at 1937 A are given in table 3. There

Table 3. Effect of copper and iron on the absorption of

arsenic at 1937 A.

Oxidant and fuel -argon (entrained air )-hydrogen

Burner total consumption

1937 A

Eleme nt

,

mg/ml

Cu 0.0

1.0

1.0

5.0

5.0

Fe 0.1

0.1

1.0

1.0

5.0

5.0

As, yg/ml Abs.

10 0.267

- .000

10 .265

- .044

10 .293

— .008

10 .277

- .029

10 .273

- .122

10 .317

Ab 3. correct

0.267

.265

.259

.269

.244

.195

ed

o is not only scattered light at the 1937 A line of arsenic,

but iron has a suppressing effect on arsenic in the cool

argon (entrained air )-hydrogen flame. Molecular fragments

9
such as CH, C~ and CN exist in various flame gases and may

contribute to the background as well as to scattered light.

The major difficulty is the correction for scattered light

or molecular absorption. A scan of the arsenic spectrum,

o figure 6, shows strong neon lines at 1916, 1930 and 1990 A.

o Also, a non-absorbing arsenic line is located at 2003 A.

o The neon lines at 1916 and 1990 A may be used to correct for

o scattered light for arsenic at 1937 and 1972 A, respectively,

A. 1890 JjatUL

Figure 6. Spectrum of arsenic over the wavelength

o o region of 18.80 A to 2005 A.

2. Effect of Band Width on Absorption

The major function of the monochromator is to separate

the resonance line from the non-absorbing lines which are

emitted by the hollow-cathode lamp.. If the spectral band

width of the monochromator is too large, non-absorbing lines

will interfere which appear as a loss of sensitivity and a 10
bending of the calibration curve. The effect of the band

width on arsenic is shown in table 4. While arsenic is

reported to be relatively free of spectral interferences,

the data would indicate that some non-absorbing lines are

in the region of the arsenic resonance line. As shown in

o figure 6, the neon line at 1930 A would interfere if the

o spectral band width exceeded 7 A. Also, there is a Ne(II)

line at 1939 A.

Table 4. Role of spectral band width on the absorption

of arsenic at 1937 A.

Oxidant and fuel argon (entrained air ) -hydrogen

Burner total consumption

- Arsenic 100 ug/ml

o Spectral band width, A Absorbance

0.4 0.229

0.8 .222

1.2 .212

1.6 .202

2.4 .169

3.2 .158

4.8 .158

8.0 .143

E. Analytical Application to Standard Reference Materials

1. Determination of Copper in Basic Oxygen Furnace

Steel and Chrome-Moly Steel - NBS-SRM 178 and 36b

In the determination of copper by atomic absorption,

iron was observed to suppress the copper. Various methods

were explored to eliminate the interference of iron on

copper. While the standard addition method was able to

correct for the suppression, the desired precision was not

attained. Subsequently, standard solutions of copper were

prepared containing the same concentration of iron as the

unknown sample. This approach improved the precision and

accuracy of copper in a ferric matrix.

For NBS-SRM 178 and 36b, a 1-g sample was dissolved in

hydrochloric acid and the solution was transferred to a

11
volumetric flask. For 36b the analysis was performed by

atomic absorption without any additional preparation. Since

copper in the basic oxygen furnace steel (NBS-178) was very

low, it was removed from the iron matrix with diethylammonium diethyldithiocarbamate (DDDC). Iron was complexed with

ethylenediaminetetraacetic acid and the solution was

adjusted to pH 7.5-8.0 with ammonium hydroxide. Under these

conditions the copper was extracted with a 0.5 percent

solution of DDDC in chloroform without any interference

from iron. The absorption measurement was then made on

the organic solution. The results are presented in

table 5.

Table 5. Summary of ] UBS-SRIA analyr ses by fl;ame emission and

atomic abso:option spectrometry.

NBSSRM Ele- No of Std Rel std

No. Material ment det ' ms: Cone, % dev dev, %

178 Basic oxygen

furnace steel

Cu 24 0.0327 0.0010 3

36 2 chrome 1 moly

steel

Cu 4 .112 .0019 2

36b Cu 32 .183 .005 3

342 Nodular iron Mg 10 .0513 .0012 2

342a ti Mg 17 .0718 .0010 1

1051 Ba cyclohexanebutyrate

Sr 2 .0158 .00014 0.9

1051b n Sr 5 .0503

yg/g

.0010 2

380 CaCOo Sr 3 2.1 .12 6

Mg 3 0.98 .05 6

Ba 3 <10 — - Li 3 <0.5 - - Na 3 0.4 .1 25

K 3 <0.5 - -

12
2. Determination of Magnesium in Nodular Iron - NBSSRM 3^2a)

The determination of magnesium by atomic absorption

spectrometry is rapid and precise. The sample is dissolved

in a mixture of HCl-HNO^ and then fumed with HCICK to oxidize

the carbon. The solution is transferred to a volumetric

flask and diluted to volume with diluted HC1. Magnesium is

determined using an air-acetylene flame. The results are

given in table 5.

3

.

Determination of Trace Impurities in Calcium

Carbonate - NBS-SRM 380

This high purity material was prepared by J. T. Baker

Co. by a method described in the literature [8], The sample

was dissolved in ultra pure HC1 and diluted to a calibrated

volume. The alkalies, strontium, and barium were determined

by flame emission with the ac scan while magnesium was

determined by atomic absorption spectrometry. The strontium

procedure has been previously described [8]. The major

changes in the procedure involved the use of the ac scan and

the measurement of the second derivative signal. This new

technique improves the precision and accuracy of the analysis.

To eliminate the major interference of calcium on barium, the

latter was determined using a nitrous oxide-acetylene flame.

The interference from the high continuum due to the CaOH

band structure was minimized with the ac scanning technique.

The magnesium was determined by atomic absorption speco trometry. The gallium line, 2874 A, was selected to correct

for scattered light and molecular absorption.

P. Service Analyses

A total of 7^ samples involving 145 analyses were

performed by atomic absorption or flame emission spectrometry

for other Divisions of the Bureau and other Government

agencies. Trace element analyses were made on a wide variety

of materials such as metallo-organics , resin beads, laser

glass, clinical, book binding material, silver chloride,

13
potassium nitrate, rubidium chloride, caffeine, calcium

fluoride, and "polymer" water.

a. Trace as well as the major elements were determined

in a series of neodymium glasses. The samples were dissolved

in a Teflon-lined pressure bomb with HF [1]. Fluoride was

removed by repeated evaporations with nitric acid. Cadmium,

copper, magnesium and zinc were determined by atomic

absorption spectrometry using an air-acetylene flame with a 10 cm slot burner. Calcium, cesium, lithium, potassium,

rubidium and sodium were determined by flame emission

spectrometry and ac scanning with an oxygen-hydrogen flame,

while the nitrous oxide-acetylene flame was used for aluminum and barium.

b. Trace quantities of gadolinium were determined in

calcium fluoride crystals. The weight of the crystals

varied from 25-50 mg which necessitated a separation and

preconcentration. The gadolinium was separated from the

calcium matrix by extraction with 2-thenoyltrifluoroacetone

in methyl isobutyl ketone [9] and was determined in the

organic phase by flame emission using the oxide band peak

at 4640 A.

c. A number of other analyses were performed by atomic

absorption or flame emission including potassium and cesium

o j- o y in RbCl and RbCl; sodium in silver chloride; aluminum

and potassium in a portion of old document; alkalies and

alkaline earth metals in rubidium chloride; aluminum,

calcium, magnesium and potassium in book binding material;

and sodium in "polymer" water.

T. C. Rains and T. A. Rush

14
2. SPECTROPHOTOMETRY AND SPECTROFLUOROMETRY

A. Introduction

The two techniques continue to demonstrate their great

applicability and versatility in the accurate analysis of

Standard Reference Materials. This accuracy stems primarily

from the elimination of systematic errors through a better

understanding of the solution and coordination chemistry

of these complex materials.

In the following section, work undertaken during the

past year is described in considerable detail. In high

sensitivity spectrophotometry, the stability and reproducibility of the 2 , 3-quinoxalinedithiol complexes of cobalt,

nickel and copper have permitted the development of

a multi-element procedure for the simultaneous determination

of these three elements at the 0.1-1 ppm level [10]. In a

related study, 3-isopropyltropolone has been established as

a new and useful reagent for the selective determination of

trace amounts of vanadium. General enhancement of spectrophotometric and spectrofluorometric sensitivity has been

achieved through continued investigation of ternary ion

association systems of the type, [ML] [R] , which are

capable of exchanging non-colored or non-fluorescent R

groups for highly colored or fluorescent ones directly in

the organic phase [11]. The increased precision and accuracy of differential spectrophotometry have been exploited

in the development of new and improved methods for the

determination of cobalt in cobalt-aluminum neutron flux

monitor wire and of molybdenum in molybdenum-tungsten

microprobe standards. In addition, a spectrophotometric

method has been developed for the simultaneous determination

of molybdenum and tungsten in NBS-SRM 480. The determination

of air-borne beryllium by solution spectrofluorometry is

also described and preliminary data are presented on the In

situ spectrofluorometric determination of rare earth elements

15
in synthetic borate and silicate glasses. The section concludes with a discussion of the spectrophotometry determination of iron and copper in high-purity gold (99.9999%) and a

summary of service analyses carried out during the past year.

B. Research Activities

1 . Development of a Method for the Simultaneous

Spectrophotometric Determination of Cobalt, Nickel and

Copper

The use of molecular absorption spectrophotometry for

multi-element analysis has achieved little success in the

past largely because of the broad, and therefore, frequently

overlapping band spectra that are characteristic of light

absorption in the ultraviolet-visible regions. With either

time-shared or in-house computers becoming available in the

laboratory, the resolution of complex spectra into their

various components has become a relatively simple task.

Consequently, greater emphasis should now be placed on the

development of additive and reproducible color systems and

less concern should be given to the complexity cf the spectra

involved.

In the method developed, a procedure is presented for

the rapid simultaneous determinations of cobalt, nickel and

copper based on the color-forming reactions of these elements

with 2 , 3-quinoxalinedithiol in aqueous ethanol. The complexes attain maximum absorbance almost instantaneously,

exhibit excellent sensitivity and reproducibility and are

relatively stable. More important however, especially for

multi-element analysis, the absorbances of mixtures are

additive over a wide range of concentrations and compositions.

a. Procedure . Because the color reactions are performed

in aqueous ethanol, the amount of water permissable is governed by the quantity that can be present without rrecipitating the complexes. Since previous studies [12] have

shown that water may be present in amounts up to 20 percent

16
(v/v), limiting aqueous volumes of 2 and 20 ml are established for final volumes of 10 and 100 ml, respectively.

For the 10-ml volume, 1 ml of 0.1 percent 2 , 3-quinoxalinedithiol is used and, for larger volumes, proportionally

more is recommended. Because the 2 , 3-quinoxalinedithiolmetal reactions are quite sensitive at pH 2 [1 ppm solutions

of cobalt, nickel and copper give absorbance readings of

0.635 (510 nm), 0.308 (665 run) and 0.354 (625 nm), respectively] sample sizes and dilutions are selected so that the

final sample aliquot contains <_10 ppm of each of these

elements

.

In practice, two aliquots are required. To one is

added sufficient IN HC1 or IN NaOH to give a final pH meter

reading of 2.0 ± 0.1 after color development and dilution to

volume with ethanol. To this aliquot, and before the

addition of the alcohol, 5-10 mg of thiourea is added to

reduce Cu(II) to Cu(I), the reactive form of this element.

The sample is diluted nearly to volume with ethanol, the

appropriate amount of the 2 , 3-quinoxalinedithiol solution is

added (10 percent v/v) and final dilution is made with

ethanol. The absorbance of this solution is then measured

at 665, 625 and 510 nm. It may be read immediately or at

any time up to 24 hours provided it is measured relative to

a 2 , 3-quinoxalinedithiol reference solution prepared at the

same time as the sample. Fortunately, the absorbance of the

reagent is not sensitive to pH changes at the above wavelengths and an appropriate reference can be prepared by

adding 2-3 drops of IN HC1 to sufficient reagent solution

(10 percent v/v) and diluting to volume with ethanol. The

absorbance of the second sample aliquot is also measured

against this reference. Following addition of the acetic

acid-sodium acetate buffer (volume added should be onetenth the final volume since tenfold dilution of the pH 4.1

buffer with ethanol gives an apparent pH of 6.0 ± 0.1), the

color is developed in the same manner as the first aliquot

,

17
but with the thiourea omitted. The absorbance of this

solution is measured at 665 nm approximately 5 minutes after

color development. The concentrations of cobalt, nickel

and copper in the sample aliquots are then calculated by

means of simple arithmetic from a series of constants

derived from a least squares treatment of the appropriate

spectrophotometric data (see Discussion).

i. Analysis of Iron-Base Alloys : For sample sizes

of <0.5g s dissolve in 10 ml of 1:1 HC1, oxidize Fe(II) to

Fe(III) by dropwise addition of concentrated HNO^ (1 ml) and

evaporate the solution to incipient dryness. Dissolve the

residue in 8N HC1, cool and transfer to a 60-ml separatory

funnel (final acid layer ^25 ml). Extract Fe(III) by

shaking for 30 seconds with an equal volume of 1:1 methyl

isobutyl ketone (hexone) and amyl acetate previously

equilibrated with 8N HC1. Separate the phases and repeat

the extraction. Backwash each of the organic layers with

10 ml of 8N HC1 and add the latter to the original aqueous

fraction. Evaporate this acid fraction to 2-3 ml, add 10 ml

of concentrated HNO.-, and 2 ml concentrated HCIO^.. Evaporate

to dense fumes (prior to fuming, HF may be added to decompose

any siliceous residue) and dilute to volume. Take suitable

aliquots and analyze spectrophotometrically as outlined above

ii. Analysis of Aluminum-Base Alloys : Dissolve

by dropwise addition of 1:1 HC1, add 2-3 drops concentrated

HNCU and approximately 10 drops of 48 percent HF, if much

silicon is present. Add 2 ml of concentrated HC10|. and

evaporate to dense fumes. Dilute to volume and take

appropriate aliquots for spectrophotometric analysis. A

tenfold molar excess of sodium citrate is added if aluminum

should hydrolyze at pH 6.

b. Discussion and Results . The absorption spectra of

the copper, nickel and cobalt complexes and the reagent are

shown in figure 7. At pH 2, distinct absorbance peaks are

18
U.B

0.7

II 1 1 1 \lCu -

0.6 VI / /

\nNi /^Oy -

0.5 l\ "

0.4

\ \ / / \m ("

\v

0.3 TV/ / \

0.2 U j/ \

-

0.1 \e: Cu, pH 6 \ -

n n \.^__ 3£ Reagent

i —

5O0 550 600

WAVELENGTH, nm

650 700

Figure 7. Absorption spectra of the copper, nickel and

cobalt complexes and of the reagent.

apparent at 510 nm (Co), 606 and 665 nm (Ni), and 625 nm

(Cu). Also apparent is the close similarity between the

nickel and copper spectra at this acidity. At pH 6, however,

the copper spectrum is considerably different (curve IV) from

that obtained at pH 2 while the cobalt and nickel spectra

remain relatively unchanged. As will be seen later, this

pronounced pH effect is used to differentiate copper from

nickel. In the latter complex, nickel is present undoubtedly

as the Ni(II) ion while there is evidence favoring both

Co(II) and Co(III) as the reactive form of this element. In

the case of copper, Cu(I) is definitely the reactive species.

19
As a result, thiourea and ascorbic acid were investigated as

potential reducing agents and the former was found more

effective at pH 2. In addition, 2 , 3-quinoxalinedithiol also

reduces Cu(II) to Cu(I). In the pH range of 2-3 the reduction is both acid-catalyzed and light-catalyzed (figure 8).

0.5

4

TIME, min

Figure 8. Reduction of copper(II) to copper(I)

by 2, 3-quinoxalinedithiol.

At pH 2, acid catalysis is the predominant factor; at pH 3,

the reaction is preferentially light catalyzed. For these

experiments, two solutions were used—one having a pH of

2 and the other a pH of 3 (2.08 ppm Cu in each). During the

first two minutes following color development each was

exposed to normal fluorescent light of the laboratory. At

the end of this period a portion of one was placed into the

spectrophotometer and repeated absorbances were measured

over a 2-6 minute time interval. During this time the

20
sample was in the light path only long enough to obtain a measurement. Simultaneously, the absorbance of the remaining

portion was measured on a second spectrophotometer. For each

measurement, a new sample (continuously exposed to laboratory

light) was always placed in the absorption cell. The second

solution was treated similarly. The terms "dark" and "light"

in figure 8 refer to these two levels of light exposure.

i. Effect of pH : The effect of pH on the absorbances of the cobalt, nickel and copper complexes is shown

in figure 9. Over this pH range the absorbance of the

u.u

1 1 1 1 1 1

S.I

0.7 "

1=1 Ob

— ^^

m \ n.

0.5 /^\

I COPPER COMPLEX (625 nm) \

0.4 H NICKEL COMPLEX! 665 nm) \

m COBALT COMPLEX (510 nm) \

0.3 - \-

0.2 - -

0.1 -

1 1 1 1 1

-

1 3 4 "PH"

Figure 9. Absorbances of the colored complexes

at various acidities.

reagent is constant. All pH values refer to meter readings

obtained with glass-calomel electrodes. At relatively

high acidities (pH 2) the apparent pH of aqueous ethanol

21
(10 percent v/v) closely parallels that obtained in an allaqueous system, i.e. tenfold dilution of an acidic sample

with water increases its pH by 1 unit. Tenfold dilution of

an aqueous sample at pH 4-5 with ethanol, however, gives an

apparent pH increase of approximately 2 units.

