IHD STATES JRTMENT OF AMERCE

UCATION

tfbrary,

Bureau f standards

Bldg

nov

%± B70 NBS TECHNICAL NOTE 546

Summary of Activities

July 1969 to June 1970

HONAL BUREAU OF STANSASSS

UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

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

NBS TECHNICAL NOTE 546

ISSUED NOVEMBER 1970

Nat. Bur. Stand. (U.S.), Tech. Note 546, 120 pages (Nov. 1970)

CODEN: NBTNA

Analytical Mass Spectrometry

Section:

Summary of Activities

July 1969 to June 1970

Edited by William R. Shields

Analytical Mass Spectrometry Section

Analytical Chemistry Division

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

/ w s

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

listed or referred to in the open literature.

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

(Order by SD Catalog No. C 13.46:546). Price $1.25.

FOREWORD

The Analytical Chemistry Division was established as a

separate division at the National Bureau of Standards on

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

Materials Research in the February 1, 1964, reorganization.

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

competences from activation analysis and atomic absorption to

vacuum fusion and x-ray spectroscopy. These competences, and

in turn the sections which they comprise, are charged with

research at the forefront of analysis as well as awareness of

the practical sample, be it standard reference material or

service analysis. In addition it is their responsibility to

inform others of their efforts

Formal publication in scientific periodicals is a highly

important output of our laboratories. In addition, however,

it has been our experience that informal, annual summaries of

progress describing efforts of the past year can be very valuable in disseminating information about our programs. A word

is perhaps in order about the philosophy of these yearly

progress reports . In any research program a large amount of

information is obtained and techniques developed which never

find their way into the literature. This includes the

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

importance also are the numerous small items which are often

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

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

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

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

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

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

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

appears will not be treated fully in regular publications are

considered in some detail here. Other results which are

being written up for publication in the journal literature

are covered in a much more abbreviated form.

At the National Bureau of Standards publications such as

these fit logically into the category of a Technical Note.

In 1970 we plan to issue these summaries for all of our

sections. The following is the fifth annual report on progress of the Analytical Mass Spectrometry Section.

W. Wayne Meinke, Chief

Analytical Chemistry Division

iv
PREFACE

The primary function of the Analytical Mass Spectrometry

Section is to establish high accuracy absolute abundance ratio

standards. The atomic weight associated with the absolute

abundance ratio is of course the real product if the element

shows no variation in nature.

As the generation of each new standard seems to take more

and more effort we have looked around for ways to keep the

rest of the staff busy during the development period. The

most logical second use of the abundance ratio measurement is

assay by isotope dilution, and for the past several years we

have made a major effort to develop this competence and apply

it to the characterization of various SRMs . As you read this

past years summary of activities you will see that indeed we

have applied this tool, and have been called on to determine

concentrations that range over seven orders of magnitude

(from nickel at 10$ to thallium at 8 ppb ) and have been able

to maintain a rather good level of precision and accuracy even

at the lower concentration.

The transfer of the spark source group to the section is

a logical extension of this work and permits even lower

determinations of concentration by isotope dilution, and at

the same time increases the number of elements that the

section can detect and analyze.

Even with all the busy work the staff has still managed

to add several new standards to its portfolio. The two new

uranium SRMs are end point standards and are the culmination

of many years of experience before ratios as large as they

contain could be certified.
In order to specify adequately some of the procedures

and equipment changes it has been necessary occasionally to

identify commercial materials and equipment in this report.

In no case does such identification imply recommendation or

endorsement by the National Bureau of Standards, nor does it

imply that the material or equipment identified is necessarily

the best available for the purpose

.

William R. Shields, Chief

Analytical Mass Spectrometry Section

VI
TABLE OP CONTENTS

PAGE

1. INSTRUMENTATION 1

A. Multistage Instruments 1

1. Magnet Control and Stabilization 1

B. High Voltage Switching System 4

1. Design and Construction 4

2. Vibrating Reed Electrometer Remote Ranging . 9

3. Performance 9

C. Mass Spectrometer, 12 inch, 90° 11

1. General Description 11

2. Electrical Components 12

3. Computer System 12

4. Programming 12

5. Performance 13

2. ISOTOPIC STANDARDS 14

A. Uranium Isotopic Standards 14

1. U-0002 and U-970 Proposed Uranium

Isotopic Standards 14

2. Mass Spectrometry (U-0002 and U-970) .... 15

3. U-0002; Determination of 235 U by Isotope

Dilution 16

4. U-970; Point Calibration of 235 U/ 238 U

Ratio 17

5. Determination of 2 3 4 U in U-0002 by

Pulse Counting 18

6. 233 U Isotope Dilution of U-970 19

B. Stoichiometry of Uranium Oxide 23

C. Plutonium Isotopic Standards 24

1. Modification of Plutonium Analytical

Procedure 24

2. Half-life of 21fl Pu 25

D. Assay of SRM 727, Rubidium Chloride 26

E. Assay of Potassium Chloride 32

3. TRACE CHARACTERIZATION BY ISOTOPE DILUTION ANALYSIS. 33

A. Methodology 33

1. Introduction 33

2. Storage of Separated Isotope Solutions and

Method of "Spiking" 34

3. Spike Calibrations 35

B. Trace Elements in Glass SRMs 35

1. Multiple Spiking Procedure and Determination

of Silver, Copper, Potassium, Lead,

Rubidium and Thallium 36

2. Determination of Uranium in TEG 53

C. Iron and Steel Standard Reference Materials. . . 6l

1. Determination of Copper 6l

2. Determination of Nickel 63

vii
Page

D. Boron in SRM 59a, Ferrosilicon 68

E. Uranium and Lead in Cation Exchange Bead

Micro standards 70

4. HIGH SENSITIVITY ANALYSIS 71

A. Silica Gel Method 71

1. Introduction 7]

2. Reagents 72

3. Mass Spectrometry 73

4. Mass Spectrometric Procedure 73

5. Results 74

6. Discussion 74

5. ATOMIC WEIGHT RESEARCH 76

6. SPARK SOURCE MASS SPECTROGRAPH 77

A. Instrumentation 77

1. Introduction 77

2. Ion Beam Deflector 77

3. Internal Source Baking 80

B. Analysis of Materials by Direct Sparking

With SSMS 81

C. Analysis by Isotope Dilution 83

1. Introduction 83

2. Materials Analyzed 85

3. Standard Reference Materials for the Spark

Source Mass Spectrograph 89

7. MISCELLANEOUS 90

A. Oxidimetric Standard Reference Materials .... 90

1. SRM 136c, Potassium Dichromate 90

B. Intercomparison of Oxidimetric Standard

Reference Materials 93

1. SRM 40h, Sodium Oxalate and SRM 83c,

Arsenic Trioxide 93

2. SRM 40h, Sodium Oxalate and SRM 136c,

Potassium Dichromate 95

C. Archaeological Samples 98

D. Air Pollution Analyses 98

8. ACKNOWLEDGMENTS 100

9. PERSONNEL AND ACTIVITIES 101

A. Personnel Listing 101

B. Publications 101

C. Talks 101

D. Committee Activities 102

10. REFERENCES 103

Vlll
PAGE

APPENDIX (Certificates of Analysis) 105

I. SRM 984, Rubidium Chloride 105

II. SRM 136c, Potassium Dichromate 107

III. SRM 40h, Sodium Oxalate 109

LIST OP FIGURES

FIGURE NO.

1. Magnet Control Circuit 3

2. Relay Board and High Voltage Reference 5

3. Power Supply and Scan Control 8

4. Electrometer Programmable-Range Control 10

5. Beam Deflector Mounted in Source Conversion Ring. 78

6. Ion Beam Current vs Deflection Voltage 79

LIST OF TABLES

TABLE NO.

1. Measurement of voltage switching panel stability. 11

2. Determination of correction factor for

calibration of 2 ^\]/ 2 ^\j ratio of SRM U-970,

Uranium Isotopic Standard 21

3. Determination of the 235 u/ 238 U ratio of

SRM U-970, Uranium Isotopic Standard 21

4. Isotopic composition of SRM U-970, Uranium

Isotopic Standard, as determined by "U-233"

isotope dilution 22

5. Isotopic composition of SRM U-0002, Uranium

Isotopic Standard 22

6. Ignition loss of SRM 950a, Uranium Oxide (U 3 8 ),

with varying cooling rates 24

7. Assay of SRM 727, Rubidium Chloride 30

8. Assay of high-purity rubidium chloride 31

9. Determination of lead in TEG standards 39

10. Determination of thallium in TEG standards. ... 40

11. Determination of copper in TEG standards 43

ix
TABLE NO. PAGE

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

Determination of silver in TEG standards. . . . Determination of potassium in TEG standards . . Determination of rubidium in TEG standards. . . Determination of uranium in TEG standards . . . Determination of uranium in 50 ppm TEG standard

Determination of copper in various SRM steels . Determination of nickel in various SRM steels . Determination of boron in SRM 59a, Ferrosilicon

Spark Source Mass Spectrographic analysis of

SRM 1264, Low Alloy Steel (0.9 C) (heat #2) . Spark source mass spectrographic isotope

dilution analysis of SRM 1265, Electrolytic

Iron

Analysis of high-purity perchloric acid by

isotope dilution - spark source mass

spectrography

Homogeneity of SRM 136c, Potassium Dichromate,

using ferrous ammonium sulfate, hexahydrate . Effective purity of SRM 136c, Potassium

Dichromate, compared to SRM 136b, Potassium

Dichromate

Effective purity of SRM 136c, Potassium

Dichromate, compared to SRM 83c, Arsenic

Trioxide

Effective purity of SRM 40h, Sodium Oxalate,

compared to SRM 83c, Arsenic Trioxide . . . .

47

52

53

60

61

62

68

69

SRM 136c, Potassium Dichromate, compared to

ferrous ammonium sulfate, hexahydrate . . SRM 136c, Potassium Dichromate, compared to

potassium permanganate solution

Effective purity of SRM 40h, Sodium Oxalate,

compared to SRM 136c, Potassium Dichromate. .

83

86

88

91

92

93

94

95

96

97
ANALYTICAL MASS SPECTROMETRY SECTION: SUMMARY OP ACTIVITIES

JULY 1969 TO JUNE 1970

Edited by William R. Shields

This report describes the advances in instrumentation and

the research activities of the Analytical Mass Spectrometry

Section during the period July 1969 to June 1970.

Advances in instrumentation include the construction of a

computer controlled mass spectrometer with appropriate interconnecting components, power supplies with greatly increased

stability and the utilization of a magnetic field control.

Elements studied during this period include: B, Cu, Ag,

Pb, Tl, U, Pu, K, Rb, Ni and Mo. Chemical procedures are given

for Cu, Ag, Pg, Tl, U, K, Rb , Ni and Mo. Mass spectrometric

procedures are given for Pb , Tl, U, K, Ni and Mo. Chemical

procedures for the intercomparison of redox standards are also

given.

Key words: instrumentation; isotopic analysis; mass

spectrometry; procedures.

1 . INSTRUMENTATION

A. Multistage Instruments

During the past year several changes and additions have

been made in the electronic components for the multistage

instrument. These changes were in two general areas; to

improve magnet control and stability and to increase the

switching speed of the accelerating potential switching

system. The changes are described in detail below.

1 . Magnet Control and Stabilization

Absolute magnet field control with a high degree of

stabilization has long been sought as an adjunct to precision

analytical mass spectrometry. Utilizing the newly released

Varian Model PR-40 Gaussmeter-Controller an absolute magnetic

field control system has been designed and installed in this

laboratory

1
Modification of the magnet power supply normally used was

necessary to provide a compatible input and to achieve a high

loop gain providing tight control. A schematic diagram of the

suitably modified magnet power supply is shown in figure 1.

An operational amplifier was used to provide a dc gain of 100

with lag-lead compensation to permit stable system operation.

Settling time for a change of 100 Gauss is less than 3 seconds

in controlled operation. The final control achieved with this

system is a minimum of 1 part in 800,000 and is typically

greater than 1 part in one million. The results at this point

have been most gratifying in that no magnet drift or instabilities have been detected in the use of the controller

during mass spectrometer operation.

It should be noted that the modifications made on the

standard magnet power supply include several changes that

improve the normal or non-field-controlled operation. These

changes may be easily incorporated in an existing system even

though no controller is to be used and these are separately

identified in figure 1.

The feedback voltage is reduced to 0-9 volts by replacing

the current sense resistor string between the cathodes of the

6l46 to ground. A voltage reference diode (1N938A) is used

to provide a very stable voltage source to the 25 turn control

potentiometer. This diode is mounted in a heat shield located

at the front right of the chassis, the most thermally stable

location on the supply. The ground from the diode as well as

that from the control pot and the current sense resistor string

must all be attached to the same specific point to avoid ground

loop and noise. The last two modifications are the additions

of a 0.1 mfd capacitor to the grid of the last 12AX7 to prevent

instability and the exchange of the input 12AY7 for a 12AX7

which increases the open loop or excess gain.
;Vl; I* 1

11 1

HQ>

-o-

¥7

o

O

"o

oO

"Sc

CO

r

3 fi>-

^nnnr-t .n

t>

r i

X

1
The modifications as described improve the current stability by at least a factor of three and have substantially

increased the useful operating time between failures.

B. High Voltage Switching System

A newly designed high voltage or acceleration potential

switching system has been installed that allows much higher

speed of switching as well as containing provision for manual

operation or operation under complete computer control

including voltage selection, timing and peak centering.

1 . Design and Construction

A different concept in voltage scanning has been employed

to eliminate the unduly long settling time of the previously

used accelerating voltage control system. In this new configuration, a second power supply is used to provide a voltage

offset of up to 1000 volts added to the accelerating voltage

(figure 2). This second power supply is a fast slewing type

(50 v/us) which behaves as an ultra stable very high voltage

operational amplifier and is operated in a resistance programmed mode. The resistances used to set the system

accelerating voltage are series switched by the voltage scan

control unit.

The voltage scan control unit contains fifteen precision

ten turn potentiometers and relay switching to permit automatic

or manual selection of any of fifteen mass locations within

the 1000 volt range of the power supply. Indication and manual

selection are done with a combined light and push button switch

associated with each voltage setting potentiometer. Each

voltage setting resistor covers a range of up to 100 volts.

The voltage offset supplied is the voltage setting selected

plus the sum of all the voltage settings of each higher number.

A sixteenth potentiometer, with an effective 100 turns of

control, is situated at the top end of the resistor string and

covers the full 1000 volts of range. This control is driven

by a variable speed stepping motor which can also be manually
Osi + OSiOqns

oc

>*— a>

as

"5

>

So

roo

OQ—

cm3

&0
or remotely controlled. The remote feature enables the

computer to operate in an automatic peak centering mode.

Under computer control, the unit is completely slaved to

a set of nine output commands or bits issued from an auxilliary

relay driver attached to the computer (figure 2). The first

eight bits specify manual (0) through voltage position 7 and

voltage positions 8 through 15. The ninth bit selects the

upper or lower group. When no bits are active, the unit operates in the manual mode. The unit is self contained and need

not be connected to any control unit for manual operation.

Implementation of the instrument logic is done entirely

with reed relays (figure 2). Three of the relays are DPDT,

and sixteen relays have one double throw reed switch and one

high voltage single throw switch. In computer or programmer

controlled operation, a series of diodes form an OR gate to

sense the presence of a control signal on the input lines,

energizing relays B & C. In this configuration, no relay

logic is performed, and each individual voltage selecting

relay is actuated solely by current sinking of the relay

drivers with relay D selecting the upper or lower voltage

group as desired (figure 2). When no control bits are present

or when the programming device is disconnected, relays B & C

are deenergized, and the unit is configured for manual operation. In this form of operation, each relay becomes a latching

circuit where the lowest number relay energized opens its N.C.

contact which denies the power return path to all higher

numbered relays. This circuit excludes the possibility of

more than one voltage relay being closed at any one time.

Transfer of control from one relay to the next is accomplished

by activating one of the other push button switches. When a

higher number push button is depressed, the negative current

path to the selected relay through the N.C. contacts of each

higher number push button switch is maintained while this path

is removed from the lower numbered relay still in control.
Negative current is still supplied to the lower numbered relay

through the N.C. contacts of relay A. When the push button

switch is fully depressed, it supplies positive current to the

selected relay via the N.O. contacts, placing the coil of

relay A in series with the coil of the selected relay. When

relay A energizes, the negative current supplied through its

N.C. contacts is removed, dropping out the lower numbered

relay and transferring control to the relay selected by the

push button. The transfer of control from a higher to a

lower numbered relay is done when the lower push button is

depressed, activating its associated relay which immediately

assumes control when its N.C. contacts open and removes the

current return path from the coil of the higher numbered relay

In each of the cases described above, the newly selected relay

circuits are established before control is released from the

previously selected circuit, ensuring a smooth and direct

transition at the output of the high voltage power supply. A

second set of contacts on relay A is available to be used as

a priority interrupt flag to halt a program and resume manual

control when a push button is depressed.

The power supply and stepping motor control circuits are

shown in figure 3. Up and down drive signals to the stepping

motor are provided either by the front panel switch or by

energizing one of the two relays . Another mode of operation

permitting single pulses to step the motor is included in the

circuit. By using the pulse forming capacitor, resistor,

diode network connected to each of the two control lines, a

timed pulse (50-200 us) issued by the relay driver unit is of

insufficient duration to pull in the relay but will couple to

the stepping motor control circuit as a single pulse. This

arrangement allows a discrete number of pulses to be generated

by the computer regardless of the setting of the speed control,
Sim o

Q =>

.. u u i> > o <z t

<_> ° o

2 z a ce v) iOO

COo

C/9

CO

a>o

Q_

ro

=5
The power dropout relay disconnects the ground return

line from the remote relay driver unit if that unit is turned

off. This is required to allow the internal ground to float,

permitting normal manual operation. Otherwise , when its negative power supply goes to zero volts output, current return

paths are supplied through the kick-back diodes located in

the driver unit

2

Vibrating Reed Electrometer Remote Ranging

A remote ranging vibrating reed electrometer (VRE) was

coupled to the computer output relay driver unit through a reed relay interface (figure 4). This was done since the

remote ranging feature of the VRE was not readily adaptable

to the customarily used relay driver circuits. The interface

circuit is no more than a set of nine relay repeaters between

the two circuits. One extra relay circuit was added to permit

remote operation of the input shorted switch, allowing for a

computer operated current integrate mode for low level measurement. A two transistor circuit was added to override

the computer control of the remote ranging by setting the

local/remote switch in the local position.

3

Performance

The characteristics of the 1000 volt fast slewing supply

are such that switching between voltages corresponding to

any two mass positions may be accomplished completely within

2.5 milliseconds.

In addition the voltage supply system shows excellent

short term stability and reproducibility as shown in Table 1.

This typical data demonstrates that a short term stability

of about 60 millivolts may be expected while the setting at

any one voltage position may be reproduced to within 20-30

millivolts. Since the flat position of a peak is nominally

4.5 volts wide with this instrument no difficulty has been

experienced with peak positioning.
o

<»•

I >

Xo

la

cr./•^ AA AAAAAAA A A

<t<D O O } K N U. K > > 3

AAAAAAA AA AA a j

T£T

~©~

1ST

9 AZh. o

oO

>o

o

>

£o

®~

w

~w

~w

w

O. O

25

3o

o vww $

-Ww\/ n pgr"-

it

Y

V Y Y V YY YY YY Y YY

"VJUUJ"

"vjuuuc-wv

O o-

~\JUUU~

"uuuu 9

oo

a>aoe

ra a:

l .£? .aE

o

-4-»

o

a>3

06

10
Table 1. Measurement of voltage switching panel stability.

a. Voltage readings taken at 1 minute intervals at 1 mass position

after 10 minute warm-up.

Time Voltage Time Voltage

minutes) (volts) (minutes) (volts)

1. 329.56 6. 329.54

2. 329.52 7. 329.58

3. 329.54 8. 328.53

4. 329.55 9. 329.58

5. 329.52 10. 329.58

b. Voltage readings taken after switching to alternate mass position. Readings taken at approximately 15 second intervals and

at approximately 0. 1 seconds after switching.

Position 12 Position 5

330.74 volts 475.18 volts

330.75 475.18

330.74 475.17

330.74 475.17

330.73 475.17

330.74 475.17

330.72 475.17

C. Mass Spectrometer, 12 inch, 90°

As a part of a cooperative project with personnel of

the Geological Sciences Division, Lunar Sciences Institute,

Manned Spacecraft Center, N.A.S.A., a new 90° automatic mass

spectrometer has been completed and tested at NBS and put

into operation at M.S.C. A description of the instrument and

its various operating systems is given below:

1 . General Description

The instrument is a 90° , 12 inch radius extended flight

path spectrometer with the magnet arranged so that the flight

tube is mounted in a horizontal plane. It is equipped with

an air operated beam valve [1], a thin lens "Z" focussing

11
source [2] and a collector with faraday cage, transmission

and electron suppressing grids [2], The collector housing is

arranged so that an electron multiplier may be mounted in

place of the faraday cage if desired, although a multiplier

is not normally a part of the collector system.

2

.

Electrical Components

The spectrometer contains a magnet field measuring-control

system as described above for the multi-stage instrument.

Although the field cannot be changed automatically as currently

arranged, the addition of this feature to the field controlled

system would be relatively simple.

This instrument is also provided with a high voltage or

acceleration potential switching system as described above.

The collector grid output is measured with a vibrating

reed electrometer (VRE) and the faraday cage output with a

second VRE. The cage electrometer contains provisions for

automatic, programmable range selection as well as an auxiliary

-10 V(PS) output. This 10 V output is connected to a -10

V(FS) , 12 bit analog to digital converter which is a part of

a small digital computer.

3

.

Computer System

An integral part of the instrument is a small high speed

digital computer which handles the functions of peak selection

(via high voltage switching), electrometer range selection,

timing and data collection, manipulation, storage and display.

