National Bureau of Standards

Library, E-01 Admin. Bldg.

1970

OCT 16

NBS TECHNICAL NOTE 544

175092 -****,

G>tl\DD

U57*2>

OCT 1 i 1975

Analytical Coordination

Chemistry Section:

Summary of Activities

July 1969 to June 1970

D NAL BUREAU OF STAND*©*

UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director ^

..."

NBS TECHNICAL NOTE 544

ISSUED SEPTEMBER 1970

Nat. Bur. Stand. (U.S.), Tech. Note 544, 151 pages (Sept. 1970)

CODEN: NBTNA

Analytical Coordination Chemistry

Section:

Summary of Activities

July 1969 to June 1970

0. Menis and J. I. Shultz, Editors

Analytical Coordination Chemistry Section

Analytical Chemistry Division

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

/

-

*"»«u of **

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.

(Order by SD Catalog No. C 13.46:544), Price $1.25

FOREWORD

The Analytical Chemistry Division was established as a separate division at the National Bureau of Standards on

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

Materials Research in the February 1, 1964 reorganization.

It consists at present of nine sections and about 100 technical personnel encompassing some 60 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.

ill
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 oublications

,

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.

We plan to issue these summaries for all of our sections.

The following is the sixth annual report on progress of the

Analytical Coordination Chemistry Section.

W. Wayne Meinke, Chief

Analytical Chemistry Division

IV
PREFACE

The sixth annual progress report of the Analytical

Coordination Chemistry Section describes the research

and development activities which, as in previous years,

have been directed toward the needs and projections of

the Standard Reference Materials Program. This year,

for example, witnessed the reissuance, after thirty-five

years, of two clay standards. The best methods presently

available for the determination of many of the constituents

in these complex materials still involve classical

analytical chemistry. As such, a tremendous demand is

placed on today's analyst to match the high quality work

of some of his predecessors. At the same time for current

instrumental needs, two new standards were issued in the

area of thermal analysis. Again, both absorption spectrophotometry and flame spectroscopy were employed for numerous

trace "determinations . One major contribution from these

two competences was the determination of various elements in

simulated lunar glasses with an accuracy within one percent

at the parts-per-million level. Finally, as stated recently

by our Division Chief, "It has been through our clinical

efforts that we, as a division, have begun to appreciate

the magnitude of the measurement problem in spectrophotometry."

Programs are well under way for the development of standards

to calibrate or check the absorbance-transmission scales

for spectrophotometry. A similar program has been initiated

more recently in spectrof luorimetry . All of these latter

efforts are strongly backed by the clinical chemists and

pathologists

While this report is fragmentary, especially in the

more recent work, It should nevertheless serve as a guide

to the approaches undertaken by the Section in an attempt

to solve some of the current problems. The reader's

v
inquiries and suggestions regarding these efforts are

strongly solicited.

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

vi
TABLE OF CONTENTS . PAGE

SPECTROPHOTOMETRY 3

A. Introduction 3

B. Solid Materials to Check the Photometric

Scale of Spectrophotometers 6

1. Colored Glass Filters 6

2. Evaporated Metals on Quartz 12

a. Preparation of the Filters 13

b. Study of the Effect of Irradiation

with Fluorescent Light 14

c. Calibration of the Filter 15

C. Liquid Filters to Check the Photometric

Scales of Spectrophotometers 17

1. Single Metal Solutions 18

2. Liquid Filters of Improved Optical

Neutrality 22

3. Organic Solutions 26

4. Spectral Properties of Chromium(III

Solutions 29

D. Instrumentation 34

1. Proposed Design and Construction of High

Accuracy Spectrophotometer 34

2. Cell Light Path 35

E. Spectrophotometric Determination of Trace

Amounts of Gold, Iron, Manganese and Nickel

in Two Glass Standard Reference Materials . 36

1. Spectrophotometric Determination of Gold. 37

2. Spectrophotometric Determination of Iron. 38

3. Spectrophotometric Determination of

Manganese .. 40

4. Spectrophotometric Determination of

Nickel . . . . . . . 41

FLUORESCENCE . . 42

A. Introduction,, 42

B. Program 43

C. Study of the Rhodamine 6G Fluorescence;

Importance of Having Corrected Spectra. . . 51

D. Fluorescence and Absorption of Rare-Earths

in Glasses 53

1. Cerium in Silicate Glasses „ 54

2. Cerium in Borate Glasses 56

ANALYTICAL FLAME SPECTROSCOPY 58

A. Introduction 58

B. Multipurpose Precision Flame Spectrophotometer 58

Vll
TABLE OF CONTENTS (CONT'D)

PAGE

1. Design of the Instrument 59

a. Optical System 59

b. Electronic Circuitry 59

c. Burner and Sprayer System 64

2. Experimental Tests 67

C. Long-path Flames 69

D. Hollow Cathode After Grimm 69

E. Spectrophotometric Instrument for Ratios and

Difference Measurements 72

F. Selection of the Analytical Line in Atomic

Absorption 73

G. Selection of Non-absorbing Line in Atomic

Absorption ...... 77

H. Phototubes 79

I. Shield for Burner. . . „ 80

J. Oxidant-Fuel Mixtures Regulation 80

K. Analytical Application to Standard Reference

Materials 81

1. Determination of Potassium, Rubidium and

Strontium in Simulated Lunar Glass ... 81

2. Determination of Aluminum by Flame Emission

Spectrometry in an Iron Matrix 83

L. Service Analyses 84

4. ANALYTICAL COORDINATION CHEMISTRY 87

A. Bilirubin Complexation 87

1. Solvent Studies 89

2. Metal Complex Formation 89

3. Metal Concentration Effect . 92

4. Stability Studies « . 93

5. Bilirubin Determinations . 96

6. Extraction 97

7. Complex Preparation, 97

8. Summary 98

B. Determination of Formation Constants of

Iron (III) and Vanadium (V) with 3-isopropyltropolone .„ . . o o . . . . 98

C. Kinetics and Mechanism of Extraction of

Iron(III) with (3-Isopropyltropolone 99

5, GASES IN METALS „...,. „ . 101

A„ The Inert-gas Fusion Apparatus for the

Simultaneous Determination of Oxygen and

Nitrogen in Metals .... .. •<>.<,•. 101

B„ Evaluation of a Special Ingot Iron for Use

as a Standard Reference Material for

Oxygen Content . . . . „ ... . o ... . 103

viii
TABLE OF CONTENTS (CONT'D)

PAGE

6. THERMAL ANALYTICAL METHODS 105

A. Introduction . . « o 105

B. The Second International Cooperative Program

on Standardization by the ICTA 105

C. The ASTM Committee E-l Subcommittee Round

Robin on Thermal Analytical Substances. . • 108

D. Standard Reference Material 755, Quartz

(SiO ) . . . 114

E. Standard Reference Material 756, Potassium

Nitrate (KNO3) 116

F. Thermal Gravimetric Analysis of Bilirubin . 117

7. ANALYSIS OF STANDARD REFERENCE MATERIALS 120

A. Introduction o 120

B. Standard Reference Materials Information and

Summary ••••<> 123

1. Lead-Bearing Alloys-SRM 53e and 1132. . . 123

2. Carbon Steel (0.4C)-SRM 20g 124

3. Stainless Steel-SRM lOlf 124

. 4. Low Carbon Stainless Steel-SRM l66c . . . 124

5. Differential Thermal Analysis Standards—

SRM 755 and 756 . . „ 125

a. Standard 755-SiO p (quartz) 126

b. Standard 756 KNO3 * ° 126

6. Metallo-Organic Standard-SRM 106lc

Magnesium Cyclohexanebutyrate 126

7. Special Steels-^RM 361, 362 and 365 . . . 126

8. PERSONNEL AND ACTIVITIES 128

A. Personnel Listing . . . 128

B. Publications 128

C. Talks 129

D. Committee Activities 131

9. REFERENCES 133

LIST OF TABLES

TABLE NO . 1. Outline of the program to develop SRMs and instrumentation for high accuracy spectrophotometry, . 4

2. Effect of four consecutive washings on the

transmittance measurements on three Schott NG-4

glasses o • • • o 11

3. Transmittance measurements on a filter of

evaporated metal on quartz „ 16

ix
TABLE OF CONTENTS (CONT'D)

./i,:- :... PAGE

4. Apparent molar absorptivities of selected aqueous

solutions of inorganic salts at 25°C 22

5. Absorbances of a diluted Thomson solution and an

NBS composite, initially, and after three and one

half months. . . . s 25

6. Intercomparison of results obtained on

chromium(III) solutions stored at room

temperature 33

7. Intercomparison of results obtained on

chromium(III) solutions after refluxing. .... 34

8. Spectrophotometric determination of gold, iron,

manganese and nickel in 500 ppm glass 39

9. Spectrophotometric determination of gold, iron,

manganese and nickel in 50 ppm glass 40

10. Outline of the proposed program 44

11. Relative sensitivity of Al I lines in atomic

absorption 74

12. Relative sensitivity of Cr I lines in atomic

absorption ..... 75

13. Selection of non-absorbing line to correct for

scattering of light or molecular absorption. . . 79

14. Summary of values for simulated lunar glass. . . 82

15. Comparison of flame emission and isotope dilutionmass spectrometry values in simulated lunar glass 83

16. Summary of NBS-SRM analyses by flame emission and

atomic absorption spectrometry 85

17. Metal ion addition to BR solutions results in

various spectral shifts 90

18. Effect of metal ion concentration on complex

formation 92

19. Stability studies of BR solutions under various

experimental conditions 93

20. Quantitative bilirubin analyses by

diazotization 96

21. Study of homogeneity in SRM 1099 104

22. Observed transition temperatures for ICTA

materials 107

23. Results reported by NBS. First and second

ICTA-DTA study 108

x
TABLE OP CONTENTS (CONT'D)

TABLE NO. PAGE

24. Transition temperatures-ASTM round robin

materials. NBS Circular 500 <, » • « 113

25. DTA transition temperatures for a solid

quartz specimen 115

260 Certified lead bearing alloy—SRM 53e and

1132 123

27. Certified carbon steel-SRM 20g 124

28. Certified stainless steel-SRM lOlf 125

LIST OF FIGURES

FIGURE NO . 1. Optical transmittance of several selected

filters 7

2<> Optical transmittance versus spectral bandpass

for a Chance ON-10 filter 8

3. Optical transmittance versus spectral bandpass

for a Schott NG-4 glass filter 9

4. Presentation of a set of provisional filters

made from evaporated metal on quartz 15

51 Absorption spectra of aqueous solutions of

cobalt(II), copper(II), chromate, dichromate

and nitrate 18

6. Apparent molar absorptivity of potassium

dichromate as a function of concentration. . . 20

-2 -

7. Absorption spectra of CrOj. , HCrOj, and

Cr

2 7

~ 2 21

8. Absorption spectra of a Chance ON-10 glass,

Thomson solution and an NBS composite solution 23

9. Absorption spectra of aqueous solutions of

chromium(III) , cobalt (II), 2 ,7-dimethyl-3,6-

diazacyclohepta-l,6-diene perchlorate and

p-nitrophenol 24

10. Effect of temperature on the absorbances of

Thomson solution, an NBS composite solution and a Cibalan Black solution over the range 15-4o°C. 26

11. Absorption spectra of aqueous solutions of

selected organic dyes •••<>.. 27

XI
TABLE OF CONTENTS (CONT'D)

FIGURE NO. PAGE

12. Comparison of the dependence of absorbance on

the size of the spectral bandpass for Chance

ON-10 glass and for an NBS composite 28

13. Suggested packaging for liquid absorbance

standards. 29

14 • The absorbance spectra of an aqueous chromic

bromide solution, initially, and after

refluxing 31

15. The absorbance spectra of an aqueous chromic

chloride solution, initially, and after refluxing 31

16. The absorbance spectra of an aqueous chromic

perchlorate solution, initially, and after

refluxing 32

17. The absorbance spectra of aqueous solutions of

chromic sulfate after various treatments .... 32

18. Corrected emission , excitation and

absorption spectra of quinine sulfate

in 0.1N sulfuric acid ^3

19. Corrected emission , excitation and

absorption spectra of europium (III) in a NaH„POK glass prepared at Hebrew University,

Israel ^5

20. Corrected emission , excitation and

absorption spectra of europium(III ) in

sodium silicate glass prepared by the Inorganic

Materials Division at NBS 46

21. Uncorrected emission and excitation

spectra of a h% cerium(III) - cerium(IV) mixture

in silicate glass obtained from the Inorganic

Materials Division at NBS 47

22. Uncorrected emission and excitation

spectra of sample OB-4 fluorescent glass .... 47

23. Uncorrected emission and excitation

spectra of 15% uranium in silicate glass

fluorescent standard 48

24. Corrected emission , excitation and

absorption spectra of 10 ppm fluorescein

in 0.1N NaOH 49

25- Corrected emission , excitation and

absorption spectra of 5 ppm pyrene in

toluene 50

xii
TABLE OF CONTENTS (CONT'D)

FIGURE NO , PAGE

26. Corrected emission , excitation and

absorption spectra of 10 ppm mesoporphyrin

IX dimethyl ester in benzene 51

27. Xenon source emission spectrum and the

uncorrected excitation spectrum for

3 ppm Rhodamine 6G in ethanol 52

28. Summary of corrected and uncorrected emission

and excitation spectra and the corrected

absorption spectra for 3 ppm Rhodamine 6G in

ethanol 53

29. Absorption spectrum of cerium(III) In silicate

base glass run versus silicate base glass

reference. .. 55

30. Excitation spectrum (emission at 385 nm)

and emission spectrum (excitation at

330 nm) of cerium(lll) in silicate glass ... 55

31. Excitation spectrum (emission at 350 nm)

and emission spectrum (excitation at

315 nm) of a cerium(lll) - cerium(IV) borate

glass o 57

32. Flame spectrometer.

Left — console with the electronic measurement

system for the scanning mode system, and power

supply for the hollow cathode.

Middle — one meter spectrometer and sprayer

and burner unit producing a premixed airacetylene flame. The pneumatic sprayer is

supplied with the analytical solution through

a two way Teflon stopcock.

Right — water pressure gauge for monitoring the

pressure in the spraying vessel and burner unit 60

33. Flame spectrometer.

Left — optical bench carrying the sprayer and

burner unit.

Middle — electronic unit for the multichannel

operation.

Right — mirror chopper, dual hollow cathode

arrangement, and gas regulating and monitoring

console 6l

3^. Flame spectrometer.

Inside view of the multichannel photomultiplier

arrangement. Seven tubes are disposed behind

individual exit slits 62

xm
TABLE OP CONTENTS (CONT'D)

FIGURE NO. PAGE

35. Sprayer and burner unit. An interchangeable

burner head is seen at the bottom of the

figure 63

36. Hydraulic trap made of glass 54

37a. Block diagram of the electronic system used in

conjunction with the multichannel spectrometer

37b. Front panel of the electronic system described

in figure 37a.

From bottom to top — dark current compensation,

channel sensitivity selectors, mode of

operation switches, power supply for photomultiplier tubes. , • 66

38. Flame fluctuation as illustrated on an

oscilloscope screen.

A — signal produced by an unsupplied premixed

o air—acetylene flame at X5893 A.

B — signal produced by the same flame supplied

with distilled water at X5893 A.

C — signal produced by the same flame supplied

with Na salt at X 5893 A 68

39. Long-path flame 30 cm long and 1*0 cm wide

produced by the premixed combustion of air with

acetylene. Experimental prototype unit. ... 70

40. Hollow cathode discharge unit after Grimm. The

hollow cathode is located in the enclosure

placed on the optical bench. The power supply

and various controls are located in the console

at the extremity of the optical bench 71

41. Calibration curves for the chromium line at

3579 A 76

42. Calibration curves for the chromium line at

4290 A 77

43. Spectrum of iron over the wavelength region of

2460 A to 2505 A . 78

44. Schematics of oxidant—fuel mixtures regulation 8l

45. Addition of Samarium(III ) to bilirubin solution

results in blue spectral shift 90

xiv
TABLE OF CONTENTS (CONT'D)

FIGURE NO . PAGE

46. Spectra depicting photodecomposition of bilirubin

to biliverdinoid pigment • 95

47. Formation of biliverdinoid pigment and disappearance of bilirubin during photodecomposition - relative concentrations as determined by curve

resolver 3 95

48. Standard calibration curves for diazotization

reactions of bilirubin and Sm( III) -bilirubin

complex 97

49. Crucible arrangement for inductive heating . 102

50a. Cooperative data for ASTM committee members

(one member with two data points) 109

50b. Cooperative data for ASTM committee members

(one member with two data points) 110

51. Cooperative data from ASTM committee membersfor stearic acid melting point Ill

52a. Cooperative data from ASTM committee members 112

52b. Cooperative data from ASTM committee members 112

53. Thermal curve of hexachloroethane 113

54. Thermogravimetric curve of bilirubin in a dry nitrogen atmosphere , 118

55. Thermogravimetric curve of bilirubin in a

dry air atmosphere 118

56. Thermogravimetric curve of mandelic acid in

a dry nitrogen atmosphere 119

57. Thermogravimetric curve of mandelic acid in

a dry air atmosphere 119

58. Types of Standard Reference Materials

analyzed ]_2i

59- Elements determined according to competences

by Coordination Chemistry Section 122

xv

ANALYTICAL COORDINATION CHEMISTRY SECTION

Summary of Activities

July 1969 to June 1970

Edited by

Oscar Menis and James I. Shultz

Progress in research and development In several areas

of analytical chemistry, as related to the Standard Reference

Materials program is described. Based on the need for

spectrophotometric standards by clinical chemists, both

solid and liquid filters for calibrating the photometric

scale are being developed. Similar needs and plans are

reviewed for fluorimetric quantum yield standards. Development of flame spectrometry instruments are described

which include a high precision multi-element flame spectrometer for simultaneous atomic absorption and flame emission,

a ratio recording double beam spectrometer, new burner

designs and the evaluation of a hollow cathode designed by

Grimm. The multichannel spectrometer provides for the

simultaneous determination of elements such as Na , K, Ca,

CaOH and Mg with Li as the internal standard, and a seventh position for background of wavelength scan, and a digital system with tape for computer calculations.

The beginning of a comprehensive study of the absorbing

and non-absorbing lines in atomic absorption is presented.

Description is given of homogeneity studies and the analysis

of glass standards containing 60 elements at the 0.2 to 500

ppm level with a relative standard deviation of 1-2 percent.

Gold, iron, manganese, nickel, potassium, rubidium and

strontium were determined, without prior chemical separations

by spectrophotometric or atomic absorption and flame emission

methods. A precise method for the flame emission determination of aluminum in ferrous materials by derivative optical

scanning is also described.

1
Solution complexation studies involve the reactions of

metals with bilirubin and the evaluation of equilibrium

constants and kinetics in solvent extraction of iron and

vanadium with 3-isopropyltropolone

.

In the area of thermal analysis, provisional certification of potassium nitrate (SRM 756) and quartz (SRM 755) for

temperature scale DTA standards, and the studies of sulfur,

stearic acid and hexachloroethane for the lower temperature

scale are reported. For gases in metals, improvements in

inert gas fusion analysis involved instrumental modifications

which permitted sample changes in less than 12 seconds.

Finally, the characterization of the following Standard

Reference Materials are discussed: lead-bearing alloys,

SRM 53e and 1132; carbon steel, SRM 20g; stainless steel,

SRM lOlf; low-carbon stainless steel, SRM 166c; metalloorganic, SRM 106lc, special steels, SRM 361, 362 and 365.

Key words: Bilirubin solvent extraction with 3-isopropyltropolone; clinical; filter; fluorimetric standards; inert

gas fusion; lead-base alloys; multi-element flame spectrometer;

spectrophotometric standards; steels and metallo-organics

;

thermal analysis DTA Standards; trace elements-glass standards.
1 . SPECTROPHOTOMETRY

A . Introduction

A major problem which presents a challenge to the

Section is the need for high accuracy spectrophotometric

measurements and a shortage of suitable calibration

standards. The current importance of this issue can be

gleaned from statements made by scientists involved in

clinical chemistry. The President of the American

Association of Clinical Chemists has estimated recently [1]

that, with the aid of automation, approximately one-half

billion determinations on bio-clinical fluids can be anticipated this year. In a review article in the "Clinical Chemist",

it was also reported by Rand [2] that over 95 percent of

clinical analyses depend on spectrophotometric measurements.

When one considers the fact that a large fragment of the

information collected by this method is being stored in

computer memory banks for future correlation with other

medical data for potential use in diagnosis and genetic

control, the importance of accurate data is apparent. For

this reason there is an urgent need for Standard Reference

Materials to calibrate not only high precision instruments,

but also provide control data for an ever increasing number

and variety of automated instruments. Thus the efforts of

the Section are concentrated in the development of appropriate standards in spectrophotometry and spectrofluorimetry

At the same time we are developing instrumental capabilites to

improve the accuracy of the measurement.

There is a need for three general types of SRM's to

assure highest precision and accuracy in spectrophotometric

measurements. To attain these requirements one needs all

three categories. The three general types of standards are

for: (1) calibrating the photometric scale, (2) calibrating

the effective spectral bandpass, (3) evaluation of stray

light effect.
During the past year, major attention in this Section

was directed toward the first category, the development

of neutral (wavelength-independent) filters for calibrating

the photometric scale. Both liquid and solid optical

filters have been under extensive investigation and will be

described in subsequent sections of this report. This

program is outlined in table 1.

Table 1. Outline of the program to develop SRMs and instrumentation for high accuracy spectrophotometry.

Solids

Colored glass filters (neutral

Corning, Chance, Schott)

Evaporated metals on quartz

Grids on quartz

Polarizers

Sectors

<! Solutions

Single metal in solution

Compound solutions

Organic dyes (black)

Mixed solutions (NBS)

Instrumentation

Design of a high accuracy

single or double beam spectrophotometer

Optical filters and

instrumentation

In addition to the above standards, one needs to check

the bandpass limitations of the instrument. Failure to do

so will lead to inaccurate molar absorptivity values

when too wide a bandpass is used in measuring the absorbance

of a compound with a relatively narrow absorption peak. For

an example, to obtain an accuracy to within 0.1 percent the

spectral bandpass must not exceed 1/20 of the natural band

width of the compound under investigation. Since instruments

vary in their capabilities, standards must be available for

determining the effects of bandpass on the accuracy of

absorbance measurements. We, therefore, proposed a program

4
to provide standards whose absorption spectra simulate those

compounds of interest to the clinical chemist . These

standards, however, would be more stable and require

relatively simple steps in their use.