For the simultaneous determination of cobalt, nickel

and copper, two acidities were selected for further absorbance

measurements pH 2.0 ± 0.1 and pH 6.0 ± 0.1. As mentioned

previously, because of the similarity of the nickel and

copper spectra at pH 2, more information was needed to

adequately differentiate between these two elements. Such

information is obtainable by making an additional absorbance

measurement at pH 6.

The concentrations of cobalt, nickel and copper employed

in these studies were 0.87 ppm, 2.00 ppm and 2.08 ppm,

respectively. The dotted portion of the nickel curve indicates a region in which this complex may precipitate.

Precipitation, however, is not only a function of pH, but

also depends on concentration and time. At pH 2 no precipitation was ever observed for nickel concentrations of <2 ppm.

When precipitation did occur at a lower pH, the absorbance

decreased rather than increased. This behavior was attributed

to the formation of relatively large aggregates instead of

the finely divided sols normally observed. The rapid decrease

in the absorbance of the copper complex with increasing pH is

undoubtedly caused by the inability of thiourea to reduce and/

or maintain copper in the +1 oxidation state at these lower

acidities

.

ii. Reaction Rate and Stability : The pH of the

aqueous ethanol (10 percent v/v) can affect both the rate ana

stability of complex formation. At pH 2 cobalt, nickel and

copper react instantaneously with 2, 3-quinoxalinedithiol to

form highly colored complexes whose absorbances may be

measured immediately. Although the reagent undergoes

appreciable decompositon with time, especially when exposed

22
to laboratory light, the net absorbances of the complexes

remain constant for at least 24 hours, provided they are

measured against a reagent reference solution prepared and

treated in the same manner as the sample. In the analysis of

mixtures at pH 6, however, the absorbance at 665 nm increases

slowly. In the present work, all measurements at this pH

were therefore made within 4-6 minutes after color development . iii. Interferences : Only iron, platinum and

palladium interfere seriously in the present method. Iron (III),

however, may be extracted readily with 1:1 hexone and amyl

acetate from 6-8N HC1. Even for relatively large amounts of

iron, i.e. iron-base alloys, one or two extractions are

sufficient. In the direct method, 2 ppm of either Fe(IIl) or

Fe(II) do not interfere. The effects of other cationic and

anionic interferences have been investigated in detail

previously [12].

iv. Spectrophotometric Equations and Their

Solutions

:

Assuming the absorbances of mixtures of the cobalt,

nickel and copper complexes are additive, the following

spectrophotometric equations can be obtained by measuring the

absorbance of each complex separately at the designated

wavelengths and acidities. The 665 nm nickel peak was

selected for all subsequent measurements because it has less

spectral overlap. In these equations the concentration of

each element (denoted by brackets) is in parts-per-million.

At pH 2:

0.030 [Co] + 0.308 [Ni] + 0.310 [Cu] = A

1 (665 nm)

0.081 [Co] + 0.290 [Ni] + 0.354 [Cu] = A

2 (625 nm)

0.635 [Co] + 0.085 [Ni] + 0.108 [Cu] = A

3 (510 nm)

S

23
At pH 6:

0.018 [Co] + 0.185 [Ni] + 0.008 [Cu] = A^ (665 nm)

0.069 [Co] + 0.196 [Ni] + 0.009 [Cu] = A

5 (625 nm)

0.555 [Co] + 0.085 [Ni] + 0.112 [Cu] = A^ (510 nm)

Since the first four equations are sufficient for differentiating between the three metal complexes, only these were

used in obtaining the following least squares equations for

estimating the unknown concentrations from the corresponding

four A readings.

s ° [Co] = -0.2452 (A 1

) - 0.2817 (A 2) + 1.6193 (A 3) + 0.1058 (A

4

) s s s s [Ni] = +3.0917 (A*) - 2.8384 (A?) + O.O836 (A 3

) + 4.6692 (aJ) & & & & [Cu] = -1.3127 (A^) + 4.1766 (A 2

) - 0.3517 (A 3) - 4.2001 (a|!)

o O O o In the derivation of the above constants the imprecision

in the pH 6 absorbance was assumed to be twice that of the

pH 2 values. A discussion of the underlying theory for this

treatment of data is given in NBS Handbook 91 [13].

Using these constants, the absorbances are additive for

various combinations of metal complexes as shown in table 6.

Extreme combinations are listed in which the concentration

of each individual element is varied by a factor of 10.

An attempt was also made to determine copper by extrapolation of the time-absorbance curves obtained from the

reduction of Cu(II) to Cu(I) by the reagent and thereby

reduce the final calculations to solving two equations for

cobalt and nickel. With copper only present, the extrapolated absorbance, corresponding to zero time, was never

zero but always equivalent to 6-9 percent of the total

copper. This behavior was attributed to concentration effects

initially present when the reagent was added, but could not

be eliminated by rapid injection of the 2 , 3-quinoxalinedithiol solution. In addition, there was some evidence

that, in mixtures, cobalt could variably alter the reduction

24
Table 6. Analysis of synthetic solutions of cobalt, nickel

and copper.

Solution Thee ry, ppm Pound , ppm Diff . , %

A Co 0.87 0.87 0.0

Ni 1.00 1.00 .0

Cu 1.04 1.02 -1.9

B Co 0.087 0.085 -2.3

Ni 1.00 .97 -3.0

Cu 1.04 1.05 +1.0

C Co 0.087 0.085 -2.3

Ni .100 .098 -2.0

Cu 1.04 1.04 0.0

D Co 0.087 0.088 +1.2

Ni 1.00 .99 -1.0

Cu 0.104 .109 +4.8

E Co 0.87 0.87 0.0

Ni 100 .103 +3.0

Cu .104 .101 -2.9

F Co 0.87 0.87 0.0

Ni 1.00 1.00 .0

Cu 0.104 0.106 +1.9

G Co 0.87 0.86 -1.2

Ni .100 .101 +1.0

Cu 1.04 1.05 +1.0

Duplicate aliquots in good agreement.

rate and create additional uncertainty in the extrapolated

values. While this approach was temporarily abandoned,

there are still reasons to believe it may eventually prove

feasible

.

v. Analysis of NBS Standard Reference Materials:

Cobalt, nickel and copper were determined by the proposed

method in three NBS iron-base alloys after extracting the

bulk of Fe(III) with 1:1 hexone and amyl acetate from 8N HC1

The extraction procedure is essentially the same as recommended by Claassen and Bastings [14]. An aluminum-silicon

alloy was also analyzed. These results are summarized in

table 7.

25
Table 7. Analysis of NBS Standard Reference Materials

( SRM ' s )

.

NBSSRM Type

462 Low alloy steel

466 Ingot iron

55e Ingot iron

87a Aluminum-silicon alloy

Prese nt

,

, Wt % Found, Wt %

Co 0.,ll a

0,,106

Ni 0.,70 a

0.,687

Cu 0.,20 a

0.,207

Co 0.,046 a

0,,046

Ni 0.,051 a

0,.051

Cu 0..033 0,.033

Co 0,,007 0,,0065

Ni 0,,038 0,.037

Cu 0.,065 0,,062

Co ^0,.01

Ni 0.,57 0,,568

Cu 0..30 0,.301

Provisional value.

vi. Summary : In aqueous ethanol, cobalt, nickel

and copper react instantaneously with 2 , 3-quinoxalinedithiol

at pH 2 to form strongly colored complexes exhibiting

absorption maxima at 510 nm, 606 and 665 nm, and 625 nm,

respectively. At pH 6 the reaction of copper can be virtually

eliminated while the cobalt and nickel reactions show only

small decreases in sensitivity. This combined behavior is

the basis of a rapid method for the simultaneous determination

of these three elements. The absorbances of the mixed complexes are additive over all possible combinations of elements in which the individual concentrations have been varied

from approximately 0.1 to 1 ppm. A least squares treatment

of the pertinent spectrophotometric data has provided a

series of constants from which the concentration of one, or

all, of the elements can be readily calculated. The procedure

has been applied to the analysis of complex ferrous and

aluminum alloys with excellent success.

26
2 . Development of New Solvent Extraction Systems

Designed Especially for High Sensitivity SpectrophotometrySpectrofluorometry

The advantages offered by the non-aqueous exchange

reactions of ternary ion association complexes were outlined

in last year's report [1]. Basically, the new technique

involves the formation of the complex, [ML ]~R , where R

initially is either a non-colored or a non-fluorescent

cation. Following extraction of [ML ]~R , a second cation,

+

x

R-.

} is added directly to the organic phase which is capable

+ of exchanging with the first R groups. In this instance,

however, R, is purposely selected to be highly colored or

fluorescent, thereby producing the highly colored or fluorescent complex [ML ]~R-. . Unreacted R, is readily backextracted, leaving only the dye-complex in the organic phase.

In the following section the determinations of gold and

uranium are described to demonstrate this technique,

a. Experimental . i. Reagents and Apparatus : Standard solutions

of uranium and gold were prepared from high purity U^On and

the metal, respectively. Working solutions were prepared as

needed by appropriate dilution of these standards with

distilled water.

Dye solutions were prepared by dissolving 30 mg of

Brilliant Green (C. I. No. 42040, HSO^" salt) or Rhodamine

6G (C. I. No. 45160, Cl~ salt) in 100 ml of absolute ethanol.

The following aqueous solutions were used: 1M ammonium

thiocyanate, 0.1M sodium benzoate and 0.01M tetraphenylarsonium

chloride

.

All other reagents were analytical grade.

Absorption spectra were obtained with a dual-beam

recording spectrophotometer whereas measurements at a fixed

wavelength were made with a single-beam instrument. Matched

1-cm absorption cells were used in all instances.

27
Fluorescence measurements were obtained with a singlebeam, uncorrected spectrofluorometer

.

Extractions were carried out in 60 -ml separatory funnels

equipped with all-Teflon fittings. A large, industrial-type

centrifuge was used to hasten the separation of phases,

ii . Procedure : Gold-thiocyanate system : The aqueous phase,

containing <20 ug Au 3+

, is made 0.02M in NH.SCN, 0.002M in

+ cKAs CI and 0.01N in HC1. Following extraction with 5.00 ml

of benzene for one minute (vigorous shaking), the sample is

centrifuged and the aqueous layer is discarded. Approximately

0.5 ml of alcoholic dye solution is added to the benzene

fraction, mixed, and the resulting solution is back-washed

with an equal volume of 0.01N HC1 to remove unreacted dye.

In this instance a 30-second shaking time is ample. The

extract is then analyzed either spectrophotometrically or

spectrofluorometrically , depending on the choice of dye.

Beer's law is obeyed over the range 1-20 ug Au . For

Brilliant Green, maximum absorbance is at 640 nm; for

Rhodamine 6G the excitation maximum is 525 nm and the

emission maximum is 550 nm.

2+ UOp - benzoate system: This is similar to

the gold-thiocyanate system except that instead of being 0.02M

in NH^SCN, the aqueous phase is made 0.05M in sodium benzoate.

Also, there is one other significant difference. The

[Brilliant Green] [UO- (C^H,-C00) ~]~ complex decomposes with

time, but can be stabilized by the addition of acetone. At

least 40 percent by volume is necessary. This composition is

achieved most readily by diluting a 2.00 ml aliquot of

acetone, previously added to a 5-ml volumetric flask, to the

mark with the benzene extract.

b. Discussion and Results . From a 0.01M CNS~

solution at pH 2, thiocyanate ions can be quantitatively

extracted into benzene as the binary complex [R] [CNS]~

using either Brilliant Green or Rhodamine 6G as the R

28
group. Consequently , in ternary complex reactions based on

metal-thiocyanate-dye systems, the above reaction can yield

excessively high blank values since, in both the binary and

ternary complexes, the R group is solely responsible for the

color and/or fluorescence.

To investigate the possible advantages of the present

approach in minimizing the [R] [CNS]~ side reaction, the goldthiocyanate system was selected for initial study. The

absorbances obtained for 10 ug Au3 + were 0.902, 0.884 and

0.887 for three independent determinations. Most important,

however, the corresponding blank was only 0.003. If the same

amount of Brilliant Green had been added to the 0.01M CNS~

solution directly, the corresponding blank value would have

been approximately 0.9, i.e. approximately the same as the

sample signal. Thus, instead of having a sample to background ratio of 1:1, the exchange approach gives a ratio of

about 300:1, in this instance.

Attempts to extract microgram amounts of U0p2+ as

+ _ the [<KAs] [U0p (CNS) .-,] were not as successful as the gold

experiments. Although various CNS~ concentrations up to 1M

were investigated, the maximum net absorbance obtained for

100 ug of U was only about 0.3 with a corresponding blank

also of about 0.3 (for 1M CNS~). This magnitude indicated

significant amounts of CNS" were being extracted as

[cKAs] [CNS]~ in the initial extraction and remaining in the

benzene phase as [Brilliant Green] [CNS] following the

exchange reaction. Attempts were made to lower the amount

of binary-bound CNS~ by back-extraction with various metal3+ 3 + ion solutions. Tests with 10 ml of Fe (1 mg Pe /ml) met

with moderate success. In this instance the absorbance of

the blank was reduced from 0.3 to 0.09, with an average

deviation of ± 0.01 for four repetitive runs.

29
The formation and extraction of the red ternary

[Rhodamine B]+[U0

2 (CgH COO]" was first reported by Feigl

[15] and later used by Andersen and Hercules [16] for

the quantitative determination of trace amounts of

uranium. In the latter work, complete extraction of

UOp^1 was obtained only when the aqueous: organic volume

ratios were 1:10. In the exchange approach, however

,

uranium is completely extracted at aqueous : organic ratios

of 2:1 and indications are that much larger ratios can be

tolerated.

Although Ruzicka and Stary [17, 18, 19] have recently

described the analytical applications of chelate exchange

in the organic phase, apparently the present work is

the first report of exchange reactions involving ternary

ion association complexes. The latter technique offers

a number of practical advantages in high sensitivity

spectrophotometry and spectrofluorometry . First and

foremost it opens an entirely new area for formation

and extraction of ternary complexes in which relatively

basic intermediate ligands (L groups) can now be used.

Heretofore, such ligands could not be employed in the

normal extraction mode because of the excessively high

blanks obtained. In the present procedure these blanks

can be kept relatively low irrespective of the intermediate ligand. This capability to further minimize the

reagent blank could have considerable impact in fluorescence analysis since, with the single beam instruments

normally employed, the blank signal is not subtracted

instrumentally . A second and perhaps equally important

advantage is that the forward and the back extractions

can be carried out in weakly acidic (in contrast to

the strongly acidic solutions previously required)

30
solutions where gross masking agents can be effectively

employed. Finally, dye purity and light fastness appear

to cause considerably fewer problems in the proposed

technique and much smaller quantities of dye are

needed.

3 • Spectrophotometry Determination of Vanadium

and Iron with g-Isopropyltropolone

A new spectrophotometric procedure was developed

for the determination of vanadium and the simultaneous

determination of vanadium and iron with 3-isopropyltropolone (IPT). IPT, also know as 3-thujaplacin,

was first described by Japanese and Chinese workers [20,

21, 22], The formation of stable complexes by various

metals with this reagent has been reported by numerous

authors [23, 24, 25, 26, 27, 28, 29, 30]. Dyrssen

[23, 24] has studied extensively the extraction equilibria of twenty-seven metal ions in IPT-chloroform

system. However, vanadium was not included in that

study. He reported that iron-IPT complex formation is

very slow, requiring 1 to 4 days to reach equilibrium.

In our initial studies, it was observed that vanadium

gives a color reaction with IPT and that the rate of

formation of the complex is very similar to the Pe-IPT

system. However, the procedure was modified to

include the addition of an alcoholic solution of IPT

to the aqueous medium. Under these conditions,

equilibrium was attained rapidly (within 30 minutes).

This led to the application of this procedure to the

determination of low concentrations of vanadium in

steels

.

31
Vanadium which is an important addition to certain types

of steels, high temperature alloys and reactor materials, is

generally determined in higher concentrations by titrimetric

methods and by spectrophotometry in low or trace quantities.

The literature on this subject is ably summarized by Kolthoff

and Elving [30]. Its separation and spectrophotometric

determination are discussed by Sandell [31]. Currently,

hydroxamic acid derivatives have been reported as reagents

for the determination of vanadium [32, 33]. A general

summary of these derivatives has been described by Bass and

Yoe [3^]. Most of the procedures lack specificity. Recently,

Kakita and Goto [35] reported a more selective procedure

using benzophenylhydroxamic acid but indicate some problems

with the instability of the complex.

In the present studies, the IPT-complex of vanadium

forms a colored chelate which can be extracted from strong

acid solutions and, thereby, eliminates a large number of

interfering ions. However, in steel analyses, a mercury

cathode separation is necessary for the removal of high

concentrations of iron and chromium. Complete separation

from iron is not essential, since a two-wavelength measurement provides a precise correction. The high molar absorptivity of 11,000, liter mole" cm" for vanadium-IPT complex

recommends it for the trace determination of this element.

NBS Standard Reference Materials of ferrous metals containing

traces of vanadium have been used to establish accuracy of

the method.

a. Experimental

i. Apparatus : Spectrophotometric measurements

were made with a single beam spectrophotometer using 1.00 cm

cells. Spectra scanning was carried out with a high precision

recording spectrophotometer. The absorption cells were

thermostated at constant temperature.

32
The spectrophotometer wavelength scale was checked with

a holmium glass standard. Measurements of pH were made with

an expanded scale pH meter,

ii. Reagents : Standard Vanadium Solution : Dissolve 0.2295g

(V-100 ug/ml of ammonium metavanadate in water and dilute to

1000 ml. Aliquots of this solution were diluted to provide

a solution containing 10 ug V/ml.