The system contains a 12 bit digital computer with 8K memory,

programmable crystal clock and 2 small magnetic tape drives

with controller. Also present are an output relay driver

control with 36 relay drivers, a six (decimal) bit nixie

display and the high speed A-D converter previously mentioned.

4

.

Programming

A versatile, two isotope program was written for this

system by Mr. Charles Krpec, Systems Analyst, Computational

and Analysis Branch, Manned Spacecraft Center.

12
The program was written in the conversational language

Focal with assembly language sub-routines to control the A-D

converter and relay drives. During programmed operation the

computer selects relays related to mass positions, chooses

the proper electrometer relay, inserts a delay time for

amplifier settling, takes data at the rate of 150 12 bit

conversions per second and scales, prints and displays the

average converter reading, ratio and average ratio.

Delay times, number of converts, number of sets of

converts and number of ratios recorded are easily set by the

operator and may be changed at will. A copy of this program

will be supplied upon request.

5 . Performance

A set of 10 analyses were made by Dr. Norman Hubbard of

the Manned Spacecraft Center on uranium standards where the

235 U/ 238 U ratio varied from 1:20 to 20:1. These analyses were

performed using the triple filament technique [3] and magnet

flipping with data recorded on an expanded scale strip chart

recorder [3]. The results of this test showed a single correction factor for filament bias (theoretical value/experimental

value) of 0.99598±0 .00124 (95% C.L. for a single analysis).

The same test was performed with voltage switching and

with the data collected with the computer. The bias factor

determined was . 99196±0 . 00038 . This defines a voltage

switching correction factor of 0.0040 or 0.134$/mass unit.

A single set of 10 analyses of the B & A shelf standard

strontium gave an average normalized value of 87 Sr/ 86 Sr = 0.70 79±0.0004/analysis.

13
2. ISOTOPIC STANDARDS

A. Uranium Isotopic Standards

1 . U-0002 and U-970 Proposed Uranium Isotopic Standards

Two new uranium isotopic standards have been analyzed

for certification. One, U-0002, is a depleted sample of U 3 8 having approximately 0.02 atom percent 2

3

5 U and the other,

U-970, is an enriched sample of U 3 8 having approximately 97

atom percent 235 U. The minor isotopes in both samples determined by isotope dilution mass spectrometry with a "U-233"

separated isotope. In addition known synthetic mixtures of

"U-235" and "U-238" separated isotopes were prepared to approximately equal the 235 U and 238 U composition of the U-970.

These mixtures were prepared to determine the mass spectrometer bias at this composition.

Samples of the two prepared standards were ignited to

give a reproducible oxide [ref. 1, p. 37]. Two 0.1 g samples

of the "U-233" separated isotope were ignited by the same

procedure and after dissolving in nitric acid (1+1), they were

diluted to approximately 100 g with water. Weighed aliquots,

using plastic syringes and platinum needles, were added to the

dissolved U-970 samples to approximately equal the 231f U or the

238 U content in the U-970 sample. Weighed aliquots of the

"U-233" solutions were diluted by weight to produce a solution

containing approximately 40 yg U per gram of solution. Weighed

aliquots of the dilute "U-233" solutions were added to the

U-0002 samples to approximately equal the 2

3

5 U or ten times

the 23It U content of the U-0002 sample.

The 235 U and 238 U mixtures were prepared in a similar

manner by adding weighed aliquots of "U-238" solutions containing approximately 1.4 mg U/g to dissolved "U-235" samples.

The first results on the "U-233" spiked samples indicated

approximately 0.4 percent difference in samples spiked with

one "U-233" solution compared to samples spiked with the second

"U-233" solution. In order to check the 233 U concentration

14
in the two spike solutions, weighed aliquots of both "U-233"

samples were spiked with two "U-235" separated isotope solutions. The agreement between this check "spike calibration"

and the calculated concentration of 233 U from the weight of

"U-233" separated isotope was within 0.05 percent. The second

"U-233" solution disagreed by 0.51 percent. The 233 U concentration was lower by 0.51 percent indicating an impure sample,

loss of sample or incorrect recording of weights. When the

corrected value is used for the "U-233" solution the results

agree within experimental error.

2. Mass Spectrometry (U-0002 and U-970)

SRM U-0002 and SRM U-970 are the end points in the series

of uranium isotopic standard reference materials. They also

represent to some degree extremes in ion current measurements

and require some additional precautions that were not critical

for some of the other uranium SRMs . The general procedure for

determination of the isotopic composition of a uranium sample

is a point calibration of the 235 u/ 238

u ratio and 233 U isotope

dilution analysis to determine 23It U and 236 U.

A 12 inch radius of curvature 68° analyzer tube mass

spectrometer was used to determine the isotopic composition

of U-970 and only the 235 U composition of U-0002. The more

important characteristics of this instrument have been discussed in previous reports [2,3]. The NBS standard collector

[2] was used as the ion current detector and the output of the

vibrating reed was used to drive an expanded scale recorder.

The 231t U composition of U-0002 was determined by pulse

counting on the multistage mass spectrometer. Characteristics

of the multistage instrument have also been previously

discussed [1,4]

The sample mounting procedure, sample degassing and a general analytical pattern are described below. Specific

details of low-temperature and high-temperature uranium analyses for instruments without "Z" optics are discussed in

Technical Note 277 [3]. The precautions taken to measure

15
large ion current ratios are given in last year's report [^].

Unless stated to the contrary the sample size per analysis

was always 200 ug for the 12 inch single stage instrument.

3. U-0002; Determination of 2

3

5 U by Isotope Dilution

A high temperature analytical procedure for the "Z" lens

source was used and the total ion current for an analysis was

i|_5xio _1

° A. Ten peak sets of data were taken for each analysis at a constant ion accelerating voltage (10 KV) and the

235 U and 233 U were scanned by changing the magnetic field

with the electromechanical scan control.

The standard procedure of a 15 minute degassing of the

sample and a minimum waiting period of 1/2 hour before starting

the analysis was not used for U-0002. Under these conditions

the estimated collector vacuum was too high and scattered particles rendered baselines at the 2

3

5 U and 233 U mass positions

indeterminate. With respect to the 238 U ion current of

^-5 X 10

_1 ° A the interference was less than a part in one

hundred thousand, but was approximately 2-5 percent of the

233 U and 235 U peak heights.

The normal continuous baseline curve was obtained when

the collector pressure was estimated to be in the low 10~ 7 torr region. To achieve this pressure it was necessary to

modify and condense the normal pumping time for a uranium

analysis as follows : Allow 5 minutes of source pumping by the

mercury diffusion pump; open the tube beam valve and allow an

additional 10 minutes for pumping; add liquid nitrogen to the

source coldfinger and start the degassing procedure.

Immediately after completing the degassing step the ion

accelerating voltage was adjusted to 10 KV and the high temperature analysis was started. After a combined total of 30

minutes of heating, the filaments were turned off, the tube

beam valve was closed and the source coldfinger was warmed to

room temperature. After a 5 minute waiting period, liquid

nitrogen was added to the source coldfinger and the analysis

restarted. A ^xio" 1 ° A uranium ion current was obtained in

16
the prescribed manner for a high-temperature analysis during

the next 20 minutes. Therefore, between 50 and 60 minutes

were necessary to arrive at a point where data could be taken

with an estimated collector pressure of 1-^xlO -7

torr. Extensive pumping either before or after degassing, even with the

beam valve open, was not utilized because the collector vacuum

would become too high before the analysis could be completed.

It was necessary to complete the analysis within 2 hours after

the start of pumping on the sample or run the risk of high

vacuums with detectable interference at the baselines.

Under conditions of the standard procedure of degassing,

minimum 1/2 hour waiting period and then analysis of a sample,

no organic background is detected at a 10~ 15 A ion current

sensitivity. A suspected organic background was occassionally

detected when the waiting period between degassing and analysis'

was omitted. A 5-10 minute waiting period was found to be

effective in reducing the suspected organic background below

the detection limit of the mass spectrometer.

The correction for mass discrimination was determined by

analyzing SRM U-500 on a cleaned source and under the same

conditions as the spiked samples . The isotopic composition

of 235 U was calculated by taking the product of the corrected

235 U/ 233 U ratio and the amount of 233 U (atom percent) added to

the sample. Contribution of 235 U from the spike was always

below the detection limit of the instrument and no correction

was made

4. U-970; Point Calibration of 235 U/ 238 U Ratio

Point calibration was mandatory for accurate measurement

of the large 235 ny 238 u ratio because of significant R-C response

of the measuring circuit when switching from a 10 _11

A ion

current to a 10~ 13 A ion current. To minimize any systematic

error contribution from R-C response, all peak top observations

for the 238 U ion current were extended to 60 seconds and only

the last 30 seconds were used as data for peak height determination. An upper limit of 5

X 10 _11

A was used for 235 U ion

17
currents to avoid operation at intensities where non-linear

response of the 10 1X ohm input resistor was a source of

systematic bias.

To accomplish the point calibration, U-970 and four synthetic mixtures with known 2

3

5 U and 238 U composition of approximately the same ratio as U-970 were analyzed in an alternate

pattern until duplicate analyses of each calibration sample

was obtained. A correction factor for mass discrimination was

determined from the ratio of the theoretical 235 u/ 238

u to the

observed 235 u/ 238

u of the calibration samples and the absolute

235 U/ 238 U ratio of U-970 was calculated.

5 . Determination of 231t U in U-0002 by Pulse Counting

The same set of U-0002 samples, which were spiked with

the "U-233" solution and used for determination of the 235 U

content, also presented an opportunity to determine the 231t U

content, which was known to be ^2 ppm. To provide a statistically useable 231f U signal of ^100 counts per second, an

equivalent 238 U signal of approximately 50 million counts was

required. The single V filament technique used for the 0.02

ppm Trace Elements in Glass series (see section 3-B) proved to

be inadequate in terms of total signal intensity available.

Therefore, a fourfold modification of the conventional triple

filament technique was used:

(1) Ionizing and sample filaments were degassed at

^2050 °C for one hour.

(2) One-half the usual amount of uranium was used;

i.e., approximately 50 ug per sample filament.

(3) A 30 minute degassing period was used prior to

analysis, with the ionizing filament set at

2150 °C and the sample filament currents set

at 1.75 A.

(^) An ionizing filament temperature of 1900 °C was

used during analysis to eliminate the contribution

of organic ions to the uranium spectrum.

18
A final 238 U signal of ^1.6 V gave the requisite 100 cps

231f U signal.

A scan of the mass region from m/e 237 through 233 during

an analysis of U-0002 spiked with "U-233" solution showed

there was no discernible organic or other contribution to mass

position 236; nor in a scan of unspiked U-0002 was there any

evidence of a contribution to the 236 or 233 mass positions.

Therefore, the only correction required for any contribution

to the various mass positions above the normal background was

for the scatter due to the tail of the large 238 beam. To

determine the magnitude of the correction, a count was taken,

immediately prior to analysis, for 100 seconds at the halfmass positions on either side of each integral mass position

of interest. An average of the two half-mass counting results

then represented an approximate scatter correction for the

corresponding integral mass position. Since the scatter correction for the 231f U amounted to ^5 percent of the total

count, the accuracy of the analysis was limited largely by

the inability to accurately correct for scatter.

A mass discrimination correction was applied by also

measuring the 233 u/ 235 U ratio and comparing with the corresponding ratio as determined by the conventional triple

filament technique.

6. 233 U Isotope Dilution of U-970

Two groups of 3 spiked U-970 samples were provided for

analysis. The three-fold purpose of the equal atom 238 U group

was to evaluate the potential of determining 2

8 U by isotope

dilution; to provide a spike within several orders of magnitude

of the 236 U abundance; to obtain data on a

231*U/ 233 U measurement of some ratio other than 1.

A low temperature analytical procedure for the "Z" lens

ion source was used. The 231t U, 236 U and 238 U were measured

with respect to 233 U with total ion currents between

5-7*10 11 A. Each set of equal atom samples was analyzed as

a group. For the equal atom 231t U solutions results were

19
obtained for each analysis in the following sequence and

number of ratios: 235/238, (5); 23V233 and 236/233 (4 each);

238/233, (5); 236/233 and 23V233 (4 each); 235/238, (5). For

equal atom 238 U solutions results were obtained for each ratio

in the following sequence and number of ratios: 235/238, (5);

238/233, (5); 23V233 and 236/233, (5 each); 238/233, (5);

235/238, (5). At all times the 235/238 and the 238/233 ratios

were measured by alternately monitoring peak tops for 30

seconds. The 23^/233 and the 236/233 ratios were measured by

normal mass scanning (magnet) but a quick-scan step (^2

seconds) was used to scan over the 235 U peak.

The correction for mass discrimination was determined by

analyzing SRM U-500 on a cleaned source and under the same

conditions as the spiked samples. Compositions of 231*U, 236 U

and 238 U were calculated by taking the product of the abundance ratio corrected for filament bias and the amount of 233 U

(atom percent) added to the sample, and where applicable,

subtracting the contribution of these isotopes made by the

233 U spike. The contribution from the spike was determined by

dividing the micromoles of the isotope in the spike solution

by the micromoles of uranium in the U-970 solution and multiplying by 100

.

The 2

3

8 U value calculated from the point calibration

value of the 235 u/ 238 U ratio and the isotope dilution values

for 231+ U and 236 U were considered to be best values and were

used to obtain the 235 U by difference.

The results of the analyses of U-0002 and U-970 are given

in Tables 2, 3, 4 and 5.

20
Table 2. Determination of correction factor for calibration of 235u/ 238U ratio of

SRM U-970, Uranium Isotopic Standard.

Calibration

sample no.

Calculated

235y/238y

Observed

235y/238y

Correction

factor

17-86 193.785 194.7911

194.8260

Average

0.994834

0.994656

0.99474

17-92 190.956 191.9724

191.8785

Average

0.994705

0.995192

0.99494

17-93 197.106 198.3268

198.1157

Average

0.993844

0.994903

0.99437

17-94 191.316 192.3996

192.2831

Average

0.994367

0.994970

0.99467

Mean Correction Factor = 0.99468

Table 3. Determination of the

235ij/ 238

U ratio of SRM U-970,

Uranium Isotopic Standard.

Run no Observed 235u/ 238u Corrected 235u/238U

3-2209 187.6788 186.680

3-2211 187.7381 186.739

3-2214 187.7164 186.718

3-2216 187.6868 186.688

3-2218 187.8737 186.874

3-2220 187.9418 186.942

3-2223 187.7633 186.764

3-2225 187.8467 186.847

Average 187.780 186.782

s.d. ±0.095

21
Table 4. Isotopic composition of SRM U-970, Uranium Isotopic Standard as determined by "U—233" isotope dilution.

234u236u238u

Sample no. atom % atom % atom %

17-76a

1.6655 0.1493 0.5233

17-78 a 1.6660 0.1489 0.5225

17-84 a 1.6655 0.1492 0.5233

17-77 b

1.6656 0.1490 0.5231

17-83 b

1.6642 0.1492 0.5228

17-85b

1.6649 0.1491 0.5232

Average 1.6653 0.1491 0.5230

s.d. ± 0.0006 ±0.0001 ±0.0003

a "U-233" solution 17-95 used.

b "U-233" solution 19-96 used.

Table 5. Isotopic composition of SRM U-0002,

Uranium Isotopic Standard.

234(j 235U

Sample no. atom % atom %

17-68 a 0.000164

17-69 a 0.000157 0.017547

17-73 a 0.017543

17-70b

0.000162

17-71 b 0.000158 0.017554

17-72 b

0.000158 0.017551

Average 0.000160 0.017549

s.d. ±0.000003 ± 0.000005 —h —

U—233" solution 17-95 used for isotope dilution.

b "U-233" solution 17-96 used for isotope dilution.

22
B. Stoichiometry of Uranium Oxide

This investigation [ref. 4, p. 19] was undertaken in the

hopes of finding an easily reproducible ignition procedure

that would give a stoichiometric U 3 8 compound. Only under

very carefully controlled conditions could this be approached.

Changes in temperature, pressure, cooling rate or oxygen content of the ignition gas result in changes in the stoichiometry

of the uranium oxide. Following the same procedure used last

year, samples of 1 g of SRM 950a, Uranium Oxide, (U 3 8 ), were

ignited in a tube furnace [1]. The samples were placed in

platinum boats and weighed on a microbalance while sealed in

a small desiccator.

Table 6 shows the results, including some reported last

year, of a series of ignitions at increasing temperatures with

varying cooling rates. Three cooling rates were used. The

samples were cooled by taking 10-15 minutes to move the furnace

back from the samples (slow cooling), by quickly moving the

furnace back from the area of the tube containing the samples

(normal cooling) or by quickly pulling the sample boat into an

iced portion of the quartz tube (fast cooling). To obtain a

stoichiometric oxide would require a loss on ignition for this

sample of approximately 0.15 percent. The only losses that

exceeded this value were ignitions in 5 and 10$ oxygen. The

loss at 1050 °C in 10$ oxygen with normal cooling was 0.166 to

0.172 percent. The loss at 1000 °C in 5% oxygen with normal

cooling was 0.175 to 0.187 percent and with slow cooling was

0.l4l to 0.154 percent. An easily reproducible ignition procedure to give a stoichiometric U 3 8 or a procedure to give a reproducible oxide without using a controlled atmosphere could

not be discovered, so; the procedure previously developed to

give a reproducible oxide will continue to be used. This

procedure is given below.

23
Table 6. Ignition loss of SRM 950a, Uranium Oxide (U 3 8), with varying

cooling rates.

Temperature

C

Slow cooling

% loss

Normal cooling

% loss

Fast cooling

% loss

850 0.076

900 0.083 0.088 0.096

950 0.086 0.102

1000 0.090 0.114 0.120

1050 0.094 0.126

Samples of uranium oxide were placed in platinum boats

formed from 0.002 inch platinum foil. The sample boats were

placed in a quartz tube, the furnace moved over the sample

area and the sample ignited overnight at 1050 °C in a dry,

carbon dioxide free atmosphere of air. After cooling the

furnace to 850 °C the samples were ignited in a pure oxygen

atmosphere for 1 hour. The samples were cooled (normal

cooling) and transferred to small glass desiccators for

weighing. All weighings were done on a microbalance

.

Although the procedure does not give stoichiometric U3O8,

it does give a reproducible oxide [ref. 5, p. 68] which can

be used for isotope dilution analyses.

C . Plutonium Isotopic Standards

1 . Modification of Plutonium Analytical Procedure

The procedure for plutonium analysis [3] is closely

patterned after the uranium procedure. Two major changes were

made and the new technique has been labelled "provisional"

until extensive testing is completed. The changes are a

larger drying current during sample mounting and elimination

of degassing.

Instead of an upper limit of 2 A for drying, the filaments

were adjusted to 2.3-2.4 A for 1 minute to convert the sample

to plutonium oxide. Heating the filament to a dull-red glow

(^2.5 A) was avoided. Several seconds of dull-red heat pro24
duced no apparent change in Pu signal response, although

there were some indications of reduced signal intensity.

During the degassing of a large number of plutonium

samples it was observed that a significant Pu signal (10 12 A)

was not detected until the filament currents were between

1.7-2.0 A. After the sample was allowed to cool for 1/2 hour

and was reheated to start the analysis, plutonium ion current

intensity was usually more than 5

X 10 n A at sample filament

currents less than 1.5 A. Careful stepwise increases in the

sample filament currents would burn-off the low temperature

signal and eventually a growing and stable signal was obtained.

A limited number of analyses were made without degassing

and it was observed that sample filament currents of approximately 2 A produced plutonium signals of l-2xl0 -11

A. The

signal intensity increased slowly and the ion current emission

was exceptionally stable. It appeared that the growth phase

could be maintained for most of the time span necessary to

measure the plutonium isotopic ratios. It is believed that

with some additional development, analysis of plutonium

samples without degassing will be a superior method to the

present procedure patterned strictly after uranium analysis.

2. Half-life of 21tl Pu

The evaluation of the half-life of 21+1 Pu was continued

on both SRM 948, Plutonium Isotopic Standard, and a United

Kingdom sample (UK-131) using the ani on-exchange separation

of americium from plutonium [ref. 6, p. 64]. The americium

separation must be as nearly complete as possible to allow the

2i|1 Pu content to be determined by mass spectrometry without

interference by the 21tl Am produced by the 3 decay of 241 Pu.

The 21+1 Am content has been growing since it is produced from

21tl Pu with a half-life less than 15 years and itself decays

with a half-life of more than 400 years. The Radiochemical

Analysis Section (310.01) used a counting technique to determine

the 21tl Am content on an aliquot of both SRM 948 and UK-131

samples that were also measured by mass spectrometry. Results

25
of the 21tl Am gamma-ray measurements indicate no more than

0.002 ppm 21tl Am in the two samples immediately after the ionexchange separation. This means the ion-exchange separation

is essentially complete and 241 Am did not affect the 21+1 Pu

measurements by mass spectrometry.

The half life of 21+1 Pu calculated from the annual determination of the isotopic composition of SRM 9^8 and UK-131 was

not significantly different from the value of l4.6±0.4 years

given in the last annual report [4]. However, the variation

of the value from year to year is greater than can be accounted

for by either a background contribution from 21+1 Am remaining

in the sample or by imprecision in the ratio measurements.

The probable cause of this abnormal fluctuation has not been

determined

.

D. Assay of SRM 727, Rubidium Chloride

Standard Reference Material 727, Rubidium Chloride, is

issued by the Office of Standard Reference Materials (OSRM)

as an intermediate purity standard which has been assayed by

silver coulometry for chloride and corrected for impurities.

Since the material is intended primarily as a rubidium

standard OSRM requested that this material be assayed for

rubidium content

.

During the course of the development of a chemical procedure for the recent redetermination of the atomic weight of

rubidium [7], it was shown that rubidium perchlorate was an

excellent weighing form for rubidium. The compound is stoichiometric and non-hydroscopic up to 90% relative humidity.