The spectrophotometrist must be aware of and have

means for measuring stray light and its adverse effect on

the accuracy of his measurements . By stray light we mean any

light reaching the detector that is outside the spectral

region isolated by the slit. If a spectrophotometer

is in adjustment, the bulk of the stray light will

arise as scatter from the optics and the walls of the

monochromator . Its effect, however, will depend upon

the characteristics of the source and the detectors that

are used. Thus, the effects of stray light are more

pronounced in those regions where one of the components of

the spectrophotometer is being extended to its limit of

performance

Stray light can introduce many and varied problems

in spectrophotometry. In some instances spurious peaks

may be observed; in others, errors may result in the

measurement of absorptivity. These errors may be either

positive or negative, depending upon whether the stray

light is absorbed or not. It is relatively easy to understand

how the presence of significant amounts of stray light can

compound the absorbance errors in clinical analyses,

since it is extremely difficult, if not impossible, to

reproduce the matrix composition in the standards. Thus,

the values reported for a particular clinical test may

vary depending upon the type of interaction of the stray

light with the supporting matrix. Because of this

difficulty in reproducing the composition of the matrix in

the standards, it is necessary that clinical chemists have

some means for detecting and evaluating the stray light

in their instruments. It is thus planned to select and
provide appropriate standards and/or procedures for measuring instrumental stray light over the spectral region of

200-700 nm.

Other aspects covered in this chapter include developments in the determination of trace elements in simulated

lunar glass SRM ' s . B. S olid Materials to Check the Photometric Scale of

Spectrophotometers (R. Mavrodineanu)

The use of solid filters for testing the correct

functioning of spectrophotometers is a common practice.

Filters for checking the accuracy of the wavelength scale,

the photometric scale, and stray light in such instruments have been available to the analytical chemists

for a long time. No single filter, however, can be used

to provide a simultaneous control of these three instrumental parameters. Since the accurate check of the

photometric scale seems to be the most critical factor,

particular attention was given to the selection and study

of those materials which are best suited as SRM's.

1 . Colored Glass Filters

These materials should fulfill the following general

conditions: have a transmittance which is independent of

wavelength, exhibit a low reflection, cover a wide wavelength interval (230 to 800 nm), be stable, and readily

available and inexpensive. Based on these considerations,

a selection was made from the various solid transparent

materials that are available. The following colored

glass filters were selected: Corning-8364 , Chance ON-10 and

Schott NG-4 . The transmission characteristics of these filters are

illustrated in figure 1.

The dependence of transmittance on the width of the

spectral bandpass was then determined for the Chance ON-10

and Schott NG-4 glasses. A discussion of this important
UJO

-z. <

oro

CO

CD<

CORNING

8364

CHANCE

ON-IO

SCHOTT

NG-4

EVAPORATED METAL ON QUARTZ

[INCONEL]

RONCHI RULING ON GLASS

100 LINES/in.

1 _L 1

200 300 400 500

X, NANOMETERS

600 700

Figure 1. Optical transmittance of several selected filters

parameter is given by Gibson [3]. For this purpose, a spectrophotometer consisting of a quartz prism double

monochromator and double beam arrangement was used. The

instrument is capable of producing measurements with a standard deviation for a single determination to better than

0.1 percent.

Figures 2 and 3 present the results obtained at four

wavelengths . It can be seen that the Schott NG-4

colored glass filter exhibits the smallest dependence of

transmittance from spectral bandpass. This property,

together with the optical neutrality, illustrated in

figure 1, were the determining factors in the selection of

the Schott NG-4- filter as a potential SRM for the photometric scale calibration in the wavelength interval of

7
BANDPASS

A

t M

48-30

%T

!

46 *^o*' "^\ — Trri'

44

42

(=}

X, NANOMETERS

400 500 600

i n 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

1

445

490

400 CHANCE ON -10 (Bl)

FILTER

"

«^*T

24

^

L

X490nm

\590nm_yt — ••"""" #.--"'X445nm ""

TRANSMITTAL vs

SPECTRAL BANDPASS

40.0 60.0 80.0 (—

)

(—

)

25

24

H23

i i i (=7=) 0.0 10.0 20.0 30.0 40.0 50.0

SPECTRAL BANDPASS, NANOMETERS

Figure 2. Optical transmittance versus spectral bandpass

for a Chance ON-10 filter.

400 to 700 nra . Following these measurements, two sets

of three NG-4 filters, 25 mm x 10 mm and having thicknesses

of 1.0, 1.5 and 2.0 mm respectively, were prepared. Each

filter was marked at one corner and placed in a metallic

holder which inserts into the sample compartment of

conventional spectrophotometers. The holder was marked at

one side to permit positioning of the glass filter. The

exposed surface of the filter, when placed in the holder,

was about 8 mm x 22 mm.

8
SCHOTT GLASS FILTER NG-4

X, NANOMETERS

400 500 600 700

0.0 5.0 10.0 15.0 20.0 250 30.0 35.0 nm

22

21 - %T

f

20

1 1 1

X465

i i k

\

\

|

\

\

1

1

1

1

1

/// ——^_X635

- X440^^

i / .^-^^xeSo i

i

i

»

L- L 1—.1 1

i\\\\i

i

i\

\\ 14 1 1 i,

9

!

0.0 200 40.0 600 80.0 1000

SPECTRAL BANDFttSS, NANOMETERS

Figure 3. Optical transmittance versus spectral bandpass

for a Schott NG-4 glass filter.

A series of measurements was then initiated to determine

the proper procedure for initially cleaning the surface of

the filters. Various wet and dry techniques were used and

the following method was finally adopted. The glass filter

was removed from its holder and placed on a lens paper.

Each surface was then washed with redistilled ethyl

alcohol followed by redistilled water. The surfaces were

dried with lens paper. The filter was then replaced in
its holder in the marked position (all manipulations were

carried out using polyethylene gloves). The last traces

of dust were removed with an artist's brush which was

attached to a rubber hose connected to a vacuum source [4],

The cleaned filters were then placed successively in the

spectrophotometer and transmittance readings were taken at

the following wavelengths: 440, 465, 590 and 635 nm,

using an effective spectral bandpass of 2.2, 2.7, 5*2 and

6.6 nm, respectively. Fifteen successive transmittance

measurements were made at each wavelength and for each

filter. The filters were then submitted to the cleaning

procedure as described, followed by transmittance measurements and the entire operation was repeated four times.

Since no blank was available, the measurements were

performed against air. The results obtained on one set of

filters are given in table 2.

From these results it can be seen that the percent

transmittance can be measured on the glass filters with a standard deviation for a single determination not exceeding

0.041 percent. This value is not affected by successive

cleanings of the filter surface using the washing procedure

described. Measurements made on a similar set of three NG-4

filters have confirmed this observation; hence, the alcoholwater washing technique was adopted as a routine initial

cleaning procedure for the glass filters. In subsequent use,

if the surface appears, by visual inspection, to be free of

contamination, the filter can be cleaned by merely breathing

on its surface and wiping it with lens paper. The remaining

traces of dust are eliminated with the brush-vacuum unit as

described

.

Several sets of Schott NG-4 filters were calibrated and

one set was forwarded to members of the Standards Committee

of the American Association of Clinical Chemists for

preliminary evaluation.

10
Table 2. Effect of four consecutive washings on the transmittance measurements on three Schott NG-4 glasses.

Wash

First

Second

Third

Fourth

Average

of Four

Washing:

First

Second

Third

Fourth

Wavelength % Standard

%

Standard

OA Transmittance

Filter A

Deviation Deviation

4400

4650

5900

6350

12.99

15.04

11.79

12.80

0.0053

o C042

o0032

.0032

0.041

.028

o027

.025

4400

4650

5900

6350

12.99

15.04

11,79

12.80

o0032

.0052

.0042

.0042

.024

.034

.036

.033

4400

4650

5900

6350

13o00

15.04

11.79

12.80

.0048

O 0042

.0042

e 0042

.037

.028

.036

.033

4400

4650

5900

6350

13o00

15.04

11.79

12.81

.0048

.0042

.0042

O 0042

.037

.028

.036

.033

4400

4650

5900

6350

12.99

15.04

11.79

12.80

Filter B

.0045

O 0044

o0039

.0039

.035

.02 9

.034

.031

4400

4650

5900

6350

19.64

22,37

19.06

20.46

0.0042

.0053

.0052

.0053

0.023

O 024

.027

.026

4400

4650

5900

6350

19.64

22.37

19.06

20.47

.0042

.0048

O 0048

.0048

o021

.022

.025

.024

4400

4650

5900

6350

19.64

22.37

19.07

20.47

o0052

.0042

.0053

.0048

.026

.019

.028

.024

4400

4650

5900

6350

19.65

22.38

19.07

20.47

O 0048

o0053

.0052

.0053

.025

O 024

.027

.026

11
Table 2 continued

4400 19.64 .0046 .023

Average 4650 22.37 .0049 .022

of Four 5900 19.07 o0051 .027

Washings 6350 20 o 47

Filter C

.0050 .025

4^00 32.88 C.048 0.015

First 4650 35o50 o0032 .009

590 31»23 .0042 .014

6350 32o65 .0042 .013

4400 32.87 .0052 o 0l6

Second- 4650 35o50 .0032 .009

5900 31.22 .0048 .015

6350 32.65 OC48 o 0l8

4400 32.87 O 0052 o 0l6

Third 4650 35.51 o0032 .009

5900 31»22 .0042 .014

6350 32.64 .0053 .016

4400 32.87 .0048 .015

Fourth 4650 35.50 .0048 .014

5900 31.22 .0048 .015

6350 32.64 .0052 .016

4400 32.87 .0050 .015

Average 4650 35»50 .0036 .010

of Four 5900 31»22 O 0045 .014

Washings 6350 32.65 O 0049 ,016

L Average of 15 individual measurements. Temperature = 25.2

2 . Evaporated Metals on Quartz

As seen from figures 1 and 2, the colored "neutral"

glass filters have transmissions which still exhibit some

dependence on wavelength.

The term "neutral" is used here in its loose meaning,

only to indicate that the optical transmittance is less

dependent on wavelength, when compared with other colored

glass filters. Light filters exhibiting less transmissionwavelength dependence and nearer to optical neutrality can

be produced by evaporating a thin semi-transparent layer

12
of metal on a transparent substrate . Such filters have only

a slight transmission-wavelength dependence, as illustrated

in figure 1, where it can be seen that the maximum change in

o o percent T is + 4 over the spectral range of 2300 A to 7500 A.

In this case, the evaporated metal was inconel and the substrate was non- fluorescent fused silica of optical

quality. From the same figure it can be seen that the transmittance of these filters extends in the ultraviolet to

o 2300 A which is an added advantage when compared with the

colored glass filters . A limitation of the evaporated metal

filters is that they reduce the intensity of a light beam by

reflecting a part of it, rather than obsorbing. This can produce, in certain circumstances, undesirable stray light in the

instrument and make the transmission measurements dependent on

the geometry of the optical path (collimated, convergent, divergent). However, since these filters are closer to optical

neutrality than the colored glass filters and since they can

be used in the ultraviolet region as well, they were included

in the studies to determine their suitability as SRMs

a. Preparation of the Filters . A series of filters

were prepared by the optical shop of the NBS according to

the following specifications: a number of non-fluorescent

optical quality silica plates, 10 mm x 25 mm and 1 mm thick,

were cut and polished. Inconel metal was evaporated on the

surface to produce nominal transmittances of 25 percent,

50 percent and 75 percent. The surface carrying the

evaporated metal was coated with a layer of optical cement

which was transparent to the visible and ultraviolet regions

o down to 2300 A. A clear plate of the same material was

used to cover and protect the evaporated metal layer.

The filter assembly was then marked at one corner to

insure its positioning in the same place. The finished

filter was then placed in a metal holder of conventional

size (approximate o.d. = 13 x 13 x 57 mm) fitting the cell

compartment of most spectrophotometers . The metal holder was

13
also marked at one side to permit positioning of the filter

in a reproducible manner.

In addition to the evaporated metal filters, a series

of units were prepared using only the clear uncoated quartz

plates and assembled with the same optical cement. These

clear filter assemblies were then used as reference units in

the blank compartment

.

b . Study of the Effect of Irradiation with Fluorescent

Light . Before submitting the evaporated metal filters to

transmittance measurements, a study was made of the effect

of radiations on the transmittance. A filter was exposed

to an accelerated test in which radiations had the same

spectral distribution as the fluorescent lighting of the

laboratory, except that they were 1000 times more intense.

The filter was exposed for an equivalent of 36,000 hours

of continuous irradiation. This test was made on a radiation accelerometer made available by the Building

Research Division of NBS . The percent transmittance was

measured before and after the exposure and gave the following

results

Transmittance, %T

Wavelength, A 2500 3800 5000 6500

o

Before exposure 44.48 51.35 48.90 47.41

After exposure 44.11 51.34 48.92 47.47

The relative standard deviation for a single determination of these measurements was 0.01 percent. As can

be seen, the only measurable change in transmittance

o occurred at 2500 A. This is probably due to the action of

the intense radiation on the organic resin used in

constructing the filter.

o The change in percent T of about 0.84 percent at 2500 A

was considered as acceptable, since It is improbable that

a filter would be exposed, in actual practice, to such

14
intense radiation for such a long period. Several sets of

evaporated metal filters were prepared and stored in plastic

cases, as illustrated in figure 4.

c . Calibration of the Filter . Several sets of these

filters were calibrated at five arbitrarily selected wavelengths, using the cleaning and measuring procedures outlined

U.S. Department of Commerce

National Bureau of Standards

Office of Standard Reference Materials

Washington, E>-C. 20234

INJ15S Standard Reference Material

A BSOUHA NCE SSC'A 1_.*3 OK JCTHOPHO'] t ) i\l l ; l i i ;>

Figure 4. Presentation of a set of provisional filters

made from evaporated metal on quartz.

15
for Schott NG-4 colored glass neutral filters. Table 3

presents the results obtained for one of the filters having

a nominal transmittance of 50 percent. Since similar

results have been obtained for the other two filters with

nominal transmittances of 25 percent and 75 percent,

these are not given. As can be seen from this table, the

reproducibility of transmittance measurements is good

(percent standard deviation 0.009 to 0.024) and is

comparable to those obtained for the colored glass filters

o at all wavelengths except 2500 A. From the data in

table 3 and from the additional measurements, it is evident

that the transmittance of the evaporated metal filter at

o 2500 A is a function of the cleanliness of the surface.

o The percent transmittance measured at 2500 A varies from

4 3 . 99 to 44.14 after washing. The difference between these

values is significant and well outside the expected average

standard deviation determined at the various wavelengths

.

It is not possible, at present, to give a satisfactory

explanation for the contributing cause of this phenomenon.

Additional studies will be needed to determine the cause

for this variation. It is recommended, however, that the

Table 3. Transmittance measurements on a filter of

evaporated metal on quartz.

Waveleng;th %

and * a

Standard Standard

Wash bandpass ,A Transmittance deviation deviation

2500 ( 3) 43.99 0.008 0.018

3500 (10) 51.23 .006 .012

First 4500 (24) 49.37 .006 .013

5500 (44) 47.62 .006 .012

6500 (70) 46.88 .004 .009

2500 ( 3) 44.14 0.004 0.009

3500 (10) 51.25 .012 .024

Second 4500 (24) 49.41 .012 .024

5500 (44) 47.67 .009 . .019

6500 (70) 46.89 .004 .009

Average of 10 measurements

16
surface of the evaporated metal on quartz filters be cleaned

only by breathing lightly on its surface, wiping it with lens

paper, and removing the dust particles with the vacuum brush.

From the several sets of evaporated metal on quartz

filters calibrated on the conventional spectrophotometer,

a set was examined by members of the Standards Committee of

the American Association of Clinical Chemists.

It is well known that grid on quartz, polarizers and

sectors will serve to check the photometric scale of

spectrophotometers, and each has its advantages and

limitations. Major attention was given, however, to the

colored glass and evaporated metal filters. The activity

will expand during the next year to include in our study

the above materials.

C . Liquid Filters to Check the Photometric Scales of

Spectrophotometers (R. W. Burke and E. R. Deardorff)

Solutions offer several unique advantages for

calibrating the absorbance or transmission scales of

spectrophotometers. Undoubtedly, their most important

advantage is that they lend themselves to close duplication

of conditions under which an unknown sample is measured.

The sample cuvette, for example, with its potential sources

of error, must be incorporated into the measurement

procedure. Other advantages include: (1) absorbances

or transmittances can be measured at any desired level simply

by varying the concentration or cuvette path length, provided

the Lambert-Beer law is obeyed, (2) provide a reference

blank, (3) offer a direct means of calibrating flow systems,

(4) conform to the shape of any cuvette and (5) present

no inhomogeneity problems. Disadvantages which may be cited

are: (1) solutions generally do not possess the permanence

nor the high degree of optical neutrality that can be

obtained with solid filters, (2) they require careful

preparation and (3) they inherently exhibit much larger

temperature coefficients than do solids.

17
1 . Single Metal Solutions

The initial work on liquid filters concerned the reexamination of those solutions which have been investigated

previously. These included potassium nitrate, acidic

dichromate, basic chromate , cobalt sulfate and copper

sulfate. The latter three solutions were studied at the

National Bureau of Standards in the 19^0' s and absorbancewavelength data for one concentration of each have been

published [5]. The absorption spectra of these solutions

are shown in figure 5- It is apparent that all absorbances

are strongly dependent on exact wavelength settings,

except in the regions near the peaks and valleys. Even

in these less critical wavelength regions, the absorbance

that one measures will be dependent on the size of the

spectral bandpass employed. The latter can be calculated

readily from the dispersion data supplied with the spectro200 300

X, NANOMETERS

400 500 600

I I

I: I i: !

' ' I ' ' ' ' ' ' ' ' 'I I _^

\ u

! V

\

.0

LU

(J

-z. <

DQ

cro

CO

DQ

<

J-QO

COBALT (I) CHROMATE (0.05 N KOH)

COPPER (H) NITRATE

DICHROMATE (0.01 N H2 S04

)

Figure 5. Absorption spectra of aqueous solutions of

cobalt (II), copper (II), chromate, dichromate

and nitrate.

18
photometer. For maximum signal-to-noise ratio one normally

employs the largest bandpass commensurable with the degree

of accuracy required. It has been shown that the spectral

bandpass must not exceed 0.1 the natural bandwidth if 0.5

percent accuracy is desired [6]. For 0.1 percent accuracy

this value reduces to 0.05.

The attractive characteristics of potassium nitrate,

cobalt sulfate and copper sulfate are the excellent

stability of both their salts and solutions, and their

low molar absorpt ivities (weighing errors are thus

minimized). Although potassium nitrate solutions may

exhibit bacterial whiskers upon standing, these can be

eliminated by previously boiling the water in which they are

prepared. Acidic potassium dichromate and alkaline potassium

chromate, likewise, display excellent stability when their

solutions are free of oxidizable contaminants. Haupt [7],

for example, observed no change above 260 nm in the spectral

properties of alkaline chromate solutions when stored in

glass containers for several years (an alkali-resistant

glass is recommended, however). Both forms exhibit

relatively high molar absorpt ivities and the concentrations

normally used are of the order of 40-50 mg per liter.

Apparently because of certain handling problems, the

alkaline chromate solutions have not been used extensively.

The tendency, Instead, has always been to use the acidic

form.

Several precautions must be observed in the use of

acidic potassium dichromate as an absorbance standard.

It has long been recognized that its apparent molar

absorptivity varies with concentration. As early as 1934,

Kortiim and von Halban [8] reported a variation of 23 percent

(figure 6) in the molar absorptivity of dichromate over

the concentration range 2 x 10~ 5 to 4 x 10~ 3 M when absorbance

measurements were made at 366 nm (0.0025M sulfuric acid

was used in these studies). This variation is attributed

19
10 20 30

CONCENTRATION X I0 3 ,mole liter" 1

Figure 6. Apparent molar absorptivity of potassium dichromate

as a function of concentration (from Kortiim and

von Halban [8] )

.

primarily to the fact that the absorption spectra of

dichromate ion and hydrogen chromate ion are significantly

different (figure 7). Moreover, the fraction of each in an

equilibrium solution is both concentration and acid

dependent, as is evident from the following equilibria.

Cr

2 7

2 + H

2 = 2HCr0

4

1

HCrO^" 1 = H

+

+ CrO^" 2

(1)

(2)

rl Neuss and Rieman [9] have reported a value of 3.20 x 10

for the thermodynamic acidity constant (reaction 2) at 25°C

of hydrogen chromate ion based on e.m.f. measurements. Their

work also yielded a value of 2.32 x 10~ for the equilibrium

constant for reaction 1. More recent work by Davies and

Prue [10] and Tong and King [11] suggests that this value

is too low. Their values for 25°C are 3.03 x 10" and

2.82 x 10 , respectively. Furthermore, Tong and King

20
5000 !

1 1

To 4000 _

i 0)o /cro;2 E

fc- 2 3000 — ^*^7~**v. \ \ -

>-" i- \ >t 2000

/ '/2Cr2 7

"2

ECO

V)

CD< >v < 1000

N^^ yy/ aJHcro4~ J

o

s

1 i i 250 300 350

WAVELENGTH, nm -2

400

Figure 7- Absorption spectra of CtOk , (from Davies and Prue [10]).

HCrO and Cr„0

?

-2

noted in sulfuric acid media a dependence of K on the

concentration of the acid. They suggest this effect may

be due to the existence, even at very low acid concentrations,

of mixed species containing sulfur and chromium. Thus,

it is quite apparent that acidic dichromate should be used

at a specified concentration, and the type and amount of acid

should be clearly stated.

The molar absorptivities , calculated for aqueous

solutions of potassium nitrate, acidic potassium chromate,

alkaline potassium chromate, cobalt sulfate and cobalt

perchlorate, are given in table 4. The value obtained

for a nickel nitrate solution is also included. This

solution and the two cobalt solutions were prepared from

the metals (>_99.99 purity) by dissolution in the designated

acids. The final pH values of these solutions are also

given in the table. All absorbance measurements were made

at 25.0 + 0.1°C in 10 mm cuvettes. The exact path lengths

and parallelism of the cuvette faces were checked by mechani21
Table 4. Apparent molar absorptlvit ies of selected

aqueous solutions of inorganic salts at 25°C

.