3-isopropyltropolone (IPT), from a commercial source,

was recrystallized twice from petroleum ether. The purity

was verified by determining the M.P. (51-52°) and by taking

thin -layer chromatograms on silica-impregnated plates using

butanol, water and ethanol in the ratio of (5:11:4) as the

developer. A solution was prepared containing 1.642 gms

(1x10"

grade.

_2 (1x10 M) of IPT in alcohol. The other reagents were reagent

b . Procedures

i. Absorption Spectra of the Reagent : Spectra

_2

were taken of 2x10 M IPT in chloroform, carbon tetrachloride,

benzene and cyclohexane.

i i . Determination of the Absorption Spectra of

the Complexes of V(V), Y(IV) a Fe(III) and Fe(II) with IPT:

Transfer an aliquot containing 20 ug of each of the two

elements to a 50 ml separatory funnel. Add 0.5 ml of HCIOk

and dilute to 5 ml. Extract with 5 ml of IPT/chloroform by

shaking vigorously for 2 minutes. Allow the phases to

separate and, after 30 minutes, record the spectra of the

organic extract.

iii. Rate of Formation of the Vanadium/IPT as a Function of pH : Transfer a 2.0 ml aliquot of the vanadium

solution (1 ml = 10 ug) to 50 ml separatory funnel. Adjust

the pH of the solutions to cover the range to 7. The

solutions were also adjusted to 1 to 6M in HClOj,. Extractions were carried out with 5 ml of IPT solution in CHCl^

and absorbances were taken at 470 nm.

33
iv. Effect of Ionic Strength : Transfer 20 ug of

vanadium to a separatory funnel and adjust the acidity to

1M in HClOh. The ionic strength was varied from 0.8M to 6M

by the addition of NaClOn. Extraction was carried out as

above

.

v. Effect of Temperature on the Formation of

the Vanadium-IPT Complex : To study the effect of temperature,

absorbances of the V(V)-IPT extracts were measured at 15°,

25°, 35°, 45°C as a function of time.

vi . Study of the Rate of Extraction of Metal-IPT

as Function of Solvent Ethanol : ^ansfer 20 ug each of

vanadium (V) and iron (III) to two separatory funnels. Add

0.5 ml HClOn and dilute to 5 ml. After adding 2 ml of

-2 alcoholic 1x10 M IPT to the aqueous phase, extract with 5 ml

of CHCl^ by shaking for 2 minutes. Measure the absorbances

as a function of time.

vii. Determination of V-IPT Species : To 1.0 ml

of 1x10 ^M vanadium, varying amounts of alcoholic 1x10 M

IPT were added. The acidity was maintained at 1M HClOn.

Extract with 5 ml of CHC1~ and measure absorbances at 470 nm,

viii. Calibration and Additive Properties of V(V)

and Fe (III) : 20-50 ug of vanadium were taken in 1M HClOj.,

-

1

2 ml of alcoholic 1x10 M IPT were added and extractions

were carried out with 5 ml of CHCl^. Absorbances were

measured at the following wavelengths: 470, 540 and 580 nm.

Similar sets of experiments were carried out with 20-50 ug

of iron as well as with mixtures of vanadium and iron.

ix. Procedure for Steel Analysis : One gram of

steel was dissolved in 10 ml of HNO^(3:5). After the

reaction subsided, 5 ml of HCIO^ was added. The solution

was fumed twice to remove the HN0~. Silica was removed by

filtration and washed thoroughly with hot dilute HCIOl

(1:100). The solution was diluted to 200 ml and electrolyzed with the mercury cathode, using a current of 5A,

until the solution gave a negative test for iron. The

34
solution was transferred to a beaKer, 10 ml HC1CK added,

fumed, and then 10 ml HC1 was added drop by drop to volatilize

chromium as CrO p Clp. After dilution to volume, an aliquot

corresponding to 20 ug of vanadium was transferred to a separatory funnel and the acidity was adjusted to 1M in

HClOn. After addition of 2 ml of alcoholic lxlO _1M IPT,

extraction was carried out with 5 ml of CHCl^. After

30 minutes, absorbances were measured at 470 and 540 nm.

Vanadium was calculated from a calibration curve. Corrections

may be made for residual iron.

c. Results and Discussion . Dyrssen [23] has

pointed out that the Pe-IPT complex takes 1-4 days to reach

equilibrium. In the case of vanadium it was found that the

absorbance increases with time, as shown in table 8. Even

Table 8. Rate of formation of the colored complex V(V)-IPT

in chloroform.

(Vanadium: 20 Ug)

Time

,

hr Absorbance

1/2

1

3

25

0.402

.435

.461

.494

after 24 hours, a constant value could not be attained.

Raising the temperature had little effect. On addition of

an alcoholic IPT solution to the aqueous phase, the equilibrium was attained within 30 minutes, both for iron and for

vanadium. The spectrum of the iron-IPT complex compares with

that of the 1:3 iron complex reported by Dyrssen. In the

study of the vanadium complex by the mole ratio procedure,

a 1:4 complex was established.

The spectral characteristics of the reagent do not vary

when taken in different solvents such as CHCl^, CCIk,

CVRV and cyclohexane. Finally, chloroform was selected as

35
the most suitable solvent since it forms a lower layer that

can be easily removed.

Dyrssen has pointed out that IPT has a high Kd value

(log Kd = 3.37). A high value of 10.41 for pKd + log Kd

favors the distribution ratio of IPT even in strongly acid

solutions. Hence extractions with this reagent were made

at acidities as high as 6M HC1CK. Spectra show that the

same complex is formed at all acidities. Absorbancer of

V(V)-IPT is constant between 0-1. 75M and 4M-6M. in the

intermediate range of 2M-4M, there is an increase in

absorbance, which cannot be explained. Acidity was maintained

at about 1M in this work. Also, the ionic strength has no

effect on absorbance of the V(V)-IPT complex.

The spectra of the V(V)-IPT complex shows an absorbance

region around 470 nm as shown in figure 10. For the VCIVJ-IPT

0. Menis and C. S. P. Iyer

2 70 —i—

r

350 450 5 50 6 50

>-o

z:<m

cco

<ji m

<

300 400 500 600

Figure 10. Absorbance spectrum of the vanadium (V)

3-isopropyltropolone complex.

^6
complex there is a continuous decrease in absorbance from

410 nm to longer wavelengths.

In the case of the Fe(III)-IPT system, the spectra of

the complex shows two bands in the visible region, one at

540 nm and another at 580 nm as shown in figure 10. In

the case of the Fe(II)-IPT systems, there is a continuous

decrease in absorbance from 410 nm. This is similar to the

V(IV)-IPT complex.

Beer's law is obeyed in the range of 10-50 yg vanadium

or iron. For solutions containing both iron and vanadium,

the absorbances were additive, table 9.

Table 9. Additive properties of vanadium and iron IPT

complexes

.

Cone A at 470 nm A at 540 nm

yg/

A, A , Ion 5 ml 470 540 Found Calc Diff Found Calc Diff

v(v) 10 0.177 0.095

Fe(III) 10 .177 .103

V(V) and 0.354 0.354 0.00 O.200 O.198 0.002

Fe(III)

V(V) 20 .354 .188

Fe(III) 20 .349 .209

.712 .703 .009 .412 .397 .015

25 .443 .234

25 .443 .260

.885 .886 .001 .503 .494 .009

To evaluate the method, two SRMs , NBS 464 and 8i,

have thus far been tested by this procedure. In ferrous

materials, a prior separation with the mercury cathode is

required. Chromium, which does not electrolyze completely,

should be volatilized as CrOpClp. Preliminary values

obtained for these two standards were 0.275 and 0.0125

percent respectively as compared with certified values of

0.295 and 0.012 percent. The lower value for Standard 464

as also noted from the change of the spectral curve may

be due to incomplete separation of chromyl chloride.

37
Further studies are under way with other materials, in

addition to the efforts to resolve the lower values obtained

for SRM-NBS 464.

4 . Direct Spectrofluorometric Determination of Rare

Earth Elements in Synthetic Glasses

The advent of the laser is responsible for renewed

interest in the luminescence of rare earth elements in

glasses. Likewise, the increasing use of inorganic glasses

as matrices for trapped radicals and ions of unusual valences

necessitates the development of non-destructive analytical

methods for the determination of trace constituents. This

interest is extended to the determination of rare earth

elements in a proposed series of SRM simulated lunar glasses

containing 6l elements in trace quantities ranging from 0.02

ppm to 500 ppm. The determination of europium and gadolinium

in sodium borate glasses carried out under a cooperative

program at the Hebrew University, Jerusalem, Israel is

described briefly and will be published in detail elsewhere

[36].

a. Preparation of the Borate Glasses . Dry rare

earth chloride, borax and boric acid (wt. ratio 2:1) were

placed in plastic vials containing glass balls and mixed for

10 minutes in an electric vibrator. Although these mixtures

melted at temperatures below 1000°C, clear transparent samples

could be obtained only after heating at 1100°C for at least

15 minutes. All melts were made in platinum crucibles.

Drops of the hot melt were allowed to fall directly onto a clean white glazed ceramic surface. The drop was placed

within a ring 1 mm thick and then pressed with a second

ceramic tile to obtain glasses of uniform (1 mm) thickness.

The glasses were inserted into a glass holder containing a

12 mm diameter opening and their excitation and fluorescence

spectra were measured at room temperature.
b . Placement of the Solid Sample in the Light Beam . To maximize the net fluorescence signal, the proper angular

placement of the glass disc in the exciting light beam must

be established (figure 11). Based on measurements of gross

UJ50

—1— " "I 1-1 1 1 1 l

^^^

RELATIVE FLUORESCENCE

1

Ui

<_> KWo

cro

3_lE 30 -

LLl > — 3 20

tu

tx. / yS BACKGROUND N. -

10

1 V 1 I 1 I I I I I 20 25 30 35 40 45 50 55 ANGLE OF SAMPLE.DEGREES

60 65

Figure 11. Optimum angular placement of glass sample

for in situ fluorescence analysis.

fluorescence and of scattered light at various angles (all

angular values refer to the angle between the perpendicula.r

to the exciting beam and the plane of the sample) an optimum

angle of 35° was established for sample positioning.

c. Discussion and Results . The excitation spectrum

of Eu(III) (fluorescence at 617 nm) is shown in figure 12

and consists of a number of sharp lines at 320, 365, 380,

395, 465, 535 and 585 nm and a broad band at 230-290 nm

with a maximum at 260-280 nm. The strongest peak is at

395 nm. Figures 13 and 14 show emission spectra excited

39
70

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

60 —

FLUORESCENCE

o

o -

RELATIVE o

1 —

20 A, /I —

10 -

1 l-H J\1 I 1 f

1 V 1 l I 1 1 1

Figure 12.

200 280 360 440 520 600

WAVELENGTH ,nm Excitation spectrum of europium (III);

fluorescence measured at 617 nm.

640 600 560 520 480

WAVELENGTH, nm Figure 13. Fluorescence spectrum of europium (III)

excitation at 395 nm with xenon source.

40
640 600 560 WAVELENGTH, (nm) Figure 14. Fluorescence spectrum of europium( III)

;

255 nm excitation with mercury arc.

at 395 nm (xenon arc) and 255 nm (mercury arc), respectively

The 365 nm excitation gave a similar spectrum, but with

lower intensities. The fluorescence bands observed are

similar at all excitations. Peaks are located at 580, 595,

600, 617 and 655 nm with the highest intensity at 617 nm.

The 5^5 peak appearing at 255 nm excitation (figure 14) is

due to impurity in the borax.

The fluorescence dependence on concentration was

measured for all fluorescence bands. The most linear

dependence was observed for the 617 nm band. The results

are given for 255 nm excitation. A two- to three-fold

decrease in fluorescence was observed when excitation was

carried out at either 365 or 395 nm.

41
Table 10. Relative fluorescence, R/F, of various concentrations of europium in borate glass; excitation

at 255 nm.

Cone, ppm R/F

10 27

100 380

2000 1140

4000 1920

8000 2470

10000 3050

13000 3600

For the determination of gadolinium in borate glass,

excitation was at 273 nm and the emission was measured at

312 nm. Linear dependence of fluorescence on concentration

was observed over the range 10 to 20,000 ppm (table 11).

Table 11. Relative fluorescence, R/F, of gadolinium in

borate glass

.

Cone , ppm R/F

10

50

100

500

1000

2000

4000

5000

6500

8000

10000

13000

20000

To test the effect of the presence of a second rare

earth, the fluorescence of gadolinium was measured in a

series of glasses containing equal concentrations of

samarium. The results are presented in table 12.

5

24

48

250

500

1200

2250

2600

3350

4500

4800

6400

10000

42
Table 12. Relative fluorescence, R/F, of gadolinium as a function of concentration in glass containing

equal amounts of Gd(III) and Sm(III).

Cone Gd(III)+Sm(III) R/F [Gd(IIl)]

ppm R/F Kario R/F [ Gd ( III ) +Sm ( IIT ) 500 180 1.38

1000 390 1.28

2000 720 1.66

4000 1440 1.56

5000 1920 1.36

65OO 1980 1.68

10000 2000 2.4

20000 2000 10.0

At concentrations up to 6900 ppm the gadolinium fluorescence

decreased by a factor of about one-third and the dependence

was linear. At higher concentrations, quenching of fluorescence was observed. It is therefore assumed that a nonradiant energy transfer takes place from gadolinium to

samarium.

C . Analysis of Standard Reference Materials (SRM's) and

Related Samples

Throughout the year the spectrophotometry-spectrofluorometry competence has determined numerous elements in

a variety of Standard Reference Materials. Although there

are many instances where well established procedures can

be used, there are numerous occasions where additional

development work is necessary before the desired accuracy

can be obtained.

1 . P recise and Accurate Determination of Cobalt In

A luminum Neutron Flux Wire (NBS-SRM 953)

Exact knowledge of the flux and homogeneity of the

neutron beam are necessary for absolute counting techniques

to be meaningful. One approach to monitoring this beam is

through the use of appropriate standards containing neutronsensitive elements. Cobalt-doped aluminum is such a material

and has been proposed as a standard monitor of neutron flux.

43
For the spectrophotometric determination of 0.1

percent cobalt in aluminum wire, two variations of the

2 , 3-quinoxalinedithiol method previously described were

used. The first was a differential procedure in which the

cobalt complex was formed and measured at pH 3. Under

these conditions, however, the aluminum matrix hydrolyzed

and a subsequent filtration step was necessary. Because

of the spread of the differential results and the question

of the homogeneity of the sample, some additional work

seemed necessary. Further checking with the Reactor Group

indicated that the most practical sample size was about

1 cm, i.e. about 5 mg.

The most obvious improvement that could be made to the

differential method was to eliminate the hydrolysisfiltration of the aluminum matrix. Initial efforts involved

the investigation of various masking agents (fluoride,

citrate, tartrate, etc.), none of which proved entirely

satisfactory. Next, attention was directed to carrying out

the complexation reactions at higher acidities and this

modification proved to be the one needed. However, since

5-mg samples had been established as a practical sample size,

the differential approach could no longer readily be used

(because of sample-volume restrictions) and, conventional

spectrophotometry was reconsidered. The results obtained on

15 sections of wire by differential spectrophotometry at

pH 3 and conventional spectrophotometry in 1.2N HC1 are

shown in table 13.

In method II, the within-set agreement is better than

the between-sets agreement. However, all samples within a set were run as a group and against a common reference

solution. With a final volume of 10 ml, it must be realized

that variations as small as ± 0.05 ml (1 drop) can create

biases of ± 0.5 percent, 10-ug weighing errors, biases of

± 0.2 percent, etc. The fact that the within-set precision

44
Table 13. Spectrophotometrlc determination of cobalt in

aluminum neutron flux wire with 2, 3-quinoxalinedi thiol.

Method I (differential spectrophotometry); sample size

50-60 mg Ol2 cm)

Sample Wt % Co Sample Wt % Co

Set A Set B Set A Set B

0.1130 0.1170 9 0.1147 0.1157

0.1121 0.1147 10 0.1146 0.1152

0.1121 0.1181 11 0.1162 0.1154

0.1130 0.1145 12 0.1160 0.1160

0.1141 0.1153 13 0.1139 0.1167

0.1120 0.1163 14 0.1177 0.1151

0.1136 0.1167 15 0.1092 0.1111

0.1144 0.1181

Mean

S.D.

Rel S.D.

= 0.1151# a

= 0.0017

= 1.5%

Method II (conventional spectrophotometry); sample size

4.2-5.5 mg (^1 cm)

Set 1 Set 2 Set 3

Sample Wt % Co Sample Wt % Co Sample Wt % Co

1-1 0.1150 1-2 0.1163 2-1 0.1159

4-1 0.1162 4-2 0.1158 3-1 0.1145

7-1 0.1142 7-2 0.1170 5-1 0.1147

10-1 0.1145 10-2 0.1169 8-1 0.1143

12-1 0.1154 12-2 0.1168 11-1 0.1149

15-1 0.1084 15-2 0.1084 14-1 0.1146

Set ____4 Set 5

Sample Wt % Co Sample Wt % Co

2-2 0.1177 6-1 0.1152

3-2 0.1169 6-2 0.1158

5-2 0.1160 9-1 0.1151

8-2 0.1172 9-2 0.1156

11-2 0.1154 13-1 0.1147

14-2 0.1157 13-2

Mean

S.D.

Rel. S.D,

0.1146

= 0.1156f*

a

= 0.0011

= 1%

Sample 15 not included in means.