When precipitated from solution, the only elements that accompany it are cesium and potassium. Also, during the analysis

of the TEGs (see section 3-B) it was shown that small amounts

of rubidium could be determined with adequate accuracy by

isotope dilution mass spectrometry. Therefore, it was proposed

to assay this material by a combination of gravimetry to

determine most (99+%) of the rubidium as rubidium perchlorate

26
and isotope dilution mass spectrometry to determine the

soluble rubidium in the filtrate from the precipitation.

Two bottles of SRM 727, Rubidium Chloride, marked Btl. I

and Btl. II were received from OSRM for analysis. The material

was dried in a desiccator over freshly exposed magnesium

perchlorate for twenty-four hours. Four samples of about 2

grams each were taken from each bottle and weighed on a

micro-balance

Each sample was then assayed for rubidium by the following

procedure. The sample was dissolved in about 70 cm 3 of water

in a 100 cm 3 teflon beaker. About 2-5 cm 3 of "ultra-pure"

perchloric acid was added and the solution was heated until

all of the rubidium perchlorate dissolved. The solution was

slowly evaporated to fumes of perchloric acid and then at higher

heat to dryness. After cooling, the rubidium perchlorate was

dissolved in about 50 cm 3 of water by heating the solution.

This solution was slowly evaporated to about 10 cm 3 to crystallize most of the rubidium as rubidium perchlorate. After

cooling the solution, 0.5 cm 3 of perchloric acid was added and

the beaker and contents were cooled to about 5 °C to reduce

the solubility of rubidium perchlorate. The crystallized

rubidium perchlorate was caught in a medium porosity, 15 cm 3 glass filtering crucible, washed with 95% ethanol and the

filtrate was reserved for the determination of soluble rubidium. The crucible and contents were dried at 100 °C for four

hours, covered with a platinum cover and further dried by

slowly increasing the temperature to 300 °C to remove occluded

mother liquor. The crucible and contents were kept at this

temperature for 16 hours, then cooled and weighed on a microbalance. The heating at 300 °C, cooling and weighing were

repeated until a constant weight was reached, that is until

the weighings agree to within 20 ug. The air weight of

rubidium perchlorate was converted to vacuum weight.

The weighed rubidium perchlorate was corrected for potassium and cesium perchlorates in the following manner. The

27
potassium in the rubidium perchlorate was determined by isotope

dilution mass spectrometry after thermally converting the

rubidium perchlorate to rubidium chloride in a covered quartz

crucible at 600 °C. This material was dissolved in water and

transferred to a tared 100 cm 3 polyethylene bottle and diluted

to 100 cm 3

. The solution was mixed and the bottle and contents

were weighed to ±0.1 mg. A weighed aliquot of about 10 g of

this solution was spiked with 41 K to produce an altered 39 K/'tl K

ratio of about 1, based on prior analysis of potassium in the

original rubidium chloride. This solution was diluted so that

1 cm 3 of solution contained 1 mg natural rubidium (0.5 Ug

spiked potassium) and the "K/^K ratio was determined. The

mass spectrometric procedure described (see section 3B) for

potassium was followed with a downward adjustment in total

potassium signal intensity in proportion to the smaller sized

sample (of potassium) being loaded. The large excess of

rubidium present generated a significant amount of scattered

background at the potassium mass positions. This background

varied with mass and grew in proportion to the signal growth.

All the potassium determinations were made on signals which

grew slowly and linearly. Background corrections were made

to the peak heights and amounted to only 1 to 2 percent of

the total. The amount of potassium in the aliquot was then

calculated and from this, the weight of potassium perchlorate

in the rubidium perchlorate was calculated. The amount of

cesium in the original rubidium chloride was only 24 ppm and

almost all of this would precipitate with the rubidium perchlorate so a correction for cesium was calculated from this value.

The solubile rubidium in the filtrate from the rubidium

perchlorate filtration was determined by isotope dilution mass

spectrometry. The filtrate was evaporated to fumes of perchloric acid, taken up with about 50 cm 3 of water, transferred to

a tared 100 cm 3 polyethylene bottle and diluted to 100 cm 3 after the addition of 2 cm 3 of hydrochloric acid. A weighed

portion of about 5 g was spiked with a weighed amount of 8 7 Rb

28
solution to produce an altered 85 Rb/ 87 Rb ratio of about 0.3.

The solution was evaporated to dryness and taken up with (1+49)

hydrochloric acid so that 1 cm 3 contained about 10 yg rubidium.

The 85 Rb/ 87 Rb ratio was then determined. The mass spectrometric procedure used was identical to the method previously

developed for rubidium chloride [ref. 4, p. 32]. The temperature used in drying the samples on the sample filaments is high

enough to convert rubidium perchlorate to rubidium chloride.

Test samples using natural rubidium perchlorate responded the

same as the chloride and gave the same isotopic ratios. The

amount of rubidium in the portion was calculated and, from

this value, the total rubidium in filtrate was determined.

Because of the small amount of rubidium in the filtrate

and also the low level of potassium coprecipitated with the

rubidium, the total assay of the rubidium is relatively insensitive to errors in both determinations. An error of 1 percent

in the determination of rubidium in the filtrate or of 10

percent in the coprecipitated potassium will cause less than

1 part in 15,000 error in the total assay.

The total rubidium in the sample was determined from the

sum of the corrected rubidium from the gravimetric determination of rubidium perchlorate and the rubidium found in the

filtrate by isotope dilution analysis.

The results of the assay of four samples from each of

the two bottles are shown in Table 7. The material assayed

99.896±0.019 percent rubidium chloride.

This procedure was first applied to a high-purity sample

of rubidium chloride in which the only detected impurities

were 24 ppm potassium, 5 ppm magnesium, and <10 ppm cesium.

Ten fused samples of- 1.7 to 2.2 g of this rubidium chloride

were assayed as described. This material assayed 99-979±0.012

percent. The results are reported in Table 8.

29
ro

</>

.o _o or

QC roo— oo Eo

CD Ovl co i—<

CD CD OO 1—I

cd CD oo CD

cd CD oo CD

CD CD CT> CD

oo 1—I

Ovl CD

CD LO Ovl OO

oo CD oo CO

oo «3" LO CD

CSJ LO Ovl LO

oo Ovl oo Ovl

CD CD UD Ovl CD oo CD

CD CD CD oo CD CD f—t OO oo oo oo OO CD CD

CD CD CD CD CD CD CD CD CD CD CD CD + \ + \ , , Ovl «=r CO

"vT Ovl i—<

CD CO oo CD *—i

CD OjO "O _i

CD LO LO CD CD GO *3" i—i

CD CO ^— o oo «3" OO OO CO LO

CD

7T = *- O CD *. -O -*= Q£ CO DO

CD oo oo Ovi oo CD CD oo OO *3- i

oo CD OO Ovl oo

CD Ovl CD «3- r-~ CD OO CD

Ovl *a- LO CD CD f—i

oo oo

r~- i-~> r-« CD CD CD 1Ovl oo i

oo r—. CD CD CD CD

.2 -o c o a: 3 oo

a> rO

TO

oo

O

JSO a>

oo CD oo 1

«=r »=r oo CD

oo Ovl LO 1

LO «v1" CD CD

«3- co oo LO oo LO CD oo

Ovl Ovl oo CD oo OO oo *3-

CnJ LO Ovl ^3- «3- 1—1 CD CD

oo Ovl oo Ovl oo *=r oo oo o = 2 oo a: 2 ~ e

CD

CD

CO I •—«

CD LO Ovl i—1|— OO

OO OO Ovl

CD CD CD >—I OO CD

CD OO CD

Ovl Ovl CO

Odvf r—

.Q E o

r*.

m o o oo SS '*— J2

GC a:

</S

«*- o

CO

aa> vt

</> o £o * o

rr

oo

o> -O

ro <* r- O ^- O

ooE O

vt o k> _.., f "» s

WDE

r—.

co ,—1CD

CO LO CD LO

Ovl CD i—4 1 OO CD CD CD

1— ^d- Ovl *3- oo Ovl OO Ovl

OO OO CO

CD CD LO

Ovl CD CD

OO

OO

CD

OO

oo LO i

OO 1 CD CD CO

CO CD CD Ovl OO t—1

«=r *3" CD CD CD OO OO t——I

r~- r-v» Ovl OO CD 1

CD OO CD oo

LO CD LO CD i—l LO CD «vT OO rv. OO CD CD CD CD CD

Ovi ovi Ovl Ovl Ovi CO OO Ovi

CD

CD

CDr

o

CD

CD

OO

CD

OO

CD

OO

OO

CD

OO

LO CD «=r oo OO Ovl co oo

Ovl Ovl 1—i Ovl Ovl oo LO CD

Ovl CD oo CD LO "vf Ovl «3- Ovl Ovl Ovl Ovl Ovl Ovl Ovl

vt

-a £

CO CD CD LO LO Ovl CD r~~ CO CD CD Ovl "3- OO CD Ovl oo CD *3- «3" <3" CD CD oo

^3- LO OO CD OO LO OO CD

LO CD LO CD 1—1 LO CD «=r OO r-v. oo CO CD CD CD CD

Ovi Ovi Ovi Ovi cvi oo OO Ovi

a>

Ovl oo LO CD oo

ro CQ CO

30
oo

to

CD

LO

r

cd

r

cd

i

r

cd

oo

CD

in

oo

CD

1

CD

CD

CD

CD

LO

CD

CD

CD

CD

CD

LO

CD

CD

CVI CD

CD

o-> cdcd

cd

cd

cd

cd

CDenCD

CD

CD

CD

CD

CD

CD

CD

CD

CD

CD

CD

CD

+1

CD

+ 1 o

o E

o

oo

«3- CD CD CO CVI CO CD «=r «=3" to

to CXI co LO CD

CD <^- LO to to

^3- CD r-^ LO LO

CVJ <=J- oo CO CVI

CVI to

^3" to

to

CVJ

CVI co

r

CO

CO

CVI CO

CO CD CD OO

CD CO CO »— to 9£ o

LO

CD

% JQ ^C oo

evi co «^- CO CD tO

CO CO LO

LO to to

LO CO «^"

I CD CD

CD tO CO

LO ^^ CD

cvi co oo

CD CO .—I —h i—- cd

cd r

i

to LO CO i—

CVI CVI CD tO

*3" tO CD LO

CD LO i—

CVJ CD CO OO CD i—

CD CD I

CVI Cvi —

—

a>

O

E

co ^ .3 .Q c: © Q£ = oa

CO i—

«3- CD CD «^- *3- CD CO CD

oo ^3- co CVJ CVJ 1

CD CVI r-» CVI

cvi CD LO CVI r-* CVI CO co ^3- r~- CD co LO to to to r

co CD to

-=r CD 1 LO LO to ^r CO CD to

CVJ *=r co CO CVI CsJ LO «iT "=3- OJ

a> « E co DO

CVJ r-~ ^3- to 1—

CD ^r cv* CVI T—1 CO CD CD CD CO CD co CO co to

LO r^. LO co co CVI LO co to CD

CVI

I

CO

•st

I—

«=3" CD CO CO *3- CD CO —

CO

CD «-r CO co «-r r-— CSJ OO «=r to

f

i—

CD co CO CD CSJ CD CO r-~ OO to '=T CD LO CD «^- CO LO i—i r—

LO to LO LO LO «=T CsJ CD to

CVI CO CO CO CVJ CVI LO "=3" CO CSJ

OO

-o

CO

st O

5*-

<3 *

COoa>

cvi co

to

to

CO

to

CsJ

to

oo

CD

CO

coCD

cvi

r-~ LO r~~ oo CO CsJ CD to

^3- CD i—

r-^ CO co 1

CD

CD ^3- CD CD CO LO CO CO

i—

CVI LO co CD t—

CD CD

LO Csl i—

CVI «=r CD T—-4 Csl CD CD r^» r

co CD CD I

CsJCsJCsJCsJCOCOCOCsJ

"st O £

o S

co CD 1-^ CO "^- to CD ^3" CD CD CD CO oo CsJ CD CD

i—

i—

i—

I—«—

CsJ CVI CVI CD

st O -2

CD *^- to CsJ CZ> Csl CD : 1 ^3" CD —

oo «~r CD CD to CD to r-~ CD

co 1—

CsJ to »—

T—

i—

1

CD CD

to "^- 1—CSJ to *3- *—

1—

CD CD

CO co LO CSJ I—

Csl -5j- CD CVI CVI to CD CD CD I-— 1 co CD CD r-~

CsJ CsJ CsJ CsJ CVI CVI CO CO CO CVI

a>

ro

CVI CO CO CD

31
SRM 727, Rubidium Chloride was originally issued as an

intermediate purity chemical. After the completion of this

work on the assay of rubidium the material was redesignated

as SRM 984, Rubidium Chloride, and is certified for assay and

absolute isotopic composition.

A copy of the certificate for SRM 984 is included as

Appendix I.

E. Assay of Potassium Chloride

The Office of Standard Reference Materials plans to issue

a high-purity potassium chloride as a standard for both

potassium and chloride. They have requested that a assay

procedure for potassium in this material be developed.

A preliminary investigation has shown that a procedure

based on the precipitation of potassium perchlorate followed

by isotope dilution determination of soluble potassium can be

used for the high accuracy assay of this material.

32
3. TRACE CHARACTERIZATION BY ISOTOPE DILUTION ANALYSIS

A. Methodology

1 . Introduction

Mass spectrometric isotope dilution analysis is a powerful

tool for the determination of trace level constituents in

materials. The method consists essentially of the following

steps :a) The addition of a weighed portion of a separated

isotope solution of known concentration to a known weight

of sample;

b) Dissolution of the sample by appropriate means and

thorough mixing of the resulting solution to ensure equilibrium of the separated isotope with the impurity element;

c) Chemical extraction of the isotopically altered

impurity element;

d) Mass spectrometric measurement of the altered isotopic

ratio; and 9 e) Calculation of the amount of impurity element present

in the sample.

The major advantages of the technique are the high accuracy attainable (better than 1 percent for most elements with

some elements at the 0.1 percent level) and the fact that

chemical separation and recoveries need not be quantitative.

The major disadvantages of the method is the problem of

facility and reagent contamination or blank. This difficulty

is common to all trace methods with the exception of activation analysis. Since the amount of the blank limits the lower

range of trace element determination, considerable effort was

focused on this problem. The facilities blank for such

elements as lead and potassium has been lowered by carrying

out chemical operations such as dissolution and evaporations

in a Class 100 clean air hood. The reagent blank has been

lowered by selection of high-purity reagents for the lowest

contamination of the elements to be determined or by in-house

33
purification by isothermal distillation. Lead blanks for the

analysis of lead in glass standards were in the range 1 to

2 ug when the analyses were carried out in the normal air of

the laboratory. This lead blank has been reduced to 0.02 ug

by carrying out the chemical operations in a Class 100 clean

air hood. Potassium blanks that were as high as 7 ug for the

analysis of potassium in the glass when carried out in normal

laboratory air have been reduced to 0.4 ug.

2 . Storage of Separated Isotope Solutions and Method of

"Spiking"

Solutions of separated isotopes are stored either in

boro-silicate glass flasks or in teflon bottles. The glass

flasks are constructed from 200 cm 3 volumetric flasks by

cutting the neck of each flask about 1 cm from the body and

tooling the neck for a serum stopper closure. These flasks

are stoppered with rubber serum septa and sealed with crimped

aluminum caps and are stored in desiccators containing a little

water to maintain 100% relative humidity on the outside of the

flasks. Solutions stored in this manner have shown virtually

no change in weight over a 1 year period.

Solutions of separated isotopes which could be contaminated by boro-silicate glass are stored in 200 cm 3 teflon

bottles. While storage in teflon has not been as satisfactory

as in glass, in no case was the weight loss of a solution

greater than 0.1 percent for a three month period.

The "spiking" for isotope dilution analysis is done by

weight. A 4-inch platinum or stainless steel needle with a

Kel-F hub is inserted thru the septum closure into the solution

A second needle which just punctures the septum serves as a

vent. A polyethylene hypodermic syringe of appropriate size

is attached to the hub of the needle. (The rubber plunger of

the syringe is covered with teflon by streching a small piece

of 7.5 mil thick teflon over it.) The desired amount of

solution is drawn into the syringe, the syringe is disconnected

34
from the needle hub, and the tip is capped with a Kel-F cap.

Any static charge that might be present is dissipated by

wiping the syringe with a damp paper towel. The syringe and

contents are then weighed on a semi-micro balance to ±0.02 mg

The spike solution is delivered from the syringe to a beaker

containing the material to be analyzed and the syringe is

again capped, wiped, and weighed. The weight of the spike

solution is determined from the weight of the syringe before

and after delivery of the solution. This method of separated

isotope spiking permits the delivery of 1 g (1 cm 3

) of spike

with less than 0.01 percent uncertainty.

3 . Spike Calibrations

The concentration of a separated isotope solution is

determined by the addition of a known amount of the natural

element (preferably a SRM of known assay) to a weighed portion

of the spike solution. The isotopic abundance ratio of the

element is then measured by mass spectrometry and the concentration of the separated isotope solution is calculated.

This is a necessary procedure since separated isotopes

are normally furnished as compounds which are of unknown total

purity.

B. Trace Elements in Glass SRMs

The Office of Standard Reference Materials has prepared

four glass SRMs in the form of wafers cut from glass canes

which have been doped with 6l elements at the 500 ppm, 50 ppm,

1 ppm and 0.02 ppm levels, respectively. Lead, silver, copper,

thallium, potassium, rubidium and uranium were determined by

isotope dilution mass spectrometry in the 500 ppm and 50 ppm

standards and, with the exceptions of copper and silver, the

same elements were determined in the 1 ppm and the 0.02 ppm

standards. Wafers about 1 mm thick and weighing about 0.3 g

were used for the analysis of the 500 ppm standard and wafers

about 3 mm thick and weighing about 1 g were used for the

analysis of the other standards. Uranium was determined in

35
separate samples while the other elements were determined by

multiple spiking of the same sample.

1 . Multiple Spiking Procedure and Determination of

Silver, Copper, Potassium, Lead, Rubidium and Thallium

a. Sample preparation, spiking and dissolution - Each wafer was cleaned by wiping with a paper towel saturated

with ethanol and by immersion in (1+9) nitric acid for 5

minutes to remove surface contamination. The wafers were

then washed with distilled water, air dried, and weighed.

Each weighed wafer was transferred to a 30 cm 3 teflon

beaker and a appropriate amount of 65 Cu, 205 Pb, ^K, 87 Rb,

1 09 Ag, and 203 T1 spike solutions were added to each sample,

except that 65 Cu and l 09 Ag were not added to the 1 ppm and the

0.02 ppm standards. These separated isotope solutions were

calibrated by using SRM 976, Copper Isotopic Standard, for the

spike calibration of the 65 Cu solution; SRM 981, Natural Lead

Isotopic Standard, for the spike calibration of the 206 Pb

solution; high purity (99.99+%) natural potassium chloride for

the spike calibration of the hl K solution; SRM 984, Rubidium

Isotopic Standard, for the spike calibration of the 87 Rb solution; high purity natural silver (99.99%) for the spike

calibration of the 1 09 Ag solution; and high purity natural

thallium for the spike calibration of the 203 T1 solution.

Three blanks were prepared by adding the same spike solution to beakers without samples. Throughout this procedure

these blanks were treated exactly as the sample solutions.

The glass wafers were dissolved by treating each sample with

10 cm 3 of (1+1) hydrofluoric acid and 5 cm 3 (2 cm 3 for the

1 ppm and 0.02 ppm standards) of perchloric acid. The beakers

were covered with teflon covers and placed on a hot plate at

low temperature for about 16 hours. The skeletons remaining

from the dissolution were crushed with teflon rods and the

wafers were allowed to react further if not completely dissolved. (A considerable quantity of insoluble CaF 2 was produced

during the dissolutions, but this material had a different

36
appearance from the wafer.) The solutions were then slowly

evaporated to fumes of perchloric acid to volatilize SiFi, and

to convert insoluble CaP 2 to soluble Ca 3 (CICO2. The sides

of each beaker were washed with water, 1 cm 3 of hydrofluoric

acid was added, and the evaporation repeated to strong fumes

of perchloric acid.

b . Separation of lead and thallium - Lead and

thallium were separated from the sample solutions by electrodeposition. Two different electrodeposition procedures were

used depending on the amount of lead present. The method

used for the 500 and 50 ppm standards (high acid) gave unsatisfactory recoveries of lead when less than 10 yg of lead was

present. The electrochemical method described for the 1 and

0.02 ppm standards (low acid) is based on the work of H. Mttller

[8] and was found to give satisfactory recoveries (>

rJ0%) with

as little as 1 yg of lead. This method is the method of

preference and would be used if the analysis of the 500 and

50 ppm standards were repeated.

Each solution from the dissolution of the 500 ppm and

the 50 ppm samples were treated as follows: The solution was

diluted to about 25 cm 3 and 1 cm 3 of nitric acid was added.

The solution was then electrolyzed at 0.02 A (about 2 volts)

using 50 mil platinum wires for both anode and cathode. The

solution was stirred magnetically during the electrolysis

which was continued for at least six hours . Lead and thallium

were deposited on the anode as Pb0 2 and T1 2 3

. Copper and

silver were deposited on the cathode as copper and silver

metal. The sample solutions were reserved for the- determinations of potassium and rubidium.

The platinum anode containing the electrodeposited Pb0 2 and T1 2 3 was weighed on a micro-balance and the deposit was

stripped from the electrode with a few cm 3 of a dilute nitric

acid-hydrogen peroxide mixture. The resulting solution was

evaporated to dryness and taken up with sufficient (2+98)

nitric acid so that the solution contained about 200 yg lead

37
and 200 yg thallium per cm 3 and reserved for mass spectrographic analysis.

