_ reau of Standards

fcQl Admin. Bldg^ u m

NBS TECHNICAL NOTE

424

Analytical Coordination Chemistry:

Titrimetry, Gravimetry, Flame Photometry,

Spectrophotometry, and Gas Evolution,

July 1966 to June 1967

^ °F '0+

^CAU 0*

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards
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UNITED STATES DEPARTMENT OF COMMERCE

Alexander B. Trowbridge, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director ^J^TECHNICAL NOTE 424

ISSUED JANUARY 1968

Analytical Coordination Chemistry:

Titrimetry, Gravimetry, Flame Photometry,

Spectrophotometry, and Gas Evolution, July 1966 to June 1967

Edited by Oscar Menis

Analytical Coordination Chemistry Section

Analytical Chemistry Division

Institute for Materials Research

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

listed or referred to in the open literature.

sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402

Price 55 cents.
FOREWORD

The Analytical Chemistry Division was established as a separate division at the National Bureau of Standards on September 1, 1963, and became part of the Institute for Materials Research in the February 1, 1964, reorganization.

It consists at present of nine sections and about 100 technical personnel encompassing some 45 different analytical

competences from activation analysis and atomic absorption to vacuum fusion and x-ray spectroscopy. These competences, and

in turn the sections which they comprise, are charged with research at the forefront of analysis as well as awareness of the practical sample, be it standard reference material or service analysis. In addition it is their responsibility to inform others of their efforts. Formal publication in scientific periodicals is 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.

ii
Thus our progress reports endeavor to present this infor- mation which we have struggled to obtain and which we feel might be of some help to others. Certain areas which it appears will not be treated fully in regular publications are considered in some detail here. Other results which are being written up for publication in the journal literature

are covered in a much more abbreviated form.

At the National Bureau of Standards publications such as these fit logically into the category of a Technical Note.

In 1967 we plan to issue these summaries for all of our sections. The following is the third annual report on pro- gress of the Analytical Coordination Chemistry Section.

W. Wayne Meinke, Chief Analytical Chemistry Division
PREFACE During the past year the research efforts of the Analytical Coordination Chemistry Section led to significant contributions to higher precision and accuracy of values reported on standard reference materials. The first four parts of this report, gravimetry, titrimetry, flame emission

and atomic absorption, spectrophotometry and spectrofluorimetry, reveal the efforts centered around analytical coordination chemistry. The fifth section, gases in metals, covers mainly high vacuum techniques for oxygen and nitrogen

in metals. This third successive annual report of this Section, while still concerned predominantly with analysis

of certified standard reference material, also aims to point out the research plans and goals of next year which

are expected to be considerably enlarged. To eliminate the diverging of effort, certain areas dealing with isotope

preparation and nuclear materials have been transferred

to another Section (310.06). Progress on several of the new methods reported only

in part here will be published shortly in scientific

journals. In order to describe experimental procedures

adequately, it has occasionally been necessary to identify commercial materials and equipment in this report. In no case does such identification imply recommendation or endorsement by the National Bureau of Standards, nor does

it Imply that the material or equipment Identified is necessarily the best available for the purpose.

Oscar Menis, Chief Analytical Coordination Chemistry

Analytical Chemistry Division
TABLE OF CONTENTS

1. GRAVIMETRY

Introduction

Accurate Determination of Beryllium by

Incomplete Homogeneous Precipitation

and Spectrophotometric Addition. . . 1.2. Introduction Experimental

D.

The homogeneous generation

of ammonia . 3 Role of complexing agents 4 Combined homogeneous precipitation

and spectrophotometric determination of beryllium 6 The role of impurities . 7 Scheme of analysis of Be-Cu alloys . . 11 Differential Thermal Analysis 11

1. Introduction ..11

2. Experimental 12

3. Data and Discussion . 12 Analyses of Samples. .............28

TITRIMETRY 29

A. Introduction 29

B. Alkalimetric Titration of Boric Acid 29

1. Introduction 29

2. Refined Procedure and Results 29

C. Spectrophotometric Titration of Beryllium. . . 30

1. Introduction ............... 30

2. Results and Discussion .31

D. Spectrophotometric Titration of Fluoride

and Pyrohydrolytic Separation 32

1. Introduction 32

2. Studies of Separation Procedures 32

3. Titration Studies . 32
TABLE OF CONTENTS (continued) PAGE

E. Separation of Nitrogen From Refractory

Nitrides . 33

F. Analyses of Samples 35 FLAME EMISSION AND ATOMIC ABSORPTION SPECTROPHOTOMETRY 36

A. Introduction 36

B. Determination of Trace Elements at the Submicrogram Level in High-Purity Zinc. . . 37

1. Introduction. 37

2. A Study of Nebulizers and Burners .... 37

3. Separation and Preconcentration 38

C. Effect of Calcium and Phosphate on the Atomic Absorption Determination of Barium 39

D. High-Precision Flame Emission Spectrophotometry ............. 40

1. Introduction 40

2. Experimental Variables 42

3. Results for Lithium 43

E. Determination of Arsenic by Atomic Absorption Spectrophotometry 46

1. Introduction. .............. 46

2. New Source of Monochromatic Light .... 47

3. Effect of Oxidant Fuel. 47

4. Determination of Arsenic in High-Purity Selenium 48

5. Determination of Arsenic in Cast Iron . . 49

F. Analysis of SRM by Atomic Absorption and Flame Emission Spectrophotometry. ..... 49 SPECTROPHOTOMETRY AND SPECTROFLUORIMETRY. .... 52

A. Introduction. ......... .. 52

B. Study of Ternary Systems 52

C. Spectrof luorimetry. ..• 60

1. Introduction 60

2. Discussion and Results. ......... 61
TABLE OF CONTENTS (continued) PAGE

3. Instrument Evaluation ......61

4. Application to Micro Samples .......63

D. Spectrophotometry Determination of Arsenic

in Cast Iron ...64

1. Introduction 64

2. Procedure. .... ....65

3. Results and Discussion ..........66

E. Arsenic in High-Purity Selenium 67

F. High Precision Differential

Spectrophotometry. .............68

1. Introduction ...... .68

2. Differencial Spectrophotometric Determi- nation of Dysprosium in Glass Beads. . . 68

a. Development of method. ........ 69

b. Procedure. 69

c. Results and conclusions. .70

3. Other Studies. ... ...... 71

G. Miscellaneous Spectrophotometric Results Obtained on Various Standard Reference Materials 71 GASES IN METALS 73 A. Introduction .................73

B. Production of Oxygen Standards for Titanium

Base Metals. .75

1. Introduction ...............75

2. Sampling and Method of Analysis. ..... 75

3. Discussion of Results. 77

4. Results from Cooperating Laboratories. . . 78

C. Studies of the Determination of Nitrogen in Metals by the Vacuum Fusion Method 80

1. Introduction . . . . c . ........ .80

2. Materials and Methods. ..... ....81

3. Results. 84
TABLE OF CONTENTS (continued) PAGE

6. PERSONNEL AND ACTIVITIES. 88

A. Personnel Listing 88

B» Publications. .......... 88

C. Talks 88

D. Committee Activities 89

E. Acknowledgements. 90

7. REFERENCES 91

LIST OF FIGURES FIGURE NO. PAGE

1. Homogeneous precipitation of Be(0H) ? plus EDTA. . ......... 9 2. Homogeneous precipitation of Be(0H) 2 plus sulfate 9 3. Flow chart of separations in the analysis

of beryllium-copper alloy. .........10

4. Typical DTA curve for potassium nitrate. ... 17

5. Typical DTA curve for hydrogen sulphate. ... 17

6. Typical DTA curve for potassium carbonate. . . 18

7. Typical DTA curve for sodium sulphate. .... 19

8. Typical DTA curve for potassium perchlorate. . 20

9. Typical DTA curve for silver sulphate. .... 20

10. Typical DTA curve for sodium carbonate .... 21

11. Typical DTA curve for silicon dioxide 22

12. Typical DTA curve for potassium sulphate ... 22 13. Typical DTA curve for potassium chromate ... 23

14. Typical DTA curve for barium carbonate .... 23 15. Typical DTA curve for strontium carbonate. . . 24

16. Typical DTA curve for aluminum oxide ..... 24 17. Typical DTA curve for stearic acid ...... 27 18. Pyrohydrolysis apparatus . ....33

viii
LIST OF FIGURES (continued) FIGURE NO. PAGE

19. Interferences of tungsten in the determination of fluorine by thorium titration. ... 34 20. Typical lithium calibration curve. . 44

21. Lithium calibration curve - scale expanded . . 44 22. AC buck-out adaptor for synchronous detector . 44 23. Uncorrected excitation and emission spectra

of Rhodamine 6G in ethanol> concentration = 40 ppb ....62

24. Absorption spectrum of 4 ppm Rhodamine 6G

in ethanol; 5-cm light path. ........62

25. Unalloyed titanium ...78

26. 6fo Al kfo V - titanium alloy 79

27. Spinning crucible. 83 LIST OF TABLES

PAGE

1. Rate of hydrolysis of urea in homogeneous

precipitation of beryllium. . 4

2. Effect of EDTA on the recovery of beryllium

in a homogeneous precipitation 5 2a. Effect of EDTA on the recovery of beryllium

in an ammonium phosphate precipitation. . . 5 3. Effect of complexing media on the recovery

of Be(0H)

2

. . . 6 4. Combined homogeneous precipitation and spectrophotometric determination of beryllium ................. 7

5. The effect of impurities on the beryllium

determination ............... 8

6. Presence of sulfates in urea; sulfate determined turbidimetrically . 8

7. Precision of the beryllium determination

in a copper alloy 11

8. Differential thermal analysis data 13

9. Endotherm transition temperatures for tricalcium silicate 26
LIST OF TABLES (continued) TABLE NO. PAGE

10. Summary of gravimetric determinations .... 28

11. Potentiometric titration of boric acid. ... 30

12. Spectrophotometric titration of beryllium

in Be-Cu alloys 31

13. Summary of titrimetric determinations .... 35

14. Comparison of detection for various burners by atomic absorption (aqueous solutions). . 38

15. Values for trace elements in high-purity

zinc 39

16. Effect of calcium and phosphate on the absorption of barium 41

17. Effect of slit width on the flame emission spectrophotometric determination of lithium 42

18. Lithium in synthetic Dy^O, glass 45

19. Determination of lithium in glass beads

for neutron flux measurement 46

20. Summary of analysis performed by flame emission spectrophotometry of standard reference material 50

21. Summary of analysis performed for copper by atomic absorption spectrophotometry

of standard reference material 51

22. Extraction of Crystal Violet and Brilliant

Green as binary complexes ......... 56 23. Comparison of three spectrof luorimeters ... 63 24. Arsenic in SRM 4j 66 25. Dysprosium content of glass beads 70

26. Miscellaneous spectrophotometric results, . . 71

27. Unalloyed titanium 77

28. 6% Al - kfo V Titanium alloy 77

29. Nitrogen values in standard reference material (ppm)<, 85 30. Comparison of nitrogen values by several methods 87
ANALYTICAL COORDINATION CHEMISTRY: TITRIMETRY, GRAVIMETRY, FLAME PHOTOMETRY, SPECTROPHOTOMETRY, and GAS EVOLUTION,

July 1966 to June 1967 Edited by Oscar Menis ABSTRACT

In the related areas of gravimetry, tltrimetry, flame emission and atomic absorption spectroscopy, absorption and fluorescence spectrophotometry, and gases in metals, the versatile aspects of coordination chemistry have, in several

instances, been uniquely exploited to yield either more precise and accurate results or lower detection limits. Fivefold improvement in the gravimetric analysis for beryllium has been obtained by means of an incomplete

homogeneous precipitation followed by a selective spectro- photometry examination of the filtrate. In the field of thermal analysis a survey of fifteen compounds has revealed

several promising, future standards for DTA studies covering

the range of 75 to 900 C. In the section on tltrimetry

highly precise procedures are described for the determination

of boron and beryllium. Various instrumental parameters

have been investigated in flame emission and atomic absorption spectroscopy in order to optimize such variables as nebulizer-burner and oxidant-fuel systems, elimination of interferences, and source difficulties. The use of chelate extraction systems has led to the extension of detection

limits to the submicrogram level for impurities in zinc and selenium, while modified electronics has permitted the precise determination of 10 percent Li in glass with a relative standard deviation of better than 0.2 percent.

In absorption and fluorescence spectrophotometry the research aspect of ternary complexes or mixed chelates
are described together with their potential use at the nanogram-picogram level. In the same area improvement in accuracy has been obtained by controlled dissolution of samples In closed systems with particular attention being

given to the determination of arsenic in cast iron. Also described in this section is the differential spectrophotometric determination of dysprosium in a glass to be used

as a neutron flux monitor, in which case the relative error

was reduced to less than 0.25 percent. Finally, in the area of high vacuum fusion a new standard was certified

for oxygen in titanium and in two titanium alloys. In addition, research in the use of the same technique for

the determination of nitrogen has apparently eliminated

the problem of low values that have in the past so fre- quently plagued the analyst.

Key words: absorption and fluoresence spectrophotometry,

arsenic, atomic absorption, beryllium, DTA studies, dysprosium

in a glass, flame emission, gases in metals, gravimetry, homogeneous precipitation, impurities in zinc and selenium, LigO

in glass, nitrogen, oxygen in titanium, titrimetry.
1 . GRAVIMETRY

A. Introduction

Our main objectives in the field of gravimetry have been

the attainment of high accuracy for the determination of beryllium and the development of suitable standards for dif- ferential thermal analysis, A new approach to the gravi- metric determination of beryllium is based on an incomplete

homogeneous precipitation of this element combined with a selective spectrophotometric determination of residual beryllium in the filtrate. In this manner the accuracy of this analysis was significantly increased over reported methods which suffer from serious systematic errors [1,2].