45
is relatively high, e.g. set 3, the homogeneity of the wire

could be 0.1 percent or better at the 5-mg level.

The accuracy of the above method is strengthened by the

close agreement between it and a spectrophotometric titration

procedure [37], both of which were applied to the determination of 1 percent cobalt in cobalt-aluminum wire [1].

2 . Simultaneous and Differential Spectrophotometric

Determinations of Molybdenum and Tungsten in Mo-W Compact

with Tiron (4 ,5-dinydroxy-m-benzene disulfonic acid)

The history and preparation of this microprobe standard

has been discussed previously [1], Because of some disagreement in the earlier results, between spectrophotometric

thiocyanate procedure and activation analysis, additional

results were needed. A brief review of the literature

indicated that molybdenum and possibly tungsten, could be

determined spectrophotometrically with Tiron.

a. Preparation of Samples . Successively wash each

sample core with carbon tetrachloride, acetone, ethanol and

water. Dry in vacuo and weigh. Etch the weighed samples

with a freshly prepared, equivolume mixture of 1:2 aqueous

nitric acid and 1:2 aqueous sulfuric acid (30 ml) for 15

minutes. Remove and retain the supernatant liquid and

washings. Dry and reweigh the samples to determine any

weight losses (no significant weight loss was observed for

any of the samples analyzed).

b

.

Dissolution . i. Solvent = 1:2:3 (v/v) HCIO^/H^PO^/R^O : Treat

5 mg (100 mg) of sample with 5 ml (10 ml) of the acid mixture

and heat gently to fuming. Add 1 ml (2 ml) concentrated

perchloric acid and continue to fume until dissolution is

complete (^10 hours). Add 0.5 ml (1 ml) concentrated

sulfuric acid and continue to fume for 2 hours to ensure

complete oxidation. If precipitation occurs at this stage,

redissolve with a few drops of concentrated orthophosphoric

46
acid. Dilute to 50 ml (100 ml) with distilled water and

maintain at a temperature of 90°C for 30 minutes. Cool,

adjust the pH to 7.0 by the cautious addition of solid

sodium hydroxide and dilute to 100 ml (500 ml) with distilled

water. Prepare standard solutions by the sample procedure,

using high purity molybdenum and high purity tungsten.

ii. Solvent = HF/HNCU : Treat 5 mg (100 mg) of

the sample with 5 ml concentrated hydrofluoric acid and add

concentrated nitric acid dropwise until dissolution is

complete. Add 0.5 ml concentrated sulfuric acid and reduce

the volume to 3 ml on a steam bath. Dilute to 50 ml with

distilled water, add phosphate buffer solution, pH = 7.0

(5 ml) and adjust the pH to 7.0 with solid sodium hydroxide

solution. Dilute to 100 ml (500 ml) with distilled water.

Prepare standards in a similar manner, using high purity

molybdenum and tungsten metals,

c . Analysis

i. Single-Wavelength Procedure : Take aliquots

containing approximately 1 mg of sample for analysis. Add

phosphate buffer solution, pH = 7.0 (5 ml), and 10 percent

(w/v Tiron solution (10 ml) and dilute to 50 ml with

distilled water. Measure the absorbance (A = 2 cm) at

380 nm of the solution against a reference solution containing reagent and buffer solution and rendered 3.6x10 M

with respect to molybdenum (VI) and 7.0x10 M with respect

to tungsten (VI). Prepare a fresh reference solution for

each aliquot analyzed.

ii. Dual-Wavelength Procedure : Proceed as

described under the single-wavelength procedure, but

measure the absorbance at 380 nm ( A = 2 cm) and 475 nm

( A = 10 cm) against a reference solution containing reagent

and buffer, and approximately the same amount of molybdenum

(VI) and tungsten (VI) as present in the sample. Prepare a

fresh reference solution for each of the sample solutions

examined. ijy
d. Results and Discussion , The results obtained

by the two Tiron procedures are shown in table 14. The

Table 14 Simultaneous differentia

analysis of Mo-W compact

1 spectrophotometric

•

Sample No

c Aliq./

sample Solvent

% Mo , (±S.D.) a

5S W

(±S.D.) Q

a cores

a

cores

4

4

4

4

HCIO^/H PO^

HCIO^/H^PO^

23.90±O.O4 e 23.76±0.17 f

76.10±O.O4

73.68±0.26

a

cores 4 3 HF/HNO 23.6l±0.09 f 75.82±0.8l

* b powder 3 4 HCIO^/H PO^ 21.59±0.02 f 78.51±0.11

powder 3 4 HF/HNO- 21.59±0.04 f 78.5 ±1.4

Five mg cores from center of compact.

Powder Mo-W used in preparation of compact.

q Number of independent samples

Standard deviations are per sample deviations based on the

statistical analysis of the sample/aliquot array of results.

Q One wavelength measurement.

f

Two wavelength measurements.

analysis of the Mo-W powder, reported in a previous report

[1], was undertaken to check the validity of the new method.

The results obtained compare favorably with the gravimetric

values but are more precise since no preparation of synthetics

was necessary.

In the single-wavelength procedure, both the Mo- and

W-Tiron complexes absorb at 380 nm, but with very different

extinction coefficients. However, it was necessary to make

the assumption that the sample was a binary alloy, since the

presence of a third component, even in relatively small

quantities, could considerably affect both the Mo and W

results. At 475 nm, only the Mo-complex absorbs. The

measurement at this wavelength was only possible after

repeated recrystallization of the reagent.

48
Alternative dissolution procedures were employed to

eliminate possible systematic errors. The 5-mg drillings

were less readily soluble in the HCIO^/H^PO^ mixture than

the Mo-W powder. With HF/HNO,. as the solvent, both forms

of the sample could be dissolved in minutes.

The deviations per sample in the analysis of the

drillings are greater than expected. Since the weight of

the samples can be determined to ± 3 Ug 3 the possibility of

inhomogeneity or an inadequate pre-etching procedure should

be considered.

3

.

Spectrofluorometric Determination of Air-Borne

Beryllium

A relatively simple spectrofluorometric procedure has

been developed for the quantitative determination of airborne beryllium. Following collection of the sample on a millipore filter, it is dry-ashed at approximately 100°C

in an oxygen atmosphere and the residue is treated

sequentially with concentrated HCIO^. and distilled water

and then warmed on a hot plate. The resulting solutions

are examined spectrofluorometrically (excitation wavelength373 nm; emission wavelength-450 nm) for beryllium, using

2-hydroxy-3-naphthaic acid as the chelating agent. Potential

interferences are eliminated by addition of a calcium

diaminocyclohexanetetraacetate masking agent [1].

This procedure has been applied recently to the

determination of beryllium in fourteen samples of air.

Detection limits of 0.005 microgram were readily obtainable

on sample volumes of 100 ml (0.05 parts-per-billion)

.

Subsequent reduction in the working volumes should permit

lowering this limit to at least another order of magnitude.

4

.

Spectrophotometric Determination of Iron and

Copper in High Purity Gold

As a part of the Division's continuing effort to

issue extremely high purity metals as standards for use in

49
solids mass spectrometry, activation analysis, metrology, etc.,

it was necessary to determine iron and copper in high purity

gold. However, before any spectrophot ometric method could be

applied, it was necessary that these two elements be separated

from the matrix. Also, it was apparent that the gold could be

more easily separated from the iron and copper than they could

be removed from the gold. However, blanks conceivably could be

larger in the former case, since larger amounts of reagents

would be required.

Eventually, two approaches were employed to remove the

gold. One involved precipitation with S0

2

, the other a solvent

extraction procedure (removal of macro amounts of gold with

ethyl acetate and residual amounts with Brilliant Green) . In

the former, all operations (precipitation, neutralization and

color development) were conducted in a closed system employing

the apparatus shown in figure 15.

Figure 15 Apparatus for dissolution extraction of iron in

high purity gold.

50
Each gold sample was dissolved and precipitated 3 times to

obtain authentic blank (initially, iron-free and copperfree gold) and spiked sample values. In the latter

procedure, multiple extractions were readily performed in

the same separatory funnel, thus minimizing the risk of

contamination.

Irrespective of the procedure used to separate gold,

the procedures for the determination of iron were identical,

i.e. extraction of the Fe(II) bathophenanthroline complex

into n-hexyl alcohol followed by spectrophotometric measurement of the red complex at 533 nm.

In the determination of copper, the same extraction

procedure employed for iron was used to separate the gold.

Copper was subsequently determined spectrophotometrically

by equilibrating the sample solution with an 0.01 percent

solution of zinc dibenzyldithiocarbamate in carbon tetrachloride. Under these conditions Cu(II) displaces Zn(II)

and gives a yellow complex whose absorption maximum is at

435 nm.

The results obtained are shown in table 15. Sample

weights ranged from 0.8 to l.lg; blank values averaged

about one-half the total signal.

Table 15. Spectrophotometric determination of iron and

copper in high purity gold.

Wire

Rod

Iron, ppm Copper, ppm

Precipitation Solvent

Procedure Extraction

0.36

.44

0.45 Wire

.47

.46

0.13

.12

.14

.17

.18

Rod .13

51
5 . Service Analyses

As a supporting service for the various Divisions at

NBS as well as other Government agencies, the following

analyses were performed during the past year (table 16 )

.

Table 16. Spectrophotometric-spectrofluorometric service

analyses

.

Element

Pd

Au

Sb

Fe

Nd

Fe

Co

Ni

B

Fe3+

Matrix

Epoxy plates

Nickel plating solutions

Neodymium glass

t!

tt

MnBeg and CrBe

g

MnBe

Method Level

spectrophotometry 1-5 ug

8

Metallic oxides

Filter residues

Ferrous dosimeters

4-6 ug

0.60$

10-15 ppm

differential 4-9$

spectrophotometry

spectrophotometry 0.4-0.6$

" 0.15$

1.6-4.5$

spectrofluorometry 0.01 ug

spectrophotometry 1-10 ppm

R. W. Burke and E. R. Deardorff

52
3. DIFFERENTIAL THERMAL ANALYSIS

The need for Standard Reference Materials (SRM) for

calibration of thermal analysis instruments and procedures,

was fully described in NBS Technical Note 45^ [1]. This

study led to a fivefold increase in the precision in the

measurement of transition temperatures for two proposed SRMs , SiOp and KNO^. It involved modification to a commercial

instrument, and provision for accurate calibration and

evaluation of the homogeneity of the two materials. Also

several SRM freezing point standards were tested. In

addition, contributions were made in organizing outside

scientific groups to provide national leadership in this

field. This involved participation, as a charter member of

a steering committee, in creating an ASTM task group and

formation of a National Society on Thermal Analysis.

A. Modification of Instrument

The commercial instrument initially used in this study

was limited in its capability to provide precise and accurate

values. This instrument was equipped with thermocouple wires

whose cold junction was dependent on the ambient temperature.

Thus the temperature measurements would vary several degrees

during the day. The hot junction was also located outside

the sample compartment. The high programming rate together

with a low sensitive recorder were limiting factors of the

initial apparatus.

The following modifications were made to ensure its use

as a research tool, especially to determine more accurately

the transition temperatures of selected compounds for use as

standard reference materials

:

1. Simultaneous use of the thermocouple for both sample

temperature readings and delta-T readings.

2. Insertion of ice bath junctions In all temperature

thermocouple circuits for voltage measurements with respect

to 0°C.

53
3. Simultaneous use of a strip chart recorder for delta

T vs time plots. The areas of these thermograms correspond

more, in theory, to heats of transitions than do the areas

delta T vs temperature plots. Simultaneously, an X-Y recorder was used for convenience for delta T vs temperature

plots

.

4. Slower scan rates were provided for minimizing

gradients between the sample thermocouple and the sample

itself, and for approximating adiabatic conditions.

5. Addition of a stable bucking voltage source was

provided for use with a sensitive setting of the temperature

vs time recorder. This increased the precision of measurement

of the sample thermocouple voltage by a factor of ten, by

permitting the scanning of 5 millivolts from the thermocouple

in ten one-half millivolt recorder spans.

6. Provision for temperature calibration of the

apparatus

:

a. Replacement of sample thermocouple with calibrated

wire . b

.

Provision for rapid comparison of calibrated thermocouple with standard voltage source.

c. Construction of non-metallic sample holders for use

with metal freezing point standards

.

B . Experimental

1. Modification of Commercial DTA - Thermocouple Wiring

The commercial unit was provided with various alloy

thermocouples together with a foam insulated box containing

cold junction connections for the temperature thermocouple.

However, regardless of the intermetallic junctions involved,

the voltage of the hot thermocouple was always measured

with reference to a cold junction or junctions completing the

circuit . The temperature of this thermocouple was thus read

with respect to ambient temperature together with the

temperatures in the apparatus at the junctions of the alloys.

Also, the hot junction supposedly measuring the sample

54
temperature was not inside the sample cup (this one was used

for the differential measurement only) but was actually the

furnace control thermocouple.

The following changes were made:

a. Changes in Thermocouple Arrangement

(1) All thermocouple wiring was removed and replaced

with platinum or platinum-10 percent rhodium wires leading to

an ice bath (see figure 16). Prom the ice bath, all copper

leads went to the recorders and amplifiers.

(2) The furnace control thermocouple previously used

for both the temperature measurement and furnace control was

now limited to furnace control. This provided the required

flexibility for its optimum placement and avoided interference

from the programmer electronics.

(3) The thermocouple in the sample cup was used for

temperature measurement (with respect to the ice bath) and

differential temperature measurement (with respect to the

reference thermocouple). (See figure 16, ) This involved

having the thermocouples provide a signal for a dc amplifier

and four recorder channels simultaneously. Using parallel

recorder inputs, as was done here, is not common practice.

However, all units were high quality potentiometric devices

and did not interfere with one another.

(4) Screw-type terminal strips were provided for

direct connections of the thermocouple leads to the ice

bath, leads of the same metal. Tests with a hot screwdriver

showed a slight potential shift due to the small dissimilarities of the Pt and Pt/Rh thermocouples. These shifts, as

expected, were small enough to be negligible to ambient

temperatures. Since then, the terminals have been replaced

with directly soldered connections.

All wiring was external with hookup wire for easy changes.

Hum and chatter were suppressed by shielding with wire braid

and copper screening and shunting the leads with 0.1 mfd

capacitors at the recorder terminals.

55
cH

in •H£

0) H

P.OooS

Fh

CD x:

Eh

VDu

•H

56
b. Recorder Changes, The two-pen recorder was used to

obtain a plot of temperature and differential temperature vs

time. To expand the entire temperature scale by a factor of

ten, bucking sources were combined with more sensitive scales.

Because of the sensitivity due to the scale factor expansion,

it was necessary to thermally insulate the bucking voltage divider and associated resistors and dry cells to suppress drift

This was done with plastic packing material. At high sensitivity, the recorder was susceptible to static electric pickup

from personnel moving nearby. It was thus necessary to

surround the apparatus with grounded copper screening.

Switches were added as shown (figure 16 ) for setting the

recorders to zero degrees centigrade without interference to

the differential circuit, and for calibrating the temperature

recorders with a standardized voltage source.

c. Lower Scanning Rates . The motor controlling the

heating or cooling of the furnace had a reliable speed range

of a factor of less than three (see figure 17). Using the

E

Q.

„ 'i i i cr i I i

i LU

iLU _„ ^ 30 — o

\-2

UJ

h-o

Q.Z „„

o: 20 — ^Mr —

3

7

o

o

2

>

§ io — y4 —

<

^~~ MOTOR STALLS

UJo

s

cro . s: 1 1 1 1 20 40 60

VARIAC DIAL POSITION

80 100

Figure 17 Model B programmer motor speed vs

rate dial setting.

57
lowest reliable setting and the gears provided with the

lowest ratio of potentiometer turns per motor revolutions,

the lowest rate available was about 5 degrees per minute.

Smaller motor gears were made, and the motor was moved to

accomodate them. Also, the electronics in the furnace

programmer were modified to lower the rate of temperature

scan. Because this modification also decreased the temperature range proportionately, the rate decrease was only a factor of 2. Using the smallest motor gears, the minimum

heating (cooling) rate was lowered to less than a degree per

minute. However, at the lower heating rates, the feedback

from the furnace sensing thermocouple was slow enough so that

the furnace would cycle above and below the proper temperature by several degrees with periods of 10 minutes or less.

To speed the feedback, the furnace control thermocouple was

welded to the nickel sample can (figure 17) which was the

closest stable point to the furnace heater windings. Even

with this modification and the optimum adjustment of the

furnace controller, the minimum heating rate that was free

of the cycling was about 1 degree per minute. Moving the

thermocouple outside the can, thus exposing it directly to

the furnace windings has further improved performance,

d. Automatic Voltage Divider for Bucking Voltage

Source . A bucking voltage source of the following properties

was designed and built (see figure 18 )

:

(1) Automatic - able to reset the recorder

(temperature) when it went off scale in either direction.

(2) Isolated from the ac power line and from ground.

(3) Stable with respect to time and temperature to

within at least 0.1 percent.

(4) Able to provide 20 increments of approximately

1/2 millivolt each.

The voltage divider was made from 2 percent carbon

resistors and trimmer potentiometers to compensate for the

58
Hikz* 6

| r^W

5^_1av^M^W—W^W %V^

6

•H>H

T3

CD

cd -pH

O

>

o

•H

-P

cdS

op

<

CO

50

•H

59
expected 4 percent resistance variation. This portion was

shielded from the control circuits, and offered no noticeable

hum.