Each solution from the dissolution of the 1 and 0.02 ppm

standards was treated as follows: The solution was evaporated

to dryness, taken up in a few cm 3 of water, and again evaporated to dryness. The residue was then taken up with 10 cm 3 of water and 1 cm 3 of a 0.5N nitric acid solution to which

1 mg of copper had been added. The solution was then electrolyzed at 0.02 A (about 2 volts) using 50 mil platinum wires

for both anode and cathode. (The copper is added to convert

the platinum cathode to a copper cathode which prevents the

formation of nitrous acid.) The solution was stirred magnetically during the electrolysis which was continued for at least

six hours . The cathode was then washed with water and the

Pb0 2 and T1 2 3 was stripped from the electrode with a dilute

nitric acid-hydrogen peroxide mixture. After evaporation,

the residue was taken up with one drop of (2+98) nitric acid

and reserved for mass spectrometric analysis.

c. Determination of lead and thallium - The mass

spectrometric procedure used for the lead analyses was the

silica gel technique which is described in a later section

(section 4, below).

The results of these determinations are shown in Table 9.

As with all analyses of very small lead samples, constant

vigilance is required to prevent abnormally large blanks. In

this series the original laboratory blanks were of the order

of 2 yg. With the use however of "ultra pure" reagents and

of small Class 100 laminar flow "clean hoods" for all dissolution and filament mounting steps the laboratory blank was

reduced to ^0,02 yg.

If thallium was to be determined on the same filament

loading a short addition to the lead procedure was used. The

filament current was increased slowly until a thallium grid

signal of 3

X 10 -1 ° A was obtained. After 1 minute the current

38
Table 9. Determination of lead in TEG standards.

500 ppm TEG

Position ppm Pb

2 426.48

13 426.17

18 425.56

48 426.09

56 426.86

66 426.00

78 426.21

106 426.68

Average 426.13

s.d. ±0.42

95% C.L. ±1.02

50 ppm TEG

Ave. blank correction -0.8 ppm

1 ppm TEG

Position ppm Pb

2 2.35

36 2.41

40 2.35

69 2.37

76 2.38

114 2.33

Average 2.36

s.d. ±0.03

95% C.L. ±0.07

Ave. blank correction -0.02 ppm

Position ppm Pb

2 38.57

37 38.68

44 38.64

68 38.51

75 38.41

114 38.62

Average 38.57

s.d. ±0.09

95% C.L. ±0.23

Ave. blank correction ~ 0.3 ppm

0.02 ppm TEG

Position ppm Pb

2 1.87

33 1.89

43 1.90

51 1.86

61 1.88

76 1.88

130 1.89

Average 1.88

s.d. ±0.02

95% C.L. ±0.04

Ave. blank correction -0.02 ppm

was reduced to give a grid signal of 5

X 10 -11

A. The signal

was allowed to stabilize for 5 minutes after which ten ratios

were measured.

The results of the thallium determinations are given in

Table 10.

39
Table 10. Determination of thallium in TEG standards.

50 ppm TEG

Position ppm Tl

2 15.66

37 15.81

44 15.75

68 15.59

75 15.54

114 15.73

Average 15.68

s.d. ±0.09

99 95% C.L. ±0.23

0.02 ppm TEG

Position ppm Tl

33 0.00834

43 0.00809

76 0.00818

Average 0.00820

s.d. ±0.00013

95% C.L. ±0.0005

d. Separation of copper and silver - The isotopically altered copper and silver were separated from the sample

solution of the 500 and 50 ppm standards by electrodeposition

as described under the separation of lead and thallium. The

silver and copper were then separated from each other as

follows: The platinum cathode containing the silver and

copper was treated with 5 cm 3 (1+9) nitric acid to strip the

silver and copper from the electrode. The resulting solution

was diluted to 25 cm 3 and silver was electrodeposited onto a 50 mil platinum cathode at a cathodic potential of 0.242

(0.0V vs S.C.E.). The solution was stirred magnetically and

the electrolysis was continued for at least 6 hours. The

40

500 ppm TEG

Position ppm Tl

2 63.58

13 60.17

18 61.47

48 61.19

56 62.27

66 61.40

78 62.26

106 61.95

Average 61.79

s.d. ±1.00

95% C.L. ±2.37

]. ppm TEG

Position ppm Tl

40 0.270

76 0.269

114 0.268

Average 0.269

s.d. ±0.001

95% C.L. ±0.005
cathode was then washed with water followed by ethanol, dried

and weighed. The silver was then stripped from the electrode

with (2+98) nitric acid and the resulting solution was evaporated to dryness. The residue was taken up with (2+98) nitric

acid so that the solution contained 500 yg Ag/cm 3 and this

solution was reserved for the mass spectrometric measurement

of the altered 107 Ag/ 109 Ag ratio.

Copper was electrodeposited onto a 50 mil platinum wire

cathode from the solution remaining from the silver separation

at -0.4V cathode potential (vs S.C.E.) The solution was

stirred in the same manner and the electrolysis was continued

for at least 6 hours. The cathode was washed with water

followed by ethanol, dried, and weighed. The copper was then

stripped from the electrode with (2+98) nitric acid and the

resulting solution was evaporated to dryness. The residue was

taken up with sufficient (2+98) nitric acid so that the solution contained 500 yg Cu/cm 3 and this solution was reserved

for the mass spectrometric measurement of the altered

6 3 Cu/ 65 Cu ratio.

e. Determination of copper - The analytical procedure presently used for all copper isotope dilution analyses

is basically the same technique described for small amounts of

copper (^20 yg) in a previous report [4]. The source material

from which copper is extracted is relatively unimportant but

the total amount of copper provided for analysis and the purity

of the solution is critical. The chromium, potassium and

sodium from the sample and filament material must be maintained

at levels so that they will decay below critical limits within

the first 25 minutes of filament heating. Large chromium ion

currents will produce significant baseline interference near

or at the 63 Cu mass position. Once the solution requirements

are satisfied the key to precise analysis is filament temperature control and adherance to a strict time schedule.

Periodic use during the past year has indicated that for

most analyses the internal change in the 63 Cu/ 65 Cu ratio can

41
be held to approximately 0.5 percent. There is a loss in

analytical precision when the copper ion current ratio of

altered samples is greater than 5:1. Similarly, there is

increased difficulty in measuring the large ion current ratios

of separated isotope solutions and blank samples of the

smaller sample size.

The Cu ion currents were measured on a single stage solid

sample mass spectrometer with a 6-inch radius of curvature-60°

analyzer tube and a "Z" lens ion source. A triple filament

rhenium ribbon source was used and the ion accelerating

voltage was 7-5 KV.

One drop of copper nitrate solution (0.5 mg Cu/cm 3

) was

placed on each sample filament. The copper was electroplated

onto the filaments at a potential difference between the

platinum wire and the filament of 3-5 volts. The current was

approximately 1 mA and was maintained for 10 minutes. At the

conclusion of the plating cycle and with the current ON, the

remaining solution was flushed from the filaments with a stream of alcohol. This step was taken to prevent redissolving

of plated copper by the nitric acid solution on the filament.

The estimated sample size was 10 ug. The filaments were

mounted in the filament block with the sample filaments

positioned away (^0.025 inch) from the edges of the ionizing

filament. The open spacing technique was used to inhibit

sample evaporation by radiant heat from the ionizing filament.

An optical pyrometer was used to measure filament temperatures. During the first minute of heating the ionizing filament

temperature was adjusted to 2120 °C (5.5-6.0 A) and the sample

filament currents were set at 0.5 A. After 5 minutes of heating the sample filaments were increased until the total copper

ion current was 4xio -ll+

A. The ionizing filament temperature

normally decreased significantly during the first 10 minutes

of heating but began to stabilize at approximately 2100 °C.

After 15 minutes of heating the signal will have normally

increased to approximately lxio" 13 A. The temperature of the

42
ionizing filament was checked and, if necessary, was adjusted

to 2100 °C. The sample filament currents were increased to

yield a total signal intensity of 2 . 7-3 . OxlO -1 3 A. During

the next 10 minutes it was necessary to focus the signal for

maximum intensity and mass scan to determine baselines of

63 Cu and 65 Cu. The ion current was expected to be 4-5 x 10~ 13 A

and growing.

Twelve peak sets of data were taken between 25 and 38

minutes after the start of heating. Each peak top was monitored for 30 seconds and the magnet current changes were made

in discrete steps. The analysis was concluded with another

mass scan to determine baselines of 63 Cu/ 65 Cu. Each analysis

consisted of two sets of six ratios each. The average of the

first six ratios were used as data and the average of the second

set of six ratios was compared with the first to determine the

point on the fractionation curve at which the data was taken.

The results of the determination of copper in the 500 ppm

and the 50 ppm TEG standards are given in Table 11.

Table 11. Determination of copper in TEG standards.

50 ppm TEG

Position ppm Cu

2 37.32

37 37.74

44 37.59

68 38.05

75 37.67

114 37.93

Average 37.72

s.d. ±0.36

95% C.L. ±0.92

a The precision of the method indicates some heterogeneity in this sample for this element.

43

500 ppm TEC1

Position ppm Cu

2 440.8 a

13 443.8

18 443.2

48 444.6

56 445.4

66 442.5

78 444.6

106 445.9

Average 443.9

s.d. ±1.7

95% C.L. ±4.0
Normally the signal intensity for most analyses can be

expected to grow for at least 40 minutes. The magnitude of

the filament bias correction was determined by monitoring the

change in 63 Cu/ 65 Cu ratio between the first and second half

of an analysis. Filament bias corrections were applied as

follows: 1.1 percent when the ratio changed less than 0.3

percent; 0.9 percent when the ratio changed between 0.3 and

0.5 percent; 0.75 percent when the ratio changed 0.6 percent.

Analysis in which the signal decayed before the end of the

first set of 6 ratio measurements usually displayed gross

fractionation (>1%) and all such analyses were terminated

because of the difficulty in precisely determining the

magnitude of the bias.

All filaments before use were degassed at 4 A for 1 hour

in a vacuum and under a potential field. The trace copper

background in the filament material decayed rapidly and was

not detectable at a 10 15 A ion current sensitivity. There

was a detectable chromium signal from degassed filamants but

it was too small to produce significant baseline interference

at the 6

3

Cu mass position.

Cross contamination between samples of different isotopic

composition was not observed. The precaution of cleaning the

source for blank determinations and analysis of separated

isotopes of copper was always followed to further minimize

possibility of memory effects.

f . Determination of silver - The basic analytical

procedure for silver is described in a previous report [3].

Adaptations of the base procedure have been successfully used

to analyze quantities of silver from 200 ug to 5 tig. The

technique is essentially independent of the source material

from which silver is extracted but it must be modified according to the total amount of sample available for analysis . As

the sample size decreased the signal intensity must be acquired

and measured over shorter time spans. A relatively high concentration of an impurity in solution with silver requires

44
higher sample filament temperatures to produce a standard

signal intensity. The net effect of higher temperatures is

an increased rate of fractionation which will produce apparent

differences in the isotopic composition. Therefore, it is

essential to provide silver nitrate solutions of high, uniform

chemical purity.

The analytical procedure developed for isotope dilution

analyses of the TEG samples would yield sufficient ion current

intensity from a 20 yg sample to measure the abundance ratio

of a natural sample with an analytical precision between 0.15

and 0.25 percent. Because the intensity during an analysis is

small (4-6xl0~ 13 a) and restricted to a narrow limit, there is

a significant reduction in precision when comparing ion currents different from 2:1. For a 20 yg sample size the large

ion current ratios of blank samples are measured at greatly

reduced precision. If it is necessary to determine the isotopic composition of separated isotopes as part of the

dilution work, the analysis should be made using larger

sample sizes or with more sensitive detection.

The Ag ions were measured on a single stage solid sample

mass spectrometer with a 6 inch radius of curvature 60°

analyzer tube and a "Z" lens ion source. A triple filament

rhenium-ribbon source was used and the ion accelerating

voltage was 7-5 KV. The source and collector slit widths

were 0.010 and 0.0^40 inch, respectively.

One drop of silver nitrate solution, 1 mg Ag/cm 3

, was

placed on each sample filament and dried for 5 minutes with a heat lamp and a 1 A current in an atmosphere of air. The

filaments were placed in a hydrogen atmosphere and the silver

nitrate reduced to metallic silver by increasing the current

to 2.5-3.0 A. Normally, there was no detectable redness in

the filament. The sample size was estimated to be 10 yg per

filament. The sample filaments were positioned away (^0.025

inch) from the edges of the ionizing filament. The open

45
spacing was used to minimize sample evaporation and ionization by radiant heat from the ionizing filament.

Ionizing filament temperatures were measured with an

optical pyrometer. During the first minute of heating the

temperature was set to 2120 °C and the sample filament currents at 0.25 A. The silver ion current was usually less

than 1x10 13 A. The ionizing filament temperature decayed

during the early stages of heating and eventually stabilized

at approximately 2100 °C. Between 5 and 6 minutes after the

start of heating the sample filament currents were increased

to yield a total intensity of 0.8x10 13 A. Exclusive of a brief period of decay after this adjustment, the signal was

expected to grow for the remainder of the analysis.

After 11 minutes of heating three options were available.

No adjustments were made if the total signal intensity was

approximately 2xio~ 13 A. If the total intensity was less than

2x10 13 A, the sample filaments were adjusted to achieve this

level. The final option was termination of the analysis if

the signal intensity was approximately 4xio~ 13 A. Analyses

in which the total ion current reached this level after only

10-11 minutes of heating were considered to be overheated

because, in general, the ion currents would eventually decay

before the end of the ratio measurement. Such analyses

usually exhibited greater than normal internal changes in the

i Q7 Ag/ i 9 Ag ratl0>

The mass scan to determine baselines was commenced after

15 minutes of heating. The ratio measurement was started

promptly after 20 minutes of heating on a growing signal of

4-5 x 10~ 13 A. Ten peak sets of data were taken between 20 and

31 minutes after the start of heating. Each peak was monitored

for 30 seconds and magnet changes were made in discrete steps.

The analysis was concluded with a mass scan to determine baselines of the silver peaks

.

The results of the determination of silver in the 500 ppm

and the 50 ppm TEG standards are given in Table 12.

46
Table 12. Determination of silver in TEG standards.

5(10 ppm TEG

Position ppm Ag

2 254.5

13 252.8

18 254.1

48 253.3

56 254.8

66 251.9

78 261.6a

106 252.3

Ave rage 253.4

s.d. ±1.1

95% C.L. ±2.7

50 ppm TEG

Position ppm Ag

2 22.72

37 22.10

44 22.09

68 21.84

75 22.09

114 22.02

Average 22.14

s.d. ±0.30

95% C.L. ±0.77

a Omitted from average.

Even at constant temperatures the 107 Ag/ 109 Ag ratio

decreases with time during an analysis. The magnitude of

this change is less than 0.25 percent for a 200 yg sample

under controlled conditions over a 20 minute period but is

more than 0.5 percent for a 20 yg sample over the same time

span. Similarly, sample sizes of 200 yg will yield growing

ion currents of 10~ 12 A for at least 1 hour but a 20 yg

sample will not normally yield growing ion currents of 10~ 13 A

for more than 40 minutes of heating.

SRM 978, Silver Isotopic Standard, was analyzed to obtain

an estimate of the difference in the observed abundance ratio

for operation at two slightly different filament temperatures

with the 20 yg sample. All parameters were held constant

except the slight differences in temperature. For the Group I

analyses, a total signal intensity of 4xl0~ 13 A was used as an

upper limit and was simply changed to a lower limit for the

Group II analyses. The uncorrected 107 Ag/ 109 Ag ratios are

given below for comparison.

47
Group I Group II

1.0830 1.0806

1.0837 1.0813

1.0833 1.0811

1.0827 1.0798

1.0832 1.0808

All filaments before use were degassed at H A for 1 hour

in a vacuum and under a potential field. Silver was not

detected in the filament material at a 10~ 15 A ion current

sensitivity. Significant amounts of zirconium from either

the sample or the filament material will contribute to a

zirconium oxide ( 91 Zr 16 0) background at the 107 mass position.

Zirconium oxide peaks are also observed at the 106, 108, 110

and 111 mass positions. Degassing will reduce the zirconium

content of the filament below critical levels and solutions

of high chemical purity eliminated background contributions

from the sample.

g. Separation of potassium and rubidium - Potassium

and rubidium were separated from each sample solution as

follows: The sample solution which was reserved from the

first electrolytic separation, was evaporated to dryness on

a hot plate. The residue was taken up with 5 cm 3 of water

and a mixture containing 2 cm 3 of nitric acid and 1 cm 3 of

hydrochloric acid was added. (The nitric-hydrochloric mixture

was added to oxidize the ammonium ion formed during the

electrolysis.) The solution was again evaporated to dryness

and taken up with 5 cm 3 of water. The potassium and rubidium

in the solution were precipitated by adding 1 cm 3 of a solution containing 1 mg of NH ion to act as a sweep and using

the free acid of tetraphenyl boron (TPB) as precipitant. The

acid form of TPB was generated by passing 5 cm 3 of a 1 percent

sodium tetraphenyl boron solution through a strongly acidic

cation exchange column (Dowex 50x8), followed by 5 cm 3 of

water and allowing the effluent containing the free TPB acid

48
to drip directly into the sample solution. (The column was

constructed from the barrel of a 5 cm 3 polyethylene hypodermic

syringe and contained about 2 cm 3 of resin.) The beaker and

contents were cooled to about 5 °C and allowed to stand at

this temperature for about 2 hours. The solution was then

filtered thru acid washed filter paper of close porosity and

the mixed potassium, rubidium and ammonium tetraphenyl borates

were washed with cold water. The mixed tetraphenyl borates

were then dissolved from the paper by washing with small

amounts of acetone (about 10 cm 3 total) . This solution was

diluted to about 20 cm 3 with water and passed thru a small

cation exchange column containing about 2 cm 3 of a strongly

acidic cation exchange column (Dowex 50x8) to remove the

tetraphenyl boron ion which passed thru the column as the free

acid. The column was washed with water until the effluent was

neutral. The K , Rb and NHi* ions were removed from the

column by elution with 30 cm 3 of 4N hydrochloric acid. The

resulting solution was evaporated almost to dryness and the

ammonium ion present was oxidized to nitrogen by adding 0.5

cm 3 of nitric acid and evaporating to dryness. To insure the

removal of nitrate, the residue was twice taken up with 0.5

cm 3 of (1+1) hydrochloric acid and evaporated to dryness. The

final residue was taken up in 10 cm 3 of (2+98) hydrochloric

acid and this solution was reserved for the measurements of

the altered 39 K/ 1+1 K and 85 Rb/ 87 Rb ratios.

h . Determination of potassium and rubidium - The

500, 50, 1 and 0.02 ppm TEG samples were analyzed for rubidium

using the mass spectrometry procedure previously described

[ref. 4, p. 32]. Since the chemical separation of rubidium

also yielded potassium, and potassium may be run mass spectrometrically under the same operating conditions as rubidium, a procedure was developed for measuring both elements from the

same sample loading. In the method adopted the rubidium was

run first, following the previously developed procedure.

Immediately after collecting the rubidium data the mass range

49
was adjusted to potassium and ten peak sets were taken over

the next 10 1/2 minutes. No adjustments were made to the

ionization or sample filaments between the rubidium and

potassium portions of the run.

A sample containing natural rubidium and potassium, both

at the 10 ug/cm 3 level, was used to test the method. The potassium was found to yield approximately the same signal level

as rubidium and followed the same pattern of signal growth and

decay as rubidium. The signals for both elements were stable

with no detectable changes in the isotopic ratio over the 10.5

minute period of data taking. Precision of better than 0.1

percent for the isotopic ratios between samples was found for

both elements in the test mixture.

Blanks for both the chemical and mass spectrometric portions of the analyses were determined for both rubidium and

potassium. Neither source of blanks was significant for

rubidium even for the 0.02 ppm TEG sample. Blanks for potassium, however, were significant and persistent for both the

chemistry and mass spectrometry portions of the analyses for

all the concentration levels of TEG samples. Improvements in

blank levels for both areas were obtained as the analyses

progressed from the 500 ppm TEG to the 0.02 ppm TEG samples.

Mass spectrometric blank contributions were smaller than the

chemical blank, partly because improved mass spectrometric

procedures could be applied to previously run samples to obtain

improved results.

Mass spectrometric blank levels for potassium were

lowered thru work done with the separated 41 K isotope via the

following steps

:

a) The ionization and sample filaments, which are

normally vacuum degassed at 4 A for 1 hour, were stored in a

covered plastic box in a Class 100 clean hood at all times.

Filaments were used within ^2 days of degassing.

b) The samples were loaded, dried and mounted on the

filament block in the Class 100 clean hood. Sample pipets

50
were also stored in the clean hood. In general the exposure

of the sample and filaments to room air was held to the

minimum possible time.

c) The 39 K signal was measured after the ionization

filament was adjusted to 1450 °C (before the sample filaments

were heated) to assure that an acceptably low level of potassium background was present from this source. At the end of

the run the sample filaments were turned off and 39 K and kl K

peaks were measured. Corrections for potassium from the

ionization filament (if necessary) were based on these ratios.

Evaluation of mass spectrometric blank levels using the

preceeding precautions was obtained by measuring the 39 K/ ttl K

ratio (reported to be ^0.0084) of the separated ki K isotope

used as a spike. Sample loading of 1/20 cm 3 at 10 yg K/cm 3 concentrations yielded 39 K/ 1+1 K ratios high by as much as 0.001

to 0.002. This corresponds to a total blank of 0.5 to 1 ng of

39 K on the two sample filaments. Considering the ubiquitous

nature of potassium in the air and dirt, increasing the size

of sample loading (when possible) is the most practical means

of further lowering the effective mass spectrometric blank.

At present 1 mg K/cm 3 concentration are being used to load

samples for potassium isotope dilution analysis. At this

level, <0.5 percent blank error would be found in the 39 K/ lfl K

ratio for the 41 K used as a spike. For the spiked sample the

mass spectrometric blanks would be undetectable with 1 mg K/cm 3 sample concentrations.

The results of the determination of potassium in the four

glass standards are shown in Table 13. These results show

that further work is needed on the method, especially with

blanks. Although blanks which were as high as 7 yg have been

reduced to less than 1 yg they are not consistant. For example,

the lowest blanks were for the 1 and 0.02 ppm standards, but

they ranged from 0.42 to 0.92 yg.