The greater accuracy of the determination of the element

in Be-Cu alloys contributed to the fulfillment of a need

for a new standard reference material. These types of alloys are presently much in demand in space, oceanographic,

and aviation systems and the SRMs will serve to calibrate instruments used to check quality control in their production.

In the other area, differential thermal analysis (DTA), efforts were concentrated on a search for suitable .standard materials for the calibration of instruments. In cooperation with the International Committee on Thermal Analysis twelve compounds were evaluated. In addition, an organic compound

and a previously studied tricalcium silicate were further

tested. The new data should aid in attaining the goal of selecting and providing much needed standards in this rapidly

growing science. Finally, the results of other analyses of SRMs by gravimetric procedures are summarized.
B. Accurate Determination of Beryllium by Incomplete Homogeneous Precipitation and Spectrophotometry

Addition

1. Introduction

A current review [1] and a symposium report [2] have demonstrated the need for a more accurate determination of beryllium. In the analytical areas of titrimetry, gravlmetry, spectrophotometry, as well as in other instrumental

methods, the problem of accuracy in parts per thousand has

not been completely solved up to now. In beryllium analysis

the current gravimetric methods based on ammonia or phosphate

precipitation in conjunction with EDTA masking still do not fulfill that need and have been the subject of considerable

dispute. Unfortunately, because of the very small ionic radius and resulting high charge density of the beryllium

ion, this separation is difficult and subject to compensating errors. The latter has often obscured the issues. Recently, while our study was in progress, two other homogeneous precipitation procedures have been reported [3*^1- The first paper offers only limited information about the results of the quantitative separation, and for the second

paper, involving the hydrolysis of acetylacetone, only a brief abstract is available. In our studies it became

evident that in the process of complexing interfering

elements, solubility losses become very serious and, based

on spectrographic data (Spectrochemical Analysis, Section

310.02), coprecipitatlon was still significant. In our approach this problem was solved by a procedure of incom- plete precipitation in which approximately 98 percent of the beryllium is precipitated homogeneously as the hydroxide

and the residual beryllium in the filtrate is determined
spectrophotometrically. Since the latter represents only a small correction, its somewhat poorer precision (l - 2$) does not contribute to a large error in the final value. Willard and Sheldon [5] first showed that they could separate iron in a two-stage homogeneous precipitation

procedure prior to quantitative determination of trace constituents in the filtrate. Our findings with beryllium

further point out the fact that under conditions of incom- plete precipitation the bulk of the impurities remain in the filtrate. In this study it has been necessary to establish optimum precipitation conditions, especially the effects of various complexing media, impurities in the reagents and glassware, and the choice of final ignition temperature for attaining a stoichiometric BeO product.

Finally, a general procedure was developed for the deter- mination of beryllium in a complex alloy.

2. Experimental

a. The homogeneous generation of ammonia . Several reagents were investigated regarding their rates of hydrolysis, the effects of diverse salts, and the influence of various complexing agents on the final pH. Initial tests of two reagents suitable for generation

of ammonia, urea and hexamethylenetetramine, revealed that

a higher pH was more readily attained with the former. The hydrolysis process with four grams of urea was complete in 30 minutes. The rate of hydrolysis at the boiling point

as a function of time is shown in table 1. A final pH of 7.3 or greater was found essential for an approximately 98 percent precipitation of the beryllium hydroxide. With 20

to 40 mg of beryllium in the sample four grams of urea were

3
sufficient to attain this pH. However, for samples containing 60 or more milligrams of Be, the amount of urea was increased to 16 grams. Table 1. Rate of hydrolysis of urea in homogeneous

precipitation of beryllium. BeCl

2

, 4 g of urea, volume 400 ml. Boiling Filtrate & (minutes)

4.1 (absorbance) 0.774

5 4.8 • 727

b .674b 10 5.5

15 6.0 • 337

20 6.5 .195 25 6.7 .147

30 6.8 .024

35 6.9 .013

40 6.9 .012

45 6.9 .001 Room temp. 7.3 .016 HJnpreclpitated Be.

b Filtrate was turbid.

b. Role of complexing agents . In gravimetric procedures

for beryllium, complexation of other elements is generally

attempted in order to avoid errors caused by coprecipitation.

In recent years the use of salts of ethylenediaminetetraacetic acid has come to the forefront when a hydroxide [6,7]

or phosphate [8] is involved. It Is claimed that the sta- bility constant of beryllium EDTA is low and Its complexation does not prevent the precipitation of beryllium. The data in tables 2 and 2a Indicate, on the contrary, that solubility losses increase with the EDTA concentration.

4
A further survey of the other complexlng media, shown in table 3* did not point up any unique systems from the stand- point of purity and completeness of precipitation. While

trien was quite effective in complexlng cobalt, it was not

as effective with other ions. For that reason a relatively

small fixed concentration of EDTA was chosen. Table 2. Effect of EDTA on the recovery of beryllium

in a homogeneous precipitation.

Conditions: Be 60 mg, urea 16 g, final volume 400 ml, colorimetric determination of beryllium in filtrate, EDTA added as the disodium salt. Filtrate

EDTA, mg Final pH Be, mg

none 7.6 0.758 none 7.6 .691 100 7.5 .956 100 7.5 1.453

ioo a 7.5 1.532

ioo a 7.6 1.267

150 7.5 1.788

150 7.5 1.813

200 7.4 2.575

200 7.4 2.625

TIDTA added as the ammonium salt.

Effect of EDTA on the recovery of beryllium

in an ammonium phosphate precipitation.

Beryllium, mg

Taken Found Difference

20.042

20.815 20.160

19.328

19«899 20.540

19.983

19.077

-0.143

- .275

- d77

- .251 See reference [8].
Table 3. Effect of complexing media

on the recovery of Be(OH) . Be recovered Millimoles gravimetric ally Disodium ethylenediamintetra0.27 97-98 Ethylenediaminetetraacetic

acid (EDTA) .68 94 Disodium nitriloacetate (NTA) .68 N-hydroxye thylethylene diamine triacetic acid (Versenol) .67 Hexamethylenetetramine

(Hexamine) -72 98 1,2-Diaminocyclohexanetetraacetic acid (DCTA) 29 Disodiumpyrocatechol-3i5-

disulfonate (Tiron) 0.32 89 Triethylenetetramine (Trien) 1.4 87

c . Combined homogeneous precipitation and spectro- photometric determination of beryllium . To eliminate the problem of coprecipitation, the incomplete homogeneous

precipitation procedure was combined with a selective spectrophotometric [9] analysis of the filtrate. The results of this procedure are presented in table 4. Prom

these data, it is evident that the accuracy based on synthetic samples prepared from high-purity beryllium is high. In most cases the agreement is better than one part

in ten thousand.
Table 4. Combined homogeneous precipitation and spectrophotometric determination of beryllium.

Beryllium Found (mg) SpectrophoTaken Difference Gravimetric tometric Total

20.200 0.677 20.877 20.869 +0.008

19.510 0.750 20.260 20.260 0.0 58.53 1.715 60.245 60.250 -0.005

58.46 I.865 60.325 60.34 -0.015

58.55fl 1.861 60.411 60.43 -0.019

60. 36

J

0.803 6l.l63 61.17 -0.007

60.75

a 0.732 61.483 61.48 +0.003

61.60 1.013 62.613 62.63 -0.017

58.83 1.540 60.370 60.37 0.0 60.25 1.623 61.873 61.84 +0.033

60.73 1.343 62.073 62.07 +0.003

98.13 2.555 100.685 IOO.69 -0.005

98.OO 2.144 100.144 100.16 -0.016

98.ll 2.307 100.417 100.43 -0.013

^No EDTA added.

d e The role of impurities . Tests were also carried

out to evaluate the effectiveness of the new method in eliminating the interference of several ions. The basis

for choosing these elements was their presence in the SRM alloys. In table 5 are presented data indicating

that on the average the relative difference was 0.2 percent. Additional problems were caused by impurities In the reagents and glassware. Teflon beakers were used In an effort to eliminate the pick up from glassware. Spectro- graph^ data indicated that traces of silicon of the order

of 10 to 100 ppm were still present in the precipitate.

The other source of impurities was the presence of sulfate

in the urea reagent. Thermogravimetric data shown in figures 1 and 2 Indicate that in the absence of sulfate a 7
The effect of impurities on the beryllium determination.

Beryllium, mg Added

20 c870 Pound 20.868 Difference

- .002 Rel. Diff.

($) .01 20.276 20.198 - .058 0.3 19.278 19.311 + .033 0.2 20.871 20.902 - .031 0.1 20,220 20.230 +0.010 0.1 20,165 20.171 +0.006 0.1 10.005 10.012 + .007 0.1 10.908 10.946 +0.04 0.4

^Impurities, mg: Al-1.7; Ni-0.12; Mn-.04; Cr-0.02. constant weight can be obtained at 700 C. However, our results with the synthetic samples show that an ignition temperature of 1100 C was required to obtain a stoichiometric BeO. This higher value suggested the presence of sulfate. Subsequent analysis of several preparations of urea (table 6) confirmed this. In the present investi- Table

Source

Presence of sulfates in ureaj sulfate determined turbidimetrically.

Mallinckrodt, AR

Merck's Ultrapure

KBS Zone Refined3, 1 pass

KBS Ion Exchange8, IO56 Sol

Wt of reagent (g)

2.5 Prepared by Section 310.09.

4.4

12.5

9.3 non-detected
V

D T A Be(0H] 2 —

h=r^ f |_ - -

_••-. 100 200

:

1 2 PERA „ C

G00 800 IU Figure 1. Homogeneous precipitation of Be(0H) 2 plus EDTA

(heating rate 15°C min. , dry air).

-x s \\

!

40

20

2 4 U TEM PERA »C 6 8 1000 Figure 2. Homogeneous precipitation of Be(0H)

2 plus sulfate (heating rate 15°C min., dry air).
gation, Mallinckrodt AR grade was used almost exclusively

and the final precipitate was ignited at 1100 C to eliminate any possible sulfate interference.

e. Scheme of analysis of Be-Cu alloys . As shown in the flow chart in figure 3 the steps of the analysis involved

the electrogravimetric determination of copper, removal of silica and separation of cobalt by anion exchange prior to its electrogravimetric determination. Beryllium was then determined in the eluate by the new procedure. Results of

Cu Be Fe Si Al Co Sn Ph Zn Ni Cr Mn Ag P

[

Anion Resin 1 y*&

| Be Al Ni Cr Mn| 1 u |

Figure 3. Flow chart of separations in the analysis of beryllium-copper alloy.
these analyses are presented In table 7. Statistical

evaluation of these data indicate that based on six degrees

of freedom the standard deviation of a single determination

is 0.004. This is a five-fold improvement over the precision stated in the last annual report.

R. K. Bell and Oscar Menis

Table 7« Precision of the beryllium determination

in a copper alloy. Alloy, SRM Duplicates Difference, d 1121 Cast 1.936 1.943 0.007

1121 Wrought 1.914 1.918 0.004

1122 Cast 1.769 1.771 0.002

1122 Wrought I.765 1.776 0.011

1123 Cast 0.466 0.468 0.002

1123 Wrought 0.461 0.466 0.005 B-[^«<a ]-M*s8sa]-»-o.«*3

C. Differential Thermal Analysis

1. Introduction

Along the lines of reasoning presented in the last progress report [10], a survey was undertaken of suitable materials as standards for differential thermal analyses.

In this initial review the round-robin arrangement of the International Conference on Thermal Analysis, Sub-Committee

on Standardization, served as the focal point. At the last meeting of the committee held in London, September 1966,

it was proposed that the members test twelve preparations.

These were selected to cover a range of temperatures from

o 100-900 C representing thermodynamic enthalpy changes

11
reported In the literature. The materials were supplied

by members of the committee. Depending on the evaluation

of the results from the participating members, future recommendations are contemplated by the committee.

In addition to examining these compounds, preparations

of an organic compound, stearic acid, were tested. Finally,

new data with a more sensitive instrument were obtained on tricalcium silicate, a compound described In the last annual report

.

2. Experimental

Two commercial instruments were used in these studies. With instrument I, weighed samples (l to 4 mg) and an alumi- num oxide reference material were spread in separate 1/4- inch platinum dishes which were placed on the ring of a platinel differential thermocouple. The thermocouple bead touched the bottom of the dishes. The sample and reference

were then heated at a linear rate in a flowing helium

atmosphere. With instrument II, the sample and an aluminum oxide reference were placed in separate 2mm capillary tubes, and chromel-alumel differential thermocouples were inserted

into the sample and reference materials. The sample com- partment was evacuated, purged with nitrogen, and then heated at a linear rate in a flowing nitrogen atmosphere.

3. Data and Discussion

Typical DTA curves as recorded by these two instruments

are presented in figures 4 through 16. The upper curves

are from instrument I and the lower from instrument II. The results for replicate runs are summarized in table 8.
Table 8. Differential thermal analysis data. Transition and fusion temperatures, C

ICTA Sample

Lit. Temp.

C KNO

128, 33Z

164, 181, 219

250, 428

622, 896

50

In 3trumer t I Instrument n

b (850

A

maxi Bmum)

A B D D 128 130 130 327 328 328

126 126 131 130 130 136 318 318 331 328 328 330

121 123 129 130 130 133 328 322 329 328 328 330 124 128 133 127 128 130

311 317 323 327 329 328

126 126 131

323 323 327

132 132 140 333 333 336

192 192 192 205 206 209

162 180 205 181 181 183 217 217 234 198 201 211

181 181 184

198 203 210

174 174 184

195 203 209

189 189 188 194 198 210

199 199 200

203 203 209

132 182 203

221 226 234

185 186 191 202 205 215 ND

ND

ND

805 876 887 ND 214 217 244

13
Transition and fusion temperatures, Instrument I ICTA Sample

Lit. Temp.