The control circuits were made from relays because

space and speed were not at a premium and simplicity of

operation was desired. The basic control units were steppin

relays that would advance and reset, and a magnetic read

switch (whose inherent hysteresis prevented chatter) that

was timed to advance the stepping relays once every two

seconds. Stepping relays advance or reset continuously

until the recorder pen is on scale. Micro switches were

added to both ends of the recorder scale, and either would

activate the recorder circuit. Additional relays provided

power for the steppers to prevent skipping immediately after

resetting, and to electrically isolate the limit switches

for reasons of safety. Only 6 volts ac were on the limit

switch binding posts, and either one could be grounded, if

necessary.

The bucker can be set manually to any of its 20

positions and reset from any position. When the limit

switch binding posts are connected, the position of the

divider will be advanced about once every two seconds

(increasing the voltage output) until it reaches the 4th,

9th, 14th or 20th position. It will then reset to the

zero position.

Indicator lamps were provided for monitoring the

magnetic reed switch (continually driven by the motor and

magnets), the position of the voltage divider and a lamp

fuse

.

Because the bucker was designed for use with a potentiometric recorder or other high-impedance device, it

exhibited high impedance (40,000 ohms) and drew very little

battery current. It was therefore not expected to supply

current. Its purpose was for a voltage source only.

60
The bucking voltage source was used either with a 1.5

volt dry cell or a mercury cell in series with an 8.2 megohm

resistor so that each step would swing a 1/2 millivolt

pen recorder almost to full scale.

Because of the scale expansion, the temperature recorder

was very sensitive to the drift of the dry cell or mercury

cell. The temperature and time stability of dry cells and

size D mercury batteries were checked separately with a potentiometer. The performance varied widely except for

new cells. All cells were temperature sensitive. The

mercury cells performed best, and remained stable to better

than 0.1 percent if insulated from ambient temperature by

several inches of plastic foam. To suppress further drift,

the bucker was enclosed in several inches of insulating

material, because of the temperature sensitivity of the

carbon resistors in the voltage divider. The bucker-recorder

combination seldom drifted over several microvolts per hour.

Short term drift was checked and was not apparent. The

effect of long-term drift was checked and was not apparent.

The effect of long-term drifts (over 20 minutes) on the

results was not critical because the entire recorder system

was calibrated with a separate potentiometer and was provided

with temperature regulated standard cells, which were used

frequently for calibration.

C. Temperature Calibration

1. Thermocouple Changes

Platinum and Platinum - 10 percent Rhodium (15 mil)

wires were calibrated by the Heat Division at NBS.

The thermocouple over which the sample cup rested was

removed, and the calibrated wires were inserted several

inches beyond the ceramic tube. The ends of the wires were

welded into a bead with an oxy-gas torch, then placed in

the same position as those of the previous thermocouple.

The reference thermocouple was withdrawn slightly to match

the position of the calibrated thermocouple. These pre61
cautions were taken to avoid bending the leads, especially

where they enter the bottom of the ceramic tubes and where

large heat gradients were expected. The leads were directed

to the ice bath containing the copper junction.

2

.

Calibration Procedure

With the zero-run switch in the operating position, the

temperature recorders were switched from the sample thermocouple to a calibrated voltage source which in this case was

a high precision potentiometer. The approximate transition

temperatures under investigation were known, so the potentiometer could be set to approximately the correct potential.

This allowed the fiducial marks to be on scale, within

several equivalent degrees of the thermogram. Fiducial

marks were taken within minutes before and after the

thermogram. Several points gave the correct scale factor

for interpolating to the potential reading of the thermocouple . As a further check on the temperature readings, NBS

freezing point standards, lead, aluminum and tin were

carefully prepared. Non-metallic cups were used with these

materials to avoid alloying with the sample. Graphite rod

was chosen because of its availability, purity, and good

thermal conductivity. This rod was cut to size, drilled,

rinsed several times in acetone, boiled in HC1, and heated

to incandescence before use.

3. S ample Cups

Platinum, nickel, stainless steel, aluminum and graphite

cups were tested. Stainless steel was unsatisfactory because

of oxidation and resultant thermogram. Nickel and aluminum

cups were adapted and the thermocouples were inserted

directly into the sample and reference. This did not improve the thermograms perhaps because the thermocouple

contacted only the small layer of sample immediately surrounding it. This layer acted as an insulator for the

remainder of the samples, which were powders or small

62
crystals having relatively poor thermal conductivity. This

approach was abandoned because the thermograms showed no

improvement and since the thermocouple was not protected,

the apparatus was more difficult to load and clean.

4 . Results

Scanning rates of 1 to 5 degrees per minute were used

over the temperature range investigated for potassium

nitrate and quartz for use as DTA standards. Temperatures

could be determined to a precision of about 0.2 degree

(2 microvolts). Data for several melting point standards

were within 2 degrees of their certified values. Repetitive

temperatures of a given sample were consistent to at least

one-half degree for a particular heating rate and at all

heating rates.

Typical thermograms of two proposed SRMs , SiO- and KN0~,

are presented in figure 19. Those for melting point

standards are given in figure 20. The departure point and

the transition peak D are marked. These data are summarized

in table 17. In all cases, the differential temperature

indicates positive deviation on the heating cycle from the

thermodynamic data obtained under adiabatic conditions.

This is to be expected since in differential thermal measurements the rate of heat transfer is the controlling factor.

On the cooling cycle the melting point standards reveal

typical supercooling effects. For KN0~, the cooling cycle

reveals the presence of two phase changes dependent on the

water overpressure. This phenomenon was recognized and

explained early by Kracek in his studies with sealed quartz

tubes [38], It is of interest to note that with the

exception of tin, the average values of A (departure point)

closely approach the thermodynamic values. The larger

deviation of SiO- cannot readily be explained and there is

a need for calorimetric data to assist in resolving this

difference.

63
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65
Table 17. DTA transition point measurements.

Sample

Rate

°c/

mm Cy

Heating

A

C

D

d

Cooling

A

c Dd Ave A Ave D

KN0 3 (127.7°)

5

2

(1)

(2)

(3)

(4)

131.6

132.3

133.4

132.9

138.6

135.4

135.4

137.2

123.0

122.7

122.6

122.8

121.2

121.1

121.2

121.6

127.3

127.5

128.0

127.8

129.9

128.2

128.3

129.4

Sn SRM 42f

(231.9°)

5

1

230.7

231.7

242.2

236.3

201.1

219.2

202.5

220.1

215.9

225.4

222.3

228.2

Pb SRM 49e

(327.4)

5

2

331.1

329.5

334.8

332.0

324.9

324.7

323.2

324.4

328.0

327.1

329.0

328.2

Si0 2 (573°)

5

1

578.2

576.5

580.2

579.0

577.9

579.4

576.2

577.0

578.0

577.9

578.2

578.0

Al SRM 44e

(660°)

5

5

664.2

662.2

676.I

675.6

654.0

656.4

650.5

648.8

659.1

659.3

663.3

662.2

aThermodynamic temperature values from NBS Bulletin 500.

Recycling the same sample below its melting point.

Departure point (see figures 19 and 20).

Transition peak (see figures 19 and 20).

Sample homogeneity, the effect of particle size and

recycling through the transition temperature below the

melting points of the compounds are summarized in figures

21 and 22. It must be noted that KNO.-,, in its first thermogram cycle, reveals a large deviation. Subsequent thermograms

of the same sample indicate consistent reproducibility. The

transition peaks in these figures show a maximum spread of

± 0.5°C which also relates to particle size and source of

material. In future work, it is anticipated that adiabatic

calorimetric data will be available to support the accuracy

of such values. In addition, it is planned to provide other

compounds covering a wider range of transition temperatures.

D. S. Bright, E. R. Deardorff and J. T. Sterling

66
HOMOGENEITY OF QUARTZ

MATERIALS

SIEVE MESH

NBS- LOT 1 >IOO

100-200

200-325

FINES

NBS-LOT2 100-200

NBS- LOT 3 100-200

NBS- LOT 4 100-200

0. L. BRAZILIAN 100-200

ICTA

• «-0.5c O

»

1 i •

• •

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•

•

•

4

•

•

•

•

•

•

• «-0.5 ,C-»

COOLING TRANSITION PEAK

HEATING TRANSITION PEAK

Figure 21. Homogeneity data on proposed SRM quartz

67
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68
4. GASES IN METALS

A. Introduction

The continued importance of interstitial elements and

compounds on the physical and mechanical properties of metals

has been demonstrated by the metal industry's increased

adoption of basic oxygen steel making practices, the large

scale use of vacuum melting techniques and the continued

interest in the determination of gases in metals at increasingly lower levels. There is a real need in the metal

industry for analytical methods and reference samples of

known gas content at less than 10 ppm level for oxygen.

Indeed, with some non-ferrous materials, such as copper,

the level of oxygen is less than 1 or 2 parts per million.

The nitrogen content is also very important because of its

affect on the physical properties of metals; hence, a method

which would provide for the simultaneous determination of

oxygen and nitrogen is desirable, especially for control

analyses. This is important since immediate analyses would

be helpful in making adjustments to the composition during

the actual production of the materials.

To provide meaningful gas measurements in metals, the

work of the section during the past year proceeded along

the following lines: (1) testing and improvement of analytical

apparatus incorporating the basic inert-gas fusion technique

for the extraction of the gases, (2) continuation of studies

on a new standard reference material containing oxygen at

very low levels and (3) supplemental work on the determination

of nitrogen in the 1090 series of SRM's.

B. A New Inert-Gas-Fusion Apparatus for the Determination

of Oxygen and Nitrogen in Metals

This new apparatus was discussed at length in the

summary of activities, July 1967 to June 1968 for the

Analytical Coordination Chemistry Section [1]. However, as

indicated in this reference, the nitrogen values obtained

69
by this procedure needed improvement. The power available

at the time was supplied by a 450 kHz high-frequency

generator and was limited to 2.5 KW, which provided a maximum

temperature of approximately 1900°C. The temperature was

limited by the coupling conditions of the high frequency coil

and by the low power output. A 10 KW, 450 kHz high frequency

converter was installed, with which it is now possible to

obtain temperatures in excess of 2300°C. With this system,

the oxygen concentration was determined on an NES maraging

steel standard and the results are reported in the following

section.

It was found that by increasing the temperature and by

using a large crucible with the platinum bath, results for

nitrogen were lower than those obtained by the Kjeldahl

method or by the pressure-bomb dissolution techniques. This

is evidenced by values of 124 ppm that were obtained on

samples of SRM lOg certified at .015 percent nitrogen.

Because of this low nitrogen recovery with the large multiple

sample technique, it was decided to modify the apparatus.

The modification involved the use of a crucible for a single

determination, rather than using the same crucible for successive extractions. The modified crucible was prepared having

the following dimensions: 9/16" O.D., 7/16" I.D. and 3/8" high.

A. furnace tube approximately 1" I.D., was fabricated of

quartz. The crucible was supported from the bottom by a

graphite pedestal whose cross section was reduced to minimize

heat conduction. This pedestal was supported by a boron

nitride rod which was held in place by a slip joint fabricated

in the ground glass plug. This was used to close the bottom

of the furnace chamber. With this equipment, it was possible,

after outgassing the crucible for 3 minutes at 2300° C and

using a cycling heating technique, to obtain a nitrogen value

of 147 ppm for SRM lOg which compares favorably with the

certified value of .015 percent. Using this method, the

70

i .
crucible is changed for each sample. The necessity for

this was demonstrated by the addition of the second and third

sample to the same crucible. It was observed that the value

of a second sample was lower and the third sample was still

lower, indicating incomplete recovery of nitrogen because

of a bath build-up in the crucible. The same experiment was

repeated with SRM 1091. The initial samples determined gave

nitrogen values of 950 ppm as compared with 9^5 ppm by the

pressure bomb solution method. However, on adding subsequent

samples to the preceding melt, the values approached 825 and

850 ppm.

A closure for the bottom of the furnace assembly has

been designed which employs 0-ring seals to permit rapid

changing of the crucible. This minimizes contamination of

the furnace with atmospheric gases.

C. The Testing of a Maraging Steel for Use as a Low Oxygen

Content Standard Reference Material . As reported in the preliminary study in an earlier

summary of activities [1], there was sufficient evidence to

indicate that this maraging steel would be sufficiently

homogeneous with respect to low levels of oxygen. Accordingly, further testing of this material and preparation for

certification as an SRM were undertaken.

The nominal composition of this maraging steel is

12 percent nickel, 5 percent chromium and 3 percent molybdenum. It was supplied in the form of steel plates

measuring l/2"x3 f x6' and weighing 300 pounds. Sections

l/2"xl/2" were forged to approximately 5/16" diameter rods

and their center ground to 1/4" diameter rods. Samples were

taken at the four corners of the plate before the entire

plate was cut into strips. The preliminary analysis of

this material is described in last year's report [1].

The material reanalyzed consisted of two samples taken

from the middle of the sheet. Because the samples taken

from the four corners were specially selected and individually

71
forged and ground to size, it was decided that those samples

taken from the center portion, marked x and y, were to be

treated exactly as actual production samples. This gave a check as to whether any appreciable change in the gas content

occurred during the processing of the material.

The very low oxygen content of this maraging material

together with a maximum sample size for analyses, made it

necessary to measure microgram quantities of oxygen. Since

it was possible to measure blanks at the 1 microgram per

minute of collection time for a lg sample, this presented

no problem.

A set of values obtained for oxygen in the maraging

steel are given in table 18.

Table 18. Oxygen homogeneity in maraging steel.

Sample

1A1

1A2

lCi

1C 2 2A1

2A2

2C1

2C2

lx

2x

iy

2y

Oxygen (ppm)

6.0. 4.0 , 3.8,, 4.0, 3.9

4.o;, 4.6;, 4.0 , 3.9, 5.6

4.l!, 3.6;, 3.8;, 3.9, 3.2

4.0: 5.6., 4.2 , 3.1, 2.5

3.8; 5.4 , 4.2', 4.1, 2.7

4.0. 3.2 , 5.6;, 5.4, 4.2

3.5, 4.3., 4.0 , 6.0, 3.6

3-1,, 3.0., 5.6', 2.6, 3.2

5.6,, 4.1 , 6.2 , 3.2, 5.1

3.0, 3.0' 3.4;, 2.6, 2.9

4.0. 3.2., 4.5 , 2.6, 3.3

4.8; 3.1., 4.5., 3.3, 4.8

All value5S

Mean = 4.00

S.D. = 0.96

Rel IS.D. =- 24.0$

Mean 2 Ppm

4.3

4.4

3.7

3.9

4.0

4.5

4.3

3.5

4.5

3.0

3.5

4.1

The values in table 18 were the result of homogeneity

studies and the sample numbers 1A1, 1A2 , etc., refer to

the position in the original plate. Samples taken from the

original material were reexamined as were samples selected

randomly from the entire portion of material after forging,

72
swaging and centerless grinding. Results based on 109 determinations gave a value of 4.5 ppm. The uncertainty of + 2 ppm

includes the variations due to inhomogeneity as well as to

the apparatus and operator biases. The final value is based

on both inert gas fusion analysis and on the vacuum fusion

analysis.

D. The Determination of Nitrogen in Ferrous Materials

The nitrogen content of those ferrous materials

currently being issued or in the process of being issued as

SRMs were reexamined with the hope that nitrogen as well as

oxygen might be certified.

The samples were determined by the spinning crucible

technique containing Ni-Ce alloy additions. They were also

determined by the inert-gas fusion methods employing a

heating cycle in which the sample is heated for 30 seconds

at a temperature of l850°C and then heated for 3 minutes at

2100°C.

The values obtained on these materials by the several

methods are given in table 19.

Table 19. Determination of nitrogen ferrous alloys.

a b Sample N2 9 ppm Method

1090

1091

1092

1093

1094

60±1 Inert-gas fusion

950+3 n ii ii l\±1 » " " 3640±76 Spinning crucible

6l±l " " " Uncertainty represents the standard deviation of a single

determination.

Based on use of a single crucible per determination.

J. T. Sterling

73
5. ANALYSIS OF STANDARD REFERENCE MATERIALS

A. Introduction

The variety of reference materials that the Analytical

Coordination Chemistry Section assisted in standardizing

during the last year are listed in table 20. The details

of analyses are discussed in subsequent sections.

Table 20. SRM's analyzed by Analytical Coordination

Chemistry Section.

Chemical Composition Standards

General Class NBS-SRM Type

Steels (Chip) 36b 2 Cr-1 Mo Low Alloy

125b 3 Si Steel

131b Low Carbon (0.0018C)

160b 19 Cr-l4 Ni-3 Mo Stainless

178 0.4C Basic Oxygen

1090 Ingot Iron

1093 Valve Steel

Steels 1138 Cast Steel No. 1

(Spectrographic) 1139 Cast Steel No. 2

1155 19 Cr-l4 Ni-3 Mo Stainless

1261 0.4C Steel

1262 0.2C Steel

1263 0.6C Steel

1265 Ingot Iron

Cast Irons 122e Car-wheel (3.5C)

342a Nodular Iron (0.07 Mg)

Ferroalloy 59a Ferrosilicon (50 Si)

High Purity Metals 685 Gold

Clays 97a Flint Clay

98a Plastic Clay

Metallo-Organic 1051b Barium Cyclohexanebutyrate

1055b Cobalt Cyclohexanebutyrate

1057b Dibutyltin bis (2-ethylhexanoate

)

1066a Octaphenylcyclotetrasiloxane

1069b Sodium Cyclohexanebutyrate

1079b tris (l-phenyl-1,3 butanediono)

Iron III

Miscellaneous 480 Electron Microprobe (20 M0-8OW)

915 Calcium Carbonate

953 Neutron Density Wire

1800 Microstandard Ion Exchange Beads

74
The wiae range of materials that the Section was

requested to analyze for certification, requires considerable

experience, competence and versatility of the staff members.