Spectr

.

BandConcentration X pass Molar Lit.

Salt g/1 nm nm Absorpt . Values Ref

.

KN0 o b 7.0-9.6 302 0.6 7-08 7-04-7.20 [12]

3 7.12 (Mean)

K 9 Cr„0 7

c 0.050 350 1.1 3150 3150 [13]

d * ' (0.01 N H o

S0,, ) 2 ^ 257 0.4 4230 4270 [13]

K.CrO, 0.040 373 1-4 4800 4820 [13]

1 (0.05 N KOH)

273 0.5 3690 3570-3860 [13]

3690 (NBS) [7]

Ni(N0 o ) o d 6.8 as Ni 394 1.5 5-09

(pH=2.7)

2.0 as C« (10 ml H

2

SO i| ) 2.0 as Co

(10 ml HCIO^)

CoS0

4

d 2.0 as Co 513 2.0 4.87

CoClO^ 2.0 as Co 513 2.0

^Tentative values

J.F. Baker (special preparation for NBS)

^NBS-SRM 136a

Prepared from metal

cal measurements and were accurate to +0.1 percent. The

molar absorptivities given were obtained on a high- precision

spectrophotometer, the accuracy of which is not known at

present. They should, however, provide a basis for

comparison with values which have been obtained on other

commercial instruments. As outlined later in this report,

plans are underway at NBS for the design and construction of

a high accuracy spectrophotometer.

2 . Liquid Filters of Improved Optical Neutrality

Two approaches are being investigated to extend the

wavelength and improve the optical neutrality of

liquid filters. One utilizes composite solutions containing

several materials, each of which exhibits one or more broad

absorption bands. These materials are selected so that the

22
absorption peak of one material complements the absorption

minimum of a second component. The other approach employs

water-soluble "black" dyes.

In 1946, Thomson [14] described the preparation of a composite inorganic grey solution consisting of chromic

sulfate, cupric sulfate, cobaltous sulfate and potassium

dichromate. We have reproduced this mixture and its

absorption spectrum is shown in figure 8. The disadvantage

of this solution is that it does not transmit below 300 nm.

To develop a liquid filter that does exhibit a high degree

of optical neutrality throughout the uv-visible spectrum, we

have combined the chromium(III ) and cobalt(II) components of

the Thomson solution with a third component, p-nitrophenol,

as the uv absorber in the 300 nm region. The absorption

spectra of this solution (henceforth referred to as the

NBS composite) and a Chance ON-10 glass are also shown in

X, NANOMETERS

200 300 400 500 600

1

i i i i i i i i i I i i i t I i i i i I 1.0

LU

o

<

00eno

CO

CO

<

1

I

\

•

•t

«

\s

•

1 y X ^ — --

CHANCE 0N-I0 1 00

THOMSON SOLUTION

NBS COMPOSITE

Figure 8. Absorption spectra of a Chance ON-10 glass,

Thomson solution and an NBS composite solution.

23
figure 8. Over the range 250-600 nm, the NBS solution

possesses a number of relatively broad maxima and minima,

while the Chance glass filter does not transmit below

350 nm. The individual absorption spectra of the three

components comprising the NBS solution are shown in

figure 9. The absorption spectrum of a fourth solution,

2 , 7-dimethy 1-3 , 6-diazacyclohepta-l , 6-diene perchlorate is

also shown in this figure. It was proposed originally for

use as a uv filter by Schwarzenbach [15] and its solutions

reportedly exhibit excellent stability. For our purposes,

however, its absorption band is too narrow to compensate

sufficiently for the broad chromium minimum that exists

in the 300 nm region. p-Nitrophenol , however, does

possess the necessary broad absorption band in this region

To date, the stability of its aqueous solutions meets

present requirements.

200

1 1 1 1 1 1 1

X, NANOMETERS

300 400 500

1 1 ' 1 1 1 1

1 1 600

i-rl.O

CHROMIUM (HI)

p-NITROPHENOL

2.7-DIMETHYL-3.6-DIAZACYCL0-

HEPTA-I.6-DIENE PERCHLORATE

COBALT (H)

V

\

\

x^

UJoZ

<

00

<roc/> m

<

-1-0.0

Figure 9. Absorption spectra of aqueous solutions of

chromium (III), cobalt(II), 2 ,7-dimethyl-3-6-

diazacyclohepta-1, 6-diene perchlorate and

p-nitrophenol

.

2k
Because of the presence of chromium (III) in both the

Thomson and NBS solutions, an "aging" period is necessary

to obtain spectral stability. About 6 to 8 weeks are

required if this aging process is carried out in sulfate

media at room temperature. Ways of reducing this

equilibration time, however, are being investigated. Some

success has been achieved in this respect, as will be noted

in a subsequent section.

The absorbance of the Thomson and NBS solutions, both

of which were prepared in sulfate media, have been

measured periodically for three and one-half months

following initial aging periods of about two months each.

The values obtained at the beginning and end of this threeand one-half months period are given in table 5 9 with the

interim absorbances falling between the extremes shown. The

concentration of the Thomson solution measured was approximately a 3:8 dilution of Thomson's recommended formulation.

NBS composite, initially , and after three and one

Table 5. Absorbances of a diluted Thomson solution and an

NBS composit

half months.

Solution A a nm Absorbance (1-cm cuvette)

Thomson

NBS Composite

Initially After 3.5 months

640 0.280 o 282

590 .320 .322

540 .301 .303

487 .242 .244

410 .385 .386

350 .525 .525

525 0o562 0.564

470 .397 .398

415 .483 .484

365 .252 .253

320 .493 .493

260 .256 .258

9. Following an initial aging period of two months

25
The effect of temperature on the absorbance of the

Thomson and NBS solutions has been measured at three

wavelengths each (Thomson-590 , 487 and 350 nm; NBS-525,

*J15 and 320 nm) . The values obtained for the most temperature

dependent wavelength of each are shown in figure 10.

Results are included also for a Cibalan Black solution (see

subsequent section). All values have been corrected for

the relatively small contribution of density changes over

the temperature range studied.

.04

ido

2 102

to 1. 01

CD<

>

I THOMSON SOLUTION (487nm)

I NBS COMPOSITE (525nm)

IITCIBALAN BLACK (575 nm)

20 25 30

TEMPERATURE,°C

35 40

Figure 10. Effect of temperature on the absorbances of

Thomson solution, an NBS composite solution

and a Cibalan Black solution over the range

15_40°C.

3 • Organic Solutions

In conjunction with the. above program using various

inorganic mixtures, an equally promising one using aqueous

solutions of organic black dyes has also been initiated.

The absorption spectra of several dyes which have been under

investigation are shown in figure 11. All exhibit some

preferential absorption at the ends of the wavelength

region for which they are intended, i.e. 220-250 nm and

26
X.NANOMETERS

200 300 400 500 600

i i i i i

I i i i i i i i i I i i i i I—-pi

A\ \

Ixl O

-z. <

CDo(S) CD<

-"-0.0

Figure 11

NEOLAN BLACK

CIBALAN BLACK

ALIZARIN LIGHT GREY

LUXOL FAST BLACK L

NIGROSINE

Absorption spectra of aqueous solutions of

selected organic dyes

550-600 nm. Because of this absorption in the red region

of the spectrum, aqueous solutions of these dyes are

not black but are various shades of blue. All of these dyes

have relatively high molar absorptivities and typical

concentrations are of the order of 40-60 milligrams per

liter

The Cibalan Black, Neolan Black and Alizarin Light Grey

dyes have been the most extensively investigated to date.

All are insensitive to variations in pH over the range 2-9,

show no significant spectral differences after heating to

boiling, and are relatively stable. Solutions constantly

exposed to the fluorescent light of the laboratory" showed

absorbance variations of approximately 1 percent over a two

months period.

The initial studies were carried out on samples of the

commercial dyes, several of which contain as much as 40

percent impurities (some were added intentionally by the

27
manufacturers to provide a fixed dye strength). With the

assistance of the Organic Chemistry Section, present efforts

are concerned with the purification of these dyes to such a level that, at least, the desired homogeneity can be

obtained (<0.1 percent for 10-20 mg samples).

The effect of temperature on the absorbance of a

recrystallized sample of Cibalan Black (figure 10) was measured at three wavelengths (315, ^00 and 575 nm) . Over the

range of 15 - 40 °C, the largest temperature coefficient does

not exceed 0.1 percent per °C. Commercial samples of Neolan

Black and Alizarin Light Grey showed similar behavior.

The underlying goal of the current program involving

liquid filters (both the inorganic composites and the

black dyes) has been to develop potential absorbance

standards that show a high degree of optical neutrality.

Using the Chance ON-10 glass for comparison, the results

shown in figure 12 indicate partial success.

0.340

0.330

Figure 12

0.290

0.280

NBS COMPOSITE (565 nm)

CHANCE ON -10 (445 nm)

CHANCE 0N-I0 (560nm)

"nbs composite (460 nm)

10 20 30 40 50 60 70

SPECTRAL BANDPASS, nm

80

Comparison of the dependence of absorbance on the

size of the spectral bandpass for Chance ON-10

glass and for an NBS composite.

28

HB^^MOlfll^HI
The final step in the development of these, or similar

liquid filters, will be to decide in what form they will be

made available to the user. Depending on the outcome of

the studies to establish rapidly equilibrium in chromium( III)

systems, the inorganic composites could be provided either

as solids or liquids. Because of the problem of accurately

weighing milligram quantities of the black dyes, present

plans call for preweighing and encapsulation of the samples

which will be used to prepare "one-shot" solutions and then

discarded. A possible package is shown in figure 13-

Figure 13. Suggested packaging for liquid absorbance

standards

4 . Spectral Properties of Chromium(III ) Solutions

The two broad chromium( III) absorption bands in the

visible spectrum, (maxima at approximately 410 and 580 nm)

together with its good transmission in the ultraviolet,

are promising characteristics which recommend the use of

this ion In various mixtures which, in turn, can be used to

prepare liquid filters of high optical neutrality. Unfortunately, solutions prepared from different chromic salts

29
possess varying spectral properties and stabilities . It has

been known for many years that aqueous solutions of chromic

sulfate exist in both a violet and a green form. The green

solutions of chromic sulfate are obtained either by heating

or aging violet solutions. Also, it was recognized that the

acidity of a boiled or aged solution of chromic sulfate was

greater than that of a violet solution of the same chromium

concentration. More recently, Hall and Eyring [16] used

conductometric titrations to study the constitution of

chromic salts in aqueous solutions. They present strong

evidence that, during the aging process, the hexaaquo

chromium( III ) ions polymerize to yield species such as those

shown below.

[

H

(H

2 0) Cr-O-Cr (H

2 0) 1

+5

, r(H >-. f

2 0)

4

Cr^ J^Cr (H^)^ a nd

H

f H H -, + 7

(H

2 0)

5

-Cr-O-Cr(H

2 0) i| -O-Cr (H

2 0) I

The observed increase in acidity is explained by the formation

of hydroxyl bridges. Hall and Eyring also showed that,

after refluxing a chromic nitrate solution for 66 hours, the

titration results were no longer affected by subsequent

heating

.

Because of the success of Hall and Eyring's experiments,

we decided to investigate the effect of heating on the

spectral properties of chromium(III) solutions. The bromide,

chloride, perchlorate and sulfate salts were used. Absorption

spectra were obtained periodically on portions of each as a function of storage time at room temperature. The remaining

portions were refluxed for various periods of time and their

absorption spectra were recorded. One effect common to both

of these experiments was that the acidity of all solutions

increased upon standing, the largest changes occurring in

30
the refluxed samples. The absorption spectra of these

chromic salt solutions are shown in figures l4 9 15 » 16 and

17 together with the conditions under which they were

obtained. Also shown in figure 17 is the absorption

spectrum of a chromium( III ) solution prepared by dissolving

the metal in sulfuric acid and aging at room temperature

for two months . The transmission of this solution extends

FTCSMLT WEMRED.pH.3.0 N. V

2hrs at RoomTemo .pH -27 \_

R£FLUXE0 2r»v,ptei.9 "\

REFUJXED 24 hrs. , (>H 1.9

300 4O0 500 600

WAVELENGTH, nm

Figure 14 . The absorbance spectra of an aqueous chromic

bromide solution, initially, and after refluxin*

300 400 500 WAVELENGTH, nm

Figure 15- The absorbance spectra of an aqueous chromic

chloride solution, initially, and after

refluxing

31
1.000

0.900

QflOO

O.TOO

rt Q600

g Q500 O

5 0400

Q300

0.200

0.100

V

[A

i

\-\

\\

\\

\\

W

\ w 1 \\ \ n

\ u

»

\

\

»»

CHROMIC PERCHLORATE i

i/— \\ \w

RCTLUKID «Mn.,pM>LM —- flCFLUBCCD 2.4,«andaha,p»t>I.M

FflCM-Y MCMMSandoftv

14 hr%. ot Mount Ttnp. , dm I.M

/

\\\

\\\

\\\

\\\V/

\\\\\\

\ \\

/

300 400 500 600

WAVELENGTH, nm Figure 16. The absorbance spectra of an aqueous chromic

perchlorate solution, initially, and after

ref luxing.

- REFUJXtD itT.. pH .!.» - R£ruaEDlhrv,pK.|J - mruBEO 2»hrv,pH •!.» - 2rrix. 01 Boom Tmp. , pH so (» + H,S0.1

250 300 400 500 600

WAVELENGTH, nm

Figure 17. The absorbance spectra of aqueous solutions of

chromic sulfate after various treatments.

significantly farther into the ultraviolet than do any other

of the salt solutions. There is a similarity, however, in

the ultraviolet between this aged solution and the freshly

prepared chromic perchlorate. The significance, if any,

that can be attributed to the difference in pH of these two

solutions (sulfate pH 1; perchlorate pH 2.7) needs to be

determined

.

32
Table 6. Intercomparison of results obtained on chromium ( III

solutions stored at room temperature.

A max

Solution

Storage

time, h

Chromic

Perchlorate 24

48

Chromic

Chloride 24

48

Chromic

Bromide 24

48

Chromic

Sulfate 24

48

Chromium

Ho S0„

in 2 mos.

—s- h

409

409

409

445

410

410

428

408

408

421

421

421

413

nm A rat io

h

s pH

573 1.19 2.72

576 1.19 2.72

576 1.20 2o70

635 0.92 3.40

576 1.23 2.88

576 1.20 2.70

624 1.13 2.70

576 1.23 2.60

576 1.29 2.42

587 0.98 2.3^

587 0.98 2.30

587 0.98 2.25

580 1.06 1.01

To facilitate the intercomparison of the spectral data

obtained, the results have been summarized in tables 6 and

7 for the unheated and refluxed solutions, respectively.

It is interesting to note that the final pH of the four

refluxed chromic salt solutions are quite similar. However,

in the case of the unheated solutions, the pH of the sulfate

is somewhat lower than the other three . The fact that the

ratio of peak absorbances in chromic perchlorate and chromic

chloride solutions appear to be identical after refluxing

for only one hour strongly suggests that spectral stability

may be readily achieved in these two systems. The bromide

and sulfate systems, on the other hand, appear too complicated

to warrant further study at this time.

33
Table 7. Intercomparison of results obtained on chromium(III

)

solutions after refluxing.

Solution

Chromic

Perchlorate

Chromic

Chloride

Chromic

Bromide

Chromic

Sulfate

Time, h

0.25

1.0

6,0

24.0

0.5

1.0

6.0

24.0

1,0

2,0

6,0

24.0

0.5

1.0

6.0

24,0

50.0

76.0

A—s411

413

413

413

413

413

413

413

413

413

413

413

423

423

423

423

422

422

max nm

A 2

576

578

578

578

579

579

579

579

578

578

580

580

587

587

587

587

586

586

A rat io

pH

1.21

1,25

1.25

1.25

1.88

1.85

1.85

1.85

1.24

1,25

1.25

1.25

2,69

1.95

1.90

1.90

1.25

1.29

1.35

1.37

2.00

1.88

1.82

1,80

0.97

0.97

0.99

0.97

O.98

O.98

2.20

1.90

1,88

1.88

1.85

1.88

D. Instrumentation (R. Mavrodineanu)

1 . Proposed Design and Construction of High Accuracy

Spectrophotometer

The transmittance data discussed in Part B were obtained with a commercial instrument in which the transmittance

scale from to 100 is divided into 1000 divisions. The

stability is such that one division (or less) or one part

per thousand can be read.

The repeatability or precision of the measurements

from tables 2 and 3 and figures 1, 2 and 3 are thus determined

to one part per thousand. This is confirmed by the values

for standard deviations given in those tables.

The accuracy of the transmittance data could not be

determined, however, since no independent means was available

to determine this number; thus, the transmittance values

discussed here have only a relative meaning.

34
The accuracy of the transmittance measurements is a parameter of fundamental significance in characterizing a

chemical species through its molar absorptivity, as well as

allowing the interchange and communication of data between

laboratories. Hence, it was decided to initiate the design

of a spectrophotometer capable of providing data of known

accuracy and precision, and to construct such an instrument.

The first phase of this program has been completed and the

design of the spectrophotometer was established. It is

hoped that the construction and testing of an instrument

can be completed during Fiscal Year 1971.

2. Cell Light Path

An important factor in spectrophotometry measurements is the length of the light path. This obviously

depends on the inside dimensions of the glass or quartz

cell used. Therefore, particular attention was given to

this factor and various procedures were developed to determine

the width of the absorption cells of various shapes and

sizes. This work was done in cooperation with Mr. J. Matwey

of the Analytical Chemistry Division.

For rectangular cells, a feeler gauge using a single

and double probe with a dial reading was used. The path

length of circular cells was determined by microscopic

techniques using translation measurements between the

inside faces of the cell.

Since the rectangular absorption cells with a 10 mm path

length are used in the vast majority of routine measurements,

a simple and practical apparatus was designed and is now being

assembled to measure this parameter. It consists of a twin

probe unit provided with a dial reading to 0.01 mm. The dial

is set to indicate 10.00 mm and any deviation from this value

is read as plus or minus values within 0.01 mm, from 9-90 mm

to 10.10 mm. The probe is calibrated for accuracy against an

NBS reference block to + 0.001 mm tolerance. Hence the measurements of the path length are accurate to at least 0.1 percent.

35
The twin probe is placed on a sliding plate which

can translate in and out of the cell. The cell itself

is located on the same plate in front of the probe between

two spring-loaded metal blocks. Due to its simplicity

and ease of manipulation, such a measuring tool could

be a useful instrument in laboratories where spectrophotometry determinations are carried out.

E . Spectrophotometry Determination of Trace Amounts of

Gold, Iron, Manganese and Nickel in Two Glass Standard

Reference Materials (R. W. Burke and E. R. Deardorff)

Two sets of glass Standard Reference Materials were

analyzed spectrophotometrically for gold, iron, manganese

and nickel. The approximate composition of the base glass

was 72 percent SiO

?

, 12 percent CaO, 14 percent Na

p

O and

2 percent AlpO~. In addition to this base composition,

equal amounts of 6l other elements were added to each melt

in order to obtain nominal doping levels of 500 and 50 ppm.

The glasses were in the form of wafers about 1 cm

in diameter. Two thicknesses were Drovided: 1 mm sections,

weighing 200-300 mg and 3 mm sections weighing approximately 1 g. Following weighing and transferring to 30 -ml

Teflon beakers, the samples were cleaned by the recommended

procedure (the wafers were rinsed successively with

95 percent ethanol, distilled water, dilute nitric acid

(1+9) and distilled water). Ten ml of hydrofluoric acid

(1+1) were added, the beakers were covered with Teflon

lids and placed on a hot plate at 5O-60°C. To hasten

dissolution, the wafers were tapped occasionally with a

platinum rod to remove the insoluble fluoride coatings (calcium

and rare earth fluorides) which formed. The resulting solutions, frequently containing small amounts of insoluble salts,

were then evaporated to dryness. For the spectrophotometry

determination of gold and nickel, 4 ml of aqua regia were

added and the solutions were again evaporated to near dryness.

Two ml of hydrochloric acid (1+1) were added and again

36
evaporated. The residues were dissolved in IN hydrochloric acid, transferred to 100 ml volumetric flasks and

diluted to volume with IN HC1. Any insoluble salts which

were present dissolved upon standing (several days were

necessary in some instances).

Prior to the spectrophotometric determination of iron,

one of the chief concerns was the magnitude and reproducibility of the iron blank. Two precautions were taken. All

dissolutions were performed in a Teflon-lined hood and

only Merck "Suprapur" reagents, or the equivalent, were

used. Following dissolution and evaporation of excess

hydrofluoric acid, 2 ml of concentrated perchloric acid

were added and the solutions were heated to strong fumes

(approximately 1 ml of the perchloric acid was evaporated)

The samples were transferred to 100 ml volumetric flasks

with distilled water and diluted to volume. Manganese was

also determined in these solutions. All standard solutions

(gold, thallium, iron, manganese and nickel) were prepared

from the high purity metals.

1 . Spectrophotometric Determination of Gold

Gold was determined spectrophotometrically in the 500

and 50 ppm glasses following extraction of the [Brilliant

Green] AuClT complex into benzene [17]. Since thallium(III)

quantitatively accompanies gold(III) in the extraction

procedure, corrections were applied based on the isotope

dilution-mass spectrometric values reported previously for

thallium by the Analytical Mass Spectrometry Section (62.0

and 15.8 ppm, respectively). The standard solutions of

gold (III) and thallium(III) were prepared by dissolving the

metals in aqua regia and then removing the excess nitric

acid by repeated evaporations with hydrochloric acid.

A more desirable approach for the spectrophotometric

determination of gold with Brilliant Green is, undoubtedly,

to eliminate the thallium(III) interference. At least

two possibilities seem worthy of further study. One is

37
the selective reduction of thallium(III) to thallium(I)

without the simultaneous reduction of gold(III); the

other is the pre-extraction of thallium( III ) following an

exchange reaction with one of the metal chelates of

dibenzyldithiocarbamic acid, possibly the zinc complex.

The spectrophotometric results obtained for gold in

the 500 and 50 ppm glasses are given in tables 8 and 9,

respectively

.