300, 525.

Ag

2 S0

4 412, 660

(850° maximum)

ND ND

ND ND

821 877 897 ND

20 nd

ND

ND

890

20 NDND

ND

796 880 891

3 300ND

300 300

10 298 298 305 301 301 302 578 597 610 ND

10 301ND

301 302

10 301ND

301 302

10 300ND

300 301

10 299

ND

300 301

10 298

ND

299 300

10 300ND

300 303

20 293

583

295

592

300

605

20 297

580 297

597

300 609

10 420 422 431 425 425 431

621 636 647 658 658 661

10 421 650

425 657 430

662

14
Rate

d

Instrument I Instrument II (850° maximum) ICTA Sample

Lit. Temp.

C A B D A B D Ag? SOA (cont) 10 425 427 432

651 658 (659) 20 4l8 420 428

632 647 653 20 420 422 435 628 648 658 Nap C0^ 20 298 303 (304) NDND

774 816 837

20 ND

ND

ND

778 805 843 Na

2C0 20 ND

ND

ND

356, 486

618, 854

573

583

so

3 10 - 10 555

10

1020 547

10 572

10 559

1020 556

562 566

580 578

578 582

301 315 349 ND

NDND

(?) (?) 571 567 569 569 572 564 560 567 570

(537) 571 573

571 571 573 569

582 582 584 584

581 508 583 584

541 565 584
Instrument I Instrument II

b (850(3 maxlmum) ICTA Sample

Lit. Temp. Rate A B D A B D Ko

Cr0,,

e 10 658 660 665 670 670 672

2 4 10 _ _ 670 629 666 671 663 10 631 665 674 (Reagent 20 662 667 670 grade) BaCO_ 3 804 806 813

3 810

10 777 791 803 - - 817

20 791 798 806 SrC0o 10 900 905 930

3 925 20 928 929 931 Na

2 S04

e 10 243ND

246 (254) 240, 890 10 240 249 (254) (Ultra pure) ND

10 237ND

243 243

20 241 244 254 238 241 249

866 874 883 - 20 241ND

242 254 238 239 246

20 246

865 246865 259

883

Definition of temperatures: A = temperature of initial change from base line value. B = temperature of intercept of base

line with extrapolated line for rapid change of temperature.

D = temperature of peak maxima. Instrument used with a low temperature furnace.

CNBS Circular 500 and American Institute of Physics Handbook.

dRate = °C/min. Sample not supplied by ICTA.

16
RATE KTC/MIN

330

RATE 10 °C/MIN Figure 4. Typical DTA curve for potassium nitrate.

210 RATE 10 °C/MINRATE 10 °C/MIN

Figure 5. Typical DTA curve for hydrogen sulphate.

17
RATE 20 °C/MIN

RATE 50 C/MIN

Figure 6, Typical DTA curve for potassium carbonate.

18
249

RATE 20 °C/MIN

Figure 7. Typical DTA curve for sodium sulphate.
300

RATE 10 C/MIN

303

RATE 10 °C/MIN Figure 8. Typical DTA curve for potassium perchlorate.

430 RATE 10 °C/MIN

RATE 10 °C/MIN

Figure 9* Typical DTA curve for silver sulphate.

20
RATE 20 °C/MIN

RATE 50 °C/MIN

Figure 10. Typical DTA curve for sodium carbonate.
RATE 10 C/MIN

RATE 10 °C/MIN Figure 11. Typical DTA curve for silicon dioxide.

RATE 10 °C/MIN

RATE 10 °C/MIN

Figure 12. Typical DTA curve for potassium sulphate.

22
f\

RATE 10 C/MIN

671 RATE 10 C/MIN Figure 13. Typical DTA curve for potassium chromate.

RATE 20 C/MIN

813 RATE 3 °C/MIN Figure 14. Typical DTA curve for barium carbonate.

23
RATE 20 °C/MIN Figure 15. Typical DTA curve for strontium carbonate.

RATE 20 C/MIN

RATE 10 C/MIN Figure 16. Typical DTA curve for aluminum oxide.

24
On examining the data* certain problems and tentative conclusions become apparent. First, several of the com- pounds yielded poor or meaningless DTA curves. The carbonates, in general, were representative of this group. On the other hand, a number of the compounds looked promising

as potential standards from the standpoint of accuracy and good DTA curves. These included SiO , KNO , KC10,, (except

for its uncertain decomposition), Ag SO., K SO,,, and SrCO . The precision and accuracy of the data, with few exceptions,

were better using instrument II. This may be due to better

contact of the thermocouples with the sample. In this instrument the sample was packed in a capillary, while in the other instrument, the contact between the pan holding

the sample and the thermocouple may have been poor. It was

also much more difficult to measure and interpolate the temperature from the non-linear scale of the latter instrument. Nevertheless, based on this brief survey, potentially

good prospects for standard reference materials are apparent. Because of concomitant Interest in several of these compounds

in other SRM programs as indicated by J. L. Hague, Coordi- nator of Inorganic Standards, Office of Standard Reference

Materials, efforts will be made to obtain pure starting material for further study. These include KNO , KC10,,

Ag SO,, SiO , K SO,, and SrCO . These also encompass the temperature range of Interest to ICTA. Prom the standpoint of purity it Is apparent that chemical characterization of these materials will be an important

factor. The results obtained on two grades of Na SO, (see table 8) readily point out the effect of common impurities.

Similarly, in the case of stearic acid (see figure 17) the

25
high purity of the preparation has an important bearing on the accuracy of the data. The upper curve represents a purer preparation.

In the continuation of last year's studies involving tricalcium silicate (table 9) the detection of endothermic peaks was accomplished by the use of instrument I. In this case the effect of the better geometry of the sample material in the dish is more favorable for the detection

of transition temperatures than the capillary arrangement.

The final small peak was now detectable. Mazieres [11] discovered this transition with his micro equipment. Table 9* Endotherm transition temperatures

for tricalcium silicate. Cycle Temperature C Heating (a) 600 915 980 990

(b) 650 906 965 990

a Cooling (a) 560 905 970 985

b

(b) 570 885 950 985 Mazieres,

bKBS.

It Is expected that progress in precision and accuracy

can be made through better understanding and control of the Instrumental variables and well characterized high-purity

preparations. It is hoped that this evaluation should lead

to the production of suitable standards much needed for the calibration of instruments which are now being used in bio- chemical, organic, and inorganic areas of science and tech- nology.

26
Figure 17. Typical DTA curve for stearic acid.

27
D. Analyses of Samples

A variety of samples, mostly standard reference materials, have been analyzed by the gravimetric procedures.

The tentative results of these analyses together with the relative precision are presented in table 10. No additional bibliographical references are given since they were covered

in the previous reports of this section.

T. A. Rush and Oscar Menis

Table 10. Summary of gravimetric determinations.

Element or Compound SRM

Cu

Cu

CuCu

CuCu

Cu

Co

CoCoPe

Si02 CaP

1121

1121

1122 1122 1123

1123 1080

1121

1122 1123 1079a

No. Rel. std. Kind Pet. Percent dev., % Be-Cu alloy cast 3 97-^1 0.02 Be-Cu alloy wrought 3 97.1+67 0.01 Be-Cu alloy cast 3 97.1^6 0.002 Be-Cu alloy wrought 3 97.1+3^ 97.116

0.002 Be-Cu alloy cast 3 0.002 Be-Cu alloy wrought 3 97.115 0.01 bis (1 -phenyl-1,3- 12 10.1+7 0.5 butanediono ) copper (II) Be-Cu alloy cast 2 0.293 1.0 and wrought Be-Cu alloy cast 3 0.217 2.0 and wrought Be-Cu alloy cast 2 2. 306 0.3 and wrought

tris (1-phenyl-l, 3- k 10.29 0.2 butanediono) iron (III) Dolomite limestone 3 1.20 0.9 Fluorspar 3 98. 11| 0.06

Reported as the compound. Based on solubility studies as in NBS Certificate 79.
2. TITRIMETRY

A. Introduction

Studies were continued along the plans presented in the last report [10] . This included the continuation of studies of spectrophotometric and potentiometric titrations

and the investigation of pyrohydrolytic separation of nitrides and fluorides. Only a relatively limited effort, however, could be carried out along these lines during

this period. The current investigation involved the potentiometric titrations of boron, spectrophotometric

titration of beryllium and fluoride and pyrohydrolytic

separations of nitrides and fluorides.

B. Alkallmetric Titration of Boric Acid

1. Introduction

A boric acid standard reference material is needed for use

in the measurement of a standard neutron cross section. For

that purpose it is also desirable to know very exactly its stoichiometric composition. One approach which was studied for

the latter purpose was the evaluation of a pH titration with a standard sodium hydroxide solution. It is obvious that the modified potentiometric method [2] is capable of a precision of 0.1 percent relative standard deviation. The present investi- gation involved refinement of the procedure to improve the pre- cision to two parts in ten thousand.

2. Refined Procedure and Results High purity boric acid was accurately weighed and dis- solved in water. The solution was then acidified with

hydrochloric acid and boiled under a reflux condenser to insure the removal of carbon dioxide without any loss of boron. It was cooled and transferred to a quartz beaker under a blanket of carbon dioxide-free air. The solution

was adjusted to pH 6.9, and 0.5 I manitol was added. It was

29
then titrated with standard sodium hydroxide. Base was added from a weight burette -until a final pH of 6.9 was attained.

The results presented in table 11 indicate a precision

of 0.02 percent relative standard deviation for a single determination based on six degrees of freedom. Thus, the desired precision can be readily obtained by this procedure.

However, the method is highly empirical in that a predetermined pH is selected for the endpoint. The method can be used to advantage in preparing a precise ratio in boron isotope mixtures. It is evident that it cannot, at present,

be used to establish absolute values. Table 11. Potentiometric titration of boric acid. Sample No. Wt. of HBO

0.25207

Wt. of NaOH gNaOH/gH

3B0

3

1 49.3807 195.898

2 0.25010 48.9869 195.867

3 0.25026 49.0278 195.908

4 0.24953 48.8908 195.930

5 0-25241 49.4700 195.990

6 0.25124 49.2301 195.952

7 0.25338 49.6471 195.935

Average: 195.925 Standard deviation: 0.040 Relative standard deviation (percent): 0.02

C. Spectrophotometric Titration of Beryllium

1. Introduction

In conjunction with studies on the gravimetric deter- mination of beryllium in a copper-beryllium alloy, an alternate method for its determination was sought. The

30
most promising method found in the literature [13^ involves

the back titration of excess sodium sulf osalicylate with

standard beryllium solution.

2. Results and Discussion

In initial studies with a standard solution of beryllium, the precision of the endpoint determination, based

on a plot of a "S" shape titration curve, was only O.65 percent relative standard deviation. This value was im- proved in six subsequent titrations to 0.25 percent, calculated by means of a computer program. Further tests were carried out with SRM copper-beryllium

alloys. The results are presented in table 12 and compared with gravimetric values. Based on this limited study the method offers a potentially rapid and reliable method for

the determination of beryllium. Its main limitation Is that it requires an accurate primary standard of beryllium.

K. M. Sappenfield

Table 12. Spectrophotometry titration

of beryllium in Be-Cu alloys. Beryllium, Percen

Sample

12

34

56

Titration

I a II

b Gravimetric

1.78 1.91 1.94

- I.89 1.92

1.75 1.76 1.77

1.72 1.72 1.77 0.42 0.41 .47 0.43 - .47 Titration in HC1 media.

bmProcedure described in section 1 of this report.

31
D. Spectrophotometry Titration of Fluoride and Pyrohydrolytic Separation

1. Introduction

The continuation of efforts for the separation and determination of fluoride in fluorspar centered around

the spectrophotometric titration of fluoride and test of several flux materials for the pyrohydrolytic separation [10],

2. Studies of Separation Procedures

Several pyrohydrolytic procedures were tested in search

of optimum conditions for the separation of fluoride from

CaF . In an attempt to increase the recovery of fluoride

at a temperature of 850 C the following three fluxes were

used in addition to the sodium tungstate flux used earlier:

(l) sodium tungstate flux plus NaOH, (2) sodium tungstate

cent, and with the sodium bismuthate about 15 percent. The reduction of sample weight from 200 mg to 100 or 25 mg resulted in a recovery of only about 16 percent in each case. Another approach, involving the use of higher temperature

is underway. For that purpose a heavy-duty furnace with a nickel

ignition tube, as shown in figure 18, has been assembled. Tests with other fluxes at temperatures above 1000 °C will be undertaken to assure the complete release of fluoride,

3. Titration Studies

A brief study of the spectrophotometric titration of fluoride by the thorium-Alizarin Red S reaction revealed a precision of 0.6 percent. The relative error is too high

for the needed accuracy of this analysis. In addition,

tests of possible interference from tungsten which may be a 32
Figure 18. Pyrohydrolysis apparatus. byproduct of the pyrohydrolysis revealed an anomolous effect.

As shown In figure 19> a negative error occurs when less than 8 mg of tungsten is present in the distillate solution, while a positive error is noted with higher concentrations.

For these reasons this approach was abandoned. Recently an ion-specific fluoride indicator electrode

was acquired. It is planned to continue this work by potentiometric titrations Involving this indicator electrode.

E. Separation of Nitrogen From Refractory Nitrides Further studies of fusion pyrohydrolysis of refractory

nitrides centered around the design of a modified apparatus.

The design of the apparatus, shown in figure 18, includes a new high temperature furnace with automatic control of tem- perature and a modified ignition tube. The tube is equipped with a Wilson valve which enables one to Insert the sample slowly into the hot section of the furnace while the main

section of the ignition tube is sealed at the entrance. A nickel guard tube is also included to prevent the molten

flux from attacking the ignition tube.