In the course of this work, atomic absorption, spectrophotometry, gravimetric, titrimetric, vacuum fusion and combustion-gravimetric techniques were effectively employed to

cover the broad scope of concentrations from the ppm to

80 percent levels. In the certification program, the application of atomic absorption accounts for approximately 25

percent of the analyses, spectrophotometry about 60 percent

and gravimetry and titrimetry approximately 15 percent.

Analyses by atomic absorption and spectrophotometry occupy

positions of increasing importance in the determination of

very small concentrations of many elements. We have

demonstrated the ability to increase detection limits and

to provide high accuracy analyses of the major components of

many composition standards by these techniques. A number

of the procedures are being adopted, as official methods, by

such standardizing bodies as ISO, ASTM and ACS. In addition

to their usefulness as general laboratory competences, they

are being used quite extensively for high speed analytical

control in metal and chemical production. A part of the NBS

and Analytical Chemistry Division's wide and varied service

to American industry and technology involves the preparation

and characterization of many Standard Reference Materials

which serve as production bench-marks for many basic industrial products such as steels, irons, ores, ceramics,

chemicals, glasses, etc. The materials must be highly stable

and homogeneous and are certified as to their composition or

their properties. Homogeneity and permanence of material

play important roles in the certification of reference

standards. The starting material should be homogeneous, but

a knowledge of the reference materials' permanence is equally

important if the standards are to be useful and meaningful.

75
There are at present, approximately 700 standard

materials that are provided by the NBS. The materials are

analyzed carefully by the NBS staff and in many cases, by

selected industrial laboratories as part of a cooperative

program that was established years ago.

The preparation of Standard Reference Materials involves

many factors. In selecting the types and compositions of the

materials to be issued as standards, NBS is guided by the

number and kinds of requests received from potential users

and by the suggestions of those engaged in a particular area

of interest. The majority of the chemical standards are

metals and alloys, that are used extensively for monitoring

thousands of analyses that are made daily in industrial

laboratories, although new standards are being provided in

such expanded areas as clinical chemistry and air pollution.

Standards of chemical composition also serve as guides in

developing new analytical methods or determining the composition of unknown materials. As industrial and scientific

needs develop, as indicated by requests from interested

parties, new chemical standards are prepared and issued.

Methods of analyses used in the certification program

in the Chemistry Division are selected or designed to give

the best obtainable results. When possible, several methods

for a given element are employed as a cross-check. For

example, copper in steels or cast irons is determined

spectrophotometrically as the carbamate complex, by atomic

absorption and by isotopic dilution and activation analysis

techniques. Values obtained by the various competences are

generally in sufficient agreement to indicate that the best

possible value has been obtained.

B. SRM Information and Summary

The following information on those standards that were

recently issued as Standard Reference Materials or on which

homogeneity studies were conducted, provides background which

76
may be or general interest. Listed are the elements certified

by the Section members along with brief outlines of the

methods and the data obtained.

1. Steel (2 Cr-1 Mo) - SRM 36b

This steel, first issued in 194l, is one of a series of

low alloy steels and represents a specific type of alloy having

good mechanical properties and high-strength. Typical applications are found in the automotive industry. Its greatest

use as a reference control standard is in the determination

of carbon, manganese, sulfur, chromium and molybdenum..

Table 21. Composition data for SRM 36b.

Elements- No. Det'ms Average Std Dev Analyst

Carbon 10 0.1l4 a 0.0003 JRB

Manganese 8 .O403b - JRB

Phosphorus 8 .007° .0004 JRB

Sulfur 8 .020 d .0002 JRB

Silicon 4 .257

e - JRB

Copper 4

8

.I86 f

.I83 g

.002

.005

SAW

TAR

Nickel 7 .192h

.01 ERD

Chromium 4 2.181 .0002 BBB

Vanadium 4 0.004 J

' .0096 BBB

Molybdenum 4 .995* .004 BBB

Combustion-gravimetric of a 2g sample by induction heating

Manganese oxidized with ammonium-persulfate and titrated

potentiometrically with standard sodium arsenite solution.

c

* Phosphorus determined spectrophotometrically as the ammonium

phosphcmolybdate complex.

lg sample burned in oxygen and sulfur dioxide absorbed in

starch-iodide solution. Liberated iodine is titrated with

standard potassium iodate solution.

Q Double dehydration with perchloric acid,

f Copper determined spectrophotometrically as the carbamate

complex.

^Atomic absorption on a lg sample dissolved in ultra pure

hydrochloric acid.

77
Nickel determined spectrophotometrically as the dimethylglyoxime complex at pH 13.

2g sample dissolved in dilute sulfuric acid (1+3), chromium

oxidized with ammonium persulfate in presence of silver

nitrate and titrated with standard ferrous ammonium sulfate

solution.

^lg sample dissolved in dilute sulfuric acid. Vanadium

determined spectrophotometrically on an aliquot portion

(O.lg) as the benzoylphenylhydroxylamine complex.

lg sample dissolved in perchloric acid. Molybdenum determined spectrophotometrically on an aliquot portion (62.5 mg)

as the thiocyanate complex.

2. High Silicon Steel (3 Si) - SRM 125b

The electrical qualities, especially the high magnetic

permeability, of this type of alloy makes it a valuable

material for use in electrical equipment, particularly by

the manufacturers of industrial transformers. Its main use

as a reference standard is in the determination of carbon

(0.03 C), sulfur (0.01 S) and silicon (3 Si).

Table 22. Composition data for SRM 125b.

Sample No.

Elements Position 1 2 3 4 Analyst

Carbon9" Top

Middle

Bottom

0.044

.031

.031

0.031

.034

.031

0.037

.031

.029

0.034

.033

.033

JRB

Manganese

Top

Middle

Top

0.282

.286

.280

0.281

.278

.277

0.286

.279

.277

0.282

.282

.277

SAW

Sulfur

Top

Middle

Bottom

0.011

.011

.011

0.010

.010

.012

0.010

.011

.013

0.011

.011

.013

JRB

Silicon

Top

Middle

Bottom

2.87

2.87

2.86

2.88

2.86

2.84

2.87

2.87

2.81

2.89

2.87

2.82

JRB

aCombustion-gravimetric

.

Manganese oxidized with ammonium persulfate and titrated

potentiometrically with standard sodium arsenite solution.

78
lg sample burned in oxygen and sulfur dioxide absorbed in

starch-iodide solution. Liberated iodine is titrated with

standard potassium iodate solution.

Double dehydration with perchloric acid.

The work to date was to establish the homogeneity of the

sample prior to acceptance of the final material. Homogeneity

was based initially on 12 test samples taken from 3 positions

along a continuously-cast bar measuring 12 feet long, 17

inches wide and 5 inches thick, for carbon, manganese,

sulfur and silicon. Additional elements will be determined

for final certification. Based on the data obtained above,

it was concluded that the material was homogeneous and

acceptable for final certification analysis.

3. Low Carbon (<0.002 C) Steel - SRM 131b

This special low-carbon alloy containing between 3-^

percent silicon was first issued in 19^9 (131-0.0028 C) and

again in 1965 (131a-0.0044 C) at the suggestion and request

of the iron and steel industry because of the importance of

extremely small amounts of carbon in transformer plate and

magnetic materials. It is used as the bench-mark for

standardizing and calibrating the many new types of chromatographic instruments specially adapted for low carbon determinations. It also serves as a suitable accelerator or flux

in the determination of carbon in metals such as nickel,

titanium and zirconium.

Element No Det T ms Average Std. Dev Analyst

Carbon 10 0.00l8 a 0.0002 JRB

Carbon was determined on composites of four 2.5g

samples by combustion in an induction furnace.

The evolved carbon dioxide was collected in an

ascarite-filled U tube and weighed. Proper blanks

were determined and deducted.

79
4 . Stainless Steel (19 Cr-12 Ni-3 Mo) - SRM l60b

The need for this "modified" stainless steel containing

2.5 percent molybdenum was firsL expressed by the Alloy

Casting Institute in 1946. By 1948 the first sample, 160,

was issued with a provisional certificate and in 1957 the replacement sample, l60a, was issued. This wrought stainless

steel grade has superior corrosion resistance to sea water

and other corrodents. It has superior strength at elevated

temperatures, is non-magnetic, and has applications for wirescreening, chemical processing equipment, etc. This particular alloy "rounds out" our stock of stainless steels.

Table 23. Composition data for SRM l60b.

Elements No Det'ms Average Std Dev Analyst

Carbon 8 0.046 a 0.0004 JRB

Phosphorus 8 .020b .001 JRB

Sulfur 8 .018 C .0005 JRB

Silicon 6 .509

d .005 SAW

Nickel 12 12.37 6

I2.l9 f

.07 ERD

SAW

Vanadium 4 0.047 s .0003 JRB

Nitrogen 10 .040 h .0003 SAW

Combustion-gravimetric of a 2g sample by induction heating.

Phosphorus determined spectrophotometrically as the

ammonium phosphomolybdate complex.

lg sample burned in oxygen and sulfur dioxide absorbed in

starch-iodide solution. Liberated iodine is titrated with

standard potassium iodate solution.

Double dehydration with perchloric acid.

e Nickel determined spectrophotometrically as the dimethylglyoxime complex at pH 13.

f Nickel determined gravimetrically as nickel dimethylglyoxinate on O.250g sample.

s 5g sample dissolved in dilute sulfuric acid. Vanadium

oxidized with nitric acid and titrated potentiometrically

with standard ferrous ammonium sulfate solution.

Sample dissolution in pressure-bomb. Nitrogen determined by

dist illation-tit rat ion. 80
As an analytical standard, its greatest use is for

carbon, chromium, nickel and molybdenum control.

5. Carbon Steel (0.4 C) - SRM 178

This medium carbon steel, the first NBS Standard

Reference Material prepared by the Basic Oxygen Furnace

method, is one of the most popular carbon steels. It has

wide application in the automotive industry, particularly in

the manufacture of connecting rods, steering arms, bolts,

studs, etc, It makes an ideal reference standard for control

analyses for carbon, manganese, phosphorus, sulfur and silicon,

Table 24. Composition data for SRM 178.

Elements No Det'ms Average Std Dev Analyst

Carbon 30 0.398 a 0.0018 JRB

Manganese 8 .822 b .0008 JRB

Phosphorus 8 .011 c .0002

Sulfur 16 .0l4 d .0003 JRB

Silicon 8 .l63 e .016 JRB

Copper 24 .033 f .003 TAR

Nickel 5 .012 g - ERD

Chromium 4 .01 5

h - JRB

Vanadium 4 .001 1 - JRB

Molybdenum 3 .003 J .0002 BBB

Combustion-gravimetric of a 2g sample by induction heating.

Manganese oxidized with ammonium persulfate and titrated

potentiometrically with standard sodium arsenite solution.

Phosphorus determined spectrophotometrically as the ammonium

phosphomolybdate complex.

lg sample burned in oxygen and sulfur dioxide absorbed in

starch-iodate solution. Liberated iodine is titrated with

standard potassium iodate solution.

Q Double dehydration with perchloric acid,

fAtomic absorption on a lg sample dissolved in ultra pure

hydrochloric acid.

a;°Nickel determined spectrophotometrically as the dimethylglyoxime complex at pH 13.

81
h

Chromium separated from bulk of the iron in a lOg sample by

precipitation with sodium bicarbonate, oxidized with ammonium

persulfate and titrated potentiometrically with standard

ferrous ammonium sulfate solution.

Vanadium separated as in (h), oxidized with nitric acid and

titrated potentiometrically with standard ferrous ammonium

sulfate solution.

^Molybdenum determined spectrophotometrically as the

thiocyanate complex.

6. Ingot Iron and Valve Steel - SRM 1090, 1093

These standards are two of a series of metals that are

certified for oxygen and nitrogen. Because of the importance

of the interstitial gases to the basic properties of metals,

such as ductility and embrittlement , it is vital that the

concentrations of these two elements be firmly established.

In addition to the inert gas fusion technique for the

determination of nitrogen, additional recheck data for this

element were obtained by the distillation-titration and

distillation-photometric methods

.

Nitrogen was determined in ingot iron (SRM 1090) by the

indophenol colorimetric method [39].

A 0.5-gram sample was dissolved by the pressure bomb

technique and the nitrogen separated as ammonia by distillation. The ammonia was reacted with phenolate ions and

sodium hypochlorite to form a quantitative nitrogen indophenol

complex. Forty-five minutes were allowed for completion of

reaction and color formation.

The absorbance of the indophenol complex was measured

spectrophotometrically at a wavelength of 625 nm. The

nitrogen content ranged from 57 to 6] ug with a standard

deviation of 0.0002. Analytical results are given below:

82
Material El eme nt Cone. % Analyst

Ingot Iron

n

tt

tt

N

t!

tt

ft

O.OO60

.0060

.0057

.0061

SAW

Table 25. Nitrogen data for SRM 1090.

Sample No.

1090

tt

tt

tt Average 0. 0059#±.0002

Nitrogen was determined also in valve steel (SRM 1093)

by the distillation-titration method.

A 0.3-gram sample was dissolved by the pressure bomb

technique and the nitrogen separated as ammonia by distillation [40], The solution was then titrated with standard

hydrochloric acid. The nitrogen content ranged from 0.480 to

0.482 percent with a standard deviation of .001. Analytical

results are given below:

Table 26. Nitrogen data for SRM 1093.

Sample No. Material El eme nt Cone. % Analyst

1093 Valve Steel N 0.480 SAW

tt tt tt .482

tt tt tt .480

tt tt tt .482

Average 0.48l#

7. Cast Steels Spectrographic - SRM 1138-1139

The development of these cast steel standards was a joint effort by NBS and the Steel Founders Society to meet

the urgent need for calibrating spectrographic instruments

for use in production control of cast steels. The two

standards represent compositions of a balanced range for the

10 elements that are certified. Although the samples have

been issued under a provisional certificate, recheck values

were requested for 3 of the elements by techniques other

than spectroscopy.

A digital pH meter was used in connection with the

titration of small concentrations of vanadium. Increased

83
Table 27. Compositi

SRM No. Element

1138 Chromium

tt Vanadium

ti Molybdenum

1139 Chromium

H Vanadium

tt Molybdenum

0.122 a 0.001 BBB

.020b .001 it .050°

1.98d .002 tt 0.224 e .0008 tt .503° .006 it

precision and a reduction in titration time were noted in

evaluating the equipment.

Composition data for SRM's 1138 and 1139.

No. Det'ms Average Std Dev Analyst

4

4

5

5

5

5

Chromium separated from the bulk of the iron in a lOg

sample by precipitation with sodium bicarbonate, oxidized

with ammonium persulfate and titrated potentiometrically

with standard ferrous ammonium sulfate solution.

Vanadium separated as in (a), oxidized with nitric acid and

titrated potentiometrically with standard ferrous ammonium

sulfate solution.

Q Molybdenum determined spectrophotometrically as the thiocyanate complex.

Oxidation with ammonium persulfate and titration with

standard ferrous ammonium sulfate solution.

Q Oxidation with potassium permanganate and titration with

standard ferrous ammonium sulfate solution.

8. Spectrographic Standards 1261-1265 (Iron and Steels)

These five standards are replacements for the original

set of eight NBS spectrochemical standards 1163-1168, that

were first issued in 1947. A graded range of approximately

30 elements in each of the five samples will be certified

to cover the broad spectrum of steels that will serve as

controls for the greater percentage of the world's steel

production. In establishing the compositions for these

important alloys, the many requests of the steel producers

were carefully considered. The samples are intended to

serve not only for composition control in the production of

iron and steel in this country, but also in customer

acceptance. 84
The initial efforts of the Section were to analyze a

number of elements in each of 4 samples for preliminary

composition acceptance. To date, the fifth sample has not

become available. The list of elements and the preliminary

values obtained are given below:

Table 28. Composition data for SRM's 1261, 1262 and 1265

Sample Element Percent found Analyst

1261 Silver , Calcium

0.0004 TAR

.0001 M Magnesium3, .0002 It Zinc a .0005 t! Nitrogen .0032 JTS

Oxygen .0010 ?t 1262 Sulfurd 0.038 JRB

Silver , Calcium

.0009 TAR

.0003 it Magnesium .0007 ti Zinc a .0011 it Nitrogen .0034 JTS

Oxygen .0010 tt 1263 Carbon f Phosphorus

0.62 JRB

.026 RKB

Sulfur d .009 it Silver 8-, Calcium

.003 TAR

.0003 tt Magnesium .0005 ti Nitrogen .004 JTS

Oxygen .0006 tt 1265 Q Carbon f Phosphorus

0.010 JRB

.002 tt Sulfur d .008 it Silver3-, Calcium

0.1 ppm TAR

1.0 " it Magnesium 0.2 " it Nitrogen .001 JTS

Oxygen .005 it

Atomic absorption.

Flame emission spectroscopy.

1'Vacuum fusion.

1 lg sample burned in oxygen and sulfur dioxide absorbed in

starch-iodide solution. Liberated iodine is titrated with

standard potassium iodate solution.

85
e Combustion-gravimetric

.

f Phosphorus determined spectrophotometrically as the ammonium

phosphomolybdate complex.

A detailed report will be available at a later date, after

the final materials have been analyzed and certified.

9. Standard Cast Iron - SRM 122e

This is a replacement standard for the very popular highcarbon cast iron. Preliminary homogeneity data for carbon

and sulfur indicated that the material was homogeneous and

could be used for final analysis and certification.

Element No. det'ms Average Analyst

Total carbon 39 3.50 JRB

Sulfur 26 0.073 "

A detailed report will be available at a later date, after

the material has been analyzed and certified.