51
Table 13. Determination of potassium in TEG standards.

500 ppm TEG 50 ppm TEG

Position ppm K Position ppm K

2 457.6 2 68.14

13 461.3 37 61.48

18 461.0 44 64.22

48 460.5 68 61.85

56 466.8 75 59.81

66 461.9 114 64.90

Average 63.40 78 463.2

106 458.1

Average 461.3

s.d. ±2.9

95% C.L. ±6.9

1 ppm TEG

Position ppm K

2 29.1

36 29.2

40 32.6

69 30.4

76 28.3

114 28.9

Average 29.8

s.d. ±1.5

95% C.L. ±3.9

s.d. ±2.98

95% C.L. ±7.65

0. 02 ppm TEG

Position ppm K

2 29.3

33 27.1

43 34.0a

51 27.3

61 29.7

76 28.0

130 27.7

Average 28.2

s.d. ±1.1

95% C.L. ±2.8

a Omitted from average.

The results for the determination of rubidium in the four

glass standards are shown in Table 14 . Since rubidium is net

a common element either in reagents or the atmosphere, the

blanks were consistantly low (about 1 ng) and were not a limiting factor.

52
Table 14. Determination of rubidium in TEG standards.

500 ppm TEG

Position ppm Rb

2 425.27

13 425.56

18 425.55

48 425.46

56 425.71

66 425.06

78 426.12

106 425.92

Average 425.71

s.d. ±0.30

95% C.L. ±0.69

] ppm TEG

Position ppm Rb

2 0.853

36 0.854

40 0.854

69 0.858

76 0.853

114 0.856

Average 0.855

s.d..±0.002

95% C.L..±0.005

50 ppm TEG

Position ppm Rb

2 31.58

37 31.24

44 31.37

68 31.50

75 31.44

114 31.50

Average 31.44

s.d. ±0.14

95% C.L. ±0.37

0.02 ppm TEG

Position ppm Rb

2 0.102

33 0.100

43 0.107

51 0.100

61 0.103

76 0.102

130 0.100

Average 0.102

s.d..±0.003

95% C.L. ±0.006

2 . Determination of Uranium in TEG

a. Introduction - The uranium content has been

determined in the 500 [ref. 4, p. 24], 50, 1 and 0.02 ppm

glasses by isotope dilution mass spectrometry using a "U-235"

separated isotope for the spike. On the first determinations

it was decided to do boron and uranium on the same samples

after fusion with sodium carbonate. The boron was extracted

[ref. 4, p. 22] and the uranium separated by ion exchange.

53
The blanks for this set were much higher than expected

(^400 ng) . While this blank can be tolerated on the 500 ppm

glass, the other glass samples, particularly the 1 and 0.02

ppm, require a smaller blank. The boron extraction was omitted

from the second set and the blank was reduced to 25 ng . Two

dissolution procedures were used on the first set of 50 ppm

glass samples. One was the sodium carbonate fusion used on

the 500 ppm glass and the second was a hydrofluoric-perchloric

acid dissolution. The uranium was separated by the ion exchange technique used on the 500 ppm glass. The blanks were

2 ng on the fusion and 1 ng on the acid dissolution. The

uranium in the second set on the 50 ppm glass and the 1 and

0.02 ppm glasses were determined using the acid dissolution

and a modified ion-exchange separation. The blank using this

procedure was 0.5 ng . Both procedures are given below.

b. Carbonate fusion - The glass samples were crushed

and 0.6 to 1.0 g was fused with sodium carbonate. After the

melt was broken up in water, weighed aliquots of "U-235"

separated isotope solution were added. Nitric and hydrofluoric

acids were added, the solution evaporated to near dryness, and

after diluting with water, the solution was filtered into a beaker containing boric acid. The solution was passed through

an ion exchange column containing a strongly acidic cation

resin, 6 mm by 7 cm. After washing the column with nitric

acid (1+150), the uranium and other cations held by the resin

were eluted with nitric acid (1+3). The solution was evaporated to dryness, taken up in nitric acid (1+1), and the

uranium separated by elution through a strongly basic anion

exchange column, 5 mm by 7 cm. The uranium was removed with

nitric acid (1+49), the solution was evaporated to dryness and

the elution through the strongly basic anion exchange column

was repeated. The sample was evaporated to dryness and after

dissolving in nitric acid (1+19) the isotopic ratios were

determined by mass spectrometry.

54
c. Acid dissolution - The glass samples were cleaned

in alcohol and dilute nitric acid, weighed and transferred to

teflon beakers. Ten cm 3 of hydrofluoric acid (1+1) were added.

Weighed aliquots of "U-235" separated isotope solution, using

a plastic syringe, were added to the beakers. After adding

7 g of perchloric acid and covering, the beakers were heated

on low heat until the glass wafers were decomposed. The

solution was evaporated to near dryness, the sides were rinsed

down with nitric acid (1+1) and the evaporation was repeated.

The salts were dissolved in about 1 cm 3 of nitric acid (1+1)

and passed through a strongly basic anion exchange column

6 mm by 7 cm. The column was washed with a small volume of

nitric acid (1+1) and then the uranium was eluted with nitric

acid (1+49). The solution containing the uranium was evaporated to dryness, taken up in a few drops of nitric acid (1+1)

and again eluted through the anion exchange column as above.

The uranium eluate was collected in a teflon beaker, evaporated

to dryness and after dissolving in nitric acid (1+19) the

isotopic ratios were determined by mass spectrometry.

d

Determination of uranium in 500 , 50 and 1 ppm

TEG - The extensive background in uranium analysis acquired

over the past decade paid significant dividends during the

determination of uranium concentrations in the TEGs . No major

or significant innovations in the existing analytical procedures

were necessary to complete work on the 500, 50 or 1 ppm TEGs.

Before analyzing a set of samples at a given level it was necessary to: (1) determine an optimum size (2) choose an optimum

signal intensity for the ratio measurement and (3) select a calibration standard to evaluate the filament bias.

Once the sample size is fixed, the task of the analyst is

to select a signal intensity that will yield maximum analytical

precision for the ion currents to be measured and still avoid

gross fractionation of the isotopes. From past experience

it was known that total uranium sample sizes of 100, 20 and 4

micrograms per analysis will readily yield ion currents of

55
5xlO _1 ° A, lxlO -1

° A and 2xl0 _11

A, respectively. Although

all of these ion current intensities could be maintained for

a much greater time than was necessary to complete an analysis,

none was used as an optimum for the TEG solutions. The factor

that weighted heavily against them was a smaller rate of

fractionation at lower filament temperatures, and consequently

lower intensities, that would satisfy the precision requirements of the peak height determination. The general rule is

to select the smaller rate of fractionation once the precision

requirement of expanded scale peak height determintion has

been fullfilled. The other major factor that influenced the

choice of optimum signal intensities was a vast amount of

experience at the 10 _11

A range. The final decision was to

use optimum sample sizes of 40, 20 and 4 micrograms for the

500, 50 and 1 ppm TEGs with corresponding signal intensities

of 5-6xlO -11

A, 1.5-2.0xl0 _1

x

A and lxio" 11 A.

For each set of TEG samples one or more of the uranium

SRMs was used as a calibration standard of known 235 u/ 238 u value to evaluate the filament bias. For maximum precision and

accuracy the calibration standard was always analyzed at the

same sample size and approximate ratio as the spiked samples.

The U ion currents were measured on a single stage solid

sample mass spectrometer with a 12-inch radius of curvature,

68° analyzer tube and a "Z" lens ion source. A triple filament rhenium ribbon source was used and the ion accelerating

voltage was 10 KV. The source and collector slit widths were

0.010 and 0.028 inches, respectively.

Uranium was supplied for analysis as uranyl nitrate,

evaporated to dryness, in a small teflon beaker. Approximately

10 minutes prior to mounting uranium on the filament, a (1+19)

nitric acid solution was added to the beaker. The volume was

adjusted so that one drop of solution would contain 1/2 of the

optimum sample size for the analysis. One drop of solution was

placed on each sample filament and dried with a heat lamp and

an electrical current. The current was adjusted as follows:

56
1 A for 5 minutes; 1.3 A for 3 minutes; slowly increased until

the yellow-orange oxide was formed. Color changes were difficult to detect for less than 20 yg of uranium per filament.

As the quantity of uranium per filament approched 1 yg a drying current of 1.9-2.0 A was used as an upper limit in

lieu of a visual color change.

The standard procedure after introducing a sample into

the mass spectrometer was a 15 minute degassing followed by a minimum time of 1/2 hour for cooling and source pumping. When

the source pressure was 2-4xio~ 6 torr, liquid nitrogen was

added to the source coldfinger and degassing was begun after

cryogenic pumping reduced the pressure below 4^10 7 torr. The

degassing procedure is as follows: adjust the ion accelerating

voltage to 8 KV; adjust the ionizing filament temperature to

2160 °C and the sample filament current to 1.5 A; increase

the sample filament currents to 1.9 A; turn off all filaments

after 15 minutes of heating.

The heating pattern or method of adjusting the filaments

to obtain a standard ion current intensity is basically the

same for all uranium sample sizes above 1 yg. If the amount

of uranium is significantly less than 1 yg, then it may be

necessary to take data on a condensed time schedule as soon as

a measurable signal is obtained. Once the signal Intensity

for a given sample size was established, the sample filament

currents were adjusted to yield some fraction of the total

intensity on a definite time schedule. Each sample filament

was always adjusted to yield 1/2 of the prescribed intensity.

The general procedure used for the TEG samples is as follows:

adjust the ionizing filament temperature to 2160 °C and the

sample filament currents to 1.5 A; after 6, 12 and 18 minutes

of heating adjust the sample filament currents to yield 1/3,

2/3 and then full intensity respectively; focus for maximum

signal intensity after approximately 7 and 19 minutes of heating. If necessary, after 24 minutes of heating reset the

sample filaments to yield full intensity. Data were taken

57
between 30 and 41 minutes after the start of heating on an ion

current that was normally growing. A mass scan was made to

determine baselines both before and after the ratio measurement. Each peak top was monitored for 30 seconds and scanning

was accomplished by a step-wise change in magnet current to

focus ion currents on the faraday cage.

e . Determination of uranium in 0.02 ppm TEG - Determination of the uranium concentration in the 0.02 ppm TEG

standard by isotope dilution required the measurement of a 235 U/ 238 U ratio of ^160 . To keep from exceeding the linear

response region of the vibrating reed electrometer for measurement of the 238 U, the 235 U signal was limited to <3xio~ 13 A,

which in turn limited the ultimate accuracy for this concentration series to 2 to 3 percent (To). Also, the determination

of the uranium composition of the base glass required a measurement of the 235 u/ 238

u ratio on ^0.05 ug of uranium. The

minimum acceptable sample size for the triple filament uranium

technique is 1-2 ug.

For these reasons, the 0.02 series was run on a double

stage mass spectrometer employing two 90 degree 12 inch radius

magnetic sectors, with a pulse counting detection system.

This instrument has been described in detail [1].

A filament loading technique was adopted from Dietz [9]

and subsequently used for the 0.02 ppm samples. The dry samples were dissolved in several drops of nitric acid (1+19) and

an estimated 0.1 ug deposited on a 50 mil rhenium V filament

which had been previously degassed at ^2000 °C. The sample

was then dried under an infra-red heat lamp for 20 minutes.

An initial filament temperature of 1400 °C was used and

was increased in 50° steps at 5 minute intervals to 1550 °C.

At <1550 °C the uranium signal decayed regularly. Successive

temperature increases of 25°/step usually produced a moderately

growing 235 U signal of 50-60,000 counts per second. Around

1600 °C the signal intensity varied strongly with a small (25°)

temperature change. For this reason, an optimum temperature

58
range of 1575-1625 °C was used with the several samples so

that count rates of approximately 60,000 counts per second

for each of the samples could be maintained.

To provide a fractionation correction factor for the

0.02 ppm series, SRM U-970 whose 235 u/ 238 U ratio approximated

that of the samples was run. A correction factor of 0.99^0

was applied to all experimental ratios.

The uranium oxide contribution to the ion beam normally

decayed rapidly during the first few minutes of an analysis,

to a final U /UO ratio of >1000. Occasionally an incompletely

degassed filament resulted in copious quantities of uranium

oxide. These runs were discarded. Since the ionization efficiency and thus sensitivity appears to be considerably greater

for the oxide, the oxide beam was temporarily considered for

analysis. However, the signal intensity per quantum of sample

was not reproducible.

The results on the four glasses are given in Table 15.

The results indicate that the samples are homogeneous within

experimental error except position 114 of the 50 ppm glass.

The second set on the 50 ppm glass (Table 16) was run to

verify the value found on position 114 and to determine the

extent of the indicated inhomogeneity . The data show that the

uranium content at position 114 is greater but, that the

inhomogeneity does not extend into the region to be used for

the SRM (positions 30 through 90).

Both procedures appear to give satisfactory results. The

acid procedure requires somewhat less time and seems to give

slightly lower blanks. The acid procedure also eliminates the

possibility of contamination in the crushing of the sample.

59
Table 15. Determination of uranium in TEG standards.

500 ppm

Position ppm U

2 461.6

13 461.8

18 461.3

48 461.2

56 462.2

66 461.2

106 461.6

Average 461.6

s.d. + 0.4

95% C.L. ± 0.9

1 ppm TEG

Position ppm U

2 0.8242

36 0.8234

40 0.8219

69 0.8226

114 0.8230

Average 0.8230

s.d. ±0.0009

95% C.L. ±0.0024

Omitted from average.

5() ppm

Position ppm U

2 37.35

37 37.37

44 37.36

68 37.36

75 37.41

90 37.41

99 37.42

114 37.66 a

Average 37.38

s.d. ±0.03

95% C.L. ±0.07

0.02 ppm TEG

Position ppm U

2 0.07149

33 07077

40 07155

51 07225

61 07208

76 07163

130 07208

Average 0.07169

s.d..±0.00050

95% C.L..±0.00123

60
Table 16. Determination of uranium in 50 ppm TEG standard.

Position Method Setl Set 2

ppm U ppm U

2 Na2 C03

37.35

37 Na2 C03

37.37

44 Na2 C03

37.36

68 Na2 C03

37.37

68 HF-HCI04

37.34

75 Na 2 C03

37.38

75 HF-HCI04 37.40

75 HF-HCI04

37.44

90 HF-HCI04

37.41

99 HF-HCI04

37.40

99 HF-HCI04

37.43

114 Na2 C03

37.63 a

114 HF-HCI04

37.67 a

114 HF-HCI04

37.68

a

Average 37.37 37.42

a Omitted from average, the precision of method indicates sample

heterogeneity at sample point 114.

C . Iron and Steel Standard Reference Materials

A number of iron and steel SRMs were analyzed for copper

by isotope dilution mass spectrometry and a few were analyzed

for nickel. These determinations were usually undertaken as

a "referee" method to settle disputes between NBS and cooperating laboratories or between laboratories at NBS.

1 . Determination of Copper

The procedure for the determination of copper in iron

and steel SRMs is outlined in last years Summary of Activities

[ref. 4, p. 26]. For material of high copper content (greater

61
than 0.5$), samples no smaller than 100 mg were taken, and the

solution resulting from the dissolution of the sample was

aliquoted by weight to obtain a homogeneous sample small

enough to "spike".

The results of these analysis are shown in Table 17.

Table 17. Determination of copper in various SRM steels.

SRM

125b

1134

1140

1141

1142

Cu Average and SRM Cu Average and

wt% estimate of

95% C.L.

wt% estimate of 95% C.L.

0.07112 1148 0.9891

0.07153 0.9885

0.07136

0.07134

± 0.00071

0.9896

0.9891

± 0.0099

0.07100 1149 0.4880

0.07131 0.4865

0.07077

0.07103

± 0.00071

0.4902

0.4882

± 0.0049

0.09550 361 0.04203

0.09586 0.04210

0.09641

0.09592

± 0.00096

0.04207

±0.00042

0.2051 1261 0.04218

0.2029

0.2040

± 0.0020

0.04165

0.04192

± 0.00042

1.0170 lOlff 0.02852

1.0162 0.02875

1.0132

1.0155

± 0.0102

0.02916

0.02883

0.02882

± 0.00029

62
2 . Determination of Nickel

Nickel was determined in a number of steel SRMs by isotope

dilution mass spectrometry because significantly different concentrations had been found using other methods. The nickel was

extracted as the dimethylglyoxime complex from an ammoniacal

solution with chloroform and back extracted from the chloroform

with a nitric acid solution. However in these solutions the

concentration of ammonium salts was too large and the solution

could not be analyzed by mass spectrometry. The solution was

diluted and passed through a cation exchange column. The

nickel was eluted with 5N nitric acid, and electrodeposited

from an ammoniacal solution.

For SRM lOlf, which contains about 10 percent nickel, a

2 g sample was dissolved in dilute hydrochloric acid and the

solution was filtered. The insoluble residue was ignited at

500 °C and was fused with potassium pyrosulfate. The melt was

dissolved in dilute hydrochloric acid and was added to the

filtrate. For SRMs 1261 and 36l, which contain about 2 percent

nickel, a 0.5 g sample was dissolved by repeated evaporation

with perchloric acid and hydrofluoric acid.

To an aliquot of the steel solution, containing approximately 2 mg nickel, a weighed portion of a standardized 6 2 Ni

solution was added to produce a

58 Ni/62 Ni ratio of from 1.5

to 2 in the sample. The iron was oxidized with potassium

persulfate and complexed with sodium citrate before the

dimethylglyoxime solution was added. The solution was neutralized with ammonium hydroxide and 2 cm 3 excess added. The

nickel was extracted as the dimethylglyoxime complex with

chloroform and back extracted into a nitric acid solution.

The solution was evaporated to dryness and the residue

dissolved in 0.1 to . 2N nitric acid. The solution was passed

through a cation column (AG50x8, 100-200 mesh). The nickel

was eluted with 5N nitric acid. Two cm 3 of sulfuric acid were

added to the eluate and the acids neutralized with ammonium

hydroxide and 2 cm 3 excess added. The nickel was separated

63
by electrodeposition and taken into (2+98) nitric acid solution

so that the final concentration of the nickel was 2.5 mg/cm 3

. A provisional analytical procedure has been developed and

used for a limited amount of isotope dilution work. Previous

efforts to analyze nickel samples were frustrated by a background mass approximately 0.05 mass units above the 5 8 Ni peak.

No interfering mass has been detected at any of the nickel

mass positions with the present technique. The technique was

patterned after the silica gel method for lead analysis (see

section 4). The preparation of a nickel sample for analysis

is nearly identical to the procedure used for lead, but

there are major differences in the mass spectrometric heating

patterns. A high purity nickel metal of natural isotopic

composition was used as a working standard to evaluate the

procedure

.

The nickel ion currents were measured on a single stage

solid sample mass spectrometer with a 6-inch radius of

curvature-60° analyzer tube and a

M Z" lens ion source [2].

The ion source was operated at 7-5 KV and a single filament

rhenium ribbon, 0.0012 x 0.030 inch, was used. All filaments

were degassed, prior to use in the mass spectrometer, in a vacuum and under a potential field to reduce the potassium

and chromium background. Large ion currents of chromium and,

especially, potassium were the source of major baseline

interference in the nickel mass range.

The same reagents used for the lead method, silica gel

and phosphoric acid, were used to mount the nickel sample on

the filament. One small drop of silica gel solution was placed

on the filament and dried for 5 minutes with a heat lamp and a

1 A current. One small drop, approximately 25 yg of nickel,

from a nickel nitrate solution with a concentration of 2.5 mg

Ni/cm 3 was dried for 5 minutes by the heat lamp and a 1 A

current. A small drop of 0.75N phosphoric acid was added to

the filament and, with the heat lamp on, dried for 5 minutes

at 1.7 A and then for 10 minutes at 2.3 A. The final product

64
was dark brown in color and was smooth and glassy in appearance.

The sample was mounted into the spectrometer promptly because

it was hygroscopic and absorbed water rapidly.

When the source pressure was approximately 1x10 6 torr,

liquid nitrogen was added to the source coldfinger and the

analysis was begun. Source pressure during an analysis was

less than 3xl0~ 7 torr. Each analysis was made on a strict

time schedule because the 58 Ni/ 62 Ni ratio changed between 0.5

and 1 percent over the time span required to complete the ratio

measurement. Failure to adhere to the time schedule, regardless

of the reason, was sufficient cause to terminate the analysis.

An optical pyrometer was used to determine filament temperatures. Within the first minute of heating the temperature

of the filament was adjusted to 1050 °C. This temperature was

too low to yield significant 58 Ni ion currents and was intended

to remove any potassium in the filament material, the reagents,

or nickel sample. Initially, the potassium ion current was

large enough to completely degrade the baseline at the 58 Ni

position. For most samples five minutes of heating at 1050 °C

reduced the potassium below the level which caused significant

interference. Chromium signals were normally too small to

cause significant interference.

After 5 minutes of heating the filament temperature was

adjusted to 1130 °C. At this temperature the potassium was

quickly reduced below the critical level that caused detectable

interference and the 58 Ni ion current was approximately

lxio 12 A and decaying. The filament temperature did not

stabilize in the neighborhood of 1130 °C but increased during

the remainder of the analysis without any further adjustments.

This unexpected response usually followed one of two general

patterns. In one type the temperature increased very slowly

during the next 15-20 minutes to 1150-1160 °C. The temperature

remained nearly constant for approximately 10 minutes and then

slowly increased to 1180-1190 °C at the end of the analysis.

The 58 Ni signal response after the adjustment to 1130 °C was

65
usually a decay to the middle 10~ 13 A range before entering a

growth phase that was approximately 50 minutes in duration.

Occassionally , the signal remained nearly constant or decayed

slightly at an intensity of 2-3 x 10 12 A before continuing its

growth trend. The temperature response described above was

the most desirable because of a relatively slower rate of

change of the 58 Ni/62 Ni ratio with time and because it was

possible to take all data on a growing ion current.