33
S 5.5 — No W added

5.28 mg F, present

10 20 30 60 70 80 90 100 W added, mg Figure 19. Interferences of tungsten in the deter- mination of fluorine by thorium titration.

A modified procedure which would permit the determination of both NH and N is contemplated. It provides the elimination of the use of hydrogen and substitution of helium as the purge gas. Under those conditions the ammonia

and the nitrogen which may form during the reaction could

be collected separately. The first could be collected in an aqueous scrubber and the latter in a molecular sieve.

34
The two components could then be determined independently

by spectrophotometrlc and gas chromatographic procedures.

B. B. Bendlgo

F. Analyses of Samples

A variety of samples, mostly standard reference materials,

have been analyzed by the titrimetric procedures. The tentative results of these analyses together with their relative precisions are presented in table 13. No additional biblio- graphical references are given since they were covered in the previous reports of this section.

S. A. Wicks

Table 13- Summary of titrimetric determinations.

Elemer t SRM

Cr 4j Cr 163

Cr 30f

Cr 3b

Cr 3c Cr 196

Fe lb Fe 1121

Fe 1121

Fe 1122

Fe 1122

Fe 1123

Fe 1123

Fe 1079a

N 3b N 3c N 4j N 30f

N 163 V 4j V 30f V 3b V 3c

Kind

No. Rel. std. Pet. Percent dev., %

Cast iron Steel

Cr-V steel White iron White iron Ferrochromium (Low C) Argillaceous Limestone

Cast Be-Cu alloy

Wrought Be-Cu alloy

Cast Be-Cu alloy

Wrought

Cast Wrought

tris (1 phenyl-1,3-

butanediono) iron (III) White iron White iron

Cast iron Cr-V steel Steel

Cast iron Cr-V steel White iron White iron

0938

982 939 0525

0465

89772 088 089

158

153 043 04l

30106 0057 0037

0089

0091 0298

182 0055

OO63

0.4 0.1

0.2

34

7

6

50.4 0.5

35
3. FLAME EMISSION AND ATOMIC ABSORPTION SPECTROPHOTOMETRY

A. Introduction

The emphasis in the fields of atomic absorption (AAS) and flame emission spectrophotometry (FES) during the past

year has been on ways to Improve the precision and accu- racy of these methods. To accomplish this goal an eval- uation of various parameters which included nebulizerburner, oxidant-fuel systems, interferences, slit widths,

sources of monochromatic light, digital readout and electronics was undertaken. During this period, some of the accomplishments include the determination of impurities

at the submicrogram level in high-purity zinc and selenium,

and a differential technique for high-precision flame emission spectrophotometry. Methods were developed for separation of trace quantities of copper and arsenic by

solvent extraction as well as for the separation of macroquantities of iron without loss of trace constituents.

The copper was extracted with 2-thenoyltrifluoroacetone, while the arsenic was extracted with diethyl ammonium diethyldithiocarbamate from an acid medium. The precision

of flame emission spectrophotometry was increased to less

than 0.2 percent by a new differential technique. This increase in precision was accomplished with the aid of a phase shifter and attenuator on our ac synchronous detector.

Also, the limit of detection of arsenic by atomic absorption

spectrophotometry was extended to 0.5 ppm with the aid of a new gas mixture of argon-hydrogen.

The basic Instrumentation remained the same as described

in the last report [10]. However, a digital readout was acquired which was found to speed the acquisition of data

with increased precision.

36
B. Determination of Trace Elements at the Submlcrogram

Level in High-Purity Zinc

1, Introduction

In the previous report [10] the determination of trace impurities in a high-purity zinc (99-999) was briefly dis- cussed. During the past year, copper, cadmium, gallium,

and potassium were determined in the material by AAS or FES at the submlcrogram level. The cadmium, gallium and potassium were determined without any preconcentration

which minimized trace contamination; however, a separation

and preconcentration of copper was necessary. The instru- mental conditions were also modified which increased the precision and sensitivity of the method.

2. A Study of Nebulizers and Burners

A study was conducted using four different burner systems

to obtain the lowest detection limits by AAS of several elements of interest in high-purity zinc. Table 14 gives

a comparison of the detection limits of the four different

burner systems. Burner B yielded the lowest detection

limit; however, this burner has a definite memory effect with samples containing more than 5 mg of solids per ml. The same was true for burner A, but to a lesser extent.

The Puwa-Vallee tube arrangement can only be used when the total solids are less than 1 mg/ml. The total consumption

burner C was slightly less sensitive but free of any memory

effect with concentration of solids as high as 50 mg/ml.

Also, this type of burner can be used for organic solvents while caution must be exercised with the premix burners.

37
Table 14, Comparison of detection for various burners

by atomic absorption (aqueous solutions). Detection limits = iig/ml/$ absorption Element Burner : A B C D Ag 0.01 0.006 0.01 _ Cd 0.04 0,001 0.01. 0.04b

_ Cu 0.02 0.01 o.oib Mg 0.005 0.003 0.01 - Pb 0.2 0.06 0,5 - A, premix burner; B, premix burner in hot mode; C, total consumption; D, Fuwa-Vallee tube arrangement [14], Organic solution.

3. Separation and Preconcentration

It was found in the initial studies with AAS that the aspiration of a high concentration of zinc leads to high

results especially when the atomic line of interest is in the ultraviolet region of the spectrum. For example, by measuring the absorption of the element in a solution con- taining 50 mg of zinc per ml at the resonance line of cadmium (2288a) , the absorption value indicated a concentration of cadmium of one ppm. As a check for scattered

light the cadmium ionic line at 2265A was tested with a standard solution of cadmium and found not to produce any absorption. However , when a solution containing 50 mg of zinc per ml was nebulized, the same absorption was observed

as found at the resonance line.

It was concluded that the observed absorption at 2288A

was due to scattered light and not cadmium. For this reason,

a preseparation and concentration step was adapted for the determination of copper in the high-purity zinc. After investigating several separational procedures including

38
anion exchange resin and chelating agents, 2-thenoyltrIf luoroacetone and ammonium pyrrolidine dithiocarbonate

,

as well as high-molecular-weight amines, a method was developed for the separation of submicrogram quantities

of copper from zinc with 0.2 M 2-thenoyltrif luoroacetone

in methy isobutyl ketone (hexone) . The results for the copper, cadmium, gallium, and potassium are given in table 15. The accuracy of the procedure was checked by

the standard addition technique [15J. Table 15 . Values for trace elements in high-purity zinc. Element, ug/g

NBS

SRM No. Method Cd Cu Ga K High-purity

zinc AAS <0.1 -.005 <0.1 <0.02

631

a AAS 0.8

-0 ' 1 6.3" 0,4

Control sample.

C . Effect of Calcium and Phosphate on the Atomic Absorption Determination of Barium

An evaluation of the effect of calcium and phosphate on the AAS determination of barium has been carried out. An experiment was performed to test the effect of calcium and phosphate using the Beckman laminar flow burner with an air-acetylene flame. The results of this experiment are given in table 16. It has been reported by Koirtyohann [l6] 39
that the intense oxide and hydroxide bands of calcium and strontium observed in emission are also observed in atomic absorption. In our study calcium was observed to have two distinct effects on the absorption of barium. First, calcium suppressed the absorption of barium and, secondly, when the calcium concentration exceeds 1 mg per ml, a relative strong absorption was observed by calcium at the resonance line of barium at 5536A. This absorption by calcium must be due to the strong CaO-CaOH band which has

a maximum at 5540A. To overcome the interference of cal- cium on barium when the ratio of calcium to barium is greater than 10, a separation of barium was affected using

PbCrOK. This procedure is described in a previous publication by this author [17^« The absorption of barium was found to be severely

suppressed by the phosphate even with concentration as low

as 0.001 M or 0.1 mg per ml. However, the phosphate inter- ference was eliminated by the addition of glycerol and perchloric acid as releasing agents.

D. High-Precision Flame Emission Spectrophotometry

1. Introduction

A new technique of differential flame emission spectro- photometry was developed whereby a precision of one part in

a thousand was obtained over a concentration gradient of a few ppm to several percent. While our efforts in this field

in the past several years have been to increase the limits

of detection of the various elements, little effort has been spent on techniques to improve precision and accuracy

of the method. The limits of detection which were reported

in our previous report [10] were obtained with a sacrifice

40
Table 16. Effect of calcium and phosphate

on the absorption of barium. Barium pre sent , Interfering ion, Barium found, Recovery , M.<g/ml mg/ml ng/ml i

10 Ca-0.01 10 100

_ 0.01

10 0.1 9.8 94 0.1 0.4

10 1.0 13.0 57

_ 1.0 7.3

10 5.0 13.2 12 5.0 12.0

10 10.0 18.5 10.0 18.5

10 H P0

4

- 0.1

J H 0.1

9.0 90

10 1.0 8.8 88

_ 1.0

10 10 3.0 30

_ 10

10 100

- 100 Recovery after correcting for calcium.

of precision. Therefore, our present aim was to ascertain

those parameters under which the precision of the measurement for FES for various elements could be optimized, and

to test our theory in the determination of lithium in standard reference material.

As flame emission and atomic absorption spectrophotometry become more and more widely used in science and industry, the relative precision of the method is reported

to be from 2 to 5 percent [15]. However, with the instru- mentation that is available, a precision of less than two percent relative error could be maintained for most elements.

The precision of the method which is normally quoted for

41
trace or milligram quantities is - 5 percent [18]. Ingamells [19] modified the Horstman method for the deter- mination of lithium, sodium and potassium in silicates,

and obtained a precision of one percent. This was accom- plished by placing a sensitivity indicating ammeter in the circuit of the spectrophotometer and applying the principle of differential measurement.

2. Experimental Variables

In our investigation various parameters were optimized

such as slit width, regulation of oxidant and fuel, and measuring the signal. The effect of the slit width in the FES determination of lithium is given in table 17. The current data are insufficient to statistically evaluate

any effect of varying the exit or entrance slit width while keeping the other constant. Table 17. Effect of slit width on the flame emission spectrophotometric determination of lithium. Slit Width >

(J- Rel. std. Entran<2e Exit Scale reading Std. dev. dev. %

25 25 74.53 0.18 0.25

25 50 85-31 0.26 0.31

25 100 78.43 0.23 0.29

50 25 84.69 0.16 0.18

50 50 89.13 0.20 0.22

50 100 83.18 0.29 0.35

100 25 75-88 0.17 0.22

100 50 84.11 0.14 0.16

100 100 94.36 0.17 0.18 Average of 6 readings.

42
The regulation of the flow of oxidant and fuel became

a critical factor in our study. It was found that flow

of gases could not be controlled precisely by the pressure reducing valves. However, by using precision rotometers

in conjunction with the reducing valves, a constant flow

of oxidant and fuel could be maintained.

Generally, in the measurement and calibration of flame

emission, a calibration curve of to 80 percent emissivity

is prepared for an element over a concentration range such

as to 5 or to 10 ppm as shown in figure 20. By this method the inability to read the data from the graph to better than one percent becomes a limiting factor. However,

by expanding a small portion of the curve as shown in figure 21, the precision can be increased to 0.1 percent.

To achieve scale expansion a phase shifter and attenuator

was designed and built for our ac synchronous detector as shown in figure 22. This modification in the electric circuit permits the aetting of any desired concentration

at zero percent transmission and then a finite concentration above this value expanded to give full scale deflection. In addition, the recorder was replaced with a digital readout which circumvented the inherent drag of the pen on the recorder and eliminated the error of trying

to measure the peak height on the chart paper.

3. Results for Lithium

To evaluate this new approach to FES, a synthetic

50 mg of AlgO , 300 mg of B0, and 124.8 mg of Li C0_. The synthetic sample was dissolved with HP and HCIO^ and then the lithium content was determined using a typical

43
Figure 20. Typical lithium

calibration curve. Figure 21. Lithium cali- bration curve - scale expanded.

Figure 22. AC buck-out adaptor for synchronous detector.

44
calibration curve and by the expanded scale technique.

The results are shown in table 18. The data shows that

the expanded scale gave an improvement by a factor of three in the precision, relative standard deviation, over

the conventional calibration curve. Table 18. Lithium In synthetic Dy

p°o glass.

(Li added as Li

2 C0 - 124.80 mg) L1

2

C °3 Std. Rel. std. Rel. std. Found, mg Average dev . dev . , % error, fo Calibra- 124.6 127.2

tion curve, 125.4 127.2

2-10 lig/ml 124.2 123.8 124.9 1.3 1*1 0.9

124.2 123.8

123.8 124.7 Expanded 125.11 124.48

scale 124.74 124.16 124.63 0.45 0.37 0.5

124.48 124.85

This technique was applied to the determination of lithium in three different glass beads which are to be used

for neutron flux measurements. To obtain a realistic value

of the precision of the method, the analysis of the samples

was performed over a period of two weeks by two operators.

The results are listed in table 19. Prom these data and subsequent work the major limiting factor of the method

was the reproducibility in the preparation of standards.

The successful analysis with a precision and accuracy

of better than 0.2 percent met the requirements for a neutron flux monitor. In addition, this technique helped

to conserve precious sample needed for the analysis of other constituents.

45
Table 19 . Determination of lithium in gla

for neutron flux measurement.

No. of determi- Li

20,$

10.177

Std. Rel. std. Rel. std. Material nations

6 dev

.