2 . Spectrophotometric Determination of Iron

The bathophenanthroline (4 ,7-diphenyl-l ,10-

phenanthroline ) procedure of Diehl and Smith [18] was

employed. The iron(III) in a 10 ml solution (pH^l) was

reduced to iron(II) with hydroxylamine hydrochloride

( 2 ml of a 10 percent aqueous solution) and the pH adjusted

to approximately 4.5 by the addition of 4 ml of 10 percent

aqueous sodium acetate. Four ml of 0.001M bathophenanthroline (reagent initially dissolved in absolute ethanol

and then diluted two-fold with distilled water) were added

and the red iron(II )-bathophenanthroline complex was extracted

into 6 ml of n-hexyl alcohol, using 30 ml separatory funnels

equipped with all Teflon fittings. Approximately 15 minutes

were allowed for the two phases to separate completely and

then the bottom (aqueous) layer was drawn off and discarded.

The n-hexyl alcohol phase was transferred to 10 ml volumetric

flasks, the separatory funnels (including stoppers) were

rinsed with small portions of ethanol and the combined

extracts and washings were diluted to volume with ethanol.

Absorbance measurements were made at 535 nm, using 1.00 cm

cuvettes

.

An important advantage of the good extractability of the

Fe(II)-bathophenanthroline complex is that it permits the

removal of trace amounts of iron from the reagents used in

the complexation reaction. The aqueous solutions of

hydroxylamine hydrochloride and sodium acetate were freed

of iron in this manner. The latter solution, in particular,

38
contained relatively large amounts of iron and at least a dozen extractions were necessary before the n-hexyl alcohol

phase became colorless. Following this treatment, the

combined reagent blank was 0.007 absorbance units, i.e.

0.18 mg of iron. The total blank (reagent + environmental)

obtained following dissolution of the glass samples in the

laminar flow, Teflon-lined hood was not distinguishable from

the combined reagent blank, thus establishing that no

detectable air-borne contamination with iron occurred.

The spectrophotometric results obtained for iron in

the two glass Standard Reference Materials are given in

tables 8 and 9.

Table 8. Spectrophotometric determination of gold, iron,

manganese and nickel in 500 ppm glass.

Gold Iron Manganese Nickel

Sample No. a ppm

37.0

ppm

c

460

d

ppm

a

2 4 81 445

13 33.7 458 485 451

18 33.9 453 485 457

48 35.3 459 487 450

56 34.3 463 492 446

66 34.

b

54. 9£ 41.8°

468 487 448

78 468 482 457

45. 2°

106 39.0 457 481 456

Average 35.

e 460.8 485.0 451.3

Std. Dev. 2 o 5.3 3.7 4.9

Rel. Std. Dev. 5o5$ 1.1$ 0.8$ 1.1$

b Sample weights 0.2-0.4g; 10/100 aliquots taken for analysis Successive samples.

d Sample weights 1.0-1.5g; 2/100 aliquots taken for analysis.

g

Sample weights 1.0-1.5g; 10/100 aliquots taken for analysis

Results on sample 78 not included.

39
Table 9. Spectrophotometric determination of gold, iron,

manganese and nickel in 50 ppm glass.

Iron Manganese

b c Gold

Sample No.

a

ppm

2 9.4

37 9.7

44 10.8

68 10.0

75 9.0

114 9.7

Average 9.8

Std. Dev. 0.6

Rel. Std. Dev. 6.2%

ppm pp.m

Nickel

a ppm

37,,7

37..8

37..7

37 .5

37..3

37 .8

37.,6

0,,2

0,.5%

49.0 40.0

51.2 39.7

51.8 39.7

52.8 39.5

52o6 39.3

52.8 39.1

51.7 39.6

1.5 0.3

2.856 0.8%

Sample weights 0.8-1.3g; 10/100 aliquots taken for analysis

Sample weights 0.9-1.3g; 10/100 aliquots taken for analysis

Sample weights 0.9-1.3g; 25/100 aliquots taken for analysis

3. Spectrophotometric Determination of Manganese

Manganese was determined spectrophotometrically

following oxidation of manganese( II) to permanganate with

ammonium persulfate-potassium periodate. The detailed

procedure is as follows: A suitable aliquot of the

manganese solution is transferred to a 125 ml Erlenmeyer

flask followed by the addition of 1.5 ml concentrated

sulfuric acid, 0.5 ml concentrated phosphoric acid and

0.2 ml concentrated nitric acid. Several crystals of

silver nitrate and 0.5 g of ammonium persulfate are added

and the resulting solution is diluted to approximately 40 ml

with distilled water. The solution is boiled over an open

flame for 5 minutes, removed from the heat, 0.3 g potassium

periodate added, again boiled over the flame for an

additional 2 minutes and then warmed for 15 minutes on a steam bath. The solution is cooled, transferred to a 50 ml

volumetric flask and diluted to volume with . IN nitric

acid (the latter was pre-boiled with ammonium persulfatepotassium periodate). A blank was treated in a similar

40

«
manner. The net absorbance at 545 nm was then determined

using 10.00 cm cuvettes (the chromium present did not

interfere and the usual sodium azide reduction of

permanganate was not employed).

The spectrophotometric results obtained for manganese

in the 500 and 50 ppm glasses are given in tables 8 and 9,

respectively

4 . Spectrophotometric Determination of Nickel

Nickel was determined spectrophotometrically by a

modified dimethylglyoxime procedure which has been

described in detail previously [19]. The complexation

reaction is carried out at pH 13, using ammonium citrate

as a masking agent. No separations were necessary in the

analysis of these two glass SRM ' s . Absorbance measurements

were made at 465 nm in 5.00 cm cuvettes. The results are

given in tables 8 and 9.

41
2. FLUORESCENCE

A. Introduction (R. A. Velapoldi)

Spectrof luorimetry is at the same place that spectrophotometry was twenty-five years ago. It is quite apparent

from the growth in publications in the past few years that

it is rapidly approaching spectrophotometry in importance as

an analytical tool. Research and use of spectrof luorimetry

is carried out in such diverse fields of interest as

clinical chemistry and testing, environmental chemistry

(defense and pollution), forensic science and analytical

chemistry

.

Spectrof luorimetry generally is more sensitive than most

spectrophotometric techniques since it depends on amplification of a signal rather than amplification of a small

difference or ratio between two signals. Thus, metals such

as magnesium or aluminum have been determined at the nanogram level or less. Spectrof luorimetry also has greater

specificity. Analyses depend not only on the emission wavelengths, but also on the exciting wavelengths.

Many fluorescence spectra reported are uncorrected and

incorporate errors produced by instrumental artifacts such

as photomultiplier inefficiencies, light source instabilities and monochromator aberrations. It is imperative that

fluorescence standards and corrected spectra be obtained [20].

Prerequisites for fluorescence standards include stability, solubility in aqueous and organic systems, ease of purification, a relatively broad fluorescence spectrum, excitation

and fluorescence in the same general wavelength regions as the compound under investigation and a constant quantum

efficiency, Q

f

, as a function of exciting wavelength [21].

Quinine sulfate is one of the most widely used and

accepted standards, although recently some concern has been

raised on the variations of Q f with exciting wavelength and

its instability in solution at low concentration. In

42
addition, reported Q f values of 0.4 to 0.6 exemplify the

need for further study on this system.

Fluorescence band spectra are somewhat narrow (100 nm at

half band width); thus development of a series of fluorescent

standards which cover the 250-750 nm region is needed.

B . Program

In view of the requirements in the field of fluorescence,

an outline of a program was proposed and is presented in table

10 which has as its main objectives the development of SRMs

the compilation and publication of corrected fluorescence

spectra with use of computer technology, and the investigation

of new analytical techniques. As can be seen, development of

solution and solid (glasses) fluorescent SRMs is planned.

The corrected spectra of two possible types of SRMs

are given in figures 18-21. Figure 18 shows spectra of

too Wavelength, nm Figure 18. Corrected emission f excitation and

absorption spectra of quinine sulfate in

0.1N sulfuric acid.

43
CD CD P a CO c G t» £ CD •H CD P P G H O M CD (D

CD •H CO +j cd

O

G

T3

C CD P W Cd CD CD •H cd m o M G rH

CD 6 CD

H

O ,G <L> .G CD >i P •H P >> 3 O U P ^ ^

cd rH Cd ,c

H co cd

C >i CD Cm cd H p fr ^ cc cd a u H .C CD cu 3 p .c S • • • • •

co ,C o •H cd X2 cd ,Q

a

CDO CC^

TO ^ o - • 6 C emu: M CO CO CD p

cd

CO

CD •H •H CQ P M o ou c £ Cm CD -H CD CO •H •H3

cd l cdC ,C 1 r-\ CO I P

CDCO

p

CO 1—1

CD

Mo o1 ro < «-- 6 o COcd rH

cd rH

CM

Go o

Ti cd ,a o T3 CD C3 • cd p

CD

Mo

rH

CD

co ^_ O CO CM C\J 2 fin o o

•HP3

rH

CO

•H

0) .H rH £ O o p CO co

,G CmO H

cd Ps

CQM

CD P

CD£

cdM

cd

H

>3hDM

CDGH

CD P

rH

C\J

rH

cdO

•H

rHapg

CD£GOM

GO

•HPM

T3G

cdo OG

cd

0)c

•HPO

OG S CD P o G -H

CD

CO

CD PC

CD

g

•H cd o cd Cm g •H rH •H rH m

CO CO 3 Cm •H > rH CQ

a ho oH H

£1<

C3?

W rHo O

Ph

cd CQ

(X o < u

CU

CD H < CQ

O • QW

M

,Q /^ cd G c

EH

OO

•HP

cd

tsl •H

TJ

Shcd T3G

cd

•HP

cdM

-Q•H

rH

cd o

cdo

•Hp

coGo

•HP

cdo

•HrH

T3

CD

COO

CUOM

Ph

Tl >> cd

a

p c M

Ga

CO cd P1 CD < < # o S • HH m -H P u MH

CD 3

an

CO <*"!

44
500 Wavelength, nm

Figure 19- Corrected emission excitation and

absorption spectra of europium (III) in a NaHpPOj. glass prepared at Hebrew University,

Israel

quinine sulfate in 0.1N HpSOj. . The absorption and excitation

spectra are identical, except for the sharp excitation peak

at 355 nm. Further work will be undertaken to determine

whether this peak is an instrumental artifact or whether

it is the hidden electronic transition [22] responsible

for the change of Q f with exciting wavelength.

The spectra presented in figures 19 and 20 are typically

produced by lanthanides and are exemplified by europium(III

in silicate and phosphate glasses. The Eu(III) in phosphate

glass was obtained from Dr. Renata Reisfeld at the Hebrew

45
Europilm(III) in Silicate Glass, O.SS

Wavelength, m

Figure 20. Corrected emission excitation and

absorption spectra of europium ( III ) in

sodium silicate glass prepared by the Inorganic

Materials Division at NBS.

University in Israel, who, In conjunction with NBS, is

developing the spectrof luorimetric chemistry of lanthanide

glasses. The Eu(III) in silicate glass was obtained from the

Inorganic Glass Section of the Inorganic Materials Division

at NBS. Very similar optical properties exist between

the two glasses. As found by Dr. Reisfeld, definite wavelength shifts occur for some of the band maxima due to matrix

effects. The emission maxima are relatively sharp.

Two other glasses, however, give emission spectra which

are fairly broad, figures 21 and 22: 75 nm half-band

46
—r > i i

4% Ce(III) + Ce(IV) in Silicate Glass

/ * * /

// v/

/ / /

1 1

300 100 500 Wavelength, nm

600

Figure 21. Uncorrected emission and excitation

spectra of a 4% cerium(III) - cerium(IV) mixture

in silicate glass obtained from the Inorganic

Materials Division at NBS.

1 —1

1 1 1

ALPHA AMERICAN / \

SAMPLE OB-4 / \

1 \ 1/ \\

1 \

^"

1

X / \

-~r^^-t — 350 450

Wavelength, nm

550

Figure 22. Uncorrected emission and excitation

spectra of sample OB-4 fluorescent glass

obtained from Alpha American, Rockford, Illinois

47
width height for the 4 percent Ce(III) - Ce(IV) in a

silicate sample obtained from the Inorganic Glass Section

of the Inorganic Materials Division and 110 nm half-band width

height for the Alpha American OB-4 sample. These two spectra

were taken on the uncorrected spectrof luorimeter because

of high inorganic salt concentration. These spectra may be

distorted due to inner filter effects. Nevertheless,

these two glasses look very promising as SRM ' s and further

developmental work is planned.

Other glasses incorporating Eu(II), and techniques such

as the addition of organolanthanides or chelates to glasses

may produce broader emission spectra due to TT*-»-f electronic

transitions (rather than narrow f*-»-f).

Figure 23 presents spectra of uranium in silicate glass

showing a broad emission spectrum. The only sample

available was one containing 15 percent uranium oxide which

is too concentrated, resulting again in inner filter and

1

Uranium in Silicate Glass 15Z

IIII

1

1

1 1

1

II

/!

1 1

1 1

1 1

1 1

1 1

1 ¥n

1

1

v.

11 A

I

1

1

1

1

1

1 1

1

1 (

1

1

\

1 1i V\vn

1 1

1 I

1 1

1

1

1

1

)

1

1

100

1 \J500 V Wavelength, m

Figure 23. Uncorrected emission and excitation

spectra of 15% uranium in silicate glass

fluorescent standard used by Carl Zeiss, Inc

48

uan^^aaaai
quenching effects which were discussed in connection with

Ce spectra [23]

The final SRM spectra will be published with the

following information: Qf

, emission intensities in absolute

energy units, inorganic salt concentrations, glass stabilities,

corrected spectra versus wave number and methodology for

attaining best results.

Corrected spectra will be published in subsequent NBS

circulars. Several typical spectra are presented in figures

24-26, fluorescein, pyrene and mesoporphyrin IX dimethyl ester.

Figure 24 is of fluorescein, which is used for tracing flows

of water and sewage in bays, streams and sewage systems.

Pyrene, spectra given in figure 25, is one of a group

of polynuclear aromatic hydrocarbons, some of which are

carcinogens . They are in polluted air and lend themselves

to sensitive spectrof luorimetric determinations.

500

Wavelength, nm Figure 24. Corrected emission excitation and

absorption spectra of 10 ppm fluorescein

in 0.1N NaOH.

49
Figure 26 presents the spectra for mesoporphyrin IX

dimethyl ester which shows the usefulness of fluorescence

in clinical and biological chemistry. The analytical

determinations of porphyrins, as well as numerous other

biologically important species, involve spectrof luorimetry

.

In future work, these corrected spectra will be produced

by feeding data from the spectrof luorimeter directly into

a computer for point by point plotting of intensity versus

wave number (rather than wavelength as presented here).

Electronic integration of the emission spectra and comparison

of known values of a developed standard will give comparative

Q„ values. All necessary data will be included in these

circulars such as concentrations, solvents, temperature

dependence, quenching effects and statistical data analyses.

. i

i

•

i

; i

!

'

i i

Pyrene in Toluene

300 400

Wavelength, nm

500

Figure 25. Corrected emission excitation and

absorption spectra of 5 ppm pyrene in

toluene

.

50
-* h

•

l

Mesoporphyrin IX Dimethyl Ester in Benzene

i

i

f\

too

1

-i i- v

500 600 Wavelength, nm

Figure 26. Corrected emission excitation and

absorption spectra of 10 ppm mesoporphyrin

IX dimethyl ester in benzene.

C. Study of the Rhodamine 6G Fluorescence; Importance of

Having Corrected Spectra (R. W. Burke and R. A. Velapoldi)

It is widely accepted that fluorescence spectra are

needed which do not include instrumental artifacts [20].

A graphic illustration of this need is presented. Rhodamine

6G in ethanol gives an uncorrected excitation spectrum,

figure 27. Sharp peaks are observed on the short wavelength

side of the excitation band which could erroneously be

assigned to electronically produced fine structure.

The xenon source has an emission spectrum (determined

by placing an aluminum block cut at a 45° angle in the

sample holder) which is also presented in figure 27.

Extremely sharp bands are noted, some of which correspond to

the 'fine structure' for the Rhodamine 6G . Substitution of a 51
Rhodamine 66 in Ethanol

Excitation uncorrected

tOO 500 Wavelength, nm

600

Figure 27. Xenon source emission spectrum - uncorrected excitation spectrum

Rhodamine 6G in ethanol

.

and the

- for 3 ppm

tungsten iodide lamp for the xenon source eliminates these

sharp peaks of the excitation spectrum which now shows only

the presence of a shoulder.

Figure 28 presents spectra taken on a corrected spectrofluorimeter operating in the corrected and uncorrected modes

and also summarizes earlier observations. The uncorrected

excitation spectrum is not the same as the absorbance spectrum

The corrected excitation spectrum has the same shape as the

absorbance spectrum and occurs at the same wavelength. It

is not hypsochromically shifted by 5 nm as is the uncorrected

excitation spectrum. There appear to be no differences

between the corrected and uncorrected emission spectra,

although measurements of Q

T s must be made as proof.

52
525 Uavelength. nm

Figure 28. Summary of corrected and uncorrected emission and

excitation spectra and the corrected absorption

spectra for 3 ppm Rhodamine 6G in ethanol

This is definite evidence, then, of confusion which

results by the publication of uncorrected spectra and underscores the need for a corrected spectra publication.

D . Fluorescence and Absorption of Rare-Earths in Glasses

(R. Reisfeld, Hebrew University).

In an effort to find suitable standards for fluorescence

(and perhaps for absorption spectrophotometry), we concentrated on the incorporation of rare-earth ions into glass

matrices which fluoresce in the ultraviolet and visible part

of the spectrum [24]. The energy transfer between Sm(III)

and Eu(III) was studied In order to find the mutual influence

of these ions on their fluorescence [25] • The determination

of absolute quantum yields for these rare earth glasses could

lead to the development of reference standards in the spectral

53
regions of interest. One factor in the production of standards

is the prerequisite that the emission spectrum of the standard

should have a wide half band width (100-150 nm) . While many of the rare-earths have narrow emission

band widths, some, including cerium(III) have wide band

widths. The fluorescence of Ce(III) is attributed to the

p transition of the electron from the 5d orbital to the F r ,„ 5/2

level. The overlap of the 5d level with the surrounding

ligand fields is rather strong, explaining the great width

of the emission band.

The experimental results of measurements made on ceriumdoped glasses are presented here. The theory is currently

being developed and it is planned to publish these results in

the near future.

1 . Cerium in Silicate Glasses

The glasses examined were of the following base composition: Si0

2 - 722; A1

2 3 - 1.52; CaO - 7-52; MgO - 42;

Na p - 152 . CeO

p

, FepO^ and in some cases F~ were added to

the base glass in the following concentration ranges: CeO„ - 0.007 to 0.32; Fe

2 0^ - 0.021 to 0.0932 and P" - 0.5 to 12.

Addition of iron serves to reduce Ce(IV) to Ce(III):

Ce(IV) + Pe(II)^±Ce(III) + Fe(III)

The absorption spectrum of Ce(III) in silicate glass

versus the base glass is presented in figure 29. The

excitation (emission at 385 nm) and emission (excitation

at 330 nm) spectra of Ce(III) are given in figure 30.

Qualitative data show that the relative fluorescence is

cerium concentration dependent. The relative fluorescence

increases with cerium concentration, e.g. a 32.42 increase

is produced by raising [Ce(III)] from 0.12 to 0.22 and

51.02 by increasing the [Ce(III)] from 0.12 to 0.32.

Increasing the Fe^O- concentration results in a slight

enhancement (7-32) of the relative fluorescence. Fluoride

54
Cerium Glass

350 300 250 Wavelength- nm Figure 29- Absorption spectrum of cerium(III) in silicate

base glass run versus silicate base glass

reference

Figure 30

Wavelensth. m Excitation spectrum (emission at 385 nm)

and emission spectrum (excitation at 330 nm)

of cerium(III) in silicate glass.

addition increases the fluorescence slightly probably due to a shift in equilibrium of iron oxidation. Equilibrium constants

of this reaction may be computed and will be done in the

future

55
These glasses will be subjected to varying periods of

ultraviolet irradiation in order to test the reproducibility

and stability with time.

2 . Cerium in Borate Glasses

The basic constituents of these glasses were borax and

boric acid in a 2:1 ratio. The detailed procedures for glass

preparation are described in earlier publications [26].

Commercial CeC1^.7H

p

was used for the preparation of the

Ce(III) glasses and CeO„ was used for the preparation of

the Ce(IV) glasses. Absorption spectra of the glasses were

measured in order to determine the distribution of Ce(III)

and Ce(IV) and the best absorption band for excitation. All

glasses showed an absorption band extending from 220 to

320 nm. This large band is clearly an overlapping of the

Ce(IV) (charge transfer) peaking at approximately 250 nm and

Ce(III) (f-*d transition) peaking at approximately 315 nm.

Regardless of the starting cerium salt, the cerium containing

glasses showed absorption spectra characteristic of a Ce(III)

and Ce(IV) equilibrium. Preparation of cerium glasses in

a reducing atmosphere to insure a preponderance of Ce(III)

is planned.

The excitation (350 nm emission) and emission (315 nm

excitation) spectra are presented in figure 31. The excitation

and emission maxima of the cerium couple in borate glasses

occur at shorter wavelengths than in the silicate glasses,

probably due to varying crystal fields exhibited by the

different matrices, substantiating extensive overlap between

the 5d orbital and the matrix. It is hoped that by producing

a matrix of appropriate silicate to borate mixtures, an

emission band with greater halfwidth will be obtained. The

influence of the exciting wavelength on the fluorescence will

also be studied.'

56
350

Wavelength, nm

Figure 31. Excitation spectrum (emission at 350 nm)

and emission spectrum (excitation at

315 nm of a cerium(III) - cerium(IV) borate

glass

57
3. ANALYTICAL FLAME SPECTROSCOPY

A . Introduction

The recognized importance of flame spectrometry as

an analytical technique is evident from the new review in

Analytical Chemistry [27]. This reflects the increasing

research in this field as well as its wide application

to the analytical needs for relatively simple, very

rapid and precise methods. This growth is not limited

to atomic absorption, but includes the revived interest

In flame emission work and in expanded efforts in

atomic fluorescence. It has been shown that as little as

10 g of an element can be detected in several milligrams of sample. Major constituents, however, can be

determined with a relative standard deviation of 0.2

percent [ 28] . In a continued effort to develop this competence,

instruments of new design are being tested; components

and flame data are being evaluated. This section describes

the progress in instrumental innovations, various flame

components, studies of relative resonance and non-resonance

line intensities, and special applications to Standard

Reference Materials

.