10. Standard Nodular Iron - SRM 3^2a

This unique alloy was first provided by NBS in 1961 at

the request of the American Foundrymen's Society. The unusual properties, high strength with good ductility, of this

type iron-base alloy makes it a very popular material for a fairly specialized segment of the metals industry. Because

of the inability of the Research Committee of the Ductile

Iron Division of the AFS to obtain agreement among various

of their laboratories for the contained magnesium, they

prevailed on NBS to provide a homogeneous and well-characterized standard, particularly for the magnesium. The intent

of the project was to determine with what degree of reliability magnesium determinations could be employed as a control

of inspection procedure for nodular iron quality.

Its main use as a control standard is in the determination of magnesium, total and graphitic carbon, sulfur and

silicon, although the material has been certified for 13

elements

.

86
Table 29. Composition data for SRM 342a.

No

Elements det ! ms

Total carbon 14

Graphite 8

Manganese 6

Phosphorus 8

Sulfur 36

Silicon 4

Copper 3

Nickel 4

Chromium 6

Magnesium 17

Average

1.84 a

1.38b

0.271°

.0l8 d

.005

e f 2.72 1

.134 s

.058 h

.035^

.072 J

'

Std Dev Analyst

0.017 JRB

.017 it .0025 BBB

.0006 JRB

.0008 ii .006 it .001 SAW

- ERD

.0001 BBB

.001 TAR

a

d

Combustion-gravimetric of a lg sample by induction heating.

2g sample dissolved in dilute nitric acid. Graphite

filtered onto asbestos pad contained in quartz crucible

and dried at 110°C. Carbon dioxide determined by combustiongravimetric procedure.

'Manganese oxidized with ammonium persulfate and titrated

potentiometrically with standard sodium arsenite solution.

Phosphorus determined spectrophotometrically as the

ammonium phosphomoiybdate complex.

Q lg sample burned in oxygen and sulfur dioxide absorbed in

starch-iodide solution. Liberated iodine is titrated with

standard potassium iodate solution,

fDouble dehydration with perchloric acid.

sCopper determined spectrophotometrically as the carbamate,

complex.

Nickel determined spectrophotometrically as the dimethylglyoxime complex at pH 13.

Chromium separated from bulk of the iron in a lOg sample by

precipitation with sodium bicarbonate, oxidized with

ammonium persulfate and titrated potentiometrically with

standard ferrous ammonium sulfate solution.

J Atomic absorption.

87
11. Standard Ferrosilicon - SRM 59a

This very Important ferroalloy has been out of stock for

a number of years, and at the request of the ferroalloy

industry, it has been renewed. To the alloy has been added

approximately 0.1 percent boron, since this element is of

interest to the producers and consumers. Ferrosilicon, like

most of the other ferroalloys, is sold on an "as contained"

basis, hence demands for very accurate control is becoming

of increasing importance.

The following tabulation shows homogeneity data

obtained for silicon on bulk material contained in 5

containers and at 3 positions:

Table 30. Percent silicon obtained on bulk material.

Container No Position

Top Middle Bottom

48.08

48.11

48.06

48.15

48.09

48.13

48.13

48.03

48.04

48.15

48.00

48.15

48.07

48.15

48.11

48.16

48.18

48.17

48.12

48.13

48.14

48.09

48.15

48.01

48.17

48.11

48.13

48.14

48.15

The data for silicon given above indicate that the

material is sufficiently homogeneous for use as a Standard

Reference Material.

Procedures for the Determination of Silicon, Manganese,

Chromium and Iron in Ferrosilicon

a. Silicon , Transfer 0.5g of the sample, accurately

weighed, to a 4 5 -ml zirconium crucible and add about 13g

of sodium peroxide. Mix thoroughly with a platinum rod and

carefully clean the rod of adhering particles by scraping

88
with another rod and by rotating the rod in 2g of additional

sodium peroxide used to cover the mixture.

Heat the crucible and contents on a hot plate for 10

minutes to expel water in the peroxide. Carefully fuse over

a Meeker flame by holding the crucible with a pair of tongs

and slowly revolving it around the outer edge of the flame

until the contents have melted quietly, and without spattering.

When the mixture is molten, rotate the crucible carefully so

that the swirling liquid will stir up any unattacked particles

on the bottom or side, the crucible and contents being

maintained at a low red heat. After fusing 3 or 4 minutes,

increase the temperature to bright redness for a minute.

Cover the crucible and allow it to cool to room

temperature. Remove the cover, invert the crucible over a liter platinum dish, and tap the bottom to transfer the cake.

Cover the dish and cautiously add, in small portions, a total

of 50 ml of water. When the reaction ceases, wash the lid

and crucible with water and add the washings to the dish.

Cool the dish and contents and carefully add 5 ml of sulfurous

acid. Police the crucible, using HC1 (1+3), and carefully

add the acid to the dish. Cool the dish and carefully add

HC1 until in moderate excess. Heat on a steam bath and, after

effervescence ceases, wash and remove the cover. Evaporate

to dryness on a steam bath.

Cool the dish, drench the residue with 20 ml of HC1,

cover the dish, and heat gently for 5 minutes. Dilute with

200 ml of hot water, digest on a steam bath for 5 minutes,

stir to break up lumps, and filter immediately through an

11-cm medium filter paper. Wash about 8 times with hot HC1

(5+95) j twice with warm HpSOj, (5+95 ) 3 and 5 times with hot

water. Transfer the paper and contents to a platinum

crucible and reserve.

Evaporate the filtrate and washings to dryness. Cover

the dish and bake at 110°C for 1 hour. Cool, drench with

15 ml of HC1, digest on a steam bath for 5 minutes, add

89
150 ml "of warm water, and stir. Filter immediately and wash

8 times with cool HCl(l+99), twice with cool H SO, (5+95),

and 5 times with cool water.

Combine the paper and contents with the reserved paper

in the platinum crucible and carefully burn off the carbon,

without flaming, by heating slowly to 550°C in a muffle

furnace. When the carbon has been completely burned,

tightly cover the crucible, gradually increase the temperature to 1150°C, and heat at this level for 45 minutes. Cool

in a desiccator for 30 minutes and weigh. Check for constant

weight by additional heating periods of 25 minutes at 1150°C.

Carefully add 1 ml of H

2 SCv(l+l) to the crucible to

moisten the silica and then add 20 ml of HF (48 percent).

Evaporate to dryness in an air bath, ignite at 1100°C for

5 minutes, cool in a desiccator 30 minutes, and weigh. The

loss in weight represents SiOp.

Calculation . Calculate the percentage of silicon as

follows

:

„.,. , AxO. 4675x100, Silicon, percent = ^-^ >

where A = weight of SiOp, g

and B = weight of sample, g

Manganese, chromium and iron have also been determined

on this materialo Outlines of the methods together with the

results are given:

b. Manganese , Dissolve lg of sample in 30 ml of HNO^-

HF(5+1) mixture.

Add 30 ml of HpSOK-H^PO^-HNO^ mixture and evaporate to

fumes of HpSOj., cool, add 25 ml of water and add back 8 ml

of HNCU,

Transfer the solution to a 500 ml Erlenmeyer flask,

oxidize the manganese with ammonium persulfate in the

presence of AgNO^ by boiling the solution for 90 seconds.

90
Cool the solution to 5-10°C, transfer to a 400 ml beaker,

and titrate the manganese potentiometrically with standardized sodium arsenite solution, 1 ml = 0.40 mg Mn.

An average value of 0.747 percent manganese was obtained

on 14 determinations.

c. Chromium . Transfer 5g of sample to a liter platinum

dish, cover, and add 40 ml of HN0-, and 2 ml of HF (48 percent).

Warm the dish gently to start reaction. Add 35 ml of HF

dropwise from a plastic separatory funnel until the sample is

completely dissolved. This requires approximately 25 minutes.

Wash the cover carefully with water and add 30 ml of

HpSO^Cl+l). Evaporate the solution to fumes of H„S0l and

continue fuming for 5 minutes. Cool, add 100 ml of water and

digest on a steam bath. Filter and wash the paper with hot

water. Reserve the filtrate. Transfer the residue to a

platinum crucible, ignite at 550°C and fuse the residue with

2g of KpSp0 7

. Dissolve the melt in 30 ml of hot water and

1 ml of HpS0|,. Combine with the reserved filtrate and

dilute to 300 ml. Add 10 ml of AgNO^ solution (0.25 percent)

and 20 ml of (NHi ,)pSp0n (15 percent) and boil for at least

30 minutes to oxidize the chromium. Add 4 ml of HC1(1+1)

to destroy the manganese color and boil for 20 minutes to

obtain a clear solution. Remove from the heat and cool to

room temperature or lower. Titrate potentiometrically with

standard Fe (NH^

)

2 (SO^

)

2

solution (23g/l).

An average value of 0.084 percent chromium was obtained

on 5 determinations.

d. Iron

Reagents

(a) Mercuric chloride solution: Prepare a saturated solution of HgClp in water.

(b) Sulfuric-phosphoric acid mixture: Mix 150 ml

of HpSO^ (sp. gr. 1.84) with 300 ml of water, cool, add

150 ml of K^POl (sp. gr. I.69), dilute to 1 liter with water

and mix.

91
(c) Stannous chloride solution: Dissolve 150g of

SnCl

2

.2H

2

in 300 ml of HC1 (sp. gr. 1.19), dilute to 1 liter

with water, and mix.

(d) Sodium diphenylamine sulfonate indicator

solution: Dissolve 0.25g of sodium diphenylamine sulfonate in

100 ml of water.

(e) Standard potassium dichromate solution (0.1N):

Transfer 4.9032g of SRM 136b, K

2

Cr

2 ?

, to a liter volumetric

flask and dissolve in water. Dilute to the mark with water

and mix. Determine the iron titer by checking against ingot

iron standard 55e.

Transfer a 0.5g sample, accurately weighed, to a liter

platinum dish, cover, and add 5 ml of HF (48 percent). Add

2 ml of HN0- (sp. gr. 1.42) dropwise at a rate of 4 to 5

drops per minute. Avoid loss by spattering. When reaction

ceases, wash the cover and wall with water.

Add 8 ml of H^SC^d+l) and heat until fumes of R^SC^

Cool, add 300 ml of water, and digest on a steam bath to

dissolve salts. Neutralize with NHlOH and add a slight

excess. Filter through a 12.5 cm coarse filter paper and

wash several times with hot water.

Transfer most of the precipitate from the paper to the

dish by washing with water and pour 30 ml of hot HCl(l+2)

onto the paper. Wash the paper well with hot HCl(l+99)j

catching the solution in the dish. Reserve the paper (A).

Dilute the solution in the dish to 100 ml and filter

through a 7 or 9 cm fine filter paper to separate a small

amount of insoluble residue, catching the filtrate in a

600-ml beaker. Wash the dish and paper well with hot

HCl(l+99). Evaporate the filtrate and washings to about

10 ml volume and reserve (B).

Transfer the paper and the reserved paper (A) to a

platinum crucible and ignite at 550°C. Cool, add lg of

K

2 Sp0 7

, and fuse the residue. Cool, and dissolve the melt

92
in 15 ml of hot water and 1 ml of HC1 (sp. gr. 1.19).

Combine the solution with the reserved solution (B).

Adjust the volume of the iron solution to about 25 ml

and cool. Add a 2.5 percent solution of KMnOh dropwise until

a distinct pink or brownish color persists. Heat to boiling,

boil gently for 5 minutes to expel chlorine. Add stannous

chloride solution dropwise while swirling the hot solution

until the color of the ferric iron disappears, and then add

just one drop more. Wash the cover and wall of the beaker

and quickly cool the solution in ice-water. Add at one

stroke 10 ml of the HgCl„ saturated solution, stir, and wash

the wall of the beaker. Allow the solution to stand for 2

to 5 minutes. Add 20 ml of HpS0|.-H^P0L mixture, dilute to

350 ml with water, and add 5 to 6 drops of sodium diphenylamine sulfonate indicator solution. Titrate with standard

KpCrp0 7 solution to a permanent blue or violet color which

does not change upon further addition of dichromatej while

stirring.

Standardize the KpCr ? 7 solution by dissolving O.250g

of SRM Ingot Iron, 55e (99.79 percent Fe ) in 10 ml of

HC1(1+1), and continue as directed in the procedure beginning

with heating nearly to boiling and reducing with SnClp.

Calculation . Calculate the percentage of iron as

follows

:

A = grams of iron used as a standard.

B = milliliters of KpCrpO y

solution used to

A titrate A. 5- = C.

D

C = iron titer, in grams per ml of KpCrpCu

solution.

D = ml of KpCrpO„ solution used to titrate the

sample.

E = grams of sample used.

Percent Fe = ^^- x 100.

93
An average value of 50 percent iron was obtained on

6 determinations.

In connection with the preliminary determination of

iron, consideration was given to the use of various sample

sizes, in addition to the need for separating and collecting

the iron by precipitation with NHlOH. The comparative use

of HOICK vs HpSCX for fuming to remove HF and to affect

complete solution of the sample was also investigated.

Approximately 26 determinations of iron were made in

an effort to establish a procedure that would provide

satisfactory results.

12 . Metal-Organic Materials

Of the 24 standard metal-organic materials that are

provided by NBS, 6 renewals have been analyzed and certified

during this reporting period. These materials were developed

essentially for use in estimating the degree of engine wear

by determining spectrographically the small amounts of

metals found in engine crankcase oils.

Listed are the materials certified together with

percentages of metal constituents and summary of methods.

Table 31. Certified metallo-organic compounds

SRM

No

1051b Barium Cyclohexanebutyrate

1055b Cobalt Cyclohexanebutyrate

1057b C Dibutyltin bis(2 ethylhexanoate

)

10 6 6a Octaphenylcyclotetrasiloxane

1069b Sodium Cyclohexanebutyrate

1079b f Tris(l-phenyl-l,3 butanediono) 10

iron III

Average

,

Det ' ms percent Analyst

9 28.79 BBB

12 14.87 ?i

12 22.92 it

6 14.13 II

7 12.11 ft

) 10 10.45 t

Barium determined by wet-ashing a 0.5g sample with H 2 S0i+

and HN0 3 , dried for 72 hours over P2O5 and the resulting

insoluble material removed by filtration, ignited at 900°C

and weighed as BaSOit.

94
Cobalt determined by wrapping the sample in filter paper,

covering with oxalic acid and then igniting at 800°C. The

resulting oxide was dissolved in HC1, electrodeposited as

cobalt from an ammoniacal solution and weighed as the metal.

Residual cobalt in the electrolyte determined spectrophotometrically using nitrose R salt to form the colored complex.

G Tin determined by wet-ashing a lg sample with R^SOi* and HN03,

dried for 2 hours over PzOs, precipitating the tin with

cupferron and converting the precipitate to Sn0 2 by ignition

at 1000°C. A second method involved preliminary treatment

with R^SCu and HNO 3 as above, reduction of the tin with

nickel and titrating with standard potassium iodate solution.

Silicon determined by wet-ashing lg sample with H2SO4 and

HNO 3, dried for 2 hours over P2O5J double dehydration of

silica, igniting at 1100°C and volatilizing the silicon with

HP.

Q Sodium determined by wrapping the sample in filter paper,

covering with oxalic acid and then igniting. The residue

was either converted to sodium chloride and weighed after

ignition at 600°C or converted to sodium sulfate and weighed

after ignition at 750°C.

f Iron determined by wet-ashing a 0.5g sample with HNO 3 and

H2SO1+, dried for 1 hour at 110°C, precipitating with ammonium

hydroxide, dissolving the precipitate in HC1, reducing with

SnCl 2 and titrating with standard K2Cr207 solution.

Determinations were also made by direct ignition to Fe20-3

of a 0.5g sample which was wrapped in filter paper and

covered with oxalic acid.

13. Clay Standards 97a and 98a

These two clay materials are of interest to the ceramic

and refractory industries and will serve as analytical

composition standards for flint and plastic clay materials.

The graded compositions are necessary to control the physical

as well as the chemical properties of the finished products.

They will serve as bench-marks for the calibration of many

instrumental methods since there have been some marked

advances in both instrumental and analytical techniques that

are applicable to these complex materials.

To emphasize the complexity of these types of materials

and their analysis, Lundell and Hoffman [41] as early as 1928

provided data to show the lack of agreement between analysts

95
who assisted in the cooperative analysis of similar materials,

and more recently Flanagan [42] of the Geological Survey

reiterated that the problem still exists.

In an effort to obtain the best possible values for the

2 major constituents, SiOp and AlpO.-,, several methods for

each were evaluated. Summaries of these methods are given in

the following sections.

a. Gravimetric Methods for SiO„

NapCO.-, Fusion - HpSC^ Dehydration. Dry a 0.5g sample

at l40°C for 2 hours and then fuse with 8g of anhydrous

NapCO.-,. Dissolve the cool melt in dilute HpSO^ (1+9) and

dehydrate the SiOp twice, with an intervening filtration

[4], Ignite the impure residue at 1200°C, weigh, and treat

with HF. Determine the amount of SiO ? from the loss in

weight. Determine spectrophotometrically the soluble SiO ? in the filtrate by the molybdo-silicic acid butanol

extraction method [4] and add to the gravimetric value.

NapCCU Fusion - HC1 Dehydration. Dry a lg sample at

l40°C for 2 hours and then fuse with 5g of anhydrous Na

?

CO^.

Dissolve the cool melt in dilute HC1 and dehydrate the SiOp

twice, with an intervening filtration [44]. Ignite the

impure residue at 1200°C and weigh before and after HF

treatment. Determine spectrophotometrically the soluble

SiOp in the filtrate and add to the gravimetric value.