.013

dev., fo

• 13

error, ^ Dy

2 Glass-A

6 10.147 .025 • 25

-B 6 10.065 .024 .24

-C 6 10.123 .033 -33

3 IO.067 .022 .22 -D 6 10.181 .014 .14

6 10.146 .018 .17 &

10.181 .10 1.0

Av. of X ; 10.139 .052 .51 .16 CoO Glass -A 6 10.020 .023 .23 -B 6 10.060 .085 .85

6 9.989 .085 .85 4 9.995 .010 .10

-C 6 10.058 .044 .44

7 10.018 .023 .23 35 Av. of X E 10.040 .058 .57 .20 In Glass-A

3 -B

5 10.008 .022 .22

6 10.075 .028 .28

-C 4 10.174 .035 .35

4 10.070 .019 .19

4 10.131 .035 .35 Av. of X

23 10.087 .064 .64 .28

E. Determination of Ar senic by Atomic Absorpti on Spectrophotometry

1. Introduction

A new method was developed for the determination of arsenic In standard reference material of high-purity sele- nium and cast iron by AAS. It involved the establishing of
new parameters for the AAS measurement and a new approach

to the separation and preconcentration of arsenic. This investigation led to a significant improvement in accuracy

of the arsenic value. Since the resonance lines of arsenic are below 2000A, very little information was available on the AAS determi- nation of arsenic [20]. Arsenic has three resonance lines which are located at 1890, 1937 > and 1972A, A preliminary

survey of these lines was made and the sensitivities were

found to be in a ratio of 1:1:2, respectively. The line at I89OA was greatly affected by the aspirating media and the presence of other cations. For this reason the line at the longer wavelength (1937A) was chosen for further investigation. The variables studied were sources of monochromatic

light, effect of multiple pass system, burners, oxidantfuel system, dissolution of sample, and ways of separating

and preconcentration of the arsenic.

2. New Source of Monochromatic Light

Since the resonance line of interest is in the far ultraviolet region of the spectrum, a line source of high

intensity is required. The hollow cathode for arsenic is very difficult to produce and has relative low intensity.

The high frequency electrodeless discharge tube described

by Meggers and Westfall [21] was investigated as a line source. This source was found to be stable and extremely

intense for arsenic. This type of source should prove

useful in future work for many elements.

3. Effect of Oxidant Fuel Various oxidant-fuel systems and nebulizer burners were

tested and the most satisfactory system was an argon-hydrogen flame with a Zeiss burner. A limit of detection of less

47
than 0.5 ppm of arsenic was obtained in this system. All systems using oxygen or acetylene were found to have strong absorption in this region of the spectrum. With the argon- hydrogen flame the light from the radiating source could be passed three times through the flame without serious loss

of radiation. Of the interferences investigated, carbon radicals in the flame from the acetylene or organic solvents

and high concentrations of solids produced a high absorption

blank. This difficulty was overcome by the use of hydrogen

as the fuel and the removal of organic material and high

solids from the nebulized solution.

4, Determination of Arsenic in High-Purity Selenium Another phase of this study was the investigation of preconcentration methods. In the determination of arsenic

in high-purity selenium several procedures were investigated

for its separation. It was found that selenium could be precipitated with sulfurous acid from a 2N HC1 medium without loss of arsenic. Since losses of As may occur during

evaporation from an HC1 medium, the arsenic was concentrated

by an extraction with diethylammonium diethyldithiocarbamate

(DEDC) -in chloroform from 2N HClk This extraction step was found to give excellent recoveries at a ratio of aqueous to organic of 20 to 1. To make the extraction of arsenic quan- +3 titative, the arsenic was reduced to As with KI and Na S in a hot water bath (55 C) . Since the organic con- stituents were found to interfere in the final determination,

the arsenic was stripped with copper from the DEDC in chloro- form by an exchange reaction. The resulting solution was analyzed for arsenic by AAS. By this method the arsenic content for a 4-5 gram

sample of high-purity selenium was found to be less than
one ug/g. All the separations were followed with As and

by the standard addition technique,

5. Determination of Arsenic in Cast Iron

In the determination of arsenic in cast iron several additional problems were encountered. It was found with

77 the aid of As that losses of arsenic do occur during the dissolution of the cast iron with HNO or HNO plus HC1 when the operation is carried out in a covered beaker. However, no loss was observed if the dissolution is per- formed in a conical flask. Several procedures were inves- tigated for the removal of the major component, iron. Of the methods surveyed, 2-thenoyltrlf luoroacetone in CCIk was found to be an excellent extractant of iron without a loss of arsenic. This general approach is described in the literature [22], By this method as much as 0.5 g of iron was removed within 30 minutes. The arsenic in the aqueous solution was then extracted with DEDC as described

previously. This procedure is being used to determine

arsenic in several SRM cast iron samples.

P. Analysis of SRM by Atomic Absorption and Flame Emission Spectrophotometry

During the past year considerable effort has been spent

in the analysis of SRM by atomic absorption as well as flame emission spectrophotometry, A summary of SRM work is given in tables 20 and 21. The copper In white iron was determined by AAS without any preconcentration or separation

using a total consumption burner. In each case recoveries

were checked by the standard addition method [15]

T. C. Rains

49
Table 20. Summary of analysis performed by flame emission spectrophotometry of standard reference material.

NBS

SRM

No. Material Element

No., of determinations Cone. ,fo Std.

dev. Rel. std. dev., %

* la

lb Limestone Na

2 816 0.316

0,040

.008

.003

37 88* 88a Dolomite Na

2 612 0.024

0.0088

.002 .0006

7

7 *

9797a Flint clay L1

2

617 0.226

0.120

.003

.001 1.51 * 9797a Flint clay Na

2

3 11 O.O65 0.034

.002

.001

3

3 9797a Flint clay K

2

618 0.532

0.528

.011

.008

2

1 98* 98a Plastic clay L1

2

517 0.0256 0.0749

.0001

.0011 0.5

1 98* 98a Plastic clay Na

2 412 0.268

0.080

.001 .0024

2 98* 98a

Plastic clay K

2

4 48 3.18

1.06

.04

.01

1

1 us/k

727 RbCl LI 4 <0. 2 - - Na 4 2. 3 .3 11 K 4 420 9 2 Cs 6 24 3 14 1121 Cu-Be alloy Ag 8 50 2 4 1122 8 54 3 5 1123 8 87 3 4 Control sample.

50
Table 21. Summary of analysis performed for copper

by atomic absorption spectrophotometry

of standard reference material.

No. of NBS

SRM No. Material

determi- nations Conc.,$Std. dev. Rel, std.

dev.., <fo * 3b White iron 7 0.051 .001 2 3c White iron 10 0.055 .001 2 41* White iron 8 0.256 .008 3 4j White iron 56 0.238 .008 3 30f White iron 13 O.076 .002 2 13e Steel 6 0.110 .002 2 163 Steel 8 .0921 .0011 1 Control sample.

51
4. SPECTROPHOTOMETRY AND SPECTROPLUORIMETRY

A. Introduction Described in the following section are the philosophy,

some of the approaches being tried, and the pertinent

results obtained during the past year in the twin areas of spectrophotometry and spectrof luorimetry. While greater sensitivity and selectivity have again been the principal

goals, precision and accuracy have also been given con- siderable attention. The evolution of improved methods

based on the formation of ternary complexes and on the controlled dissolution of samples in closed systems has been especially encouraging. Likewise, the speed and simplicity with which high-accuracy results have been obtained by differential spectrophotometry suggests the need for even more extensive studies in this area. While

some experience has been gained in the use of variable path-length cells and scale expansion, the added advantages

of digital readouts have thus far not been exploited.

Although the studies in fluorimetry are still very much

in the planning stage, considerable effort has been spent

in evaluating several of the currently available instruments. An objective summary of this study is given in the text.

B. Study of Ternary Systems Although a tremendous amount of effort has gone into

the development of more sensitive and selective chelating

agents, the net result has not been overly rewarding. Most of the complex or chelate systems that are presently

used in inorganic absorption spectrophotometry are binary

ones, i.e., one or more metal ions are combined with one

or more ligand molecules of the same type. Unfortunately,

52
especially from the standpoint of trace analysis, such systems are generally not very selective and may prove unsuitable in practical applications unless adequate sep- aration procedures can be developed. While one of the more successful approaches to selectivity in the past has been

the introduction of steric hindrance into reagent molecules

near their chelating center, one should be cautioned that

such improvement is closely related to the manner in which

they are later used. Thus, although a reagent is specific within the context of spectrophotometry the same may not

be true when it is utilized in an extraction system.

In recent years a more promising approach to selec- tivity has been through the use of ternary complexes. In these systems not one but two different ligands react with

the central ion. As a result the selectivity of such systems can be considerably improved since an additional

variable has been introduced which may eliminate many

potential Interferences. An added dividend in that sensi- tivity may also be higher because it is often possible for

a much more complex absorbing organic molecule to be placed

around the metal ion. There are two principal ways in which ternary complexes

can be formed [23]. In the first, the situation must arise

that one ligand does not fully satisfy all the coordinative requirements of the ion and therefore a second ligand

species may still react, I.e., neither ligand alone must form a coordination-saturated complex with the ion. The other alternative is that the first ligand, on entering

the coordination sphere of the cation, satisfies it only

in a dative fashion so that the primary complex still bears
an overall positive or negative charge which may then ion- associate with an appropriate dyestuff or other similar molecule

.

As illustrative of our experience with the first type was the determination of zirconium in a variety of white

cast irons through utilization of the Zr-EDTA-Pyrocatechol

Violet complex. This reaction was first described by Flaschka and Sadek [24], and more recently has been studied

in detail by Raber [25]. It exploits the unique property

of zirconium (and hafnium) of being able to present 8 coor- dination positions for bonding. Since EDTA is capable of utilizing only 6 of these, 2 positions remain for additional complexation . In this instance these latter 2 positions are occupied by a Pyrocatechol Violet (PCV) molecule and the overall stoichiometry is Zr-EDTA-PCV. More recently, we have made numerous unsuccessful attempts to incorporate the Zr-EDTA complex into a solvent extractable 4-membered ion- association system of the type R [Zr-EDTA-R 1 ] . Intorre

and Martell [26], however, have studied a number of mixed complexes of the type Zr-EDTA-R in which the R ligand contained one or more sulfonic acid groups. Combining their results with the recent discovery [27] that some chelating

agents containing a single sulfonic acid group can be extracted may eventually prove useful. Furthermore, it may be possible to extract the Zr-EDTA-PCV complex directly

in this manner.

The second type of ternary complex, the ion-association

system, has commanded most of our attention to date. During

the past year we have described [28] a highly reliable method for antimony in various materials, especially cast

irons. In this method an Sb-complex of the type R SbCl^-

- 54
is extracted from a strongly acidic solution leaving the excess dye, R , in the aqueous phase. West and co-workers

have described similar procedures [29,30] for a number of metals that are initially complexed with 1,10-phenanthroline

and subsequently with Bromopyrogallol Red or Rose Bengal

Extra.During the course of studying the [Brilliant Green]

SbCl^- reaction, it became apparent that for such systems

to have general applicability detailed information must be obtained regarding the direct interaction of such dyes with

the intermediate ligand and also the effect of acidity on such interactions. The principal reactions that must be considered in such systems are as follows:

(1) M + L~ ML"

(2) R

+

+ ML" = RML

(3) R

+ + L" = RL

(4) H

+ + L" = HL

M = metal ion. L~ = simple intern edia

as F , CI , Br , CNS , etc. large dye cation such as derived from Crystal Violet, Brilliant

Green, Methylene Blue, etc.

non-extractable hydroxy complexes. The desired sequence of reactions as given by equations (l) and (2) then becomes:

Au+3

+ 4L" = AuL

~
Reactions (3) and (4) represent competing reactions and must be eliminated or at least minimized in order for suCh systems to be applicable. To do so an extensive investigation of several R cations was carried out with various

L ligands at three concentrations and at three acidities.

The extent to which reactions (3) and (4) occurred was

studied by making absorbance measurements on benzene

extracts. The analytical conditions were as follows:

-3 -2 -1 L cone. = 10 J

j 10 , and 10 M

H

+

cone. = 10~ 2

, 1 and 6M H SO^

R+

= 0.01$ w/v Aqueous Vol.= 25 ml Organic Vol.= 5 nil Table 22 gives detailed results for the extraction of Crystal Violet and Brilliant Green as simple binary complexes

Table 22. Extraction of Crystal Violet and Brilliant Green as binary complexes

Absorbancej 1-cm cell Ligand Cone

.

i/iolet Green Ligand Added, M H+

Cone

10" 2 M 590 mu 0.010

625 m

Cl~ 10J 0.040

10

10"

10"

22 0.007

0.017

O.O56

Cl" 1 0.005 0.010

1

1 0.002 0.001 0.019

Cl~ ft*

6

6

6 0.005

0.003 0.000

0.000

0.000

0.000

(continued)

56
Table 22. Extraction of Crystal Violet and Brilliant

Green as binary complexes (continued)

Absorbance, 1-cm cell Crystal Brilliant Ligand Cone

Violet Green Ligand Added, M H

+

Cone

10" 10"

10"

., M

2

2

2

590 mu 0.022 0.094 0.990

625 m^i Br~

-

Br~ 11

1 0.007

0.0" - 0.008

-

Br~ 6

6 0.000

0.000

- 6 0.000 - CNS~ 10"

10" 10

22 inf.

inf.

inf.

inf.

inf.

inf. CNS~

io

-i

1 0.010 0.052

1 0.039 0.680

10

x

1 inf. inf. CNS" 6 0.000 0.000

6 0.005 0.008

6 0.010 0.039

I" 10" 10

10"

2

22

°' 395

a inf.

inf.

a

-

I" «>:i ^

11

1 0.07ia 0.775*inf.

-

I" 6 o.oi8a

_ 6

6 0.053a

- (cont inued)

57
Extraction of Crystal Violet and Brilliant

Green as binary complexes (continued)

.