B . Multipurpose Precision Flame Spectrophotometer

(R. Mavrodineanu)

The program established in this field was directed

toward the design and construction of a precise flexible

flame spectrophotometer capable of performing measurements

in the flame emission, atomic absorption, and flame

fluorescence modes. Further requirements were that single

and simultaneous multielement measurements be possible with

an electronic integration of the optical signals, and with

data presentation in analog (recorder) form and simultaneous

digital print-out, punch-out form.

58

tBHHMBHHHB
1 . Design of the Instrument

a. Optical System . The instrument was designed

and built along a one meter grating spectrometer using

the Czerny-Turner optical arrangement and capable of

functioning in the scanning mode (variable exit slit),

photographic mode (2 n x 8" plate holder), and simultaneous

multichannel arrangement (compartment accepting up to

18 side-on photomultiplier tubes and a multiple slitcarrying plate). A rigid 160 cm long lathe bed- type

optical bench was placed along the optical axis in

front of the entrance slit of the spectrometer, as

illustrated in figures 32 and 33- The following equipment is assembled on the optical bench using appropriate

carriers: a quartz lens which produces a demagnified

image of the analytical flame on the entrance slit; the

burner and sprayer unit with its dual sample supplying

system; a second quartz lens which produces a demagnified

image of the hollow cathode in the flame; a mirror chopper

which generates an ac signal and at the same time combines

in one beam the emission from the two hollow cathodes

in succession along the optical axis. The lenses, flame,

chopper and hollow cathodes can be positioned with

precision along the optical axis in the x-y-z direction and

tightly secured in the correct location (see figures 32 and

33).

b . Electronic Circuitry . The electronic equipment

with the scanning mode is shown in figure 32. It consists

of a differential preamplifier capable of handling separately

two signals, A or B, as well as presenting their difference

A-B. This preamplifier is followed by a selective

amplifier, a lock-in amplifier, an analog to digital

converter with digital presentation and a recorder. The

power supply for the hollow cathodes is also shown in the

figure and consists of a current stabilized unit (^ ± 0.1$).

The electronic circuitry used with the multichannel mode

59
Figure 32 Flame spectrome

Left - console

system for the

supply for the

Middle - one me

and burner unit

acetylene flame

supplied with t a two way Teflo

Right - water p

pressure in the

ter . with the electronic measurement

scanning mode system, and power

hollow cathode.

ter spectrometer and sprayer

producing a premixed airThe pneumatic sprayer is

he analytical solution through

n stopcock,

ressure gauge for monitoring the

spraying vessel and burner unit

60
Figure 33- Flame spectrometer.

Left - optical bench carrying the sprayer and

burner unit

Middle - electronic unit for the multichannel

operation

Right - mirror chopper, dual hollow cathode

arrangement, and gas regulating and monitoring

console

was available from previous work [ 29] and is shown in

figure 33. The same figure shows the console which

carries the gas regulating and monitoring system for

61
Figure 3^. Flame spectrometer.

Inside view of the multichannel photomultiplier

arrangement . Seven tubes are disposed behind

individual exit slits.

both fuel and oxidant (pressure regulators, high

precision gauges, 250 mm flowmeters). Figure 3^ illustrates

the photomultiplier arrangement in the rear of the multislit

carrying plate. Seven tubes are used to receive the optical

signals from Na (5893 A); K (7667 A); Li (6707 A); Ca (4227 A);

CaOH (6230 A); and Mg (2852 A); the seventh tube is used in

conjunction with the scanning mode. The first 6 photo62
Figure 35- Sprayer and burner unit . An interchangeable

burner head is seen at the bottom of the

figure

63
multiplier tubes are connected to the multichannel electronic

system, (figure 33), while the seventh tube is connected to the

scanning electronics shown in figure 32. c. Burner and Sprayer System . The burner and

sprayer system was available from previous work [ 30] and is

shown in more detail in figure 35. It consists of a pneumatic

sprayer spraying vessel and burner body made of alumina

(99 percent purity), and of a water cooled burner plate made

of tantalum. This unit is corrosion and erosion resistant

and flame proof. The gas mixtures which can be used with

this flame are: air-acetylene, nitrous oxide-acetylene;

nitrous oxide-propane.

The spraying vessel is connected to a drain bottle

through a glass hydraulic trap and is illustrated in figure 36

(available from a previous work; see reference 30 ).

TO SPRAYER

DRAIN •TO WATER MANOMETER

RUBBER PAD

Figure 36. Hydraulic trap made of glass

64
The functioning of the spectrometer in the scanning mode

is conventional and does not require further discussion.

(Since the electronic measuring system for the scanning mode

uses a lock-in amplifier, a mechanical chopper is placed

between the emitting flame and the entrance slit of the

spectrometer.) The multielement mode, with simultaneous

flame emission and atomic absorption measurements, will be

described briefly since it is a less conventional operation.

The heart of the system is the electronic measuring

and data displaying unit (figure 33)- This unit has a capacity of 8 channels. Two channels and the electronic

design are illustrated in the block diagram in figure 37a.

The signal from each photomultiplier tube (PM) is fed to

individual integrating capacitors where it is stored and

then sequentially converted to measurement in digital form.

The digital readout is displayed by a printer and paper tape

puncher. In the latter, the data are compatible from direct

input to an IBM 1130 computer. The light measuring channels

P. MIS D-i

i

i

i

UD- FILT a

RECT.

INTEGR. ON-OFF SWITCHES

£>

>

SERIAL CHANNEL

SWITCHING ANALOG

TO

DIGITAL CONVERTER

CONTROL

DATA OUTPUT

INTERFACE

Figure 3?a. Block diagram of the electronic system used in

conjunction with the multichannel spectrometer

65
can be used to accept either ac or dc inputs in any

combination. The former is used in conjunction with the

flame atomic absorption mode, while the latter is used for

the emission mode (see reference 29) . Every channel has

a sensitivity adjustment and a dark current compensation

capability. The integration time can be selected stepwise

as needed from 10, 20, 40, 100, 200, 400, and 1000 seconds.

The measurements can be made in 1, 2, 3 or 4 replications or

continuously, the sequence in this case being interrupted

manually (figure 37b). The simultaneous digital printed or

punched-out display contains the following information:

1 -Mint (write — •

ii.i rich vonict n«i« sumr tiu'iimiinntH

^F < WW

ram IU» MtHMmm

Figure 37b Front panel of the electronic system shown in 37a

From bottom to top — dark current compensation,

channel sensitivity selectors, mode of operation

switches, power supply for photomultiplier tubes.

66
channel number, sensitivity setting, integration time, and

the arbitrary counts corresponding to the charge of the

individual capacitors. The arbitrary counts are then

converted to meaningful information through calibration with

analytical solutions containing known amounts of analyte.

In the present configuration, the electronic system is

set to accept four signals in the dc mode for flame emission

measurements of Ca (CaOH) K, Na, and Li which is used as an

internal standard, and four signals in the ac mode for

measurements by atomic absorption techniques . From these

four ac channels, only two are used in the present arrangement to determine Mg and Ca using the mirror chopper at 45°

on the optical axis, and using two hollow cathodes (figure

33). If a two-element Mg-Ca hollow cathode tube is used,

then the chopper equipped with a normal blade is placed at

90° on the optical axis

2 . Experimental Tests

To determine a suitable chopping frequency, both in

the emission and atomic absorption mode, a series of measurements was designed and performed to determine whether the

analytical flame itself exhibits any periodicity in its

radiation which could interfere with the chopper frequency.

These measurements were made by an oscilloscope in cooperation with Mr. F. E. Ruegg, Analytical Chemistry Division,

Technical Services. The results are shown in figure 38

where it can be seen that the unsupplied flame exhibits

a "white noise" type of periodicity of low amplitude. When

an element, such as Na, was supplied to the flame, the

resulting signal indicated a strong periodicity at a

frequency of 25 Hz. As a result of these measurements,

the chopping frequency for the measurements in the ac mode

was selected to avoid interferences with the fundamental

frequency of the flame or any of its harmonics.

The scanning electronic system was tested to determine

its general functioning conditions by using the single

67
B

C

Figure 38. Fla.me fluctuation as illustrated on an oscilloscope

screen. A — signal produced by an unsupplied premixed air-acetylene flame at A 5893 £. B - signal

produced by the same flame supplied with distilled

water at A 5893 A. C -- signal produced by the same

flame supplied with Na salt at A 5893 A.

68
signals (A or B) from Na and Li as the differential A-B

signal. In this latter mode, the signal from B can be

produced by the radiation from a constant concentration of

Li, while A can be produced by a variable concentration of

Na . The differential signal A-B will then, to some extent,

represent an internal standard operation and should result

in an improved stability of signal A (Na) . The results

obtained under these conditions indicate that when using the

sprayer and burner unit (figure 3 5) , a reduction of the

"noise" of signal A by a factor of 3 was observed.

Further evaluation of the electronic systems for their

sensitivity, stability and reproducibility will be made

by using a constant source of radiation in the form of a fluorescent material excited by tritium (half-life

12.5 years). The flame emission and atomic absorption

spectrometer described earlier will then be used for

measurements in conjunction with clinical analytical problems.

C. Long-path Flames (R. Mavrodineanu)

In addition to the sprayer and burner unit shown in

figure 3 5s an experimental unit was designed and constructed

to produce a premixed acetylene—air flame having a long path.

This prototype unit, made of glass and copper is illustrated

in figure 3 9. The flame produced with this burner is 30 cm

long and 1.0 cm wide. The all glass external pneumatic sprayer

supplies the flame with the analytical sample at the rate of

about 0.3^g/min for a sample consumption of 18 ml/min. The

evaluation of this unit is now in progress.

D. Hollow Cathode After Grimm (R. Mavrodineanu)

In 1968 Grimm gave a detailed description of a glow

discharge unit which was capable of operating as a flat

discharge or as a hollow cathode discharge [31]. It is well

known that hollow cathode discharges are particularly suitable

for the excitation of small amounts of many chemical species

with great sensitivity [32]. Hence, it was considered

desirable to test the detection capabilities of such an

69
Figure 39 Long-path flame 30 cm long and 1.0 cm wide

produced by the premixed combustion of air

with acetylene. Experimental prototype unit

excitation source in conjunction with chemical species of

particular interest to the clinical chemist. A Grimm hollow

cathode discharge unit was available and was set-up in

conjunction with the 1 m grating spectrometer discussed

previously; figure 40 illustrates the arrangement. Pure

copper hollow cathodes were supplied with varying amounts

of Mg in aqueous solution using a volume between 3 and

10 u 1 containing 0.3 to 5 ng Mg. The transfer of the

sample was made under a microscope using micromanipulator

70
Figure 40. Hollow cathode discharge unit after Grimm. The

hollow cathode is located in the enclosure

placed on the optical bench. The power supply

and various controls are located in the console

at the extremity of the optical bench.

techniques. The spectra were recorded photographically

for an exposure time of 20 sec using a 1200 line/mm

grating in the second order. The argon pressure was

1 Torr and the current supplied to the hollow cathode

unit was 200 mA . Under these experimental conditions the

detection limit for Mg was 0.3 ng.

71
E . Spectrophotometry Instrument for Ratios and Difference

Measurements (T. C. Rains)

An instrument capable of measuring the ratio or difference

in two signals has been designed, built and is being evaluated.

In the absorption mode, variations produced by the source can

be cancelled out by taking the ratio of the light flux coming

from the absorption cell and from the source directly. In

flame emission, the problem is one of separating the background radiation from the signal produced by the radiant

intensity of the analytical line. The isolation of the

radiant intensity of the analytical line is accomplished by

subtracting the common background radiation.

The instrument consists of a 0.5m and a 0.25m monochromator, light-beam-chopper disk, beam splitter, dc power

supply, lock-in amplifier and digital voltmeter. The lockin amplifier and digital voltmeter were constructed by the

Measurement Engineer Division of the National Bureau of

Standards. It contains two identical channels, one for the

signal and the other as a reference for obtaining the ratio

or difference. Each channel derives its input from a multiplier phototube which is powered by a single dc power

source. The output from the photodetector is amplified and

fed into a digital readout. In the absorption mode, the

outputs of two filter-amplifier stages provide the two

potentials for the ratio measurement. In the emission mode

the two outputs are combined at a summing junction of

resistors, if algebraic differences are desired. The voltage

output of this operational stage is the difference signal

which is fed to the digital readout.

The instrument is presently being tested for flame

emission and atomic absorption spectrometry under various

operating conditions.

72

aaanaanM
F. Selection of the Analytical Line in Atomic Absorption

(T. C. Rains and T. A. Rush)

The selection of the appropriate resonance line for

atomic absorption spectrometry is often made empirically,

and this information may often be lacking. The analyst more

often seeks the most sensitive analytical line for a given

determination and assumes that the line used by other workers,

or the one listed by the manufacturer, produces the highest

sensitivity. For example, the resonance line of lead at

o o 2170 A is 2.5 times as sensitive as the line at 2833 A.

However, the latter is usually recommended because the line

o at 2170 A is subject to spectral interference from copper,

especially if a monochromator of poor dispersion is used.

Occasionally a less sensitive line is desirable to extend

the dynamic range of the analysis to higher concentrations

without having to dilute the sample. For most elements,

the analytical line is generally the resonance line with

the largest oscillator strength corresponding to the

transition from the ground state to some higher excited

state. If the ground state is a multiplet with only

slightly different energies, then the number of atoms

occupying the higher energy levels may be greater than those

in the lower energy level, and thus provide higher

sensitivity. For aluminum, the ground state (0 eV)

o resonance line at 3082 A has a gf (product of statistical

weight, g, and oscillator strength, f) of O.38. Although

o the lower energy level line at 3093 A is 112 kaysers or

0.014 eV, with a gf value of 0.79; it is twice as sensitive

o as the 3082 A line. A comparison of the sensitivity of the

Al I lines using a fuel rich nitrous oxide—acetylene flame

is given in table 11.

If the gf values could be accurately established, the

sensitivity of the major analytical lines could be readily

73
Table 11. Relative sensitivity of Al I lines in atomic

absorption.

(Oxidant-fuel: N

2 - C

2

H

2 (fuel rich))

° Sensitivity

Wavelength, A gf ug/ml/% abs . 3092.7 0.79

3961.5 • 31

3082.2 .38

3944.0 .15

2373. In

2373.

4

s

• 31

.061

2667 .1 .15

2269.1 .092

2567.9 .10

2378.4 .015

2. 1

3.

H.

5- 2

5.• 5

8

10

16

50

calculated. This can be shown from the relationship of the

oscillator strength of an analytical line to the LambertBeer Law in the following manner. The Lambert-Beer Law

states that the absorbance of an analytical line is

proportional to the absorptivity, a, of the analyte sprayed

into the flame, to the concentration, c, of the absorbing

atoms and to the length of the absorption cell, b, and is

given by

A = 0.4343 a b c

If the absorbance is measured over the entire width of the

2 absorption line, a is equal to f.. ire where f.. is the

J mc d oscillator strength for the transition involving the upper

level, j, and the lower level, i, e is the charge of the

electron, m is the mass of the electron and c is velocity

of light [33] • If the lower energy level is the ground

state, then c is simply related to the number of atoms in

the ground state N . If energy levels above the ground

state are involved in the absorption of energy, then the

number of atoms in the excited state, i, is given by the

Boltzman expression

74
g -E AT

N. = N — e

x 1 o g&o The Lambert-Beer law can be rewritten in the following form

2 N -E./kT

A = 0.43^3 IL^- — g. f.. e

± mc g

Q

&i ji

or simplified to

N -E./kT

A = K -2. g. f .. e

1

gQ

1 Ji

-E. ,kT 1/

For ground state resonance lines, the expression e would be equal to one. Therefore, the absorbance, A, is

proportional to the statistical weight factor, g, and the

oscillator strength, f.

Table 12 gives a listing of the most useful Cr I lines

that have analytical applications in atomic absorption.

The most sensitive line using a fuel rich air—acetylene

o flame is 3578.7 A. A typical example of the usefulness of

this information can be noted from the data shown in

figure 41. From a calibration curve of to 5 vg/ml of

chromium, a linear relationship is obtained with a maximum

Table 12. Relative sensitivity of Cr I lines in atomic

absorption

(Oxidant-fuel: N o - C H (fuel rich))

o 2 2

Xi 2

Wavelength, A gf

3578.7 1.6

3593.5 1.4

3605.3 1.0

4254.4 0.54

4274.8 .41

4289.7 .26

3615.6 .0069

2364.7 .033

Sensitivity

yg/ml/jK abs

22

29

• 35

.55

.77

1 .1

20

45

75
Ill 2 05

<o

E

tfl m

<

4

(A)

Cr.ji/g/ml

(B)

5 Curve (B) 50 Curve (A)

Figure 4l. Calibration curves for the chromium line at

3579 A.

absorbance of 0.1. By working with concentrations of to

50 u g/ml of chromium, the curve is extended to 0.9 absorbance

units. These absorbance values can be extended to higher

values by using scale expansion. On the other hand, if one

desired to work with concentrations of to 500 yg/ml of

chromium, the length of the optical path of the flame cell

would have to be reduced or a less sensitive chromium line

could be selected. The choice of line would depend upon the

concentration of chromium. Table 12 could aid the analyst in

the selection of the appropriate line. Typical calibration

o curves are shown in figure k2 for the chromium line at 4290 A.

However, the published gf values are known to be in error,

o especially for those lines below 2500 A. A program has been

initiated to evaluate the sensitivity of all neutral lines

for 50 elements. These data will then be correlated with the

best gf values.

76
' (A)

03)

50 Curve (B) 500 Curve (A) Cr.^g/n

Figure 42. Calibration curves for the chromium line at

4290 A.

G . Selection of Non—absorbing Line in Atomic Absorption

(T. C. Rains and T. A. Rush)

The application of atomic absorption spectrometry to

trace analysis for many elements offers a high degree of

precision and a solution of the sample can be aspirated

directly without prior separation. However, errors may

result from scattering of light from the solid particles

within the flame or from molecular absorption when

aspirating the sample with a high solid content. To correct

for this type of interference, a non-absorbing line must be

selected and the absorption signal produced by the sample

measured. The absorbance obtained at the non-absorbing line

is substracted from the value obtained at the analytical

o line. The non-absorbing line should be within 100 A of the

analytical line and in some applications the measurement

should be made within a few angstroms of the analytical line

77
The non-absorbing line can be selected in various ways.

With a continuous source, the measurement is made just off

the peak of the analytical line. To obtain a non-absorbing

line from within the analyte source (hollow-cathode lamp)

a scan is made of the spectrum that is produced by the hollow

cathode lamp. A typical example is iron, figure 43. The

o iron spectrum shows the resonance line at 2483 A and two

o strong lines at 2488 and 2491 A. The latter lines are not

ground state lines and show no absorbance at concentrations

of up to 5000 u g/ml of iron. Therefore, either line can be

used to correct for scattering of light or molecular

o absorption of extraneous ions on iron at 2483 A. The analyst

should always check the selected non-absorbing line with a relatively high concentration of the analyte to verify

that absorption of the analyte will not occur at that

wavelength. By scanning the spectrum of each hollow—cathode

lamp and identifying all emission lines, a wavelength can be

selected to correct for light scatter. If no non-absorbing

Figure 43. Spectrum of iron over the wavelength region of

2460 A to 2505 A.

* - Ground state resonance line.

78
o line is observed within 100 A of the analytical line, a line

from some other light source (hollow-cathode lamp) can be used

The observed height within the flame cell and the slit width,

however, must not be changed. Some typical spectral lines,

that have been successful in correcting light scattering,

are given in table 13-

Table 13» Selection of non-absorbing line to correct for

scattering of light or molecular absorption

o o Analyte Wavelength, A Non-absorbing line A

Ag 3281 Ne - 3369

As 1937 Ne - 1930

1972 As - 1990

Ba 5536 Mo - 5533

Mg 2852 Ga - 2874

Pb 2170 Re - 2214

2833 Ga - 2874

Se 1961 As - 1990

Zn 2139 Re - 2214

H. Phototubes (T. C. Rains)

In a continuing effort to improve our instrumentation

for flame emission and atomic absorption spectrometry, two

new multiplier phototubes were evaluated. A new S-20 trialkali phototube (Centronics 4283) having a spectral response

o of 2000 to 8500 A was tested. The tube has a relative low

dark current which permits the operation of the tube at

voltages up to 1500 V. With the low dark current and high

voltage, an improvement in signal-to-noise ratio was obtained

for all elements tested by flame emission spectrometry.

For applications In atomic absorption spectrometry, a

cesium-tellurium solar-blind phototube (R-166) was tested.

With a relatively high resolving monochromator , this phototube offered no advantages over a phototube with a S-5

response; however, in applications of atomic fluorescence

79
where no monochromator is used, the phototube gives an

improvement in detection limits for those elements which have

o resonance lines between 2000 and 3000 A [34].

I. Shield for Burner (T. C. Rains)

The nitrous oxide—acetylene flame with a temperature of

2955°C is being extensively used in flame emission and

atomic absorption spectrometry to increase the atom

population for many of the refractory elements and to

minimize condensed phase type of interferences. This flame

requires a special type of burner head to prevent a flash

back and is 18 to 24" in height in its normal mode of

operation. Therefore, excessive thermal radiation is produced

which may have an adverse effect on the monochromator as well

as the operator. To minimize this effect, a heavy shield was

designed to fit the burner head. The shield eliminates drift

of the wavelength due to changes in ambient temperature in

the monochromator and protects the operator.

J. Oxidant—Fuel Mixtures Regulation (T. C. Rains)

The higher temperature and lower burning velocity of

the nitrous oxide—acetylene flame eliminates most of the

condensed phase interference encountered with the alkaline

earth metals. The major disadvantage of the nitrous oxideacetylene flame is the loss of sensitivity due to ionization

of easily excited atoms. To overcome this loss, a gas flow

system was constructed and is shown in figure 44. With this

system, air and nitrous oxide are mixed to provide a temperature range of 2300°C for the air—acetylene to 2955°C

for the nitrous oxide—acetylene flame. In the determination

of calcium, magnesium and strontium, a mixture of nitrous

oxide and air (80-20) -acetylene under fuel rich conditions

eliminates most of the condensed phase type of interferences

without loss of sensitivity due to ionization.

80
2 - Stage Regulator To Burnei

TfOI Air Cylinder

To Burner

Figure 44. Schematics of oxidant-fuel mixtures regulation

K . Analytical Application to Standard Reference Materials

(T. C. Rains and T. A. Rush)

1 . Determination of Potassium, Rubidium and Strontium

in Simulated Lunar Glass

The simulated lunar glasses consist of the base material

which is 72 percent SiO

?