The second type of general temperature response after

the filament was adjusted to 1130 °C was a more rapid increase

during the remainder of the analysis . The temperature was

approximately 1180 °C after 30 minutes of heating and was

significantly more than 1200 °C at the end of the analysis.

The corresponding signal response was as follows: a rapid

growth to a 3-5*10 12 A intensity; a brief period of decay;

and then a short growth cycle which was followed by a continuously decaying signal. The entire cycle from rapid growth to

continuous decay was completed within 1/2 hour after the

initial adjustment to 1130 °C. In this case all analyses

were terminated and no data was obtained.

For each analysis 10 peak sets were taken between 30 and

4l minutes after the start of heating. Each peak top was

monitored for 1/2 minute and magnet changes were made in

discrete steps.

At the present stage of development of the nickel mass

spectrometric procedure fractionation of the isotopes is the

foremost problem. It was possible to routinely produce changes

of several percent in the 58 Ni/62 Ni ratio within an analysis

by simply using temperatures 20 °C higher than normal. Failure

to precisely reproduce the same filament temperatures for

different sample loadings was the cause of equally large differences between analyses. The full effect of the constantly

changing filament temperature during an analysis has not been

determined but it will be essential to hold this change to a

66
narrow limit if no means is found to stabilize the filament

at some constant temperature.

The critical areas in the sample mounting procedure are

the amount of silica gel on the filament and the magnitude

of the drying current. Superior analytical performance was

obtained when the silica gel solution dried as a thin film or

as a faint spot of crystals on the filament. Filaments with

large and bulky silica gel deposits yielded adequate signal

intensities but the stability was poor and too erratic for a precise ratio measurement. When such filaments did yield

stable signals, the rate of change of 58 Ni/ 62 Ni with respect

to time was much less than normally observed.

Electrical currents of 2.3 A during the final step of the

sample mounting procedure usually gave the best analytical

performance. Samples dried at either a few tenths of an ampere

above or below 2.3 A gave unsatisfactory analytical performance. The signal intensities were abnormal and the long term

stability was not adequate for a precise ratio measurement.

When nickel samples were heated in the spectrometer, the

brown glossy substance on the filament was collected on the

drawing-out plate and the lower side of the source shield.

This substance was sticky and moist and, at the present time,

no effort has been made to determine its composition. No

detrimental effect other than a minor increase in the background source pressure was detected. This substance was

soluble in acetone and water. Acetone was used to spot clean

the drawing-out plate after each analysis with the source

mounted in the spectrometer. At the end of the day the shield

and drawing-out plates were thoroughly flushed with acetone.

The results of the isotope dilution analyses are shown

in Table 18. Each value for the lOlf samples represents the

average of 4 mass spectrometric analyses. The remaining

values represent the average of duplicate analyses. The 95$

analytical limit of error for a single measurement of the

58 Ni/62 Ni was 0.48 percent.

67
Table 18. Determination of nickel in various SRM steels.

Sample no. Found, % Average , %

101f-2-l 9.945

101f-2-2 9.983

101f-5—

1

9.950

101f-5-2 9.999

101f-8-l 9.999

101f-8-2 9.972

lOlf-9-1 9.964

101f-9-2 9.978

lOle 9.485

361-1 2.012

361-2 2.010

1261-1 1.999

1261-2 2.000

9.972

9.485 a

2.011

2.000

Certified as 9.48.

D. Boron in SRM 59a, Ferrosilicon

Boron was determined in SRM 59a, Ferrosilicon, by isotope

dilution mass spectrometry. The ferrosilicon was fused with

sodium carbonate and digested in water. A weighed portion of

a standardized solution of 10 B was added so that the 11 B/ 10 B

ratio was approximately 1. The solution was acidified with

nitric acid and the boron extracted into a chloroform - 2-ethyl-l ,3-hexanediol mixture. The organic layer was washed

with water and the boron back extracted into a sodium hydroxide

solution. This layer was acidified with nitric acid and the

boron again extracted with chloroform - 2-ethyl-l ,3-hexanediol

mixture, except 2 cm 3 of the chloroform - 2-ethyl-l, 3-

hexanediol mixture were used instead of 20 cm 3 as used in the

first extraction. The sodium hydroxide solution, used to back

68
extract the boron, was evaporated to dryness and the residue

dissolved in 2 cm 3 of water. The solution was passed through

a mixed resin bed and sodium carbonate was added to the eluate

so that the B/Na ratio was 2 [4],

A detailed discussion of the mass spectrometric procedure

and an evaluation of the critical parameters for boron analysis

are given in NBS Special Publication 260-17 [10]. A single

filament tantalum-ribbon (1x30 mils) source is used. The

analytical technique is the one that was devised for use with

an optical pyrometer. Briefly, the temperature of the tantalum

filament is adjusted in a series of steps to 750-760 °C over a 1/2 hour interval. Data are taken after 40 minutes of heating

on a slowly decaying total signal intensity of 3-2xl0~ 12 A.

The 11 B/ 10 B ratios were determined by measuring the

molecular ions Na2 11 B02 and Na2 10 BO2 at masses 89 and 88

respectively. The contribution of Na2 10 B

16 O17 O at the mass

89 position had been experimentally evaluated by measuring

the ratio Na 2

* 1 B1

1

0/Na 2

1 1 B

1 G 2 of a

ll B separated isotope

solution. A value of 0.00079 was obtained for this ratio and

was used to calculate the contribution from Na 2

1 °B 1

1

0.

The results (duplicate analyses of each sample) are

shown in Table 19

Table 19. Determination of boron in SRM 59a,

Ferrosilicon.

Sample no. Found, %

59a-l 0.0591

59a-l 0.0590

59a-2 0.0595

59a-2 0.0597

Average 0.0593

69
E. Uranium and Lead in Cation Exchange Bead Microstandards

Uranium has been determined on two sets of proposed

microstandards and lead on one set by isotope dilution.

The first set of samples loaded with uranium and mercury

in U/Hg ratios of approximately 1:10, 1:100, and 1:1000; were

dried, weighed and transferred to teflon beakers. After adding

a weighed aliquot of "U-235" (see section 3-A for details of

the spiking procedure), about 2 cm 3 of nitric acid were added,

and the solution was evaporated to 5 cm 3

. The sample was filtered, evaporated to dryness and dissolved in 2N hydrochloric

acid. The mercury was held on a strongly basic anion exchange

column while the uranium was eluted. The uranium fraction was

evaporated to dryness, dissolved in nitric acid (1+19), and

the 235 u/ 233 U ratio determined by mass spectrometry. The

uranium content was calculated from these measured ratios,

the isotopic composition of the uranium in the spike and sample,

the amount of spike added, and the weight of sample.

The second set of samples; loaded with uranium and lead

in U/Pb ratios of approximately 1/10, 1/100, 1/1000; were

spiked with both "U-235" and "Pb-206". After adding nitric

acid and evaporating to about 5 cm 3 as in the first set, the

solution was diluted to 20 cm 3 with water and the lead was

electrolytically deposited as Pb0 2 . After weighing, the lead

was dissolved in dilute nitric acid and hydrogen peroxide,

and the solution was evaporated to dryness. The samples were

dissolved in nitric acid (1+49) and the 206 Pb/ 208 Pb ratios

determined by mass spectrometry. The uranium was determined

in the sample solution after the electrolysis. The solution

was evaporated to dryness, taken up in nitric acid (1+1) and

eluted onto a strongly basic anion exchange resin. The uranium was removed with nitric acid (1+49). The solution was

evaporated to dryness, dissolved in nitric acid (1+19) and

the 235 U/ 238 U ratio determined by mass spectrometry. The

lead and uranium content of the beads were calculated as done

in the first set.

70
4. HIGH SENSITIVITY ANALYSIS

A. Silica Gel Method

1 . Introduction

The precise mass spectrometric determination of the

isotopic abundance ratios of samples of lead has proven to be

a relatively simple process providing sufficient sample is

available. Using samples, large enough to give a solution

concentraion of 20 mg/cm 3 solution, it has been possible to

analyze lead isotopically using the triple filament technique

with a precision and accuracy of 0.02 percent [11]. Using

reasonable care the blanks obtained with these large samples

are usually of no consequence and, in general, corrections for

the blanks are not necessary.

A completely different problem is presented however when

very small samples or samples with a very small lead concentration are available. The triple filament lead procedure has

not proven successful with a total lead sample of less than

approximately 30-50 yg. A variety of procedures have been

used by various investigators to isolate and ionize small lead

samples but perhaps the easiest and most widely adopted method

is to precipitate the sample as PbS which is subsequently

deposited on a filament, mounted in the mass spectrometer and

analyzed. This method has, however, several disadvantages.

The ionization efficiency is quite low, sodium and potassium

which might be present (usually from scraping the sides of the

centrifuge tube in collecting the precipitate) greatly reduce

or "poison" the ionization and blanks tend to be a significantly large proportion of the total sample. Akishin et al

[12] have reported that a silica-zirconia gel acted as a

catalyst to produce abundant lead ions thus overcoming one of

the above objections to small sample lead analysis. Cameron

et al . , [13] in a thorough investigation of this procedure

noted that silica gel alone was as effective as the zirconia

mixture and published a procedure both for the preparation of

71
the catalyst and the subsequent analysis of nanogram size

samples of lead. In the procedure of Cameron et al . , however,

a tandem spectrometer was required and an upper limit of 0.5

ug lead was necessary to prevent an ion beam too large for the

ion counting detection system in use.

We were able to duplicate the results of Cameron et al

.

on a similar (though not identical) spectrometer [2] using a different ion detection system [1] with very pure lead samples,

SRMs 981, 982, 983. However, we noted a seemingly uncontrollable variation in ion beam size which seemed to be dependent

on the amount and crystal size of the silica gel used. We

also experienced some difficulty in preparing silica gel which

was sufficiently free of lead to give a negligable background.

The method did however seem to merit further investigation

and extensive experimentation was done to carefully define the

optimum conditions for precise and accurate lead analysis.

2 . Reagents

a. Silica gel - Thirty grams of meta-sodium silicate

(Na2Si0 2

* 9H 2 0) was dissolved in 200 cm 3 of nitric acid solution

(1+19). The nitric acid had been previously isothermally

distilled from "ultra-pure" nitric acid. The solution was

evaporated nearly to dryness at 160 °C ("low" setting on a hot

plate). This procedure was repeated but the evaporation was

carried to dryness. About 200 cm 3 of nitric acid solution

(1+99) was added to the residue and the solution allowed to

boil for 10 minutes. The hot solution was filtered through a medium textured filter paper. The residue was washed back

into a beaker, diluted with 200 cm 3 of redistilled water,

boiled for 10 minutes and allowed to cool and settle for

approximately 1/2 hour. The water was carefully decanted and

the washing repeated 3 or 4 more times . After the final washing and decanting the residue was diluted with 10 times its

volume with redistilled water and transferred to a teflon

bottle. The solution was shaken thoroughly 2 or 3 times a day for 3 days and then after a 3 hour settling time the liquid

72
layer was carefully decanted into a second teflon bottle.

This colloidal suspension is the "silica gel" referred to in

all subsequent operations.

b. Phosphoric acid - A phosphoric acid solution was

prepared by carefully dissolving "ultra pure grade" resublimed

phosphorous pentoxide in redistilled water in a teflon bottle

and diluting to make a solution 0.75N in phosphoric acid.

In the preparation of all solutions only teflon ware was

used and all steps were carried out within a small Class 100

laminar flow "clean" hood.

3

Mass Spectrometry

Filament preparation - A single center rhenium (0.001 x 0.030 inch) filament which had previously been degassed was

used in all cases. A small drop of the silica gel suspension

was placed on the filament and dried for 5 minutes with a heat

lamp with a current of 1 A through the filament. When dry,

only a faint spot was visible and no large particles of silica

could be seen.

A single drop of the lead solution containing 0.1 to 1.5

ug lead in nitric acid (1+19) was placed on the filament and

dried for 5 minutes with a heat lamp and with a current of 1 A

A drop of the 0.75N phosphoric acid was added and dried

for 5 minutes with a heat lamp with 1.7 A current and then 10

minutes with a heat lamp and a current of 2.4 A. At the end

of the 10 minute period the filament current was carefully

raised until the entire filament was heated to a dull red

color. This normally required a current of 2.5 to 2.7 A. The

filament was then mounted in the spectrometer for analysis.

4Mass Spectrometric Procedure

The samples were analyzed in a 12" radius mass spectrometer with an accelerating potential of 10 KV. The following

analytical procedure was used:

73
Time from start Procedure

(minutes

)

0-1 Temperature set at 1100 °C

5 Temperature set at 1150 °C

10 Temperature set at 1200 °C

20-25 Base line scanned

30 Data taking begins. Data taken in the

following pattern: 4- 208/206 ratios; 4-

207/206 ratios; 8- 204/206 ratios; 4- 207/206

ratios; and, 4- 208/206 ratios

NOTE: Decaying signals are always observed at 1200 °C. The

signal decays quite rapidly at first but the rate of

decay decreases at about 20 minutes to give slowly

dying signals. A common lead sample of ^1 yg will

normally give a

208 Pb ion current beam current of

^3 X 10" 10 A.

5

.

Results

A series of lead standard samples (SRM 98l) were analyzed

and the analyses showed a precision (2 sigma) of . 06 percent

for the lead 208 Pb/ 206 Pb ratio, 0.03 percent for the

207 Pb/ 206 Pb ratio and 0.1 percent for the 201t Pb/ 206 Pb ratio.

The method has been applied to a series of glass samples

containing from 1 to 500 ppm lead in glass and to a variety

of archaeological and pollution samples.

The total amount of lead loaded on a filament has been

as small as 0.2 yg and undoubtedly may be reduced even further

when the laboratory blank is reduced.

The method has also been used for the analysis of thalliun

in glass samples containing from 0.008 to 60 ppm.

The results of these analyses are reported elsewhere in

this publication.

6

.

Discussion

a. Phosphoric acid preparation - In early attempts

to prepare a suitable phosphoric acid solution, commercial

74
reagent grade phosphoric acid was carefully purified to remove

residual lead by following the purification system of Cameron

et al . [13]. This procedure did, indeed, remove lead but

almost always resulted in a large organic background in the

spectrometer which died away very slowly. In an attempt to

remove the organic material the phosphoric acid was passed

through a column of carefully prepared charcoal which removed

all the organic material but resulted in a lead blank higher

than before. The use of "ultra pure" resublimed phosphorus

pentoxide resulted in an undetectable lead blank.

b. Silica gel preparation - Silica gel prepared

even with the use of "ultra pure" nitric acid always showed a small, but not negligable, lead blank. When the nitric acid

was isothermally distilled the resultant silica gel gave a completely undectable lead signal.

c. Mass spectrometry - As noted by Cameron et al.,

[13] a small organic signal was always noted at temperatures

below 1100 °C. Above 1100° however this signal decayed very

rapidly and at 1285 °C was not detectable.

The use of zone refined rhenium ribbon as filament

material nearly always resulted in more stable signals.

75
5. ATOMIC WEIGHT RESEARCH

A paper describing the measurement of the absolute isotope

abundance ratio and atomic weight of rubidium was published

[7]. A preliminary investigation into a high precision - high accuracy method for the determination of potassium was

initiated. This method, patterned after that used for

rubidium, is based on the purification of potassium chloride

by crystallization as the perchlorate followed by thermal

conversion to the chloride. Solutions of this purified

potassium chloride are then assayed by conversion of weighed

portions to potassium perchlorate.

76
6 . SPARK SOURCE MASS SPECTROGRAPH

A . Instrumentation

1

Introduction

The spark source instrument was transferred this year

from the Spectrochemical Analysis Section into the Analytical

Mass Spectrometry Section. Description of the equipment and

the type of work that has been performed with the spark source

can be found in the yearly progress reports of the former

section [14 ,15 ,16 ,17 ,18] . In recent years techniques suitable

for isotope dilution analysis with the spark source mass

spectrograph (SSMS) have been developed in order to provide

ppm level analysis on a number of Standard Reference Materials.

In this work R. Alvarez, who is still in the Spectrochemical

Analysis Section, has provided the preconcentration, separation

and spiking competence for these joint efforts. Description

of his work on the SSMS isotope dilution analysis is included

in both Section's report in order to give a complete picture

of the work.

2Ion Beam Deflector

Beam chopping has been shown [19] to be an effective means

of improving precision for high level impurities by increasing

the volume of sample consumed on short exposures. Deflecting

electrodes, controlled by a pulse generator of variable width

and frequency, allow passage of a fraction of the ions being

generated in the r.f. high voltage spark. Such a system allows

a wide range of exposures to be made each using approximately

the same sample volume. In addition the r.f. spark frequency

and duration, which normally must be varied to cover the wide

dynamic range of exposure levels used, can be held constant

with a beam chopper, thus maintaining identical sparking

conditions for all exposures

As a start toward development of a beam chopping system,

ion beam deflecting electrodes have been built for our instrument. A photograph of the electrodes is shown in figure 5.

77
\

Figure 5. Beam Deflector Mounted in Source Conversion Ring.

They are mounted in a conversion ring added to the source when

it was switched from 15 KV to 24 KV operation. These electrodes are symmetrical about the instrument "optical axis"

and are located approximately one half inch behind the final

defining slit in the source. Deflection of the ion beam

occurs perpendicular to the z axis of the instrument (i.e.,

the electrodes are parallel to the final defining slit). A

test pair of deflecting electrodes was made 0.25 inch square

by 1 inch long with a 0.25 inch gap between electrodes. The

dotted line in figure 6 shows the ion beam current as a function of deflecting voltage. The ion beam current was dropped

by more than a factor of 10 5 by using either -600 V or +800 V

for deflection. Since these voltages are somewhat high to use

conveniently j the gap between electrodes was reduced to 0.125

inch by replacing the 0.25 inch square electrodes with 0.3125

inch square by 1 inch long electrodes . The solid line in

78
figure 6 shows the ion current vs deflector voltage for the

0.125 inch gap. A negative 400 V will obviously be adequate

to turn off the ion beam current.

cc

cr

z>u

o

-9 —

1l'O/fi IIH.KJ ftoArA D

1 H*»-«ks /

'X

•

-10

/ /

\

\

-11 '

J -

<t -12

i

-13

\

-14

i 1

-15

I 1 i

' , 1 -600 -200 200 VOLTS

400 600

Figure 6. Ion Beam Current vs Deflection Voltage.

The 20 ys ion pulses generated by our instrument would

require rise times of 10 ns or less for the beam chopper

deflecting voltage in order to effectively "chop" individual

pulses. Since this short rise time could be difficult to

obtain, the tentative plans are to synchronize the chopper

with the r.f. spark and to pass the entire pulse of ions

generated by an individual spark. The deflector plate voltage

could then be switched in the millisecond range time interval

between pulses with no difficulty.

79
3 . Internal Source Baking

Hydrocarbon interferences in an analysis can normally be

minimized thru baking of the source vacuum chamber and by presparking of the surface of the sample. A source chamber bake,

to be effective, must last several hours since the sample

electrodes and some source parts are insulated electrically,

and therefore thermally, from the vacuum chamber. Presparking

lowers hydrocarbons thru physical removal of the contaminants

on the sample surface and also thru heating of sample and

internal source parts. On occasion, hydrocarbon interferences

have caused some difficulty with our isotope dilution analysis

on the SSMS . Since isotope dilution samples are either plated

or evaporated onto the surfaces of a pair of high purity

(69 grade) gold electrodes, presparking cannot be used as it

would remove the sample itself. Long baking of the source

vacuum chamber is not practical when relatively fast sample

thruput is desired.

An electron bombardment system is being tested as a means

of baking the sample internally. A 0.030 by 0.001 inch tantalum ribbon was mounted in the space between the final defining

slit and the second aperture (both at ground potential).

Electrical feedthrus are located on a flange once used for

an ion gauge. A power supply for the bakeout unit provides:

1) 0-10 V ac power from a filament transformer

2) to -300 V filament bias

3) an emission current meter

4) 0-1 ma meter in the 24 KV ion accelerator power

supply (at ground potential).

With the ion accelerator on, electrons are drawn thru the

second aperture at ground potential to the first aperture

plate at 24 KV. Some of the electrons pass on thru the first

aperture to the sample electrodes also at 24 KV. A test of

this system gave a maximum heater current of 3.3 A ac. A

maximum of 15 ma emission current and . 4 ma ion accelerator

current was obtained when the bias voltage was -70 V. This

80
provides 33 watts IR heating and 5 watts electron bombardment

heating to the region of the final defining slit and second

aperture, and 10 watts of heating to the first aperture and

sample from the ion accelerator current.

A test sample using this system showed a significant

pressure rise during baking with a subsequent decrease in the

hydrocarbon content in SSMS spectra as compared to the unbaked

sample. A mass spectrum recorded during baking (ionization

was by electron bombardment and not by the r.f. spark) gave

major peaks at masses 16 , 17, 18, 19, 28 and 44, however the

ion current was only in the 10 * 5 A range. A different filament transformer appears necessary in order to improve electron

emission so that higher currents to the 24 KV aperture can be

obtained.

Commercial bakeout units similar to this one have been

produced; however due to various modifications made to our

instrument it was simpler to build a unit than to adapt a commercial unit.

B. Analysis of Materials by Direct Sparking With SSMS

As in previous years a number of materials were examined

directly with the SSMS. Most of the samples were Standard

Reference Materials and of relative high purity. Some of the

samples run were high purity silver, cadmium and molybdenum

metals, and compounds such as thallium chloride, potassium

dichromate and arsenic trioxide. In none of these analyses

were any standards available containing known impurity levels

in the same matrices; therefore only estimated concentration

levels could be reported. For silver, cadmium and molybdenum

however, residual resistivity ratios (RRR) measurements were

used to select samples containing the lowest and highest

(electrically active) impurity levels. The relative concentration reported by SSMS then gave an indication of which

impurities were controlling the observed RRR.