Absorbance, 1-cm cell Crystal Brilliant

Ligand Cone. Violet Green Ligand Added, M H

+ Cone, I

10

10

1 590 ma 625 mu cci coo" 1.42

inf. inf. 2.0

inf.

inf. cci coo" i

l

l 0.015

inf. 0.046

inf.

inf. cci coo" 6 0.010 0.010

6 0.025 0.080

6 0.039 0.142

F" ">:i &

10" 10"

10"

2

2

2 0.000

0.000

0.000

0.003 0.002

0.005

F~ -1

£-1

ll 0.000

0.001 0.000

0.001

l 0.004 0.001

F" 6

6

6 0.000

0.000

0.002 0.000

0.000

0.001

None _ 10" 2 0.015

- l 0.014 -

- 6 0,017 - 7H

5 2

- 10

10" 10"

2

2

- 0.030

1.75

C 7H

5 2

- 11

- pptd,

pptd.

1 - pptd.

CH COO" 10"

1 2

- 0.055

0.037

6 - 0.001 Absorbance due primarily to air oxidation of I 58
Prom the results giver it is apparert that reactior (3) becomes a serious problem in those extraction-spectrophotometric systems when the intermediate ligand concentration

and acidity reach certain designated values. Not only are

the reagent "blanks" quite high in such instances but also their stability is much less than the corresponding ternary

complexes. As seen in table 22, CNS~ and CC1 C00~ extract considerably at low acidities but their effects become much

less pronounced at high acid concentrations. Bromide ion

is somewhat intermediate in behavior whereas the smaller

CI and F ions exhibit negligible extraction over the con- centration and acidity ranges investigated.

In comparing the extraction ability of the two dyes it Is seen that, under essentially the same conditions of acidity and ligand concentration, the absorbances obtained with Brilliant Green are generally higher than those obtained with Crystal Violet. Undoubtedly these differences

are attributable to the lower solubility of the reaction products of the former dye. While Crystal Violet contains

only methyl-substituted amino groups, Brilliant Green has

two diethyl-substituted ones which, by means of their greater inductive effect would be expected to more effec- tively stabilize their respective dye cation.

The availability of data of this nature should allow

one to more readily select the optimum conditions for the selective formation of a particular ternary complex. The only additional question is whether, under the conditions

selected, there is sufficient intermediate ligand available

to complex the metal ion.

59
C. Spec tr of luorlmetry

1. Introduction

The sensitivity of absorbance measurements is limited

by two factors, both of which suggest that the lower limit

of detection is about 10 M for any complex in solution.

The first factor is the inability of most spectrophotometers

to measure less than 0.001 absorbance units while the second

is that all molecules have a limited capacity to absorb

light. Braude [31] has discussed this point extensively

and has shown that the maximum extenction coefficient for

any organic molecule is about 100,000. Scaling down of solution volume has permitted some increase in absolute sensitivity but the problems associated with reproducible

cell positioning has frequently masked any marked improvement. As a result of these limitations we have recently

initiated studies into the closely related field of fluo- rescence. In these systems greater selectivity is achieved because of the added characteristic excitation variable whereas sensitivity is also generally improved because one

is no longer concerned with measuring a ratio of light intensities. While instrumental amplification in absorption spectrophotometry only permits the use of narrower

slits, amplification of a fluorescence signal leads to a smaller detection limit whose ultimate value is governed

by signal-to-noise considerations. Furthermore, measurements on small volumes contained in capillaries are also much simpler in the case of fluorescence » No longer does

one need to carefully mount such cells in an end-on position, but, when mounted vertically, the effect of scattered

light may become a limiting factor.

60
2. Discussion and Results

As the first step In our Investigations of fluorescence

we have made an effort to evaluate several commercial

instruments. The compound studied was Rhodamine 6G, the butyl derivative of Rhodamine B. Structurally, both of these materials are quite similar to the triphenylmethane

dyes previously employed in spectrophotometric studies and can readily be incorporated into ternary systems. They

are especially well suited for evaluation purposes since they have closely overlapping excitation and emission spectra and consequently any problems associated with

instrumental light scatter should be readily discernable

In addition, their excitation spectra, as typified in figure 23, exhibit considerable structure. For the purposes

of comparison, the absorption spectrum of Rhodamine 6G is given in figure 24, Its expected similarity to the excitation spectrum is quite apparent. An important difference,

however, is the fact that in the former case the solution

is essentially 500 times more dilute (100 x 5) than the solution on which the absorption measurements were taken.

3. Instrument Evaluation

Three instruments have recently been under study. For

the purpose of evaluation they are Identified only as instruments A, B, and C. All yield essentially non-corrected spectra, although C is capable of operating in a ratio mode insofar as the source is concerned. A brief summary of their design and capabilities are given in table 23°
CD -H

ft B

U 05 - O T3 ,

33Nvayosav

c -p .c £! o o -^ a

•H CD CD ft

A1ISN31NI 3AllVH3a
Table 23. Comparison of three spectrofluorimeters

Instrument Ident

Monochromators Two single Four single Two single

gratings gratings gratings Filter facilities Yes Yes Yes Range , mu 220-700 220-700 220-650; 220-800

Slits Fixed; Fixed 3 Variable

,

1-20 mu 2-32 mu 1-40 mu Source 150-Watt 150-Watt 150-Watt xenon xenon xenon Wavelength drive Mechanical Electrical Electrical

Resolution, mu 2 2 0.5

No. scanning speeds 8 2 3 Standard sample volumes 3 ml-2 u l 3 ml-4 ul 3 ml-200 ul Scatter Moderate Low Low

Approx. cost including recorder $6,000 $7,000 $8,500

4. Application to Micro Samples Both spectrophotometric and spectrof luorimetric tech- niques have been considered for the analysis of micro

samples. While not as broadly applicable at the moment,

the fluorescence approach appears more promising not only because of the inherently higher sensitivity (100-10,000-

fold) but, as previously mentioned, cell positioning is much less a problem. Recently, while attempting to extend sensitivity to a maximum, we have been able to obtain

63
meaningful measurements on solutions containing approx- imately 5 picograms of Rhodamine 6G with a signal-to-noise

ratio of better than 3:1.

D. Spectrophotometric Determination of Arsenic in Cast Iron

1 o Introduction

The procedure that is generally used for the wetchemical determination of arsenic in ferrous materials is dissolution in an oxidizing acid, reduction of As(v) to As(lll) and separation of the arsenic by distillation of the trlhalide. This practice, however, is subject to systematic errors that lead to poor accuracy. Not only

do dissolution problems compound the uncertainty of the results, but also it has recently been shown [32] that high combined carbon contents can lead to low results

when a halogen acid (HX) is present. Presumably, this

loss is due to the reduction of arsenic by the carbon and

its subsequent volatilization as AsX . Even when the carbon content is relatively small it is our opinion that low results are obtained when only a few micrograms of arsenic are present. When the need recently arose for the accurate determination of arsenic in SRM 4j , a cast iron, we applied to advantage the procedure outlined below:

(1 ) Dissolve sample in sealed tube with HC1

(3) Back extract with water and oxidize As(lll)

to As(V) with Br . (4) Determine arsenic as the heteropoly molybdate,

following reduction with hydrazine sulfate.

64
The novel features of this method are that the sample

can be dissolved with no danger of losses by volatilization

and, by carrying out the dissolution in hydrochloric acid,

the arsenic is obtained only in the 3 state which is necessary for the quantitative extraction. The SnCl prevents

any possible oxidation of As (ill) by the residual air entrapped in the sealed tube. Although in most cases the iron matrix would no doubt serve the same function, the fact that one obtains no ferric color during dissolution

also verifies that the system was air-tight. If by chance

any colored solutions are obtained, they are discarded.

2. Procedure

A 0.1-gram sample is added to a dissolution vial followed by 10 ml concentrated HC1 and 4 mg Sn(ll). The mixture is immediately frozen In a 1:1 carbon tetrachloride

and chloroform-dry Ice slush and the tip sealed off. The vial Is placed in a steel shell, dry ice is added to com- pensate for pressure that will develop upon dissolution and

the whole is heated overnight at 250 C. Upon removing from

the furnace and cooling, the sample is taken from the shell, frozen, and the tip opened by means of a torch. It is quickly thawed under tap water and transferred to a 60-ml separatory funnel. The vial is rinsed with 5 ml concentrated HC1 and then 5 ml of concentrated H SO, is cautiously

added to the funnel. Before adding the H SO, prior cooling

of the sample in ice water Is advisable to minimize the heat of mixing and the evolution of HC1 gas. The sample

is then extracted twice with 20 -ml portions of chloroform

by shaking vigorously for 2 minutes. The combined extracts

are backwashed with two 10-ml portions of HO (l minute

shaking time) and the aqueous layers transferred to a

65
to volume an appropriate aliquot is taken and analyzed by

the molybdenun blue procedure [33]

•

3. Results and Discussion

Table 24 lists the results obtained on SRM 4j when the above procedure was employed. Table 24. Arsenic in SRM 4 J

.

Can number w~t % Arsenic

3 0.0270

9 0.0282

13 0.0285

16 0,0272 Average and standard deviation: 0.0277 - 0.0006 Recommended value and estimated

uncertainty: 0„028 - 0.001

The accuracy of the above values was ascertained from

tracer studies, from spike additions and from analysis of control sample 4i . The average value obtained for the latter sample was 0.0202 percent as compared with the certificate value of o 0l8 percent. The certificate

result was based on the average of those obtained by four cooperating laboratories, i.e., 0.018, 0.016, 0.020, and 0.017. Such variations clearly demonstrate the need for

a more reliable method of determining arsenic in these types of materials. During the course of developing the proposed procedure,

77 tracer experiments with As showed that considerable

arsenic was retained in the insoluble residue, especially

66
when relatively large samples were analyzed. At the 0.5 gram level approximately 35 percent of the tracer was found in the residue while at the 0.1 gram level less than

5 percent was retained. Consequently, as pointed out in the procedure , a maximum sample size of about 0.1 gram is recommended. It is possible that a closer examination of the dissolution temperature on the percentage of arsenic retained will permit the use of larger samples. While dissolutions in this study were carried out at temperatures near 250 C it is conceivable that some lower temperature may be just as effective insofar as dissolution is concerned, but that absorption on the SiO (a probable

mechanism) may be somewhat less.

E. Arsenic in High-Purity Selenium

Arsenic has recently been determined in high-purity

selenium by the heteropoly molybdenum blue procedure. It was quantitatively separated from the matrix (>99$ from

tracer results) by reduction of the latter to the metal with SO . The procedure used was essentially the one recommended by Reed [3^]« The major drawback encountered In this study was the variability of the reagent blanks. This difficulty was ultimately attributed to impurities in the plant steam which was initially employed in the evaporation steps. By changing to a small electrically-heated water bath

this variability was reduced approximately tenfold. However, when this procedure was applied to the analysis of 1-gram samples the residual variation still limited the matrix sensitivity to about 2 ppm. As a result, we have

only been able to report the arsenic content of SRM 726 (99«9$ selenium) to be - 2 ppm.

67
F. High Precision Differential Spectrophotometry

1. Introduction Differential techniques are now being employed to extend spectrophotometry methods into the domain of macroanalysis. While such determinations have been carried out

in the past primarily by gravimetry and titrimetry, the differential spectrophotometric approach today frequently

presents itself as a simple and rapid alternative. Although

the precision presently obtainable is only about one part

in a thousand, the use of digital readouts and averaging

circuits and the closer control of experimental parameters

should ultimately yield values at least 10-fold better than

this.

2. Differential Spectrophotometric Determination

of Dysprosium in Glass Beads

A high precision method has been investigated for the determination of dysprosium in small glass beads which are ultimately to be used as monitors of neutron flux. The nominal composition of these beads was: V, (92^ B

10

) 35^

Si0

2 30% Dyp o^ 20%> Li

2 \0%

A1

2 3

<D% For the results to be useful a minimum value of - 0.25 percent of the amount present was established as the cutoff point. Since the sample was limited and additional

analyses would be required by other techniques, it was further advised that as much sample as possible be conserved.

68
As is well known, the absorption spectra of the rareearth ions are characterized by a number of exceedingly

sharp peaks. For good quantitative analysis a high resolution monochromator is both desirable and necessary. Because these ions have relatively low molar absorbancy

indexes and require no additional complexing agent, they

are especially well suited for differential analysis.

a. Development of method . Perchloric acid solutions

of Dy

p Oo exhibit three major absorption peaks, at 350, 807, and 909 nip. . While all are of nearly equal sensitivity, measurements at the latter two wavelengths are complicated

by OH absorption and require that the water content be closely controlled. In actual sample analysis, however,

fuming associated with the dissolution step. These two wavelengths were subsequently abandoned in favor of the

350 rry peak. By use of scale expansion (full scale = 0,100 A ), absorbances could be measured to the nearest 0.0002 A

s unit. This variation represented an uncertainty in the dysprosium concentration of - 0.005 mg/ml . Thus, by making differential measurements on samples containing

approximately 2 mg Dy/ml (the reference solution contained

1.75 mg Dy/ml), it was possible to reduce the relative

error to the prescribed 0.25 percent.

b. Procedure . Half -gram samples of the crushed glass were taken for analysis, treated with 4 ml HC10, and heated

to strong fumes with several additions of HF . A clear

solution was normally obtained after 3-4 evaporations.

Upon dilution to 50 ml, spectrophotometric measurements

69
were then carried out at 350 ny in 10-cm cells. To facilitate the establishment of the baseline and to obtain more meaningful sample measurements, the following procedure is recommended:

(1) Record differential sample absorbance at 350 mu while keeping wavelength fixed.

(2) Record differential sample absorbance at 400 m^j again keeping wavelength fixed.

(3) Scan from 400 to 325 m|i, (4) Record differential sample absorbance at 350 mu

.

(5) Subtract the best estimate of (2) from the average of (l), (3), and (4) to obtain the net absorbance and convert to dysprosium by- means of a calibration curve.

c. Results and conclusions . The results obtained

for the dysprosium content of several samples of glass

beads are listed in table 25. The slope of the calibration curve was 0.129 A /mg/ml

.