, 14 percent Na

? 0, 12 percent CaO and

2 percent A1„0^ and four lots containing 61 elements at the

0.02, 1, 50 and 500 ppm level. The determination of potassium,

rubidium and strontium in such a complex matrix became a challenge to the flame photometrist . The first major problem

encountered was the dissolution of the sample without

contamination. The sample (wafer) was rinsed with ethanol,

water and dilute HNO^ to remove surface contamination. The

weighed wafer was then transferred to a platinum dish and

ultra pure HF and HC1CK were added. After standing overnight, the sample was heated to strong fumes of perchlorate

to complete the dissolution.

Potassium, rubidium and strontium were determined by

flame emission spectrometry using the repetitive optical

81
scanner In the derivative mode [35]- The high continuous

background produced by the complex matrices, especially at

the 50 and 500 ppm levels, prohibits the use of the normal

flame emission mode. However, by the technique of repetitive

optical scanning the interferences due to broad bands and

continuum are removed. Potassium and rubidium were

determined in an oxygens-hydrogen flame while the strontium

was determined in nitrous oxide and air (80-20) -acetylene

flame mixture.

The rubidium in the base material and at the 0.02 level,

was extracted with sodium tetraphenylboron (NaTPB) in a mixture of methylisobutyl ketone (MIBK) and cyclohexane

(3:1) [36]. The addition of the cyclohexane prevents the

formation of an emulsion during the equilibration without

affecting the distribution coefficient. The rubidium

is determined in the organic phase with appropriate standards

prepared with NaTPB in MIBK and cyclohexane. A summary of

the results is presented in table 14.

As a check of the accuracy of this method, the values

for potassium, rubidium and strontium at the 0.02, 1 and

50 ppm level were compared with the technique of isotope

Table 14. Summary of values for simul ated lunar glass.

Ele- Repli - Cone . , Std. Rel. std.

Sample ment Sample cates yg/g dev. dev., %

Base K 8 6 36.9 0.92 2.5

Material

Rb 8 2 <.3 - - Sr 8 2 39.1 .66 1.7

0.02 ppm K 7 2 29.1 • 55 1.9

Rb 7 2 <..3 - - Sr 7 2 43.1 .63 1.5

1 K 8 2 29.9 • 32 1.1

Rb 8 2 0.82 .03 3.7

Sr 8 2 47.2 • 65 1.4

50 K 6 2 64.5 .83 1.3

Rb 6 4 33-2 .41 1.2

Sr 6 4 80.8 .70 0.86

82
Table 15. Comparison of flame emission and isotope

dilution-mass spectrometry values in simulated

lunar glass.

Values reported yg/g

Samp

0.02

le Element Flame emission Mass spec . Difference

ppm K 29 .1 29 2 -0 1

Rb .3 0. 10 + .2

Sr 43 .1 43 2 - .1

1 K 29 .9 29 .7 + .2

Rb 0.132 .855 - .035

Si 47 .2 46 .1 + 1 .1

50 K 64 • 5 63 .4 +1 .1

Rb 33 .2 31 .4 + 1 .8

Si 80 .8 78 .6 + 2 .2

dilution-mass spectrometry reported by the Mass Spectrometry

Section. As shown in table 15, there is good agreement

between the two methods for these three compositions.

2 . Determination of Aluminum by Flame Emission

Spectrometry in an Iron Matrix

The determination of aluminum by flame emission

spectrometry in an iron matrix has been described previously

[37]. However, with an oxygen—hydrogen or oxygen—acetylene

flame, the resonance lines of aluminum have very low

sensitivity and suffer from many spectral interferences. To

overcome these interferences and increase the sensitivity,

aluminum was extracted by early workers into an organic

solvent which increased the sensitivity to 0.5 ug of

aluminum per ml

Slavin [38] has reported a detection limit of 0.1 yg/ml

for aluminum by atomic absorption with a nitrous oxideacetylene flame. By flame emission spectrometry using a fuel—rich nitrous oxide—acetylene flame, the sensitivity of

aluminum in aqueous media was 0.1 yg/ml. The strong C

?

, CH and CN bands, however, made the analysis difficult by the

normal flame emission mode. With the repetitive optical

83
scan [35], the interferences from the C„, CH, and CN bands were

eliminated and the sensitivity of aluminum was increased to

0.01 y g/ml

.

A comparison of the precision of the two methods

(emission vs absorption) was made using a ferrosilicon sample

(NBS-SRM-59a) . To correct for any matrix effect due to the

iron, aluminum standards were prepared to contain the same

iron concentration as the samples. The iron used in the

preparation of the standards was high purity Mossbauer iron.

The values obtained by absorption and emission on four

replicates of five samples were 0.350 and 0.3^2 with

standard deviation of .006 and .001 respectively. The

improved precision by flame emission with the optical scan

led to the use of this method for the determination of

aluminum in several types of ferrous alloys.

Table 16 gives a summary of analyses by flame emission

and atomic absorption spectrometry for the past year.

L. Service Analyses (T. C. Rains and T. A. Rush)

A large variety of samples submitted by other Divisions

of the Bureau, as well as other Government agencies, were

determined for various elements. These included sea water,

high—purity barium metal, cell residue from an electrolytic

process, ferrous filings, high—purity potassium chloride,

zeolite, resin beads, calcium fluoride, and "polymer" water.

Lithium was determined in a series of sea water samples

for the Naval Ordnance Laboratory by flame emission using

the optical scan. The lithium concentration varied from

0.166 u g/ml for the unexposed sea water to 0.250 u g/ml for

the sample in the test site. The relative standard deviation

of the method was 1 percent.

As a service to a Division within the Bureau, sodium

was determined in "polymer" water. The major difficulty

is the analysis of a sample of less than 10 ul and the

elimination of sodium contamination. To overcome these

84
Table 16. Summary of NBS-SRM analyses by flame emission and

atomic absorption spectrometry.

NBS-SRM

125b High silicon

steel

1208

113^

1140

1141

1142

High Temp,

alloy

Element

59a Ferrosilicon Al'

Ca!

Cu

Al :

Cac

High silicon Al

steel

Ductile iron Alc Ductile iron Alc Ductile iron Al c

1263 Spec, steel Mgo Ca*

Ag"

Zn

t 1264 Spec, steel Ng a Ca^

Agf

Zn

I d-glucose Mg,

Ca

c

No. of

detms Cone . . %

20

48

38

0.342

.0393

.0519

.328

00136

332

Std.

dev

. UUJ.

.0011

.0007

.0020

.00016

.0036

Rel. std

dev. 3 %

0.3

3.0

1.4

0.6

1.1

13 .0081 .00036 4.0

8 .0054 .00043 8.0

3 .0848

u g/g

.0008 1.0

4

2

2

6

5.3+0.5

3 +1

30 +1

13 +2

4

4

3

4

8.3+0.2

3. +1

65 +2

33 +0.7

2

2

<0.5

1 +0.5

Flame emission spectrometry

'Atomic absorption spectrometry

problems small plastic tubes were mounted in plastic support

caps and cleaned. The tubes were individually tested and

placed in a desiccator. After the addition of 25 u 1 of ultra

pure water to each tube, 2 to 5 pi of the sample of polymer

water was added. The total sodium content was then

determined by flame emission using the repetitive optical

scan.

85
Magnesium, calcium and strontium were determined in a sample of barium metal. The protective oil coating was

removed and the metal dissolved in dilute acid. The calcium

and strontium were determined by flame emission using the

optical scan in an oxygen—hydrogen flame and found to be

0.06 and 0.68 percent, respectively. The concentration of

magnesium was determined by atomic absorption and was

0.0045 percent. By these methods barium did not interfere

in the determination of magnesium, calcium, or strontium.

A number of the other analyses performed included

rubidium in a cell residue, nickel, manganese, and

chromium in ferrous filings, sodium and rubidium in

zeolite, calcium and magnesium in cell buffer solutions,

trace as well as the major components in laser glass.

86

HMHBHMIMi
4 . ANALYTICAL COORDINATION CHEMISTRY

The various programs of the Section (ACCS) in both

instrumental and classical analytical methods are interrelated with problems of solution complexation and

coordination chemistry. This portion of the report represents

some of the background work reported in the other competences.

In evaluating spectrophotometric methods for the characterization of bilirubin, an investigation of its complexation

with metal ions was undertaken. Similarly the spectrophotometric method for the determination of vanadium [39] led to

the evaluation of the equilibrium constants and the kinetics

of the extraction of vanadium and iron with 3-isopropyltropolone

A. Bilirubin Complexation (R. A. Velapoldi)

In Clinical Chemistry, the analysis of bilirubin (BR),

although not definitive in itself, aids greatly in determining

the various causes of jaundice. In cases of severe jaundice

of the newborn, however, the analysis plays a major role in

establishing the necessity for total blood transfusion.

Thus research in the analytical procedures and the characterization and development of standards for BR has been extremely

important in past years [40].

One of the major analytical problems has been the

preparation of stable standard solutions for calibrating

spectrophotometric measurements . Bilirubin is unstable in

solution with reported rates of degradation varying from

1 percent per day in chloroform to 40 percent per day in

basic solution.

Bilirubin is produced by the metabolic breakdown of

hemoglobin [41]. It is a linear tetrapyrrole consisting of

two conjugated dipyrrole segments joined by a methylene

bridge. Several tautomeric forms exist; two of which are

the bis-lactam (I) and bis-lactim (II) structures [42].

Recent reports [43] suggest the existence of a hydrogen bound

mono-lactim structure (III) which contains a nucleophilic

87
I. bis-Lactam

M = -CH 3

V = -CH=CH

P = -CH2 -CH2 -C00H

II. bis-Lactim

III. mono-Lactam - mono-Lactim

Hydrogen Bound Bilirubin

88
nitrogen and circular structure, both conducive to metal

complex formation analogous to the porphyrin moiety. In

addition, two brief papers [44] report the formation of a relatively stable zinc-bilirubin complex in ethanolic

solution. With this information, a program was initiated to

extend the study of metal-BR complex formations and to

determine the feasibility of stabilizing bilirubin solutions

by complexation with metals.

1Solvent Studies

Bilirubin (e = 60,100 ± 800 liters cm

- mole" ) was

dissolved in various solvents (chloroform; absolute

ethanol: chloroform, 1:1; methanol: chloroform, 1:1;

tetrahydrofuran; and dimethylsulfoxide ) . Ascorbic acid was

also added to some solutions to determine its effect as an

oxidation inhibitor. An inert atmosphere of nitrogen,

further dried and purified by passage through a sodiumpotassium alloy, was used in conjunction with a nitrogen

manifold and specially constructed Schlenk-type

spectrophotometric cells to insure air exclusion in

specified solutions. Solvents used in these cases were

distilled under nitrogen and were considered to be air

and oxygen free. The best solvent system found for

stability and complex formation was the 1:1 v/v ethanol:

chloroform (see Stability Section).

2Metal Complex Formation

Metal acetates, chlorides, or sulfates were dissolved

in ethanol, added to BR solutions and spectral changes

were observed with time. The following is an example of the

method used: 0.05 cc of 2.42 x 10 _3M samarium(III) acetate in

ethanol was added to and mixed with 1.3 cc of a 4.6 x —6

10 M BR solution in ethanol: chloroform resulting in a

4:1 molar ratio of Sm(III) to BR. Spectra were recorded

at 25.0°C versus elapsed time on a recording spectrophotometer equipped with constant temperature cell

blocks. A typical series of spectra obtained after

89
Figure 45-

LU / \

( 1 V / ^ X 9 \

Ss£ \ \

<

CD

oroCO

GO<

; /

/ //

/// - if/ fi if //

/////

-... Vs\

1. BILIRUBIN *-.\ ^

' / / 2. +Sm(IE) AFTER 5 min V. \

3. AFTER 45 min \\ \

4. " 90 min \ • \

5. " 1005 min (EQUIL.VALUE) \JVk

1 1 1 400 450

X. NANOMETERS

500

Addition of Samarium(III ) to bilirubin solution

results in blue spectral shift

.

given elapsed times is presented in figure 45- Spectral

shifts obtained by addition of various metal ions to BR

are summarized in table 17-

Table 17. Metal ion addition to BR solutions

results in various spectral shifts.

Wavelength, nm

Metal " Peak 1 Stability- Peak 2

Zn(II) 476 No

Cu(II) 420 No 352

Co(II) 423, 470(B) No

Ni(II) 476 No

Fe(II) 424 No 463

Fe(III) 450(B) No

Sm(III) 395 Yes

Nd(III) 391 Intermediate

La(III) 425(B) No

Ca(II) 464, 495(S)

Na(I) no shift

[M]/[BR] = 4, (B) = broad, (S) = shoulder.

90

Stability

No

Yes
As can be seen, the addition of two metals, Fe(II)

and Sm(III), resulted in stable complex formation.

Spectral shifts were both hypsochromic (violet shift) a and

bathochromic (red shift) suggesting complex formation and

not simply salt formation or interaction with the

propionic acid functional groups. After reaching

equilibrium values the addition of strong coordinating

ligands (ethylenediaminetetraacetic acid or 1 ,2-diaminocyclohexanetetraacetic acid) to the Sm(III)- and Fe(II)-BR

complexes resulted in a shift back to the free BR spectrum

(454 nm), proving metal complexation with BR and not

metal complexation with oxidized BR (which yields

biliverdin, known to form metal complexes) [42, 43].

The addition of Fe(II) to BR results first in a rapid hypsochromic shift followed by a slower bathochromic shift. The addition of a reducing agent, such as

sodium dithionite to the iron complex absorbing at

463 nm results in a hypsochromic shift to approximately

430 nm. This produced shift, observed in similar ironporphyrin systems [45], is indicative of Fe(III)

reduction to Fe(II). A proposed reaction scheme follows

for the iron-BR system:

(rapid) (slow)

BR + Fe(II) ^ ^Fe(II)-BR^—^Fe(III)-BR

(454 nm) EDTA (424 nm) sodium (463 nm)

dithionite

The presence of an isosbestic point observed in the

spectra during the oxidation step suggests the presence

of Fe(II) and Fe(III)-BR complexes only. By using a

curve resolver to separate Fe(II) and Fe(III) spectra and

thus relative concentrations, plots of relative concentration versus time were obtained giving straight lines

indicating second order kinetics for the oxidation

step

91
The most stable lanthanide complex is formed with

Sm(III). Neodymium(III ) addition results in complex

formation (hypsochromic shift to 391 nm). It is approximately ten times less stable than the Sm(III) complex.

Lanthanum (II I) addition does not result in a complex

formation. Stability results may be attributed to increased covalency in Sm(III) (larger charge to size ratio).

Addition of metals, such as Cu(II), Ni(II) or Co(II),

causes rapid BR oxidation. These ions have strong tendencies

to form square planar complexes and in this case introduce a strain at the BR methylene bridge [46], which contributes to

the rapid oxidation as observed by Fog [47].

3- Metal Concentration Effect

The effect of changing the concentration of metal ions

with respect to BR concentration is summarized In table 18.

The best molar ratio for complex formation was determined

to be 4:1, metal:BR. Less than this ratio, as in Cu(II) or

Co (II), results in incomplete complex formation, although

disappearance of the BR absorbance peak occurs slowly.

Table l8» Effect of metal ion concentration on complex

formation.

Metal [M]/[BR] Peak 1

(nm)

Zn(II) 100

4

492

476

Pe(II) 4

1

424

445(B)

Co(II) 10

4

1

420, 475(B)

422, 471(B)

425, 468(B)

Cu(II) 100

4

1

0.1

418

421

425

no observable shift

Sm(III) 10

4

395

39S

(B) = broad, solvent =1:1 Ethanol : Chloroform

92
4 . Stability Studies

Data obtained from the investigation of the stabilities of BR under various experimental conditions is

summarized in table 19. From these data it is evident

that a 1:1 methanol: chloroform mixture is not a good

solvent for BR. On the other hand a 1:1 chloroform:

ethanol solvent system showed extremely low percent

degradation in air or under N--0.051 percent per day

versus 1 percent per day in chloroform. However, BR is

not very soluble (^5mg/100 ml) in this system

and this factor is a drawback. It is not necessary to

maintain solutions under nitrogen as the percent

degradations for solutions 3 and 4 of table 19 were

Table 19. Stability studies of BR solutions under various

experimental conditions.

Length

of Test

Percent

Degradation

No. Solvent Additions

in air

days

5

per day

(1) MeOH:CHCl k particulate

matter present

in both tests .

<-2.) Me0H:CHCl^ Ascorbic Acid 40 0.625

(3) ET0H:CHC1^ in air 40 .051

(4) ET0H:CHC1^ under N~ 63 .053

(5) ETOHtCHCl^ Ascorbic Acid 40 .086

(6) ETOHiCHCl^ + Sm(III) 63 .045

(7) ETQH:CHC1^ + Nd(III) 56 .495

(8) ET0H:CHC1

3 + Fe(II) 60 .051

(9) Solution(4) in refrigerator ^4 °C

46 .013

(10) Solution(4) at room temp.

^25 °C in dark

10 .301

(11) Solution(4) at room temp. 4 24„73

^25 °C in light

f"As measured by absorbance decrease

1:1 volume /volume

93
approximately the same. The lower percent degradation per

day for the Sm(III)-BR complex (0.045 vs 0.051 percent

for Et0H:CHCl~ alone) is probably not significant. On

the other hand, the Nd(III)-BR complex degrades approximately eleven times as rapidly; exemplifying differences

in the lanthanide-BR complexes stabilities.

A short study was made to determine the effect of

temperature and light on BR in solution. This study

was made using solutions 4, 9, 10 and 11 of table 19.

Solution 4 was kept in the dark and under refrigeration

for the entire test period and showed lowest percent

degradation, 0.013 percent per day . Solution 9 was kept

in the dark and under refrigeration, but was warmed to

25°C and spectra were taken every two or three days

.

This solution showed 0.051 percent degradation per day.

Solution 10 was kept in the dark at room temperature (24-

25°C) and showed the next highest degradation, 0.301

percent per day. Solution 11 was kept at room temperature

and in light and showed an average percent degradation

of 24.73 percent per day - definite evidence that

increased temperature and especially light increase the

rate of BR disappearance.

Figure 46 presents spectra of solution 11 over the

4 day test. The final spectrum with peaks at 377 nm,

700 nm and a shoulder at 665 nm is undoubtedly due to

biliverdin [48].

Resolution of individual curves and plotting the area

(relative concentrations) versus time results in

figure 47. This is a typical zero order plot suggesting

a reaction sequence similar to the following:

CHCl^ + hv^-CHCl

2 + • CI

'CHC1

2 + BR+-BR + CH

2

C1

2

BR + -C1+HC1 + BVD

94
Figure 46.

1 ' 1 /-; 1 1 ' 1 >

BILIRUBIN AFTER 1 DAY AFTER 2 DAYS A AFTER 3 DAYS ft

In

1 '"*. 1 AFTER 4.4 DAYS

hi / / \ 1 (EQUILIBRIUM) U

z // v 1 <

CD II! ]

'/ i 1

' 1 a.o

CO

CD in n

lii

\\ -, \ <

v\ "

\

** / /

\ \ \ /A

\ \\4

\ A .« ,--- \ *\

1 1

.<.**-f>' N% i i i i i,i, 300 400 500 600 WAVELENGTH, nm

700 800

Spectra depicting photodecomposition of

bilirubin to biliverdinoid pigment

BILIVERDIN

SLOPE: + 0.0453.

INT.: -0.157

BILIRUBIN SLOPE: -0.0453-

INT.: +4.376

20 40 60 80 100 % AREA UNDER CURVE ,( RELATIVE CONCENTRATION)

Figure 47. Formation of biliverdinoid pigment and

disappearance of bilirubin during photodecomposition - relative concentrations as determined

by curve resolver.

The same slopes for the disappearance of BR and BVD

appear in figure 47 and the isosbestic point in figure 46

proves there are only two absorbing species in this

reaction, BR and BVD.

95
Absorbance Std. dev

.

Rel. s td . dev

.

ME JGN ME JGN ME JGN

0.056 0.035 0.005 0.004 9.45 11.87

.203 .132 .006 .003 3.12 2.32

.434 .238 .018 .007 4.08 2.86

.715 .515 .010 .005 1.38 0.979

5 . Bilirubin Determinations

Quantitative BR analyses are performed usually by a diazotization reaction. The Malloy-Evelyn (ME) [49] and

the Jendrassik-Grof-Nosslin (JGN) [50] methods were used

for the determination of BR. Table 20 summarizes data

obtained for both methods. The JGN method gives a better

Table 20. Quantitative bilirubin analyses by diazotization.

Concentration

mg/100 ml

1

5

10

20

straight line calibration (no typical break in line at

high concentrations) than the ME method, figure 48.

However, the absorbance values are lower. Also plotted

on figure 48 are the results of ME diazotization on the SmBR complex. The absorption peak in this case is shifted

to 567 nm as opposed to 545 nm for usual diazotization.

The interesting fact, however, is that increased absorbance

readings are obtained indicating a higher molar absorptivity for the Sm-diazotized BR than the diazotized BR

alone. The previously mentioned solubility problem coupled

with the extra analytical step (addition of Sm(III) and

equilibration) are deterrents to further developmental

work on this system; however, metal addition after diazotization may be useful

.

To increase solubility, the polar solvents dimethylsulfoxide, tetrahydrofuran and potassium cyanide in

dimethylformamide were used. However, no metal-BR complexes

formed, probably due to 'stronger' solvation of the metal

ions . 96
1.0

0.8

I 0.6

0.4

0.2

i A MALLOY1

- EVELYN METHOD O MALLOY - EVELYN METHOD

D JENORASSIK -GROF MODIFIED METHOD

Sm(ffl)- BILIRUBIN COMPLEX -

/

/ y BILIRUBIN ONLY

/

/

/ ^BILIRUBIN ONLY

/ -

a' -

/

/ > — /^/x

1 1 10 20 MILLIGRAMS BILIRUBIN / 100 mL

30

Figure 48 . Standard calibration curves for diazotization

reactions of bilirubin and Sm( III) -bilirubin

complex.

6 . Extraction

Attempts were made to extract a chloroform solution

of BR by various concentrations of perchloric acid

solutions of Fe(II), Zn(II) and Sm(III); however, no

extraction occurred.