LiBOp Fusion - Ion Exchange Dissolution. Dry a 0.5g

sample of SRM 97a, flint clay, and a 0.25g of SRM 98a,

plastic clay, at l40°C for 2 hours and then fuse with a fivefold weight of lithium metaborate [45] in a graphite

crucible at 950°C for 20 minutes. Swirl the melt gently and

then carefully transfer to a Teflon beaker containing 100 ml

of water. Grind the solid in an agate mortar, mix with

double the MEQ weight of dry cation exchange resin (Bio Rad

Ag 50w, X4 ) required for aluminum and lithium present. Stir

the water mixture, sample and resin for 1 hour. Elute the

Si0 9 and B 9 0~ with 400 ml of water and reserve for subsequent

d 6 96
determination of silicon. The NapCO^-HpSOj. and the

Na ? CO q -HCl dehydration procedures provided the best precision

data and gave values that agreed favorably with the certified

values for NBS-SRM T s 97 and 98 that were used as control

standards. The latter work has been temporarily suspended,

but will be reactivated at an early date. At that time more

details of the procedure, along with analytical data, will be

presented.

b. Gravimetric Methods for AlpCU

LiBO„ Fusion, Cation-Exchange Resin, Anion Exchange

Resin, NHlOH Precipitation, AlpO^. Dry a 0.5g sample

of 97a, flint clay, and a 0.33g of 98a, plastic clay, at

l40°C for 2 hours. Separate SiOp and BpO~ on cation

i exchanger. Separate aluminum from titanium and iron with

HC1 on an anion exchanger [46, 47] and then precipitate the

aluminum with NH.OH, ignite and weigh as AlpCU.

LiBOp Fusion, Cation-Exchange Resin, Anion Exchange

Re s i n-, NH^OH, AlpO^, NaOH-F Titration. Dry a 0.5g sample

at 140°C for 2 hours. Pass samples through cation and anion

exchange resin as above, but divide the eluate into 2 equal

portions. Determine aluminum gravimetrically in one portion

as above, and in the second portion add sodium fluoride to

react with sodium aluminate to form an alkali hydroxide.

Titrate the hydroxide with standard acid. Preliminary

results indicate the values run low by the latter method.

LiBOp Fusion, Acid Dehydration, Anion Exchange, NH^OH,

AlpO ~ Dry a 0.5g sample of 97a and a 0.3g sample of 98a

at 140°C for 2 hours. Remove SiOp by double dehydration with

HC1. Volatilize boron as methyl borate. Pass solution

containing aluminum through an anion exchange resin with

HC1. Determine aluminum in the eluant by precipitation

with NHnOH and ignition to AlpO^. Residual impurities

such as titanium, iron, chromium, magnesium and silicon

97
were determined spectrophotometrically and corrections

apolied to the impure AlpO~.

LiBO„ Fusion, Cation Exchange, Anion Exchange Homogeneous

Precipitation of Aluminum . Dry a 0.5g sample of 97a and a

0.3g sample of 98a at l40°C for 2 hours and then fuse in a

fivefold weight of lithium metaborate. Remove SiO

? and Bp 0^

by cation exchange. Separate aluminum by an anion exchange

in 12N HC1 and precipitate homogeneously [48, 49] with

succinic acid and urea.

NapCCs Fusion, Acid Dehydration, 8_Hydroxyquinoline

Precipitation . Dry a lg sample at l40°C for 2 hours and

then fuse in 5g of NapCO^. Remove SiO

? by double dehydration

with HC1 [50]. Fuse the residue with KpSpCU, leach and

dilute to 250 ml. On a 50 ml aliquot portion, precipitate

aluminum with 8-hydroxyquinoline in an alkaline solution

containing citric acid, hydrogen peroxide and sodium cyanide

and weigh.

Mixed Acids Solution, NaOH, NH^OH Separations,

8-Hydr~oxyquinoline Precipitation 7~ Dry a 0.5g sample at

l40°C for 2 hours and dissolve in a mixture of HpSO^-HNO^-HFHpO. Fuse any insoluble residue with NapCO^ and combine

with main solution. Remove, iron, titanium, magnesium, etc.

by separation with NaOH. Separate aluminum by precipitation

with NH^OH and finally precipitate with 8-hydroxyquinoline,

and weigh. This latter procedure provided the best precision

data and gave values that agreed favorably with the certifie

values for NBS-SRM's 97 and 98 that were used as control

standards

.

C. ASTM Activities

In cooperative work with ASTM, analyses of various

types of iron and steels for sulfur by the Nydahl gravimetric

method were made to evaluate its use for a Task Force group in

the Ferrous Division of Committee E-3 on Chemical Analysis of

Metals. The method consists of adsorption of sulfur as

sulfuric acid in a perchloric acid solution on a column

98
of alumina, elution with ammonium hydroxide, and gravimetric

determination as barium sulfate. The sulfur content of the

samples ranged from 0.006 to 0.6 percent. The values obtained

were slightly low, ranging from 0.003 to 0.01 percent less

than the certified value. The 10 samples tested include

wrought iron, ductile iron, white cast iron, carbon steel,

tool steel, valve steel, and stainless steel.

If this procedure proves satisfactory, after evaluation

by all Task Force members, it will be recommended as the

official ASTM method for the gravimetric determination of

sulfur (RKE).

J. I. Shultz

99
[1

[2

[3

[4

[5

[6

[7

[8

[9

6. REFERENCES

Menis, 0., Editor, NBS Technical Note 45^ a July, 1968.

Menis, 0., Editor, NBS Technical Note 424 , January,

1968.

Giese, A. T. and French, C. S. , Appl. Spectry. 9, 78

(1955).

Dean, J. A., "Flame Photometry", McGraw-Hill, New York

I960, p. 211.

Dean, J. A., Burger, J. C, Rains, T. C. and Zittel,

H. E., Anal. Chem. 38, 585 (1966).

Koirtyohann, S. R. and Pickett, E. E. , Anal. Chem. 38 , 585 (1966).

Billings, G. K. , Ph.D. Thesis, Rice University,

Houston, Texas (1963).

Rains, T. C. } Zittel, H. E. and Ferguson, Marion,

Anal. Chem. 34, 778 (1962).

Rains, T. C, House, H. P. and Menis, 0., Anal. Chim.

Acta 22, 315 (I960).

[10] Burke, R. W. and Deardorff, E. R. , Talanta, submitted

for publication.

[11] Burke, R. W. , Talanta, submitted for publication.

[12] Burke, R. W. and Yoe, J. H., Anal. Chem. 34 , 1378

(1962).

[13] Natrella, M. G., NBS Handbook 91, Chapter 6 (1963).

[14] Claassen, A. and Bastings, L. , Z. Anal. Chem. l60 , 403 (1958).

[15] Feigl, F., "Spot Tests in Inorganic Analysis",

5th ed., Elsevier, Amsterdam, 1958.

[16] Andersen, N. R. and Hercules, D. M. , Anal. Chem. 36 , 2138 (1964).

[17] Ruzicka, J. and Stary, J., Talanta l4_, 909 (1967).

[18] Stary, J. and Ruzicka, J., ibid 15, 505 (1968).

[19] Stary, J., ibid 16, 359 (1969).

[20] Nozoe, T., Bull. Chem. Soc Japan 11, 295 (1936).

100
[21] Nozoe, T., J. Pharm. Soc . Japan 3, 17 2

* (1949).

[22] Pan, K. and Hseu, T. M., J. Chin. Chem. Soc,

Series II, 2, No. 1, 23 (1955).

[23] Dyrssen, D., Acta Chem. Scand. 15, l6l4 (1961).

[24] Dyrssen, D., Trans. Royal Inst. Tech., Stockholm No. Ij8

3 (1962).

[25] Hseu, T. M., J. Chin. Chem. Soc, Series II, 7, 2, 124

(I960).

[26] Dyrssen, D., Acta Chem. Scand. 16, 785 (1962),

[27] Dyrssen, D., "Extraction of Metal Ions with Chelating

Acids", 16th Annual Analytical Summer Symposium,

Tuscon, Arizona (1963).

[28] Dutt, Y. and Singer, R. P., Indian J. Chem. 4_, 214,

424 (1966).

[29] Gupta, B. P., Dutt, Y. and Singer, R. P., Indian J.

Chem. 5, 214 (1967).

[30] Kolthoff, I. M. and Elving, P. J., "Treatise on

Analytical Chemistry", Part II, 8_, Interscience, New

York, 1966.

[31] Sandell, E. B., "Colorimetric Metal Analysis", 3rd ed.,

Interscience, New York, 1959.

[32] Priyadarshini, U. and Tandon, S. G., Anal. Chem. 33 , 435 (1961).

[33] Tandon, S. G. and Bhattacharya, B. C, Anal. Chem. 3_3,

1267 (1961) and 3.6, 1378 (1964).

[34] Bass, V. C. and Yoe, J. H., Talanta 13, 735 (1966).

[35] Kakita, Y. and Goto, W., Sci. Rep. Ritu, A-17, 32

(1965), (Sendai, Japan).

[36] Reisfeld, R. and Greenberg, E., Anal. Chim. Acta, to

be published.

[37] Flaschka, H. , and Ganchoff, J., Talanta 8, 885 (1961).

[38] Kracek, P. C, J. Phys . Chem. 34_, 225 (1930).

[39] Kallmann, S., Hobart, E. W. , Oberthin, H. K. and

Brienze, C. B., Jr., Anal. Chem. 4£, 332 (1968).

101
[40] Menis, 0. and Wicks, S. A., Pittsburgh Conference

on Analytical Chemistry and Applied Spectroscopy,

Cleveland, Ohio, March, 1968.

[41] Lundell, G. E. F. and Hoffman, J. I., NBS J. Res. 1,

91 (1928).

[42] Flanagan, F. J., U. S. Geological Survey, Geochim.

et Cosmochim. Acta 33., 81-120 (1969).

[43] Bell, R. K. , "Methods for the Chemical Analysis of

NBS Copper-base Spectrochemical Standards", NBS

Misc. Pub. 260-7, 82 (1965).

[44] Peck, L. C, Systematic Analysis of Silicates, U. S.

Geological Survey Bulletin 1170, pps. 21, 62 (1964).

[45] Govindarajn, K. , Anal. Chem. 40, 24 (1968).

[46] Kraus , K. A. and Nelson, F., Proc. Inter. Conf. on

Peaceful Uses of Atomic Energy, Geneva, J_, 113 (1956).

[47] ASTM Special Tech. Pub. 195 (1956).

[48] Willard, H. H. and Tang, N. K. , Anal. Ed., Ind. & Eng. Chem. 9, 357 (1937).

[49] Gordon, L. Salutsky, M. L. and Willard, H. H.

,

"Precipitation from Homogeneous Solution", Wiley, New

York, 1959.

[50] Lundell, G. E. F. , Bright, H. A. and Hoffman, J. I.,

"Applied Inorganic Analysis',' 2nd ed . , Wiley, New York,

1953, 507.

102
7. PERSONNEL AND ACTIVITIES

A. Personnel Listing

Oscar Menis, Section Chief

James I. Shultz, Assistant Section Chief

Mary B. Pantazis, Section Secretary

J. R. Baldwin R. L. Olsen

R. K. Bell (Guest Worker,

B. B. Bendigo Hamline University,

R. W. Burke Saint Paul, Minnesota

E. R. Deardorff T. C. Rains

C. S. P. Iyer T. A. Rush

(Guest Worker, Bhabha J. T. Sterling

Atomic Research Center, S. A. Wicks

Trombay, Bombay, India

B. Publications

1. T. C. Rains and Oscar Menis, "High-Precision Flame

Emission Spectrometry", Spectroscopy Letters _2, 1 (1969).

2. Oscar Menis and T. C. Rains, "Determination of

Arsenic by Atomic Absorption Spectrometry with an Electrodeless Discharge Lamp as a Source of Radiation", Anal. Chem.

41, 952 (1969).

3. T. C. Rains, "Chemical Aspects of Atomic Absorption",

ASTM Special Technical Publication 443, 1969.

4. T. C. Rains, "Chemical Interferences in Condensed

Phase", Chapter in Flame Emission and Atomic Absorption

Spectrometry , Vol. 1, John A. Dean and Theodore C. Rains,

eds., Dekker, New York, 1969.

5. John A. Dea.n and Theodore C. Rains, eds., Flame

Emission and Atomic Absorption Spectrometry , Vol. 1, Dekker,

New York, 1969.

6. Oscar Menis and T. C. Rains, "Sensitivity, Detection

Limits, Precision and Accuracy in Flame Emission and Atomic

Absorption Spectrometry", Chapter in Analytical Flame

Spectroscopy , Selected Topics, R. Mavrodineanu, ed., Centrex,

Eindhoven, in press.

7. R. W. Burke and E. R. Deardorff, "Simultaneous

Spectrophotometry Determination of Cobalt, Nickel and Copper

103
with 2,3-Quinoxalinedithiol", Talanta, submitted for

publication.

8. R. W. Burke, "Exchange Reactions of Ternary Ion

Association Complexes Directly in the Organic Phase", Talanta,!

submitted for publication.

C. Talks

1. D. K. Christopher and Oscar Menis, "The Differential

and Simultaneous Spectrophotometric Determination of

Molybdenum and Tungsten", 4th Middle Atlantic Regional

Meeting, ACS, February 12, 1969.

2. T. C. Rains and Oscar Menis, "Application of

Flame Spectrometry to Simulated Standards for Dust

Particulates", 12th Conference on Analytical Chemistry in

Nuclear Technology, Gatlinburg, Term., Oct. 8-10, 1968.

3. T. C. Rains, "An Evaluation of Electrodeless

Discharge Lamps as a Source for Atomic Absorption

Spectroscopy", Eastern Analytical Symposium, New York, N. Y.,

Nov. 13-15, 1968.

4. T. C. Rains, "Atomic Absorption Spectroscopy",

American Chemical Society Short Course on Atomic Absorption

Spectroscopy, Tarrytown, New York, Nov. 16-17, 1968.

5. T. C. Rains, "Atomic Absorption Spectrometry: Past,

Present, Future", Society for Applied Spectroscopy, BaltimoreWashington Section, Silver Spring, Md., Nov. 26, 1968.

6. T. C. Rains, "Atomic Absorption and Flame Emission

Spectrometry for Major Constituents", Twenty-second Annual

Symposium en Modern Methods of Analytical Chemistry,

Louisiana State University, Baton Rouge, La., Jan. 20-23,

1969.

7. T. C. Rains, "Atomic Absorption Spectrometry in a National Laboratory", Society for Applied Spectroscopy,

Houston Section, Houston, Texas, Jan. 23, 1969.

8. T. C. Rains and Oscar Menis, "A Critical Evaluation

of Some New Techniques for Atomic Absorption and Flame

104
Emission Spectrometry", 4th Middle Atlantic Regional Meeting

cf ACS, Washington, D. C, Feb. 12-15, 1969.

9. Oscar Menis and T. C. Rains , "Derivative Flame

Emission Spectrometry", Pittsburgh Conference on Analytical

Chemistry and Applied Spectroscopy, Cleveland, Ohio,

March 2-7, 1969.

10. T. C. Rains, "Atomic Absorption Spectroscopy", ACS

Short Course on Atomic Absorption Spectroscopy, St. Paul,

Minn., April 12-13, 1969.

11. Oscar Menis and T. C. Rains , "Precise Micro Sample

Analysis by Flame Emission Spectrometry", 157th National

Meeting of ACS, Minneapolis, Minn., April 13-19, 1969.

12. T. C. Rains, "Recent Developments in Atomic

Absorption and Flame Emission Spectrometry", Analytical

Group of the American Chemical Society, Delaware Section,

Wilmington, Del., May 20, 1969.

13. J. I. Shultz, "NBS Standard Reference Materials"

Industrial Management Club cf Cumberland County, Vineland,

N. J., April 23, 1969.

D. Committee Activities

O scar Menis

Member ASTM, Committee E-3, Div. I.

Member ASTM, Committee E-10, Subcommittee I.

Divisional Representative, American Chemical Society - Program Committee for Middle Atlantic Region.

Editorial Eoard Member, Chemical Instrumentation, A

Journal of Experimental Techniques in Chemistry and Biochemistry.

Member National Committee Clinical Laboratory Standards

(NCCLS) - Instrumentation.

Titular member of the International Union of Pure and

Applied Chemistry Commission V3 on Analytical Nomenclature.

105
James I. Shultz

Member ASTM, Advisory Beard, Committee E-3.

Member ASTM, Vice Chairman, Div. F, Committee E-3.

Member ASTM, Secretary Editorial Subcommittee, Committee

E-3.

Member ASTM, Committee E-3, Div. M.

Member ASTM, Committee E-3, Div. C.

Coeditor, ASTM Handbook of Methods of Chemical Analysis

of Metals.

U. S. Delegate to ISO, Technical Committee 17,

Subcommittee 1.

Chairman, Auditing Committee, Washington Professional

Chapter, Alpha Chi Sigma.

T. C. Rains

American Chemical Society Committee on Reagents

Specifications, Subcommittee on Atomic Absorption.

J. T. Sterling

Member ASTM, Chairman, Div. I., Committee E-3.

Member ASTM, Advisory Board, Committee E-3.

Member ASTM, Editorial Subcommittee, Committee E-3.

R. K. Bel.1

Member ASTM, Committee E-3, Div. N.

Member Auditing Committee, Washington Professional

Chapter, Alpha Chi Sigma.

E. R. Deardorff

Member ASTM, Task Force Chairman, Div. F, Committee E-3.

R. W. Burke

Member National Committee Clinical Laboratory Standards

(NCCLS) - Instrumentation (UV-Vis Spectrophotometry).

106
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