Table 25. Dysprosium content of glass beads, Sample »j£v *

1 19.93

2 19.88

3 19.93 While slightly greater instrument noise was observed

at the 350 mu setting than at either 807 or 909 mu, the uncertainty was still considerably less than that caused

by OH absorption and variable HO content at the longer

wavelengths. The accuracy of the results was established

by comparison with standard solutions (w/w) prepared from
3. Other Studies

In addition to dysprosium, other systems that are cur- rently under investigation are those of cobalt and of chromium. The results of these studies will be published

in a subsequent report.

G. Miscellaneous Spectrophotometric Results Obtained on Various Standard Reference Materials

Summarized in table 26 are the results obtained for

six elements of interest in a variety of SRM samples.

The methods used for Mn and P are standard ASTM procedures,

while that for nickel has been fully described in an earlier report [10]

R. W. Burke and E. R. Deardorff

Table 26. Miscellaneous spectrophotometric results.

No. of Rel. Ele- SRM determi- Percent std. Referment^ No. Kind nations found dev. ,% ence

Mo 3b White iron 4 0.0020 14 35

3c White iron 5 0.0019 7

4j Cast iron 8 0.080 2 163 52100 steel 8 0.0296 0.9

Ti 4j Cast iron 8 0.0514 0.7 36 Mn 3 b White iron 2 0.351 0.3 37

3c White iron 2 0.301 0.3

4j Cast iron 4 0.781 0,4

30f Cr-V(SAE 6150) steel 4 0.790 0.1

163 52100 steel 4 0.894 0.4

(contin ued) 71
Table 26. Miscellaneous spectrophotometrlc results

(continued)

.

No. of Rel. Ele- SRM determi- Percent std. Refer- ment No. Kind nations found dev. ,fo ence

Ni 3b White iron 2 0.013 1.5 10

3c White iron 2 0.014 1.5

4J Cast iron 4 0.068 2 30f Cr-V(SAE 6150) steel 4 0.071 1 163 52100 steel 4 O.O83 2.5

4 10 1121 Be-Cu alloy 4 0,013

1122 Be-Cu alloy 4 0.012 4 1123 Be-Cu alloy 4 0.012 4

P 3b White iron 3 0.087 2 38

3c White iron 2 0.100 2 30f Cr-V(SAE 6150) steel 5 0.010 2 1121 Be-Cu alloy 4 0.0048 2.5 39 1122 Be-Cu alloy 4 0,0045 2.5 1123 Be-Cu alloy 4 0020 2.5

Cu 4J Cast iron 11 0.235 2.5 40
5. GASES IN METALS

A. Introduction

The determination of gases in metals has been, and will continue to be in the future, of vital importance in all sectors of the metal industry, both to the producers

and the fabricators. This stems from the correlation

between the interstitial content (gas components) of metals and their physical and mechanical properties. This

has led to recent developments of vacuum steel-making

practices on a commercial scale as well as other controlled

atmosphere processes for heat treatment and fabrication in order to produce cleaner metals.

The need for oxygen standards in titanium has grown rapidly over the past few years. This is due to the increase in the applications of titanium and its alloys

especially in aircraft and other aeronautic applications,

as well as in general usage requiring materials of high resistance to corrosion. It has been demonstrated that

the gas content of the titanium base metals has a marked

effect on the hardness and other physical properties and especially on the f abricability of these materials. Most

often these effects are deleterious. The ultimate answer

for production and fabrication of these "cleaner metals"

of all types must lie in the development of metal processing techniques which would prevent the initial introduction

as well as subsequent accumulation of gas in deleterious

amounts. Accurate analytical methods are, therefore, essential in control of these processes.

We have at NBS tried to supply standards by means of which these analytical procedures can be kept under control. Two new Standard Reference Materials Nos. 355 and 356,

73
which were issued this year, are of this nature. These

samples are an unalloyed titanium and a 6 percent aluminum4 percent vanadium titanium base alloy, which are repre- sentative of many of the titanium base materials which are now in general commercial use. These samples were certified

for their oxygen content.

The problem of the determination of nitrogen in metals

has also plagued the analytical chemist for many years; the determination of nitrogen by the vacuum fusion method has fallen into disrepute. There has been a general consensus

of opinion that nitrogen values obtained by the chemical dissolution of the metal and the subsequent determination

of the ammonia formed by titration or spectrophotometric methods were more reliable. There is reason to believe, however, that the determination of nitrogen by the vacuum

fusion method is potentially as sensitive and often more

accurate than any of the chemical methods now in use for

the determination of nitrogen in metals.

We have, therefore, been investigating variations of the vacuum fusion method. Mainly, a crucible arrangement

is employed by means of which it is possible to empty the crucible between each analysis without breaking the vacuum

and thus analyze each sample in an effectively clean out- gassed crucible. Also, the role of nodulizing alloys as additions which will increase the fluidity of the melt

have been studied.

It is possible to show that with certain materials

such as ferrous metals containing high-silicon additions,

the results obtained by the usual chemical methods are indeed low; and other methods such as alkaline fusion or
possibly sealed-tube dissolution methods must be employed

in order to effect complete recovery of the nitrogen.

B. Production of Oxygen Standards for Titanium Base Metals

1. Introduction

The issuance of two Standard Reference Materials Nos.

355 and 356 for oxygen content in unalloyed titanium and

in 6 percent aluminum-4 percent vanadium titanium alloy is the first certification of a non-ferrous material for oxygen content, thus bringing to completion: (l) the lengthy process of developing suitable test methods, (2) selecting and procuring adequate materials, and (3) the testing necessary for proving homogeniety and certifying

oxygen content of the material.

2Sampling and Method of Analysis

The Standard Reference Materials 355 and 356 are in the form of 1/2" and .245" diameter rods respectively, and are

2 inches long. The samples were analyzed at KBS using the following conditions:

(1) Method - Vacuum Fusion.

(2) Furnace Temperature - 1950 C.

(3) Initial Furnace Pressure - <10 Torr

(4) Collection Time - 4 minutes.

(5) Bath Material - Platinum (2 to 3 grams).

(6) Flux Material - Platinum (Pt:Sample = 10:1).

(7) Carbon Monoxide Determination - Infrared Absorption

The material received was in the form of four-inch bars, centerless ground, that has been cut from the original rods

and marked in such a manner as to retain the positional

relationship of each piece with respect to all the others.

In the case of the unalloyed titanium (355) there were 18

75
original long bars, and in the case of the 6 percent Al4 percent V alloy (356) there were seven original long bars. Samples were taken from both ends of each bar as well as a sample from the center. These samples were retained for homogeniety testing and analysis.

It was found that a slice with a thickness of approximately 0.1 inch, cut from the original bar stock that was

then quartered through the center with a jeweler's hacksaw, produced a sample that was representative of the total cross section of the bar and of the proper size for analysis. The surfaces of these specimens were then cleaned by careful filing with a clean, oil-free fine mill file. The cleaned

sample was then wrapped in platinum wire that had been specially prepared to have a low oxygen content. The ratio

of the weight of platinum to sample was maintained at 10 to

1. The sample with platinum flux was then dropped into a previously outgassed (>2100 C) graphite crucible containing

2 to 3 grams of platinum as a bath material. When the sample is dropped into the hot crucible at 1950 C a reaction takes place which is very strongly exothermic, as indicated by a sudden flash when the sample and platinum melt. This exothermic reaction aids in the quantitative recovery of the oxygen from the titanium. It was observed that when this reaction is not evident low recovery

of oxygen always occurs.

The gases evolved are then pumped into the gas measurement system by means of a high-speed oil diffusion pump

(150 liters/sec.), and the oxygen is determined as carbon monoxide by an infrared absorption measurement. Blanks were determined after every fourth sample. The value of the mean of these blanks was six micrograms per

76
minute. In this case, four-minute collection periods were

used for both the blank and the sample. Whenever unusual variations in the blank were noted, experimental conditions

were checked and tests were repeated until a normal blank

was attained.

3. Discussion of Results

The values obtained on the two titanium base materials

are shown in tables 27 and 28. In order to obtain information on the homogeneity of the material as well as the oxygen content of the material, the original rods were

sampled at each end and the center, and a single rod was

also analyzed at all three positions throughout the course

of the investigation.

Table Material

27. Urn No. of det. 54

27

illoyed titani Oxygen

mean, ppm

3031

3067 k% V Titanium

Oxygen

mean, ppm

1332

am.Std. dev. ppm

Rel.std.

dev. ,% 18 rods sampled, both ends & center

Single rod sampled, both ends & center

57

48 alloy.

Std. dev. ppm

1.9

1.6 Table 28. Material 6% M - No. of det.

63

Relo std. dev. ,%

7 rods sampled, both ends & center 77 5.8 Single rod sampled, both ends & center 12 1322 50 3.8 These results indicate that the variation observed in both materials reflects at least partially the inhomogeneity

present in the metal. We would expect that samples taken from a single rod of unalloyed titanium and a 6 percent
Al-4 percent V titanium alloy to show a relative standard deviation of only 1.5 percent and 4.0 percent respectivelyo

4. Results from Cooperating Laboratories

These same samples were also analyzed for oxygen content

by several cooperating laboratories. The results are shown graphically in figures 25 and 26. Prom an inspection of these results it can be seen that of the twelve laboratories reporting on the unalloyed titanium, by one or more methods,

seven laboratories reported mean values that were within

+3 S.D.

+2 S.D.

Figure 25. Unalloyed titanium.

78
Figure 26. 6% Al K% V - titanium alloy. three standard deviations of the certified value. Four laboratories were within two standard deviations. In the case of the laboratories falling outside the three standard deviation limits, four of these laboratories reported mean values on the low side which is the usual bias shown when

the method or equipment Is not under complete control. For the 6 percent Al-4 percent V titanium alloy, all

ten laboratories reporting results were within two standard deviation units of the certified value, and five laboratories

were within one standard deviation.

79
Co Studies of the Determination of Nitrogen In Metals by

the Vacuum Fusion Method

1, Introduction

Jordan and Eckman [41] reported as early as 1929 that

the total nitrogen content of steels could be quantitatively

determined by the vacuum fusion method. There has developed

over the years, however, a feeling of distrust with regard

to nitrogen contents as determined by the typical vacuum

fusion procedures. In a review article, Goward [42] discusses this question quite thoroughly and points out that the vacuum fusion procedure is potentially as sensitive

as, or more sensitive than, any other method currently in use for the determination of nitrogen.

Traditionally, wet chemical methods have been in the forefront for the analysis of metals for nitrogen content. These methods date back to Boussingault [43], Kjeldahl [44], and Allen [45], Essentially these methods consist of dissolution and digestion of the sample in excess acid, distillation of the ammonia from this solution in the presence of excess alkali, and determination of the ammonia

by titration or use of color reactions. In recent years

these chemical methods have been generally accepted as more

reliable, as mentioned above, than the vacuum fusion procedures. However, Karp, Lewis, and Melnick [46], among

others, have shown that with certain metals such as heat- treated ferrous materials containing silicon, the chemical procedures must be drastically modified in order to obtain accurate results. They employed an alkali fusion in the presence of hydrogen in order to obtain accurate results on this type of alloy. 80
Recently, Evens and Passel [47], Dallmann and Fassel [48], Masson and Pearce [49], and Gerhardt, Kraus, and Frohberg

[50] have, by several modifications In conditions for analysis, made reliable nitrogen determinations by the vacuum fusion or inert gas fusion methods.

The basic apparatus of Gerhardt et al . [50] has been procured at NBS. Studies are being made on the determination of nitrogen in ferrous materials and the results compared with those obtained by the chemical methods.

2. Materials and Methods

For the most part, the materials studied in this program

are SRM samples in chipped form which have been analyzed in the past by chemical methods or are in the process of being

analyzed. Presently both methods (i.e., vacuum fusion and chemical) are being used concurrently.

The sample size used in most of the studies by vacuum

fusion was approximately 0.5 grams. The chipped material

was, if possible, compressed into 1/4-inch diameter pellet

by means of a steel die and hydraulic pressure. This per- mitted a coherent sample to be obtained which may be dropped into the hot crucible without disintegration. However, with some chips, such as the cast iron, which will

not form coherent compacts by cold pressing, the samples were contained in nickel capsules prepared from type 205 nickel tubing. The samples were dropped into a previously outgassed

graphite crucible (>2100°C) and reacted at l650°C along with a piece of nickel-cerium alloy that has been saturated with carbon. The weight of the Ni-Ce flux is such that the resulting melt (sample + Ni-Ce alloy) contains approximately

0.5 percent cerium.

81
By means of a high-speed oil diffusion pump, the gases were then transferred from the furnace section of the apparatus to the measuring chamber containing a thermal conductivity detector. This operation was completed in approximately two minutes. The gas collected consists of carbon monoxide, nitrogen, and hydrogen. The amounts present are measured by physical methods. The thermal con- ductivities of carbon monoxide and nitrogen are identical,

but that of hydrogen is about eight times greater. It is possible to obtain the sum of the nitrogen and carbon monoxide by means of a conductivity measurement of the gas

at a given total pressure. In order to obtain this constant

total pressure before each measurement, pure hydrogen is admitted to the measuring chamber. The carbon monoxide

fraction of the gas obtained from the sample is found by

the use of an infrared analyzer. The amount of nitrogen

is then found as the difference between the two results.

The blanks were determined after every sample and sub- tracted from it. During the period of these tests, the average blank was 2.8 micrograms per minute.

The calibration of the apparatus is achieved by means

of a valving system which allows known amounts of pure

gases, carbon monoxide and nitrogen, to be added to the furnace chamber from a supply vessel. These gases are added in increments of 10mm and, taking into account the temperature and volume of the calibration system which are held constant, and the atmospheric pressure, the actual amounts of the gases added may be derived by computation.

This calibration system is also used to recheck the analysis

of the unknown sample by adding known amounts of the pure

82
gases through the calibration system equivalent to that obtained from the sample measurement.