7 . Complex Preparation

Several attempts were made to prepare and isolate for

characterization the solid metal-BR complexes by: (a)

addition of a hot solution of metal acetate in glacial

acetic acid to a refluxing solution of BR in chloroform,

followed by refluxing for varous times [51]; (b) use of

tetrahydrofuran as solvent and proceed as in (a) under

anhydrous conditions in an inert atmosphere; (c) reflux

50 mg BR and 200 mg metal acetate with and without sodium

acetate in 50 ml ethanol for various times [52]; and (d)

simple addition of scaled up (from spectrophotometric

studies) amounts of the metal acetate in ethanol to BR

in chloroform. All the above were unsuccessful.

97

J
8 . Summary

The stability of BR in solution was increased

substantially by use of a 1:1 ethanol: chloroform solvent

system or by metal complexation with Pe(II) or Sm(III).

Other metal ion or ascorbic acid addition and different

solvent use resulted in oxidation or degradation of the BR.

Diazotization of the Sm(III)-BR complex by the (ME) method

results in higher absorbance values than the usual BR

diazotizations ; however, decreased solubility and the

extra analytical step are deterrents to further studies

along these lines.

Metal-BR complexes do not form in more ionic solvents.

Attempts at isolation of the complexes were unsuccessful;

however, interesting chemistry is involved and successful

isolation followed by characterization would elucidate some

of the problems now associated with the chemical and

structural aspects of bile pigments.

B. Determination of Formation Constants of Iron (III) and

Vanadium(V) with S-Isopropyltropolone (0. Menis,

Bo E. McClellan and D. S Bright)

The. role of adduct formation in the chelate extraction

systems is of interest in methods used for analytical

separations. This led to the study of the ft-isopropyltropolone (HIPT) chelates of V0

?

and Fe and to the

comparison of the values of the various equilibrium

constants calculated by graphical and least square methods.

Dyrssen [53] studied the extraction characteristics of

many metals with (HIPT). Dyrssen [53] as well as Singh and

Dutt [5^] have also determined the various stability

+++

constants of Fe with HIPT using spectrophotometric

methods. Hseu [55 1 also determined spectrophotometrically

the pK of HIPT at several ionic strengths. Recently,

a

+ Menis and Iyer [39] studied the extraction of V0

?

with

HIPT for the separation and determination of vanadium in

98
steel sampleso The current investigation led to the

establishment of the several extraction equilibrium constants

of the adduct complex of VOp IPT.HIPT and new values for

the Fe(IPT)_ complex.

Equilibrium constants of ferric and vanadyl ions for

the formation of the chelate with 3-isopropyltropolone

(HIPT) were determined by the extraction method. The

values for these constants were derived by graphical and

least squares computer calculations. The constants for the

vanadyl system are reported for the first time. It is

postulated that an adduct V0

2

IPT:HIPT is formed and Its

formation constant, log 3^ = K, K

T , was determined as 13.8

and 13.6 (standard error of 0.8) by graphical and least

square calculations, respectively. The partition constant,

KDr,, was 2.5 and 2.6 + 0.4 respectively. The values for the

Fe(IPT).-, complex were for log 3 N

, 37-7 and 37.8 + 0.1,

respectively, while the log K

nr, was 2 and 2.0 + 0.1,

respectively. It was also possible to calculate the overall

stepwise constants, log 3-, = 13.0 + 0.2 and by 3

p = 24.8 + 0.1 by the least squares method, the uncertainties indicated

are standard errors of the computed values. The other

experimental parameters studied were the effect of solvent

and ionic strength.

Details of this study are presented in a manuscript

submitted for publication in Analytical Chemistry [56].

C . Kinetics and Mechanism of Extraction of Iron(III) with

3-1 sopropyltropo lone

Honaker and Freiser [57] and McClellan and Freiser [58]

pointed out that, in favorable cases, solvent extraction

can be used to study the rates of rapid chelation reactions.

Many workers [53, 54, 59] have studied the extraction

characteristics of metal ions with 3-isopropyltropolone

(HIPT)

Dyrssen [53] indicated that the extraction of Fe(III)

with HIPT occurs very slowly from acid solution, and

99
postulated that some step in the formation of the extractable

complex, Fe(IPTK, is slow. The purpose of this study- was

to apply the extraction technique for studying the kinetics

of reaction to the Fe(III)-HIPT system. It was hoped that

an analysis of the kinetic data would lead to the

elucidation of the mechanism and rate determining step in

the extraction process. Iyer and Menis [39] found VOp to

extract relatively rapidly (2 hours) into CHC1- compared to

the slow ( 1 — A days) extraction for Fe(III) reported by

Dyrssen [531- Both of these metals extract from acid (1M)

solution. Hopefully, a detailed study of the kinetics of

extraction of the system would lead to a method for the

separation of Fe(III) and V0„ based on the large difference

in the extraction rates.

The kinetics and mechanism of the reaction between

Fe(III) and $-isopropyltropolone (HIPT) were studied by

the extraction technique. The reaction was found to be

first order in Fe(III) and in HIPT, indicating the addition

of the first ligand to the Fe(III) to be the ratecontrolling step in the reaction. A first-order dependence

on NaClOj, was observed. No dependence on [H ] was observed

in the rate under the acid (1M) conditions of the extraction.

The rate constant for the reaction was 1.5 x 10 M~ . Addition of ethanol prior to extraction greatly enhances

the reaction rate.

The full description of this study will be found in

the manuscript submitted for publication in Analytical

Chemistry [60],

100
5. GASES IN METALS

The importance of the interstitial elements, oxygen

and nitrogen, insofar as their deleterious effects on

the mechanical and physical properties of metals and

alloys has been discussed in Technical Note 504 [39].

The problem of analysis for these elements in metals has,

from 1925 [6l] until the present, been a continuing

interest of the National Bureau of Standards . The

current problems of analysis were Investigated by using

several approaches which will be discussed in the following

sections of this report.

A. The Inert-gas Fusion Apparatus for the Simultaneous

Determination of Oxygen and Nitrogen in Metals (J. T. Sterling)

It was shown in the past, that complete recovery of

nitrogen in ferrous metals is possible provided the proper

operating conditions are available. The conditions

necessary for this complete recovery are a high operating

furnace temperature (2000 °C) and the use for each analysis

of a new or emptied reaction crucible.

The apparatus, as designed originally for these

determinations, consisted of a small graphite crucible

supported on a graphite pedestal whose cross section has

been greatly reduced to minimize the heat loss due to

conduction from the heated reaction crucible. Using this

crucible arrangement it was demonstrated that nitrogen

values for ferrous material agreed with those obtained by

chemical solution methods [39].

The apparatus arrangement was selected to test a set of

conditions and procedures and quantitatively extract the

gases with a minimum of time and effort. Figure 49 is a schematic drawing of the apparatus that was constructed and

used initially in this work. The glass interjoint was sealed

with wax and during each determination this seal was melted.

Therefore, changing the crucible between each analysis

involved considerable work and time. Not only is this

101
BALL JOINT

WAXED J JOINT

GRAPHITE FELT INSULATION

GRAPHITE CRUCIBLE S PEDESTAL

QUARTZ FURNACE CHAMBER

BORON NITRIDE SUPPORT ROD

WAXED I JOINT

Figure 49. Crucible arrangement for inductive heating

procedure time consuming, but it also allowed atmospheric

gases to diffuse into the furnace section, thus increasing

the apparatus blank and adding to the difficulties of

outgassing of the furnace section. The furnace section of

the apparatus was redesigned with the following modifications;

see also figure 49.

(1) The diameter of the quartz reaction section of the

furnace chamber was enlarged to provide room for additional

insulation between the hot crucible and the water cooled

furnace wall.

(2) A thin wall (0.003" thick) split radiation shield was

installed between the crucible and the insulating material.

102
(3) The top of the reaction tube was simplified by

eliminating standard taper adapter and relying on a single

ball joint.

(4) A metal adapter between the furnace tube and

the sample addition tube was designed and an O-ring groove

was incorporated to eliminate any source of leakage.

(5) The closure for the bottom of the furnace

section was newly designed and constructed of AISI 431

stainless steel. An air motor was adapted to close

the bottom automatically when the electrical circuit was

actuated. It was experimentally established that the

removal and replacement of the reaction crucible with a sample can now be accomplished in less than 12 seconds.

(6) It is also planned to install several solenoid

operated gas valves to reverse the gas flow in the furnace

section. This would essentially eliminate that part of

the blank due to gases absorbed from the atmosphere on the

surface of the furnace reaction zone.

B. Evaluation of a Special Ingot Iron for Use as a Standard Reference Material for Oxygen Content (J. T. Sterling)

This special iron (NBS 1099) is the first of a series of five ferrous materials which will be investigated for use as a standard for oxygen in metal . This

material is unique in that it is part of a larger program

in which a single heat of metal will be processed to form

the following:

(a) Rods 1-1/4 inches in diameter for use as optical

emission and X-ray spectrometric standards.

(b) Rods 1/8 inch in diameter for application in

electron microprobe analysis and spark source mass

spectrometric analysis.

(c) Chip material for wet analytical analysis.

(d) Rods 1/4 inch in diameter for gases in metals.

It then will serve as a single source of standards covering

the analytical methods of interest.

103
The material under (d) for gas analysis has been

designated as SRM 1099-

Preliminary testing of this material has begun with

the results shown in table 21. From a study of this table

it is noted that one of the rods (AIT) from batch A has a

significantly higher oxygen content. It was therefore

decided to analyze each bar before the lot was certified.

This work is in progress, and should be completed in two

months

.

Table 21. Study of homogeneity in SRM 1099-

Standard

Rod No - Mean a deviation

ppm ppm

A3T 62.4 1.84

C4T 66.5 2.03

C3T 65.2 2.36

C4L 63.3 2.25

A1TU 131.4 19.68

C2L 66.8 0.91

A7T 59.0 1.45

A3T 61.4 1.61

Relative

standard

deviation

< I

2 .94

3 .05

3 .62

3 • 55

14 .97

1 .36

2 .46

2 .62

.Average of 3 determination.

One of a series of rods which has a higher oxygen content.

104
6. THERMAL ANALYTICAL METHODS

A

Introduction

The need for materials that are suitable for use as

temperature standards in differential thermal analysis

methods has been discussed in earlier editions of the

NBS Technical Notes 45^ [17] and 50^ [39] and the need for

these standards continues

The exigency for these standards has been shown

by the attention paid to this problem in recent years

by the Committee on Standardization of the International

Confederation for Thermal Analysis. Currently the newly

formed Subcommittee on Thermoanalytical Test Methods in

Committee E-l of the American Society for Testing and

Materials has delegated to one of its major study groups

the responsibility for the preparation and procurement of

these standards. Progress in the standards programs of both

groups as related to the participation by the National

Bureau of Standards as well as the programs of this

Section for issuing two new Standard Reference Materials

will be discussed.

BThe Second International Cooperative Program on

Standardization by the ICTA (J. T. Sterling and 0. Menis)

There have been circulated to about forty laboratories

throughout the world, nine samples of materials that

have been proposed as temperature standards for

differential thermal analysis. These nine samples included

potassium nitrate and quartz which were provided by the

National Bureau of Standards. The latter will be discussed

separately in this report.

All of the materials, except strontium carbonate, were

analyzed with instrument #1, to determine the temperatures

of the solid-*solid or solids-liquid transformation. This

equipment, with the calibrated thermocouples inserted into a capillary tube has been modified to permit the recording

of the sample temperature and the differential thermal

105
curve by means of a variable span, adjustable zero two

pen recorder as described in Technical Note 50 U

.

The strontium carbonate was analyzed using the modified

apparatus (Instrument II) which is also described in

NBS Technical Note 50^.

The conditions used in these determinations were as

follows for both instruments, except as noted:

Reference material - Alumina (A1„0^)

Weight reference material - approximately O.lg

Furnace atmosphere - Dry nitrogen

Plow rate - 500 cc min

Pressure - Atmospheric

Heating Rate - 5°C min

Sample Weight - Approximately O.lg

Sample Container - Instrument I - 4 mm dia. quartz tube

Instrument II - Platinum cup

The results of these studies in our laboratories are

presented in table 22. Results from the cooperating laboratories are not available. However, a comparison

of results obtained in this laboratory from the previous and

current ICTA tests are presented in table 23. The second

results show an overall improvement, in that large differences

have been eliminated. In part they reflect the improvement

in instrumentation. In all cases, as noted previously [39] , the differential temperature indicates positive deviation on

the heating cycle from the thermodynamic data obtained under

adiabatic conditions . This can be attributed to the rate of

heat transfer which is the controlling factor in DTA . The

value listed in NBS Circular 500 for Ag

p

SCv is quite different

from the value obtained in this study. Similar differences

have been reported by other cooperating laboratories.

106
t-- bm

O in o b- ^T

p b- LO t>- o in o b-. r-\ Ln o> CO o 1 rH o Ln =T

CO o en o rH o r-\

LPv CO Ln o O o cn o d • • • • o • • • • Q cd H OA on b- r-1 ON =r -=r i_n

CD OA VO rH co cn ^3" CM b- o S CM MO -=3" in CM H rH in OA # VD t-- F— o CO O o o t-~ p rH m t— o in O o o in o CO G\ •=? in in in o in a\ o CO o in O PN r-\ o HO O CM o CM CO CM o CO CO O d O PQ cd O r-\ t— b- t— in -=T in CO

CD OA t— o co a> in CM C~-n o S CM VO ^r in r-\ i-\ H n CT\ # O t— o- o cn o o b- >- p o LO e— o in o O in in o OA -=r in in in O cr\ OA

CO o in

O £1 rH

O o CM o CM CO CM o CO CM

d < cd o i—

o- b- b~ in J=T CO

O

(D a\ b- o co OA in CM b- r-{ s CM U3 -=r in r-{ r-\ r-\ m o\

o- C>- o o O o O CO

O

o- LO o o O o O =r

O

p

m 0\n in in in in

m

O

CO o r-\

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cd

CM

LPi CO CO CO CM CM OO -=r o d • • • • P cd H O r-\ vo in CO o in VO

CD o l>- cn CO cn in cn b- cn S on VO -=r in CM i—

H in o\ # o b- t-~- b- o o b~ CO \>- p o fr- [— r-\ o o b- -=r CM in LTA m OO o in in in in

O CO • • • • o O H

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co • • • • o CM o rH o H

cd

cn

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cu CT\ md CM CO on in CM t— CM S CM MO ^r in CM rH rH in OA

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cd ' v /•->

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CDCOcd ,Q

CD

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cd

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cq cd CD CD 0) P P -P

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t3 t^ t3

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107
Table 23. Results reported by NBS. First and second ICTADTA study.

Transition

Compound type

KNO~ s+s

KC10 i| s+s

Ag

2

SO i] s + s SiOp (quartz) s-*s

KpSO^ s-*s

KpCrO^ s+s

BaCO^ s+s

SrCO^ s->s Sn s->l

In s+1

Circ. 500 a °C

1st ICTA

"B" °C

129

2nd ICTA

"B" °C

127.7 129.5

299.5 300 300.8

412 426 427-5

573 57 574.4

583 577 586.0

665 668 668.5

810 791 - 925 905 929.3

231.9 - 233.0

157 - 157.8

aNational Bureau of Standards Circular 500. Selected values

of chemical thermodynamic properties (1952).

C. The ASTM Committee E-l Subcommittee Round Robin

on Thermal Analytical Substances (J. T. Sterling and 0. Menis)

Under the chairmanship of 0. Menis of NBS, the

Standards Section of the ASTM Committee on Thermal

Analytical Methods has conducted a round robin test on thermal

analytical substances. Samples of three materials, intended

to cover the lower temperature scale not studied by ICTA,

were sent to sixteen laboratories which had indicated an

interest in cooperating in such studies.

The results from nine laboratories cooperating in this

study are shown graphically in figures 50a, 50b, 51, 52a and

52b. The means obtained for the departure "A", the intersection "B", and the peak "D" temperatures for the various

transitions have been plotted against assigned laboratory

numbers, (NBS No. 10). The NBS Circular 500 [62] values for

the transitions occurring in these materials are given in

table 24.

108
SULFUR SOLID (I) - SOLID IT

4 5 6 7

LABORATORIES

Figure 50a. Cooperative data for ASTM committee members

(one member with two data points).

109
SULFUR MELTING POINT

2 3 3a 45678 9 10

LABORATORIES

Figure 50b. Cooperative data for ASTM committee members

(one member with two data points).

110
STEARIC ACID MELTING POINT

80.0

78.0

76.0

74.0

72.0

70.0

68.0

66.0

64.0

62.0

60.0

58.0

56.0

54.0

52.0

50.0

_ \ \

/

' \ * P o A

23 3a 456789 10 LABORATORIES

Figure 51. Cooperative data from ASTM committee members

for stearic acid melting point.

Ill
55.0

53.0

51.0

49.0

47.0

45.0

43.0

41.0

39.0

i i i i i i i r i i r

HEXACHLOROETHANE RHOMBIC -TRICLINIC

J L L J L 01 233 456789 10

LABORATORIES

78.0

76.0

74.0

72.0

70.0

68.0 I66.0

i—

r

i—

r

i r HEXACHLOROETHANE TRICLINIC -CUBIC

D

B

I I I I J I I I L 2 3 3a 456789

LABORATORIES

10

Figures 52a, 52b. Cooperative data from ASTM committee

members

.

112
Table 24

Material

Transition temperatures—ASTM round robin

materials. NBS Circular 500.

Sulfur

Sulfur

Hexachloro ethane

Hexachloroe thane

Stearic Acid

Transition

Type

C TT Rhombic-*C

T Monoclinic

C T Monoclinic-*Liquid

c iii^c ii

c n"c

i

C+Liquid

Temperature

°C

95.4

119.0

(45.1) a

71 .2

69.1

"From reference only

TRANSITION I D

TRANSITION I A - 47.8 °C

B - 48.3 °C

D - 50.7 °C

TRANSITION H /

A-72.3°C /

B-72.3°C /

D - 76.4 °C /

/

93.TC

/' D

79.9°C

- TRANSITION E — 64.7 °C

— 49.7 °C

34.0 °C

Figure 53. Thermal curve of hexachloroethane

113
A study of the results of this investigation reveals

that while some agreement between laboratories was attained,

especially when the intersection "B" is used as the measure

of transition temperature, there is still a wide disagreement between certain laboratories. Thus the need for

Standard Reference Materials is again well supported by

this latest study. Of the three compounds, hexachloroethane

,

shown in figure 53, especially because of its two transition

temperatures at approximately 48° and 72°C, would be of great

value for calibration purposes. An effort will be made to

certify it as a Standard Reference Material.

D - Standard Reference Material 755, Quartz (SiO )

(J. T. Sterling)

The preparation and certification of Standard Reference

Material 755, (Quartz) for use in checking the performance

of differential thermal analysis equipment were completed

during the last year

.

This material is a natural crystalline quartz that has

been ground, cleaned and sized to minus 100 mesh (0.149 mm)

and plus 325 mesh (0.044 mm).

This material was analyzed at NBS and at one other

laboratory

.

The following conditions were used to determine the

transition temperature of this reference standard.

Sample sizes - 3 to 300 mg

Sample container - Graphite or platinum cylindrical

crucible, or alumina cylindrical

sample block.

Heating rates - 1 to 10 degrees celsius per minute

Reference material - Alumina (AlpO_)

Atmosphere - Static dry air or nitrogen

Thermocouple - Located on the axis of the material with

the sensing element or bead at or

near the midpoint of the specimen.

114
The transition temperature obtained using the values

recorded from three instruments in two laboratories is 575°C

for the intersection point and 577°C for the peak point as

normally observed in a differential thermal analysis

curve [63]

An interesting experiment conducted in conjunction

with the testing of this material involved the use of a single large crystal of the quartz. This crystal was

from the same lot of material used for the Standard Reference

Material. A cylindrically shaped test specimen 0.125 inch

in length and 0.10 inch diameter was cut with a glass saw.

A hole large enough to contain the DTA thermocouple was cut

into the center of the quartz cylinder and along the long

axis to a depth of approximately 1/16".

The differential thermal analytical curve was run,

the transition temperatures being shown in table 25.

These data are in remarkable agreement with the

reported thermodynamic value of 573°C [64].

Table 25. DTA transition temperatures for a solid quartz

specimen.

Heating Transition Temperature, °C

Intersection (B) Peak (D)

Mean 574.1 574.1

Number of Det. 4 4

Standard Deviation 0.1 0.1

Cooling Transition Temperature, °C

Intersection (B) Peak (D)

Mean 573-1 572.9

Number of Det. 4 4

Standard Deviation 0.1 0.1

115
E . Standard Reference Material 756, Potassium Nitrate (KNO -)

The preparation and certification of Standard Reference

Material 756, (Potassium Nitrate) for use in checking the

performance of differential thermal analysis equipment were

also completed during the last year. This potassium nitrate

was a specially prepared high purity material whose mesh

size was approximately minus 50 to plus 100.

The following conditions were used to determine the

transition temperature of this reference standard:

Sample Condition - Because the first heating of this

material is not a reproducible

measure of the transition temperature,

the sample must be cycled through

the transition temperature in situ

before recording data. This

precaution holds whenever the

specimen is allowed to be at room

temperature and exposed to the atmosphere for more than one hour.

Sample sizes - 3 to 300 mg

Sample container - Graphite, quartz or platinum

cylindrical crucible or alumina

cylindrical sample block.

Heating rates - 1 to 10 degrees centigrade per minute

Reference material - Alumina (A1„0^).

Atmosphere - Static dry air or nitrogen

Thermocouple - Located on the axis of the material with

the sensing element or bead at or near

midpoint of the specimen.

The average values based on three cooperating laboratories using different equipment are as follows:

Intersection ----- 130°C

Peak 131°C

116
P. Thermal Gravimetric Analysis of Bilirubin (J. t. Sterling)

In conjunction with the certification of SRM ' s for

clinical chemistry, samples of bilirubin and mandelic acid

were analyzed by the thermal gravimetric method. The

heating rate for both materials was 50°C per minute.

Samples were run in dry air and in dry nitrogen.

Representative curves obtained under these conditions

are shown in figures 5^, 55, 56 and 57. For the bilirubin

samples, a self-heating effect, probably due to oxidation of

the carbonaceous material, takes place just below 300°C

when the samples are heated in air. No similar effect

was observed for bilirubin when it was heated in dry

nitrogen. For the mandelic acid sample, the self-heating

effect is not observed when the samples are heated either In

dry air or nitrogen. From a study of these weight-loss

curves along with other ehemieal data observed, it is

possible to obtain valuable insights as to the best sources

of materials which can be used as standard materials. It

is postulated that samples having a higher and sharper

decomposition temperature may be purer.
6.0

5.0 -

4.0 -

en£

x 3.0

CD

LU

2.0

.0

1 1 1 1

BILIRUBIN >v

HEATING RATE- 10 °C MIN"1 N.