81
Acceptance testing was performed on a series of new SRM

steel samples being produced mainly for emission spectrometry

use. Test samples from the various heats of SRMs 1261 thru

1264 were examined by a number of different techniques, with

the SSMS reporting on 13 to 15 elements. The available SRMs

ingot irons, used as standards, were certified for only a few

of the elements assigned to the SSMS for analysis. Some of

the other elements were compared to values reported by other

techniques on the test sample of SRM 126l and the remainder

were computed from estimated sensitivity factors.

Due to a number of factors the 1264 steel was remade

with some changes in element concentrations. The acceptance

testing of the new sample (1264 heat #2) by SSMS was based on

a comparison to the first sample (1264 heat #1) and to SRM

1261 on which actual analysis values for certification were

then becoming available. The results of these analysis are

given in Table 20. The results are based on a 1, 3 3 10, 30,

etc., set of graded exposures and therefore only about three

exposures each were measurable on the "standard" and "unknown".

The first column gives the ratio of the amount of an element

found in heat #1 to that found in heat #2. The values in the

second column are ppm by weight in heat #2 of 1264 computed

using the preliminary analysis values assigned to the first

heat. Some of the values used from the first heat are based

on known standards (one or more steps removed) and others are

from estimated sensitivity factors. The last column gives an

analysis of the second heat based on a direct comparison to

SRM 126l. All values for 1261 except for lanthanum are considered reliable. The agreement on the 1264 heat #2 analysis

using the two different samples as standards is good considering the use of estimated sensitivity factors in the original

analysis of the heat #1 sample. The factor of 2 agreement

between the lead values is reasonable considering that the

lead concentrations in the samples used as "standards" differed

by a factor of approximately 600. Similar differences in

82
concentration between the two "standards" also existed for

bismuth (40/1), antimony (10/1) and silver (20/1).

Table 20. Spark source mass spectrographic analysis of SRM 1264,

Low Alloy Steel (0.9 C) (heat #2).

D ,. , 1264 heat #2

Rat, ° of nc/iu * T/i 1264 heat #1

ppm wt

vs 1264 heat #1

ppm wt

vs 1261

Bi 0.06 13 20

Pb 1,6 200 400

Hf >20

j

50

Pr 0.18 0.7

Ce 0.15 5 5 La 0.12 1 2 to 5 Te 0.03 1 2

Sb 1 300 200

Sn 0.07 20

Ag 0.003 0.2 0.2

Se 0.15 2 3

Ge 1.4 30

Zn 0.01 0.4

Analysis by Isotope Dilution

1. Int rodtiction

The Spark Source Mass Spectrograph has two characteristics

important to isotope dilution:

a) With the high voltage r.f. spark used on the SSMS

all elements, regardless of ionization potential, can give a

just detectable signal with from 10 10 to 10 :1

g of material.

(Considerably more is actually required to obtain reliable

measurements of istotopic ratios.)

b) The photographic plate covers the mass range from 7

to 240; thus all elements are detected simultaneously. It is

therefore possible to simultaneously determine many elements

of diverse ionization potentials from a single sample loading

83
with sensitivities below 1 ppm. The multi-element capability

of the SSMS enables efficient use of time on the chemistry

and the SSMS; however it also enables the use of relatively

simple group separation techniques which in turn tend to hold

down blank problems.

Based on previous experience we would consider it feasible to attempt analysis by SSMS isotope dilution if 0.1 yg

(1*10

-7

g) or more of a spiked element could be loaded into

the SSMS for sparking.

The photographic plate detection system presently used

imposes a ±5 percent precision on the results of an isotope

dilution analysis. This does not compare favorably with better

than 0.1 percent precision possible with thermal ion source

mass spectrometers; however the work with SSMS supplements

thermal ion work and does not attempt to compete with it.

Analysis for elements at the ppm level which would be impossible

to perform with thermal ion units can be done with SSMS isotope

dilution techniques. The work in general has only been applied

to elements and concentration levels where other more precise

techniques cannot be used.

In last year's annual report [18], a stable isotope

dilution-spark source mass spectrographic method was outlined

(ID-SSMS) for analyzing ingot iron. Silver, copper, molybdenum

and nickel were simultaneously determined in the 100-mg samples

of SRM 1165 using a chemical preconcentration step to separate

the spiked analytes from the matrix. The concentrations ranged

from 0.0005 percent for silver to 0.025 percent for nickel.

Cobalt, a mononuclidic element, was also determined at the

same time by adding known amounts of cobalt to half of the

samples used for the isotope dilution determinations and

measuring the 59 Co/ 60 Ni and 59 Co/ 58 Ni ratios. Details of the

method including a comparison of the results obtained with

the certified values was published recently in Analytical

Chemistry [20].

84
2 . Materials Analyzed

a. Steel standard reference materials - The preceding method [18,20] was applied to the analysis of SRM 1265,

Electrolytic Iron, intended as a renewal standard reference

material. The procedure was altered somewhat in order to

investigate whether other elements could also be separated

and thus determined. Titanium was of particular interest.

After extracting the iron into the organic phase, the aqueous

phase was evaporated to a few tenths of a cm 3 instead of being

electrolyzed as in the published procedure. The residue was

transferred to high purity gold wires and ignited at 450 °C

for 20 minutes in a tube furnace equipped with a quartz tube

liner. The wires were then sparked in the mass spectrograph

and the spectrum was photographically recorded. A line corresponding to SO , which is an ion fragment from the sulfate

in the residue, interfered with an intensity measurement of

the line produced by the l+8 Ti. The sulfate in combination with

alkali cations is not removed by ignition. Some of the sulfate

came from the k7 Tl spike solution, since sulfuric acid had been

used to dissolve the enriched isotope material. Moreover,

during the subsequent dilutions of the 1 mg/cm 3

I* 7 Ti stock

solution, to prevent hydrolysis, the acid strength had been

maintained with sulfuric acid. Had the production of SO with

this procedure been anticipated, these dilutions could have

been performed with perchloric acid. Because of interferences

of this type and those from combinations of anions and cations,

it was preferred to incorporate an electrodeposition step in

the previous analytical procedures that had been developed.

This has the advantage of providing the isotopically altered

analytes relatively free of other anions and extraneous

cations thus greatly simplifying the photographically recorded

spectrum.

Although titanium was not determined, other spiked analytes yielded interference-free lines on the emulsion. The

results for these elements are given in Table 21.

85
Table 21. Spark source mass spectrographs isotope dilution analysis of

SRM1265, Electrolytic Iron.

Element

Average

concentration

percent by weight

95% Confidence

limits

Number of

determinations

Cu 0.0058 0.0003 8

Cr 0.0075 0.0002 9

Ni 0.040 0.001 9

Mo 0.0041 0.0005 6

In the analytical procedure, most of the iron and some of

the molybdenum is extracted with methyl isobutyl ketone (MIBK)

and if the molybdenum present in the sample and the molybdenum

spike were not in equilibrium, erroneous results would be

obtained. This attainment of equilibrium, an essential condition of the method, is usually ensured by cycling analytes

and spikes through oxidation-reduction states. However, in

attempting to determine several trace elements simultaneously,

indiscriminate use of reagents, other than those of highest

purity, would prohibitively increase the method blank for

common elements thus precluding their determination.

Because of the several stable valence states that molybdenum possesses, one tends to be even more concerned regarding

the attainment of equilibrium between that analyte and its

spike. Consequently two additional experiments were run in

which the spiked samples were dissolved as before in hydrochloric acid but then evaporated to dryness and treated with

concentrated nitric acid. Individual results of 0.0039 percent

and 0.00^42 percent were obtained. It was concluded from this

that equilibrium of the molybdenum oxidation states was not

causing difficulty in the analysis.

In another series of experiments designed to determine

titanium, the isotopically altered trace elements were electrodeposited at a current density lower than usually employed.

Although under these conditions, titanium was electrodeposited

86
as was evident from the mass spectrum, it could not be determined because of interference from the doubly charged 95 Mo on

the singly charged 1+8 Ti. The relative amount of molybdenum

compared to titanium on the gold wires was greater in this

case than in the evaporation procedure. This interference

from the doubly charged 96 Mo was eliminated by extracting the

solution with MIBK before electrolysis. Obviously with this

extraction step, molybdenum would be replacing titanium as an

analyt e

Thus none of the procedures attempted permitted both

molybdenum and titanium to be determined simultaneously from

the samples already spiked and available. Therefore titanium

was not determined since it would require twice as much work,

and another technique was already providing results on

titanium.

An ID-SSMS method was developed for determining a number

of chemically diverse elements in low-alloy steel. Copper,

silver, cerium, neodymium, selenium, tellurium and zirconium

ranging from 0.040 percent for copper to 0.00031 percent for

neodymium were determined in a steel material subsequently

issued as SRM 126l, Electrolytic Iron. The procedure will be

detailed in a manuscript being prepared for publication.

b. Botanical materials (Orchard Leaves ) - This is

the first of a series of plant standard reference materials

being issued to calibrate analytical procedures. A number of

trace elements, essential to plants, are being determined by

ID-SSMS. In addition, the method yields upper concentration

limits for a number of elements. Of particular significance

is the presence of an abnormally high concentration of lead.

c

High-purity reagents - The purity of reagents is

fundamental to reliable trace element determinations by most

analytical methods. Samples of high-purity perchloric acid

were analyzed by an ID-SSMS procedure to determine their suitability as reagents for high-purity materials. Approximately

50 cm 3 of each sample were spiked with enriched isotope

87
solutions of fourteen elements of interest. An aliquot of

the spiked solution was evaporated to a small volume and

transferred to a pair of high-purity gold wires. The wires

were then ignited in a tube furnace to remove hydrocarbons

and residual perchloric acid. The mass spectra were photographically recorded and the results were calculated from the

measured isotope ratios, and the other experimental data. The

results for two lots of perchloric acid are listed in Table 22.

Table 22. Analysis of high-purity perchloric acid by isotope dilution - spark source mass spectrography.

Concentrations in parts per billion

(ng/g)

Lot "A" Lot"B"

Ag < 0.5 < 0.5

Ca 40 7 Cd 2 4 Cr 22 18

Cu 2 3 Fe 15 10

Mg 14 4 K 7 9

Ni 4 < 0.5

Pb 14 16

Sn < 2 < 1 Zn 22 17

Ba < 10 10

Ti 3 2 All fourteen impurity elements were determined simultaneously. In this method, if the enriched isotope spikes and

impurity elements are in physical and chemical equilibrium,

possible losses that may occur during the preconcentration and

handling steps do not affect the final results . This should

be true for these elements under these experimental conditions.

Moreover, providing that enough material is recovered to detect

the "spiking" isotope, either an actual concentration or upper

limit can be reported.

88
3. Standard Reference Materials for the Spark Source

Mass Spectrograph

NBS has produced one Standard Reference Material specifically for SSMS use. This is SRM 685 a high purity gold sample.

In addition there are several SRM samples not produced for

just the SSMS but having impurity levels ideal for SSMS needs.

These are: (a) a high purity platinum sample, SRM 680, and a companion sample of platinum doped with 12 elements in the 0.5

to 12 ppm level, SRM 681; (b) two zinc samples in shot and

bar form, SRMs 728 and 683, of the same composition with 7

impurities determined from 20 ppb to 11 ppm. To date response

to these SRM samples has been modest.

Based on formal and informal discussions of standards at

SSMS users meetings and on the results of a survey on standards

taken for one of these meetings it is apparent that standards

requirements cover almost all conceivable types of matrices.

Since the needs are so widespread there does not appear to be

any one matrix which is of interest to a sufficient number of

laboratories to justify its production as a standard for SSMS

needs alone.

For the forementioned reasons NBS is not presently engaged

in producing standards specific for SSMS needs. This would be

changed if there was sufficient interest shown in a given

matrix in the future. There are a number of materials, however,

being produced for other uses which will meet some of the needs

of the SSMS. The gold, platinum and zinc SRMs mentioned are

available now and the series of iron SRMs and orchard leaf

samples are in the process of being certified. In addition a series of Trace Elements in Glass (TEG) samples now being

certified could be useful for glass and possibly rock analysis.

These samples have been doped with 6l elements at the 500, 50,

1 and 0.02 ppm level. About one third of the elements are

being certified.

89
7. MISCELLANEOUS

A. Oxidimetric Standard Reference Materials

1 . SRM 136c, Potassium Dichromate

The replacement for SRM 136b, Potassium Dichromate

oxidimetric standard to be designated SRM 136c, was submitted

for the determination of homogeneity and effective purity.

The effective purity was also determined coulometrically by

George Marinenko of Section 310. 03

.

Twenty drums of 25 lb each of potassium dichromate were

received and after mixing, a representative sample of approximately 50 g was removed from each drum. Pour composite

samples were prepared by mixing 10 g of material from 5 of

the representative samples of potassium dichromate for each

composite

.

For the determination of homogeneity of the potassium

dichromate, each of the 20 representative samples was run and

12 were repeated. Ferrous ammonium sulfate, hexahydrate was

used for the comparison between samples. All values fell

within ±0.01 percent of the mean except Nos. 8 and 17 but on

repeat runs they were also within these limits (Table 23).

At the same time the homogeneity determinations were made

SRM 136c was compared to SRM 136b. The effective purity of

SRM 136b is 99.978 percent. The effective purity of SRM 136c

was found to be 0.011 percent higher than SRM 136b using the

homogeneity runs (Table 23) and 0.009 percent higher than

SRM 136b using the composite sample runs (Table 2k) for an

average of 0.010 percent higher than SRM 136b. The effective

purity of SRM 136c would be 99.988 percent when compared with

SRM 136b.

90
Table 23. Homogeneity of SRM 136c, Potassium Dichromate using ferrous

ammonium sulfate, hexahydrate.

SRM 136c SRM 136b

Bottle 8 Fe(NH4 )2(S04 )2

- 6H2 g Fe(NH4)2(S04 ) 2

- 6H2

Date no. per g K2 Cr2 7

per g K2 Cr2 7

9/15 1 8.01025 8.00960

3 8.01003 8.00969

5 8.01056 8.00928

7 8.01002

9 8.01048

11 8.01013

13 8.00991

15 8.01004

9/17 17 8.00784 a 8.00896

19 8.00935 8.00906

2 8.00962

4 8.00992

6 8.00951

8 8.00423 3

10 8.00964

12 8.00948

14 8.00918

9/19 16 8.00909 8.00844

18 8.00944 8.00858

20 8.00910

4 b 8.00956

5 b 8.00924

8 b 8.00962

17

b 8.00941

10/13 l b 8.00951 8.00892

8

b 8.00965 8.00877

9 b 8.00947 8.00878

17 b 8.00961

10/16 3 b 8.00983 8.00883

7 b 8.00998 8.00895

ll b 8.00985 8.00867

13 b 8.00983

15 b 8.00970

Average 8.00971 8.00896

s.d. ±0.00037(0.005%) ±0.00037(0.005%)

a Omitted from average.

b Repeat runs. 91
Table 24. Effective purity of SRM 136c, Potassium Dichromate

compared to SRM 136b, Potassium Dichromate.

SRM 136c SRM 136b

Composite g Fe(NH 4

) 2(S04

) 2

- 6H2 g Fe(NH 4

) 2(S04) 2

- 6H

2

no. per g K2 Cr 2 7 per g K2 Cr 2 7

I 8.00994 8.00892

II 8.01009 8.00877

III 8.00965 8.00878

IV 8.00962

IV 8.00950 8.00883

III 8.00976 8.00895

II 8.00952 8.00867

I 8.00923

Average 8.00966 8.00882

s.d. ±0.00027(0.003%) ±0.00010(0.001%)

The effective purity of SRM 136c, when compared to SRM

83c, Arsenic Trioxide (99.987$) , was determined to be 99-984

percent. The results are given in Table 25. George Marinenko

found 99.982 percent by coulometry. The average of the three

determinations gives an effective purity for SRM 136c, Potassium Dichromate of 99.984 percent. The details of the assay

will appear in NBS Special Publication 260-24 [21].

92
Table 25. Effective purity of SRM 136c, Potassium Dichromate

compared to SRM 83c, Arsenic Trioxide.

Composite

no. g K2 Cr 2 7

g As2 3a

5 "2 W, 2 W7

per g As2 3

Effective purity

(%)

I 0.990797 0.999499 0.991294 99.991

II 0.991312 0.999954 0.991358 99.985

III 0.991617 1.000361 0.991259 99.994

IV 0.991803 1.000530 0.991278 99.992

IV 0.991584 1.000158 0.991427 99.978

III 0.991270 0.999857 0.991412 99.979

II 0.991283 0.999907 0.991375 99.983

I 0.991404 0.999957 0.991447 99.976

I 0.991420 1.000036 0.991384 99.982

II 0.991455 1.000059 0.991397 99.981

III 0.991378 1.000038 0.991340 99.986

IV 0.991080 0.999653 0.991424

Average

s.d.

99.978

±99.984

0.006

Effective purity of SRM 83c, Arsenic Trioxide = 99.987%.

B . Intercomparison of Oxidimetric Standard Reference Materials

The intercomparison of the oxidimetric standard reference

materials has been completed. A special publication [21] will

be published giving the results and the details of methods for

this intercomparison.

1. SRM 40h, Sodium Oxalate and SRM 83c, Arsenic Trioxide

A potassium permanganate solution was used to compare

SRM 40h, Sodium Oxalate and SRM 83c, Arsenic Trioxide. The

procedure for the titration of SRM 40h with potassium permanganate is given on the Certificate of Analysis (see Appendix

III) . The recommended procedure for the dissolution of arsenic

93
trioxide calls for sodium hydroxide and acidifying with hydrochloric acid. Since the possibility of a side reaction of

hydrochloric acid and potassium permanganate existed a study

was made to eliminate hydrochloric acid from the procedure.

In the modified procedure, SRM 83c was dissolved in a sodium

carbonate solution and acidified with sulfuric acid. An

osmium tetroxide solution and a manganous sulfate solution

were used as catalysts.

SRM 40h, Sodium Oxalate was found to have an effective

purity of 99.9^1 percent when compared to SRM 83c, Arsenic

Trioxide (99.987$) Table 26.

Table 26. Effective purity of SRM 40h, Sodium Oxalate compared to SRM 83c, Arsenic Trioxide.

Composite

no.

g KMn04

sol.

per g Na2 C2 4

g Na2 C2 4

per g As2 3a

Effective purity

(%)

I

145.1841 0.737968 99.953

II 145.1777 0.737936 99.948

III 145.1539 0.737815 99.932

IV 145.1628 0.737860 99.938

IV 145.1459 0.737774 99.926

III 145.1624 0.737858 99.938

II 145.1695 0.737894 99.943

I

145.1598 0.737845 99.935

I

145.1730 0.737912 99.945

II 145.1718 0.737906 99.944

III 145.1715 0.737904 99.944

IV 145.1694 0.737893 99.942

Average 99.941

s.d. ±0.007(0.007%)

gKMn04

per gAs2 3 = 196.735.

94
2 . SRM 40h, Sodium Oxalate and SRM 136c, Potassium

Dichromate

Sodium oxalate and potassium dichromate can not be compared directly. Sodium oxalate and ferrous ammonium sulfate

were titrated with a potassium permanganate solution and then

the potassium dichromate was compared with the ferrous ammonium sulfate. The ratios of SRM 136c to the ferrous ammonium

sulfate is given in Table 27, the ratio of SRM 136c to potassium permanganate solution in Table 28, the ratios of SRM 136c

and SRM 40h in Table 29 along with the effective purity of

SRM 40h. The effective purity of SRM 40h was found to be

99.967 percent when compared to SRM 136c.

Table 27. SRM 136c, Potassium Dichromate compared to ferrous ammonium sulfate, hexa hydrate.

g Fe(NH4) 2(S04) 2 -6H2

Composite no. per g K2Cr2 7

I

8.01026

II 8.01025

III 8.00965

IV 8.00948

IV 8.00965

III 8.00994

II 8.00961

I 8.00911

I

8.00965

II 8.00971

III 8.00996

IV 8.00995

Average 8.00975

s.d. ±0.00032(0.004%)

95
Table 28. SRM 136c, Potassium Dichromate compared to potassium permanganate solution.

g KMn0 4 sol. g KMn04

sol.

per g Fe(NH4

) 2(S04) 2

- 6H

2 per g K2 Cr2 7 a

26.2957 210.6220 b

26.2904 210.5795

26.2885 210.5643

26.2898 210.5747

26.2842 210.5299

26.2869 210.5519

26.2856 210.5411

26.2862 210.5459

26.2879 210.5595

26.2887 210.5659

26.2889 210.5675

26.2885 210.5643

Average 210.5586

s.d. ±0.0149(0.007%)

a

l g K2 Cr 2 7 = 8.00975 g Fe(NH4) 2(S0 4

) 2 -6H 2 (Table 7).

b Omitted from average.

96
Table 29. Effective purity of SRM 40h, Sodium Oxalate compared to SRM 136c, Potassiurr Dichromate.

Composite

no.

g KMn04

so!.

per g Na2 C

2 4

g Na

2 C2 4

per g K

2 Cr2 4

a ' b

Effective purity

(%)

I 153.8730 1.36839 99.841 c

II 154.0710 1.36663 99.970

III 154.0741 1.36661 99.971

IV 154.0513 1.36681 99.956

IV 154.0492 1.36682 99.956

III 154.0679 1.36666 99.967

II 154.0646 1.36669 99.965

I 154.0953 1.36642 99.985

I 154.0486 1.36683 99.955

II 154.0395 1.36691 99.949

III 154.0902 1.36646 99.982

IV 154.0470 1.36685 99.954

IV 154.0623 1.36671 99.964

III 154.0787 1.36657 99.974

II 154.0896 1.36647 99.981

I 154.0743 1.36660 99.972

Average 99.967

s.d. ±0.011(0.011%)

a

l g K

2 Cr2 7 = 210.5586 g KMn04

sol. (Table 8).

b

Effective purity SRM 136c, Potassium Dichromate = 99.983%.