One of the principal differences between this apparatus

and most vacuum fusion systems is that the furnace is designed in such a manner that the crucible, which is cone shaped (figure 27) , may be rotated by means of a high-speed

motor and emptied of its contents by centrifugal force. This method of emptying of the crucible after every analysis

provides an essentially clean melting container for every

analysis This procedure, of course, then prevents the accumulation of "Kish" or dross from previous melts as well *4

s'

Figure 27. Spinning crucible.

83
as the buildup of insoluble graphite in the melt. The latter condition has been observed to give unreliable results for nitrogen. The use of the Ni-Ce alloy additive prevents the precipitation of flake graphite in the melt during the out- gassing of the sample. This flake form of graphite markedly

increases the viscosity of the melt. However, the addition

of the Ni-Ce alloy causes the graphite to form in a spheroidal form which contributes to lower viscosity and the melt

can be, under these conditions, degassed more quickly and easily. A quantitative recovery of the nitrogen in the sample can, under the above conditions, be attained,

3. Results

Table 29 shows the results obtained on SRM materials, as well as some samples for Bundesanstalt fur Material-prttfung

(BAM) in Berlin, by both chemical and the spinning-crucible vacuum-fusion method. Table 30 contains the reported results

of Dallmann and Passel [48] which were obtained at Iowa State University by the platinum bath-platinum flux method in both helium fusion equipment and by vacuum fusion. As can be seen from both tables, the results show good agreement with the chemical method and methods of Dallmann and Passel. For the most part, the new results are higher in contrast to the previous low values expected from vacuum fusion techniques.

This is especially noticeable in several of the cast irons

and the SRM 125a steel which contain appreciable amounts of silicon. As was noted earlier, Karp, Lewis, and Melnick [k6] demonstrated that materials containing appreciable amounts of silicon are very difficult to decompose by ordinary chemical procedures, and require an alkali fusion in the presence of hydrogen gas for complete recovery of the nitrogen. This

84
has been vividly demonstrated by sample SRM 125a on which

results of 20 ppm nitrogen were obtained by regular Kjeldahl

procedures, but when treated by the alkali fusion method

yielded results twice as high or about 42 ppm. These higher

values were also obtained by the vacuum-fusion spinning- crucible method. In the cases of SRM 30f and SRM 163, on which slightly lower results were obtained, there is some Indication that the chromium content of sample 30f may be interfering. We have not as yet resolved the deficiencies

observed in the analysis of sample SRM 163. Both of these problems will be studied at much greater length by both the vacuum fusion and inert gas fusion methods, and also by chemical methods as mentioned elsewhere in this report. Table 29. Nitrogen values in standard reference material(ppmj

Chemical Vacuum fusion

No. of Kjeldahl No. of spinning crucible Material det method deto method

SRM 3a White iron

Si - 1.12$ 4 86 t 4 17 147 ±13

SRM 3b White iron 3 84 t 5 23 92 t 4 SRM 3c White iron 3 46 t 4 21 52 t 1 SRM 4i Cast iron

Si - 1,45$ 2 70 9 85 +

- 5 SRM 4j Cast iron 7 37 - 2 20 46 +

- 3 SRM 30f Cr-V steel

(SAE 6150) 6 75 ± 5 27 79

+

- 5 SRM I63 (SAE 52100) 8 80 b 4 30 73 +

- 5 (continued)

85
Table 29. Nitrogen values in standard reference material(ppm)

.

(continued) SRM 5k Cast iron _,_ Si - 2.08$ 5 SRM 51 Cast iron 19 SRM 6f Cast iron

Si - 1.85$ 3 SRM 6g Cast iron 15 BAM

Cr Mo Ni #5 118 - 4 10 BAM

Steel #9 43-5 6 BAM + Cr Ni Mn #1 682 - 17 4

161 t 16

58 t 5

74 t 3 66 t 4 n7 i 2 48 t 2 667 - 6

Standard deviation of a single determination. Cooperating laboratory.

Samples obtained from and values attested by Bundesanstalt

fur Materialprufung (BAM) in Berlin-Dahlem. These samples

are presumably certified on basis of chemical solution methods for determining nitrogen.
Table 30. Comparison of nitrogen values by several methods,

(nitrogen, percent) Vacuum

Chemical fusion

He- Kjeldahl Vacuum spinning Material fusion method fusion crucible Remarks

125a -3.3$

High silicon .0045 .0039 .0043-. 0004 (1) lOld, Cr 18N19

(SAE 304) .023 0.024 0.024 .0222-. 0008 (2) 129b High sulfur

(SAE xll2) 0.014 .014 .0143-. 0006 (3) Remarks: (l) 0.002 % NBS certified value, ,0042^ N obtained by alkaline-fusion method.

(2) 0.024 % NBS certified value.

(3) 0.014 % NBS certified value, ^Values of Dallmann and Passel, Anal. Chem 39_, 133R (1967).

J. T. Sterling
6. PERSONNEL AND ACTIVITIES

Personnel Listing

Oscar Menis, Section Chief Leona M. Puff enberger, Section Secretary

R. K. Bell T. A. Rush

B. B. Bendigo K. M. Sappenfield

D tt t, , (Prom Jan. 1967 - R. W. Burke '

, . ___ '^ Section 310.06)

E. R. Deardorff J. T. Sterling

T. C. Rains S. A. Wicks Publications

1. R. W. Burke and Oscar Menis, Extraction-Spectrophotometric Determination of Antimony as a Ternary Complex",

Anal. Chem. 38_, 1719* November 1966.

C. Talks

1. Oscar Menis, "Differential Thermal Analysis Standards", International Conference on Thermal Analysis, Sub-Committee

on Standards, Hopatcong, New Jersey, June 26, I96J

.

2. J. T. Sterling, "The Determination of Nitrogen in Steels by Vacuum Fusion, Kjeldahl and Caustic Fusion", Annual Meeting, Division I, Committee E-3, A.S.T.M., San Diego, California, April 4-6, 1967.

3. J. T. Sterling, "Task Force on Oxygen In Nickel", Annual Meeting, Division I, Committee E-3, A.S.T.M., San Diego, California, April 4-6, 1967.

4. Oscar Menis and R. K. Bell, "Homogeneous Precipitation of Beryllium in a Cu-Be Alloy—A Comparison of Methods

Study", Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 6-10, 1967.
5. T. C. Rains and Oscar Menis, "High Precision Atomic Absorption and Flame Emission Spectrophotometry", Pittsburgh

Conference on Analytical Chemistry and Applied Spectroscopy, March 6-10, 1967.

6. J. T. Sterling , B. B. Bendigo, and Oscar Menis,

"The Determination of Nitrogen Ferrous Materials by the Vacuum Fusion Method", Pittsburgh Conference on Analytical

Chemistry and Applied Spectroscopy, March 6-10, 1967.

7. Oscar Menis, "Chemical Spectrophotometry", Rapporteur Report, 1st Materials Research Symposium held

at NBS - October 3-7, 1966.

8. T. C. Rains, "Determination of Trace Elements in High Purity Zinc by Atomic Absorption and Flame Emission

Spectrophotometry", American Chemical Society, New York, N.Y., September 15, 1966.

D. Committee Activities

Oscar Menis

Member, ASTM - Committee E-3, Div. I, Committee on Gases

in Metals.

Member, ASTM - Committee E-10, Subcommittee I, Nuclear

Fuel Burnup. Divisional Representative, American Chemical Society - Program Committee for Middle Atlantic Region. Editorial Board Member, Chemical Instrumentation, A Journal of Experimental Techniques in Chemistry and Biochemistry.
J. T. Sterling

Member , ASTM - Chairman, Committee E-3, Div. I, Committee on Gases in Metals.

R. K. Bell

Member, ASTM - Committee E-3, Div. N, Committee on Non- Ferrous Metals.

T. C. Rains Program Subchairman, Society for Applied Spectroscopy - Atomic Absorption and Flame Emission.

E. Acknowledgements

The Section acknowledges Mrs. R. S. Maddocks's assistance

in preparing this report. Special appreciation is expressed

to Mrs. L. M. Puffenberger as the Section's secretary for her tireless efforts in getting this report typed.

90
7. REFERENCES

[I] Smythe, L. E. and Florence, T. M., "Recent Advances in the Analytical Chemistry of Beryllium," Progress in Nuclear Energy, IX, vol. 3, P« 191* Pergamon Press 1963*

[2] Hunt, F. C. and Martin, J. V., "The Analytical Chemistry

of Beryllium," Proceedings of Symposium, Blackpool,

June I960, PG Report 171 (s) UKAEA 1961.

[31 Prasail, T. P. and Sastri, M. N., Talanta 13., 1517 (1966).

[4] Boyle, W. G. and Otto, C. H., Jr., Abstract of ACS Meeting, Miami Beach, Fla., April 10, 1967.

[5] Willard, H. H. and Sheldon, J. L., Anal. Chem. 22_, 1162 (1950).

[6] Pribil, R, and Kucharsky, J,, Collection of Chem. Czech. Comm. 1_5, 132 (1950).

[7] Brewer, P. I., Analyst 77, 539 (1952).

[8] Hure, J., Kremer, M., and Berquier, F., Anal. Chim, Acta, 7, 37 (1952).

[9] Athvale, V. T., Iyer, C. S. Padmanabha, Tilher, M. M., and Vaidya, G. M., Anal. Chim. Acta, 24, 263 (1961).

[10] Menis, Oscar, editor, NBS Technical Note 402 (I967).

[II] Mazieres, C, Anal. Chem 36, 602 (1964).

[12] ASTM 1967 Book of Standards , "Chemical Analysis of Metals," Part 32, p. 146.

[13] Florence, T. M. and Farrer, T. J., Anal. Chem. 35., 712 (1963).

[14] Fuwa, K. and Vallee, B. L., Anal. Chem 8, 942 (1963).

[15] Dean, J. A., Flame Photometry , McGraw-Hill Book Co., Inc., New York, i960.
REFERENCES (continued)

[16] Koirtyohann, S. R. and Pickett, E. E., Anal. Chem. 38, 585 (1966).

[17] Rains, T. C, "Flame Photometry," pp 566-75, in Reagent Chemicals and Standards by Joseph Rosin, 5th edition, Van Nostrand, New York, 1967.

[18] Horstman, E. L., Anal. Chem. 28, 1417 (1956).

[19] Ingamells, C. 0., Talanta 9, 781 (1962).

[20] Robinson, J. W., Atomic Absorption Spectroscopy , Marcel Dekker, Inc., New York, 1966.

[21] Meggers, W. F. and Westfall, F. 0., J. Res., NBS 44, 447 (1950).

[22] Rains, T. C, Ferguson, Marion, and House, H. P., Anal. Chem. 33., 1645 (i960).

[23] West, T. S., Analyst 91, 69 (1966).

[24] Flaschka, H. and Sadek, F., Z. Anal. Chem. 150, 339 (1956).

[25] Raber, W. J., Paper 74, Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March (1962).

[26] Intorre, B. J. and Martell, A. E., J. Am. Chem. Soc . 8_3_, 3618 (1961).

[27] Zolotov, Y. A. and Bagreev, V. V., Zh. Analit. Khim. 21, 649 (1966).

[28] Burke, R. W. and Menis, Oscar, Anal. Chem. 38., 1719 (1966).

[29] Dagnall,R. M. and West, T. S., Talanta 11, 1627 (1964).

[30] Bailey, B. W., Dagnall, R. M., and West, T. S., Talanta

13, 753 (1966).

[31] Braude, E. A., J. Chem. Soc, 379 (1950).

92
REFERENCES (continued)

[32] Butenko, G. A., Rodionova, E. M., and Kovgh, V. P., Zavodsb, Lab. 2J_, 808 (1961).

[33] Rodden, C. J., J. Res., NBS 24, 7 (1940).

[34] Reed, J. P., Anal. Chem. 3£, 1122 (1958).

[35] Shultz, J. I., NBS Misc. Publ. 260-6 (1965).

[36] Bendlgo, B. B., Unpublished Work.

[37] ASTM 1966 Book of Standards , "Chemical Analysis of Metals," Part 32, p. 78. [38] Hague, J. L. and Bright, H. A., J. Res., NBS 26, 405 (1941).

[39] Bell, R. K., NBS Misc. Publ. 260-7 (1965).

[40] Hague, J. L., Brown, E. D., and Bright, H. A., J. Res., NBS 47, 38O (1951) . [41] Jordan, L. and Eckman, J. R, , NBS Scientific Papers

22, 467-85 (1927).

[42] Goward, G. W., Anal. Chem. 37, 117R (1965).

[43] Boussingault, J. B., Comp. Rend., Acad. Sci. 53, 77 (1861).

[44] Kjeldahl, J., Z. Anal. Chem. 22_, 366 (1883).

[45] Allen, A., J. Iron and Steel Inst. 8, 184 (1888).

[46] Karp, H. S., Lewis, L. L,, and Melnick, L. M., J. Iron

and Steel Inst. 200, 1032 (I962).

[47] Evens, P. M,, and Passel, V, A., Anal. Chem. 36, 2115 (1964).

[48] Dallmann, W. E. and Fassel, V. A., Anal. Chem. 39, 133R (1967).

93
REFERENCES (continued)

[49] Masson, C. R. and Pearce, M. I/., Trans. AIME. 224 , 1134 (1962).

[50] Gerhardt, A., Kraus, Th., and Frohberg, M, G., "Development of a Method for the Rapid Determination

of the Nitrogen Content of Steel Based on the Vacuum

Fusion Method with Special Consideration of the De- gassing of Carbon Saturated Iron Melts." Based on dissertation of A. Gerhardt for The Institute of General Metallurgy of The Technieche Universitat s Berlin , 1965. Edited, translated and made available

by Balzer High Vacuum Co., Liechtenstein.

94
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