ATMOSPHERE-DRY NITROGEN

1 1 1 1

Figure 5^

100 200 300

TEMPERATURE °C

400 500

Thermogravimetric curve of bilirubin in a dry

nitrogen atmosphere.

6.0

5.0

4.0 -

enE

i 3.0

UJ

2.0 -

1.0

Figure 55.

1 1 1 1

-

BILIRUBIN

HEATING RATE-I0°C MIN"

1 ^V

- ATMOSPHERE-DRY AIR \-

-

1 1 1 1 100 200 300

TEMPERATURE °C

400 500

Thermogravimetric curve of bilirubin in a dry

air atmosphere.

118
b.U

5.0

1 1 1 1

4.0 ^V^ _

E

h-X 3.0 - >v —

LlJ MANDELIC ACID \.

2.0 HEATING RATE- 10 °C MIN

-1 X,

ATMOSPHERE- DRY NITROGEN

—

1.0 -

1 1 1 1

Figure 56.

100 200 300

TEMPERATURE °C

400 500

Thermo gravimetric curve of mandelic acid in a dry nitrogen atmosphere.

6.0

5.0 -

4.0

E_ x 3.0

UJ

2.0

1.0

Figure 57

MANDELIC ACID

i-i HEATING RATE- 10 °C MIN" ATMOSPHERE- DRY NITROGEN

100 200 300

TEMPERATURE °C

400 500

Thermogravimetric curve of mandelic acid in a dry air atmosphere.

119
7 . ANALYSIS OF STANDARD REFERENCE MATERIALS

A. Introduction (J. I. Shultz)

At least 50 percent of the activities of the Section,

during the last year, involved the analysis or characterization of a wide variety of materials for the Office

of Standard Reference Materials. These activities

require considerable versatility and experience on the

part of the staff members.

Atomic absorption and flame emission spectroscopic,

gravimetric, titrimetric, spectrophotometric , combustiongravimetric and thermal conductivity techniques were effectively employed to cover the broad scope of concentrations

from the parts-per-million level to at least 50 percent. As

requirements for lower detection limits become increasingly

more demanding, atomic absorption, flame emission, spectrophotometric and thermal conductivity techniques occupy positions of greater importance. However, for those materials

containing elements in the ranges above 10 percent, as in

ferroalloys, metallo-organics and clays, it becomes quite

apparent that well established gravimetric and titrimetric

procedures must be relied upon.

Investigations into possible new absorbance

standards for use in calibrating spectrophotometric

instruments concerned the development and evaluation of

a number of solids and liquids. The details of the

investigation and description of the proposed standards

have already been given in a previous section.

The accompanying diagram, figure 55, more graphically

illustrates the variety and types of standards that were

analyzed either for provisional or final certification

or for establishing homogeneity of the materials. Figure 56

identifies those elements that have been determined

during the year by one or more of the competences within

the Section in connection with the certification of Standard

Reference Materials.

120
Figure 58. Types of Standard Reference Materials analyzed

121
Figure 59. Elements determined according to competences

by Coordination Chemistry Section.

122
B - Standard Reference Materials Information and Summary

The following information on those standards for

which the Section was responsible for the overall direction and coordination of the technical measurements,

provides background which may be of general interest.

1 . Lead-bearing alloys-SRM 53e and 1132

Non-ferrous alloy 53e is a renewal standard of

lead-base bearing metal in the form of finely-divided

powder (170/325 mesh), while 1132 is a new standard of

similar composition and is available in disc form for

spectrographic use. These alloys are typical bearing

materials widely used by the automotive and diesel

industries. Composition control is becoming increasingly

more important not only for the major elements, such as

antimony (10$) and tin (6%), but for the minor elements,

such as copper, arsenic, bismuth, iron and nickel. The

data are presented in table 26.

Table 26. Certified Certifie lead bearing alloy-SRM 53e and 1132.

No.

Element Det T ms

Antimony 4

4

Tin 8

4

Copper 8

Bismuth 8

Arsenic 16

Iron 2

Nickel 8

Average

Method %

Distillation-titration 10.22

H

2

S0 i| -H

2

S0 -KBrO 10.24

KI0~ titration 5.83

Cupferron-SnO„ 5.86

Cupric bromide photometric 0.053

Thiourea photometric .052

Arsenomolybdate photometric .058

1,10-phenanthroline photometric <.001

Dimethylglyoxime photometric .004

123
2. Carbon Steel (0.4Q-SRM 20g

This medium carbon steel is the most popular of the

carbon steel standards. Its wide application is in the

automotive industry where it is used for bolts, studs,

connecting rods, steering arms, etc. It is an ideal

reference standard for the control of carbon, manganese,

phosphorus, sulfur and silicon analyses. Data are

presented in table 27.

Table 27. Certified carbon steel-SRM 20g

Element

Carbon

Manganese

Phosphorus

Sulfur

Silicon

Copper

Nickel

Molybdenum

Aluminum

No.

Pet 'ms Method

18 Thermal conductivity

14 Persulfate-arsenite

8 Molybdenum-blue photometric

18 Combustion-titration

8 Perchloric -acid dehydration

^ Diethyldithiocarbamate

photometric

12 Atomic absorption

4 Dimethylglyoxime photometric

8 Thiocyanate photometric

12 Atomic absorption

Average

0.457

.666

.011

.028

.308

.034

.033

.034

.007

.040

3. Stainless Steel-SRM lOlf

This low carbon stainless steel contains 18 percent

chromium and 10 percent nickel and was prepared by a

pre-alloyed powder metallurgical process which included

argon atomization and hydrogen annealing. This standard

was prepared primarily for use in the steel industry for

standardizing chemical methods of analysis particularly

for carbon, sulfur, chromium and nickel. The data are

presented in table 28.

4. Low Carbon Stainless Steel-SRM 166c

This special low-carbon stainless steel is provided as

a control standard for very low levels of carbon. Newer

instrumentation, such as thermal conductivity, now provides

means for detecting very low levels of carbon in ferrous

124
Table 28 . Certil

No.

Element Det 'ms

Carbon 20

Manganese 12

8

Phosphorus 8

Sulfur 12

Silicon 8

Copper 12

4

Nickel H8

Chromium 4

8

Vanadium

Molybdenum 12

Cobalt 11

Certified stainless steel-SRM lOlf.

Method

Thermal conductivity

Activation analysis (Sec. 9)

Periodate photometric

Molybdenum-blue photometric

Combust ion- titration

Perchloric acid dehydration

Activation analysis (Sec. 9)

Spark source isotope dilution

(Sec. 6)

Dimethylglyoxime gravimetric

Spark source isotope dilution

(Sec. 6)

Peroxydisulfate oxidation

FeSO.K titration

Coulometric titration (Sec. 5)

HNC> oxidation-FeSO^ titration

Activation analysis (Sec. 9)

Activation analysis (Sec. 9)

Average

%

0.014

.090

.085

.007

.008

.876

.029

-030

9-96

9.97

18.52

18.47

0.034

.007

.087

alloys- This standard will serve as a bench-mark for

standardizing and calibrating the many new types of

instruments especially adapted for low carbon determinations.

Using a thermal conductivity method, the carbon content

based on 18 determinations was 0.0077 percent.

5. Differential Thermal Analysis Standards-SRM 755

and 756

These two compounds are the first materials that were

made available for use as DTA standards. This work was

undertaken with the cooperation of the Standards Committee

of the International Conference of Thermal Analysis (ICTA).

It is anticipated that additional materials will be investigated for use as DTA and DSC standards covering subambient

125
to very high operating temperatures. Additional details

were presented in a previous section.

a. Standard 755-SiO n (Quartz

)

. The phase transition

of this material is at approximately 575 °C and is the mean

of the values obtained on several differential thermal

analysis instruments. Generally, the differential temperature curve value may be somewhat higher than the adiabatic

value and may vary for different equipment and heating

rates. The standard is furnished in 2-gram units sized

from 100 to 325 mesh.

b - Standard 756-KNQ ^. The phase transition of this

material is approximately 130 °C, and, like the quartz

standard, is the mean of the values obtained on several

differential thermal analysis instruments. The standard

is furnished in 5-gram units as fine crystals

.

6

.

Metallo-organic Standard-SRM 106lc Magnesium

Cyclohexanebutyrate

This is one of a series of standards that were

developed for use by the railroad and trucking industries as a basis for maintenance schedules and predictions

of equipment failures. The amount of wear and the

probability of failure of an internal combustion engine

may be determined by analyzing its lubricating oil for

metals. These analyses are made by optical emission

spectroscopy. The certification of the magnesium was,

however, determined by the gravimetric method as MgpP ? 7

. The value of magnesium based on 12 determinations was

6.45 percent.

7

.

Special Steels-SRM 361, 362 and 365

These 3 standards are part of a series of 5 graded

steels that will eventually be certified for approximately

35 elements. However, the initial certification will be

based on C, Mn, P, S, Si, Cu , Ni, Cr, V and Mo.

126
Standard 361 is a 0.4 carbon steel, grade AISI 4340.

This material is being analyzed cooperatively by four

industrial laboratories.

Standard 362 is a low alloy steel (0.15C), grade

AISI 94B17, containing small amounts of tungsten, cobalt,

niobium, tantalum and zirconium. This material is being

analyzed cooperatively by 4 industrial laboratories.

Standard 365 is electrolytic iron containing very

low levels of all other elements, except nickel, which is

about 0.04 percent. Provisional certification includes

nickel, in addition to 12 elements whose values are all

<0.008. Later additional elements will be determined for

inclusion on a final certificate.

R. K. Bell T. A. Rush

J. R. Baldwin J. T. Sterling

E. R. Deardorff S. A. Wicks

T. C. Rains

127
B. E. McClellan (summer)

T. C. Rains

T. A. Rush

J. T. Sterling

R. A. Velapoldi

S. A. Wicks

8. 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. K. Bell

D. S. Bright (part time)

R. W. Burke

E. R. Deardorff

R. Mavrodineanu

B

.

Publications

1. M. Tsutsui, R. A. Velapoldi, K. Suzuki, F. Vohwenkel,

M. Ichikawa and T. Koyans , "Unusual Metalloporphyrins

IV. Novel Methods for Metal Insertion into Porphyrins",

J. Am. Chem. Soc 91, 6262-66 (1969).

2. W. Snelleman, T. C. Rains, K. W. Yee , H. D., Cook

and 0. Menis, "Flame Emission Spectrometry with Repetitive

Optical Scanning In the Derivative Mode", Anal. Chem. 42 , 394, 1970.

3. R. W. Burke and E. R. Deardorff, "Simultaneous

Spectrophotometric Determination of Cobalt, Nickel and

Copper with 2 , 3-Quinoxalinedithiol" , Talanta 1J_, 255 (1970).

4. R. W. Burke, "Exchange Reactions of Ternary Ion

Association Complexes Directly in the Organic Phase",

Talanta 17, 240 (1970)

.

5. R. J. Kline and R. A. Velapoldi, "The Kinetics of

the Acid Hydrolysis of t rans N itroaquobis ( 2

, 4-pentanedionato)-

cobalt(III), Inorg. Chem. 9, 1312-14 (1970).

6. 0. Menis and B. E. McClellan, "Kinetics and

Mechanism of Extraction of Iron(III) with B-Isopropyltropolone, submitted for publication to Analytical Chemistry.

7. 0. Menis, B. E. McClellan and D. S. Bright,

"Determination of the Formation Constants of Iron(III) and

128
Vanadium(V) with $-Isopropyltropolone Using the Extraction

Method"; submitted for publication to Analytical Chemistry.

8. R. Mavrodineanu, "Sprayer and Burner Units for

Flame Emission and Atomic Absorption Measurements'5 , Develop. iin Applied Spectry 8_, (1970); in print.

C. Talks

1. R. Mavrodineanu, "Sprayer and Burner Units

for Flame Emission and Atomic Absorption Measurements','

Mid-America Symposium on Spectroscopy, Chicago, 111.,

May 1969.

2. T. C. Rains, "Atomic Absorption Spectroscopy",

ACS Short Course on Atomic Absorption Spectroscopy,

Dartmouth College, Hanover, New Hampshire, July 6-7, 1969 . 3. R. Mavrodineanu (presented by T. C. Rains),

"Sprayer and Burner Units for Flame Emission and Atomic

Absorption Measurements", International Atomic Absorption

Spectroscopy Conference, Sheffield, England, July 14-18,

1969.

4. T. C. Rains, "Applications of Atomic Absorption

Spectrometry to the Determination of Major Constituents",

Atomic Absorption Workshop, Center for Professional

Advancement, Morristown, N. J., Aug 25-27, 1969.

5. T. C. Rains, "Atomic Absorption and Flame Emission

Spectrometry —General Theory and Methodology", Southeastern

Section of the Society for Applied Spectroscopy, Knoxville,

Tennessee, Sept. 6, 1969.

6. T. C. Rains, "Future Trends in Atomic Absorption

Spectrometry", Anachem Conference, Detroit, Michigan,

Sept. 16-18, 1969.

7. T. C. Rains, "Atomic Absorption Spectroscopy",

ACS Short Course on Atomic Absorption Spectroscopy,

Washington, D. C, Oct. 25-26, 1969.

129
8. T. C. Rains and 0. Menis, "AC Scanning in the

Derivative Mode", Eastern Analytical Symposium,

New York, N. Y., Nov. 19-21, 1969.

9. T. C. Rains, "Special Applications and Future

Developments of Atomic Absorption Spectrometry", BaltimoreWashington Section of the Society of Applied Spectroscopy,

W. R. Grace Research Center, Clarksville, Md . , Dec. 16, 1969

.

10. R. A. Velapoldi, "Induced Oxidation of Metalloporphyrins by Unsaturated Hydrocarbons',' Oslo University

Rikshospitalet , January, 1970.

11. 0. Menis, "Determination of the Formation Constants

of Iron(III) and Vanadium(V) with 8-Isopropyltropolone

Using Extraction Method", 159th American Chemical Society

Meeting, Houston, Texas, Feb. 23, 1970.

12. 0. Menis and B. E. McClellan, "Spectrophotometry

Determination of Vanadium in Steels as the 3-Isopropyltropolone Complex", Pittsburgh Conference on Analytical Chemistry

and Applied Spectroscopy, March 1-6, 1970, Cleveland, Ohio.

13. T. C. Rains , T. A. Rush and 0. Menis, "Selection

of the Appropriate Absorbing and Non-Absorbing Line for

Use in Atomic Absorption Spectrometry", Pittsburgh

Conference on Analytical Chemistry and Applied Spectroscopy,

March 1-6, 1970, Cleveland, Ohio.

14. R. W. Burke and E. R. Deardorff , "Simultaneous

Spectrophotometric Determination of Cobalt, Nickel and

Copper with 2 , 3-Quinoxalinedithiol, Pittsburgh Conference

on Analytical Chemistry and Applied Spectroscopy, March 1-6,

1970, Cleveland, Ohio.

15. Radu Mavrodineanu, "Burner and Supplying Systems

for the Determination of Sodium and Potassium in

Microliter Sample Volumes by Flame Spectrophotometry,

Fifth Annual Meeting of the Association for the Advancement

of Medical Instrumentation, Boston, Mass., March 23, 1970.

16. R. W. Burke, "The Use of Solutions for Checking the

Absorbance Scales of Spectrophotometers" Fifth Annual

130
Meeting of the Association for the Advancement of Medical

Instrumentation, Boston, Mass., March 23, 1970.

17. 0. Menis, "Status of Thermal Analysis Standards",

ASTM-NBS Symposium on Current Status on Thermal Analysis,

NBS, April 20, 1970.

D . Committee Activities

Oscar Menis

Member ASTM, Committee E-3, Div. I., Thermal Analytical

Test Methods Subcommittee on Standards.

Member ASTM, Committee E-10, Subcommittee I.

Editorial Board Member, Chemical Instrumentation, A

Journal of Experimental Techniques in Chemistry and Biochemistry.

Institutional Representative, Standards Committee,

International Confederation on Thermal Analysis.

Participant, National Committee Clinical Laboratory

Standards (NCCLS) - Instrumentation.

Titular member of the International Union of Pure and

Applied Chemistry Commission V3 on Analytical Nomenclature.

Referee, "Critical Review in Analytical Report".

James I . Shultz

Member ASTM, Advisory Board, 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. G.

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.

131
T. C. Rains

American Chemical Society, Committee on Reagents

Specifications, Subcommittee on Atomic Absorption.

Member ASTM, Committee E-2, Subcommittee X.

J. T. Sterling

Member ASTM, Chairman, Div. I., Committee E-3.

Member ASTM, Committee E-l, Thermoanalytical Test

Methods.

R. K. Bell

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).

Radu Mavrodineanu

Technical Coordinator of the Professional Development

Program for Scientists Society for Applied Spectroscopy,

Fall Session 1969, Baltimore-Washington.

132
9 . REFERENCES

[1] Melville, R., Eastern Analytical Chemistry Symposium,

New York, Nov. 1969.

[2

[3

[4

[5

[6

[7

[8

[9

[10

[11

[12

[13

[14

[15

[16

[17

[18

Rand, R., Clinical Chemist 15, 839 (1969).

Gibson, K. S., Spectrophotometry, NBS Standard

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Edisbury, J. R., "Practical Hints on Absorption

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Gibson, K. S., NBS Standard Circular 484, pp. 42-44,

1949.

Cary Instruments Application Report AR 14-2, September,

1964.

Haupt, G. W., NBS J. Res. 4_8, 4l4 (1952).

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1045 (1955).

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1139 (1940).

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133
2, 4 , 6-Tripyridyl-s-Triazine, Phenyl-2-Pyridyl ketoxime",

2nd ed . , pp. 21-23, G. Frederick Smith Chemical Co.,

Columbus, Ohio, 1965.

[19] Menis, 0., Editor, NB S Technical Note ^02, 1967.

[20] Chapman, J. H. , Forster, Th . , Kortum, G., Parker, C. A.,

Lippert, E., Melhuish, W. H. and Bebbia, G., J. Appl.

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[21] Udenfriend, S., "Fluorescence Assay in Biology and

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,

Clin. Chim. Acta 5, 283 (I960).

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[24] Reisfeld, R., Honingbaum, A., Michael! , G., Harel, L.

and Ish. -Shalom, M., Israel J. Chem. 7, 613 (1969);

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[25] Reisfeld, R. and Kirshenbaum, L. B., paper submitted

to meeting of the Israel Chemical Society, 1970.

[26] Reisfeld, R. and Greenberg, E . , Anal. Chim. Acta 4_7_,

155 (1969); Reisfeld, R., Gur-Areh, Z. and Greenberg,

E. , ibid 50, 249 (1970) . [27] Winefordner, J. D., Vickers, T. J., Anal. Chem. 4_2,

206R (1970).

[28] Rains, T. C, and Menis, 0., Spectrosc . Lett., 2, 1

1969.

[29] Mavrodineanu, R., Hughes, R. C. and Kohler, T. R.,

"Direct Reader for Flame Emission Measurements,"

Philips Laboratories Tech. Report. No. 173, June 24,

1964; Ziedens, G., "Electronic Readout System for

Multichannel Flame Spectrophotometer," Philips

Laboratories Tech. Rept . No. 228, Oct. 1968.

134
[30] Mavrodineanu, R., "Sprayer and Burner Units for

Flame Emission and Atomic Absorption Measurements",

Developments in Applied Spectroscopy, Vol. 8, 1970

(in print )

[31] Grimm, W., Spectrochim. Acta 2_3B, 443-454 (1968).

[32] Mavrodineanu, R., "Bibliography on Flame Spectroscopy,

Analytical Applications 1800 to 1966", Chapter 2.2,

Hollow Cathode Discharge Tubes, 140-143; NBS

Misc. Publ. 281 , 1967; Mandelstam, S. L. and Nedeler,

V. V., Spectrochim Acta 17, 885-894 (196l).

[33] Corliss, C. H. and Bozman, W. R., NBS Monograph 53,

1962.

[34] Walsh, A. "Atomic Absorption Spectroscopy," ASTM

Special Tech. Publ. 443, pp. 3-18, 1969.

[35] Snelleman, W., Rains, T. C, Yee , K. W., Cook, H. D.

and Menis, 0., Anal. Chem. 4_2, 394 (1970).

[36] Feldman, C. and Rains, T. C, Anal. Chem. 3.6, 405

(1964).

[37] Eshelman, H. C., Dean, J. A., Menis, 0. and Rains,

T. C, Anal. Chem. 31, 183 (1959).

[38] Slavin, W., Appl. Spectry. 20_, 28l (1966).

[39] Menis, 0., Editor, NBS Technical Note 504, 1969

[40] With, T. K., "Bile Pigments", Academic Press, New

York, 1968 and numerous references contained within.

[41] Lemberg, R. and Legge, J. W. , "Haematin Compounds

and Bile Pigments", Interscience Publishers, New

York, 1949; Pullman, B. and Perault, A. M., Proc . Natl

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[42] Gray, C. H., Kulczycka, A. and Nicholson, D. C,

J. Chem. Soc, 2268 (1961).

[43] Gray, C. H. , Kulczycka, A. and Nicholson, D. C,

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Morell, D. B., Biochem. Biophys . Acta 177 , 599 (1969);

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137



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NSRDS provides quantitative data on the physical

and chemical properties of materials, compiled from

the world's literature and critically evaluated. Product Standards. Provide requirements for sizes, types, quality and methods for testing various industrial products. These standards are developed cooperatively with interested Government and industry groups

and provide the basis for common understanding of product characteristics for both buyers and sellers. Their use is voluntary.

Technical Notes. This series consists of communications and reports (covering both other agency and

NBS-sponsored work) of limited or transitory interest. Federal Information Processing Standards Publications. This series is the official publication within

the Federal Government for information on standards

adopted and promulgated under the Public Law

89-306, and Bureau of the Budget Circular A-86

entitled, Standardization of Data Elements and Codes

in Data Systems.

Order NBS publications from: Superintendent of Documents

Government Printing Office

Washington, D.C. 20402
U.S. DEPARTMENT OF COMMERCE

Washington. D.C. 20230

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