CiOmitted from average.

97
C. Archaeological Samples

As for the past several years the cooperative program

with Dr. Robert H. Brill, Curator, Corning Museum of Glass

has been continued. This program is aimed towards determining

the suitability of using precision lead isotopic analyses for

the dating and/or tracing of objects of archaeological

interest

.

Some examples of the various parts of this program are:

a series of samples of lead extracted from bronze vessels

from Sardinia were examined. Sardinia has been proposed as

the source of lead in some Etruscan bronzes . Also examined

were a series of ancient Egyptian kohls (mostly finely

powdered galena) dating from 2200 B.C. to 1300 B.C. These

give an idea of the kinds of galena ore actually in use in

Egypt at that time. For this same use samples of lead pigs

from the British Museum known to have been from English lead

mines were analyzed. Also analyzed were a set of samples from

ancient coins as well as ore samples from the same areas and

a variety of other objects.

As an extension of the above cooperative effort a number

of additional samples have been examined where it was hoped

that the high precision lead analyses would help in determining the authenticity of art objects held in the collections

of public museums. Again, as examples, samples from the

"Etruscan Horse" held by the Metropolitan Museum of New York

and of a smaller horse of known origin have been analyzed.

The analyses of lead pigment samples from a large variety of

paintings of known origin have also been completed. Dr. Brill

is serving as coordinator for these various programs.

D. Air Pollution Analyses

The assay of the lead content of a series of air sample

filters taken from Boston and Hilo, Hawaii has been completed.

As might be expected those taken in Boston contained a relatively large amount of lead O50 yg) and the analyses presented

98
no particular challenge. The filters collected from Hawaii

however (through which about four times the volume of air had

passed) contained a much smaller quantity 02-4 ug) of lead.

The successful analysis of the lead content of these was

completed utilizing the small sample plating technique for

separation and the silica gel technique for the isotopic

measurements. Both of these methods are described in detail

in earlier sections.

This preliminary work was done in anticipation of receiving for analysis a series of air sample filters to be taken

this fall on an Antartic Expedition. The Antartic filters are

expected to contain even smaller quantities of lead in the

order of 0.2 to 1 ug.

It is hoped these analyses will contribute to an understanding of the global distribution of air polluting materials

and ultimately, to the control of these materials.

99
8. ACKNOWLEDGMENTS

The overall performance of the Section is aided by many

people not listed as Section personnel.

Ron Shideler of 310.00 the Division Technical Services

Group has been of invaluable assistance in interfacing various

instruments t'o the Section's small computers and with the

design of various new circuits.

Ralph Orwick, Ira Shoemaker, Godfrey Vaughn and Marvin

Wilke, all of the NBS instrument shops are the mainstay of

the instrument construction program, with Godfrey Vaughan

taking over as watch dog from Joe Mammano when Joe retired

last fall.

The list of guest workers, who each contributed something

to the Section's performance, with their name, affiliation and

specialty follows:

Norman Hubbard, Manned Spacecraft Center, Houston, Texas,

isotope dilution analysis of rare earths.

Charles Krpec, Manned Spacecraft Center, Houston, Texas,

computer programming.

Hermogenes Sanz, Spanish Nuclear Energy Commission,

isotopic analysis of nuclear materials.

Tom Stern, U.S. Geological Survey, chemistry and isotopic

analysis of Pb , U and Th

.

And I must give a special acknowledgment to Joy Shoemaker,

the Section secretary, who makes order out of chaos when the

Section produces a manuscript.

100
9 . PERSONNEL AND ACTIVITIES

A

Personnel Listing

William R. Shields, Section Chief

Joy J. Shoemaker, Secretary

Mass Spectrometry (absolute isotope ratio) —

Ernest L. Garner

Mass Spectrometry (isotope dilution) —

Larry J. Moore

Mass Spectrometry (nuclear materials) —

I. Lynus Barnes

Stoichiometry —

Thomas J . Murphy

Stoichiometry (nuclear materials) —

Lawrence A. Machlan

Separation and Purification —

Keith M. Sappenfield

Design and Fabrication —

William A. Bowman, III

Spark Source Mass Spectrometry —

Paul J. Paulsen

Charles W. Mueller

B. Publications

1. Analytical Mass Spectrometry Section: Summary of

Activities July 1968 to June 1969, NBS Technical Note 506

,

Ed. W. R. Shields, (1970) . 2. P. J. Paulsen, R. Alvarez and C. W. Mueller, "Spark

Source Mass Spectrographic Analysis of Ingot Iron for Silver,

Copper, Molybdenum, and Nickel by Isotope Dilution and for

Cobalt by an Internal Standard Technique", Anal. Chem., 42 , 673-675 (1970).

C. Talks

1. I. L. Barnes , K. M. Sappenfield and W. R. Shields,

"The Mass Spectrometric Analysis of Sub-Picogram Quantities

101
of Lead", International Conference on Mass Spectroscopy in

Kyoto, Japan, September, 1969.

2. P. J. Paulsen, R. Alvarez and C. W. Meuller, "Determination of Trace Elements in Iron Using Isotope DilutionSpark Source Mass Spectrometry", 8th National Meeting of the

Society for Applied Spectroscopy, Anaheim, California,

October, 1969-

3. I. L. Barnes , K. M. Sappenfield, T. J. Murphy and

W. R. Shields, "The Mass Spectrometric Analysis of Subpicogram

Quantities of Lead", Eastern Analytical Symposium, Inc.

Session of Microanalytical Standards, New York City, November,

1969-

4. W. R. Shields, "Fabrication and Use of Ultra-High

Vacuum Systems for Mass Spectrometry", American Vacuum Society

Meeting, NBS , December, 1969

.

5. R. H. Brill , W. R. Shields and J. M. Wampler, Seminar:

"Application of Science in the Examination of Works of Art",

Museum of Fine Arts, Boston, June, 1970.

D. Committee Activities

L. A. Machlan

Member, Chemistry Panel of Interagency Board of Civil Service

Examiners

Member, ANSI Standards Committee N101

T . J . Murphy

Member, Chemistry Panel of Interagency Board of Civil Service

Examiners

Member, Meeting Arrangements Committee, Chemical Society of

Washington

Member, Committee on Annual Report of Atomic Weights,

American Chemical Society

Manager, Chemical Society of Washington

Member, Committee on Analytical Reagents of the American

Chemical Society

102
10. REFERENCES

[1] W. R. Shields, Editor, NBS Technical Note 456 (1968).

[2] W. R. Shields, Editor, NBS Technical Note 426 (1967).

[3] W. R. Shields, Editor, NBS Technical Note 277 (1966).

[4] W. R. Shields, Editor, NBS Technical Note 506 (1970).

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

[6] 0. Menis, Editor, NBS Technical Note 275 (1965).

[7] E. J. Catanzaro, T. J. Murphy, E. L. Garner and

W. R. Shields, J. Res. NBS, 73A, 511-516 (1969).

[8] H. Muller, Z. Anal. Chem. , 113, l6l (1938).

[9] L. A. Dietz and H. C. Hendrickson, Mass-Spectrometric

Isotopic Analysis of Uranium and Plutonium using the V

Type Surface-Ionization Fialment in R. J. Jones (Ed.),

Selected Measurement Methods for Plutonium and Uranium

in the Nuclear Fuel Cycle, U.S.A.E.C. (1963).

[10] E. J. Catanzaro, C. E. Champion, E. L. Garner,

G. Marinenko, K. M. Sappenfield and W. R. Shields,

Boric Acid; Isotopic and Assay Standard Reference

Materials, NBS Spec. Publ. 260-17 (1969).

[11] E. J. Catanzaro, T. J. Murphy, W. R. Shields, and

E. L. Garner, J. Res. NBS, 72A, 261-267 (1968).

[12] P. A. Akishin, 0. T. Nikitin, G. M. Panchenkov,

Geochemistry (U.S.S.R.) No. 5, 500 (1957).

[13] A. E. Cameron, D. M. Smith, R. L. Walker, Anal. Chem.,

41, 525-526 (1969).

[14] P. J. Paulsen and P. E. Branch, NBS Technical Note 286

(1966).

[15] B. F. Scribner, Editor, NBS Technical Note 401 (1966).

[16] B. F. Scribner, Editor, NBS Technical Note 422 (1967).

[17] B. F. Scribner, Editor, NBS Technical Note 452 (1968).

[18] B. F. Scribner, Editor, NBS Technical Note 502 (1969).

103
[19] P. F. S. Jackson and I. Whitehead, Anal. Chem., 39,

1737 (1967).

[20] P. J. Paulsen, R. Alvarez and C. W. Mueller, Anal.

Chem. , 42, 673-675 (1970)

.

[21] NBS Special Publication 260-24 , "Comparison of Redox

Standards", (in process).

104
U. S. Depart

Mauri

of Commerce

. Stans THIS IS A PRELIMINARY ISSUE OF

THE PRINTED CERTIFICATE WHICH

WILL BE MAILED WITHIN' HO DAYS

APPENDIX I

(Utrtxixtntt of (Analyst*

Standard Reference Material 984

Rubidium Chloride

RbCl, rubidium assay, weight percent ... 99 . 90 ± 0.02

Absolute abundance ratio, 8 5 Rb/ 8Rb . . . 2 . 593 ± 0.002

This lot of rubidium chloride was prepared to ensure material

of intermediate purity and high homogeneity. The material is

somewhat hygroscopic, absorbing approximately 0.6 percent moisture

in a 75 percent relative humidity at room temperature, but can be

dried to the original weight by desiccation over freshly exposed

P 2 5 or Mg(C10ij2 for twenty-four hours. The material should

therefore be stored with a desiccant such as P2O5.

The assay of this material is based on the determination of

rubidium by a combination of gravimetry and isotope dilution analysis on eight samples of about 2 g each of the dried RbCl. More

than 99% of the rubidium was precipitated, filtered and weighed as

rubidium perchlorate. The weight of RbClOi, was corrected for

potassium and cesium perchlorate. The soluble rubidium was determined by isotope dilution mass spectrometry. The total rubidium

was the sum of the rubidium from the rubidium perchlorate and the

rubidium from the filtrate. All weighings were corrected to vacuum

and the atomic weights used in the calculations were from the 1969

Table of Atomic Weights. The indicated tolerance is at least as

large as the 95% confidence level for a single determination.

Chloride was determined by silver coulometry to be 29.32 weight

percent. Preferential oxidation of iodide and bromide showed that

the material contains <0.001% I and <0.003% Br. Flame emission

spectrometry indicated lithium, <0.02 ppm; sodium, 2.3 ppm, potassium, 420 ppm; and cesium 24 ppm. Emission spectrographic

examination indicated, in addition, calcium, <10 ppm; magnesium,

<10 ppm; silicon, <10 ppm; and aluminum, detection questionable.

The loss on ignition at 500 °C (20 hours) was 0.010% and the

insoluble matter was 0.0001%. A materials balance shows that

99.99 ± 0.02 weight percent of the material is accounted for.

105
The absolute abundance ratio of 85 Rb/ 87 Rb was determined by

triple-filament solid-sample mass spectrometry. Mixtures of known

85 Rb/ 87 Rb ratio, prepared from nearly isotopically pure separated

rubidium isotopes, were used to calibrate the mass spectrometers.

The indicated uncertainties are overall limits of error based on

95 percent confidence limits for the mean and allowances for the

effects of known sources of possible systematic error. Details

of the preparation and measurements are described in a published

paper [J Res NBS , 73A , 511-516 (1969)].

The following members of the Analytical Chemistry Division

contributed to the characterization of this material: T. J. Murphy

and P. J. Paulsen - rubidium assay; G. Marinenko - chloride assay;

T. C. Rains and T. A. Rush - flame emission determinations; E. K.

Hubbard - emission spectrographic analysis; and E. J. Catanzaro

and E. L. Garner - absolute ratio determination.

The overall direction and coordination of the technical

measurements leading to certification were performed under the

chairmanship of W. R. Shields.

The technical and support aspects involved in the preparation,

certification, and issuance of this Standard Reference Material

were coordinated through the Office of Standard Reference Materials

by J. L. Hague.

Washington, D. C. 20234 J. Paul Cali, Acting Chief

July 27, 1970 Office of Standard Reference Materials

106
U. S. Department of Commerce APPENDIX II

Maurice H. Stans

Secretary

National Bsreau of Standards

L. M. Bransccmb, Director

(Eerttfttate of JVnal^t*

STANDARD REFERENCE MATERIAL 136c

Potassium Dichromate

(Oxidimetric Standard)

Purity on basis of effective oxidizing power 99.98 ± 0.02 percent

This lot of material was prepared to ensure material of high purity and uniformity. It conforms

to the American Chemical Society specification for analytical reagent grade material, but is not to be considered as entirely free from traces of impurities. It is certified only for its effective oxidizing

power. -^

Standardizations have been made by the coulometric method bvu^s^aWienko (see NBS J. Res.

67A, 453 (1963)), by direct comparison with arsenic trieoa4e»S(llVR83c7 and by comparison with

the previous SRM 136b through ferrous ammonium striate B^nK^Sappenfield. Impurity tests to the

ACS specifications were made by W. P. Schmidt^ermssionjsppetrography by V. Stewart, and spark- source mass spectrography by C. W. MueUer.^^ \\ x^-^

Drying tests indicate that lossesof the ordeiLPJr 0.005 percent are obtained on a few hours drying

at 105 °C; long time drying injliqai^feinat rpsses approach 0.01 percent. The problem of occluded

and surface moisture will bemuaifedTbqfore a final certificate is issued. The effective assay is based on the sample as issuad^TF^k toljwance indicated is at least as large as the 95 percent confidence

limits for a single^5v>rali»a^fearfand include terms for inhomogeneities in the material as well as analytical error. \SA

The overall direction and technical measurements leading to certification were performed under

the chairmanship of R. A. Durst.

The technical and support aspects in the preparation, certification, and issuance of this standard

reference material were coordinated through the Office of Standard Reference Materials by J. L. Hague.

Washington, D. C. 20234 J. Paul Cali, Acting Chief

March 24, 1970 Office of Standard Reference Materials

107

U. S. Department' of Commerce APPENDIX III

Maurice^ Jl. Stans

Secretary

National BbreSfc of Standards

A. V. Afttmr--Director

derttfttate of flitml])s\%

Standard Reference Material 40h

Sodium Oxalate

Na2 C204 , effective purity 99.95 ± 0.05 percent

This lot of sodium oxalate was prepared to ensure material of purity and

uniformity compatible with its use as a working standard for oxidation-reduction

reactions. The material conforms to the American Chemical Society specification for

reagent-grade material, but should not be considered as entirely frt& from impurities

such as moisture, sodium hydrogen oxalate (0.03%V afed sowjrt hydrogen

carbonate (0.03%). The material is not appreciably hy""

The effective purity of the sodium oxalate cambtkjealized in the standardization of KMn04 solutions by use of th^^n^tiQg^pn this certificate. Homogeneity

testing, effective purity, sodium^yMroge^xo^ate and sodium hydrogen carbonate

determinations were mad^byil K/^I.'Sappenfield; American Chemical Society

specification tests we^r-^aa^sjby W. P. Schmidt of the Analytical Chemistry

Division.

The overall Cwecnon and coordination of the technical measurements leading

to certificatio^were performed under the chairmanship of W. R. Shields.

The technical and support aspects involved in the preparation, certification,

and issuance of this Standard Reference Material were coordinated through the

Office of Standard Reference Materials by J. L. Hague.

Washington, D. C. 20234 W. Wayne Meinke, Chief

April 24, 1969 Office of Standard Reference Materials

109
DIRECTIONS FOR USE IN OXIDIMETRY

Standardization of 0. IN permanganate. Transfer 0.3 g of sodium oxalate (dried

at 105 °C) to a 600-ml beaker. Add 250 ml of diluted sulfuric acid (5+95)

previously boiled for 10 to 15 minutes and then cooled to 27 ± 3 °C. Stir until the

oxalate has dissolved. Add 39 to 40 ml (0.3 g of sodium oxalate requires

approximately 44.8 ml of 0.17V KMn04 ) of O.liV potassium permanganate at a rate of 25 to 35 ml per minute while stirring slowly. Let stand until the pink color

disappears (about 45 seconds; if the pink color should persist because the

permanganate is too strong, discard, and begin again, adding less of the KMn04 solution). Heat to 55 to 60 °C and complete the titration by adding permanganate

until a faint pink color persists for 30 seconds. Add the last 0.5 to 1 ml dropwise,

with particular care to allow the solution to become decolorized before the next

drop is introduced.

Determine the excess of permanganate required to impart the permanent pink

color to the solution. This can be done by matching the color by adding

permanganate to the same volume of the specially treated dilute sulfuric acid at 55

to 60 °C. This correction usually amounts to 0.03 to 0.05 ml.

In potentiometric titrations the correction is negligible if the end point is reached slowly.

For the standardization of more dilute solutions, the same conditions are recommended except that the initial volume and size of sample are proportionally

reduced.

In very accurate work the correction is best obtained iodometrically [cf. W. C. Bray, J. Am. Chem. Soc. 32, 1205 (1910)] as follows: Cool the titrated

solution to 25 °C, add 0.5 g of KI, 2 ml of starch solution, and titrate the liberated

iodine with 0.02iV thiosulfate. To obtain the ratio of the thiosulfate to the

permanganate solution, add 1 ml of the O.liV permanganate to 350 ml of the diluted

sulfuric acid (5+95), stir, add 0.5 g KI, and titrate with the thiosulfate solution,

adding starch just before the end point is reached.

USCOMM-NBS-DC

110
Latest developments in the subject area of this publication, as well as

in other areas where the National Bureau of Standards is active, are

reported in the IMBS Technical News Bulletin. See following page.
HOW TO KEEP ABREAST OF NBS ACTIVITIES

Your purchase of this publication indicates an interest in the research,

development, technology, or service activities of the National Bureau of Standards.

The best source of current awareness in your specific area, as well as in other NBS programs of possible interest, is the TECHNICAL NEWS BULLETIN,

a monthly magazine designed for engineers, chemists, physicists, research

and product development managers, librarians, and company executives.

If you do not now receive the TECHNICAL NEWS BULLETIN and would like to subscribe, and/or to review some recent issues, please fill out and return the

form below.

Mail to: Office of Technical Informatior and Publications

National Bureau of Standards

Washington, D. C. 20234

Name

Affiliation

Address

P.ity Statfi 7ip

| 1 Please send complimentary past issues of the Technical News Bulletin.

|

| Please enter my 1— yr subscription. Enclosed is my check or money

order for $3.00 (additional $1.00 for foreign mailing).

Check is made payable to: SUPERINTENDENT OF DOCUMENTS.

TO 546

3"

to

>-l to


NBS TECHNICAL PUBLICATIONS

PERIODICALS NONPERIODICALS

JOURNAL OF RESEARCH reports National

Bureau of Standards research and development in

physics, mathematics, chemistry, and engineering.

Comprehensive scientific papers give complete details of the work, including laboratory data, experimental

procedures, and theoretical and mathematical analyses. Illustrated with photographs, drawings, and

charts. Published in three sections, available separately: • Physics and Chemistry

Papers of interest primarily to scientists working in these fields. This section covers a broad range of physical and chemical research, with major emphasis on standards of physical measurement, fundamental

constants, and properties of matter. Issued six times a year. Annual subscription: Domestic, $9.50; for- eign, $11.75*. • Mathematical Sciences

Studies and compilations designed mainly for the mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment design,

numerical analysis, theoretical physics and chemistry, logical design and programming of computers

and computer systems. Short numerical tables. Issued quarterly. Annual subscription: Domestic,

$5.00; foreign, $6.25*. • Engineering and Instrumentation

Reporting results of interest chiefly to the engineer

and the applied scientist. This section includes many

of the new developments in instrumentation resulting

from the Bureau's work in physical measurement,

data processing, and development of test methods.

It will also cover some of the work in acoustics,

applied mechanics, building research, and cryogenic

engineering. Issued quarterly. Annual subscription:

Domestic, $5.00; foreign, $6.25*.

TECHNICAL NEWS BULLETIN

The best single source of information concerning the Bureau's research, developmental, cooperative and

publication activities, this monthly publication is designed for the industry-oriented individual whose

daily work involves intimate contact with science and

technology

for engineers, chemists, physicists, re- search managers, product-development managers, and

company executives. Annual subscription: Domestic,

$3.00; foreign, $4.00*.

• Difference in price is due to extra cost of foreign mailing.

Applied Mathematics Series. Mathematical tables,

manuals, and studies. Building Science Series. Research results, test methods, and performance criteria of building materials, components, systems, and structures. Handbooks. Recommended codes of engineering

and industrial practice (including safety codes) developed in cooperation with interested industries,

professional organizations, and regulatory bodies.

Special Publications. Proceedings of NBS conferences, bibliographies, annual reports, wall charts,

pamphlets, etc. Monographs. Major contributions to the technical

literature on various subjects related to the Bureau's

scientific and technical activities. National Standard Reference Data Series.

NSRDS provides quantitative data on the physical

and chemical properties of materials, compiled from

the world's literature and critically evaluated.

Product Standards. Provide requirements for sizes, types, quality and methods for testing various industrial products. These standards are developed cooperatively with interested Government and industry groups

and provide the basis for common understanding of product characteristics for both buyers and sellers. Their use is voluntary.

Technical Notes. This series consists of communications and reports (covering both other agency and

NBS-sponsored work) of limited or transitory interest. Federal Information Processing Standards Publications. This series is the official publication within

the Federal Government for information on standards

adopted and promulgated under the Public Law

89-306, and Bureau of the Budget Circular A-86

entitled, Standardization of Data Elements and Codes

in Data Systems.

Order NBS publications from: Superintendent of Documents

Government Printing Office

Washington, D.C. 20402
U.S. DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20230

OFFICIAL BUSINESS POSTAGE AND FEES PAID

U.S. DEPARTMENT OP COMMERCE

PENALTY FOR PRIVATE USE, $300