National Bureau of Standi.

Library, N.ff. Bldg

JUL ^ 1 1966

^ecknical <y[ote

1 bs

taken from tiie library.

286

SPARK SOURCE MASS SPECTROGRAPH PROGRAM

JULY 1964 TO JUNE 1965

PAUL J. PAULSEN AND PAUL E. BRANCH

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards is a principal focal point in the Federal Government for assur- ing maximum application of the physical and engineering sciences to the advancement of technology

in industry and commerce. Its responsibilities include development and maintenance of the national

standards of measurement, and the provisions of means for making measurements consistent with

those standards; determination of physical constants and properties of materials; development of methods for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices

for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Govern- ment; assistance to industry, business, and consumers in the development and acceptance of commercial standards and simplified trade practice recommendations; administration of programs in cooperation with United States business groups and standards organizations for the development

of international standards of practice; and maintenance of a clearinghouse for the collection and

dissemination of scientific, technical, and engineering information. The scope of the Bureau's

activities is suggested in the following listing of its three Institutes and their organizational units. Institute for Basic Standards. Applied Mathematics. Electricity. Metrology. Mechanics. Heat. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radiation Physics. Radio Standards

Laboratory:* Radio Standards Physics; Radio Standards Engineering. Office of Standard Reference

Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.* Materials Evaluation Laboratory. Office of Standard Refer- ence Materials. Institute for Applied Technology. Building Research. Information Technology. Performance

Test Development. Electronic Instrumentation. Textile and Apparel Technology Center. Technical

Analysis. Office of Weights and Measures. Office of Engineering Standards. Office of Invention and

Innovation. Office of Technical Resources. Clearinghouse for Federal Scientific and Technical

Information.**

* Located at Boulder, Colorado, 80301. Located at 5285 Port Royal Road, Springfield, Virginia, 22171.
NATIONAL BUREAU OF STANDARDS

Technical Note 286

ISSUED APRIL 15, 1966

SPARK SOURCE MASS SPECTROGRAPH PROGRAM

JULY 1964 TO JUNE 1965

Paul J. Paulsen and Paul E. Branch

Spectrochemical Analysis Section

Analytical Chemistry Division

Institute for Materials Research

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

listed or referred to in the open literature.

For sale by the Superintendent of Documents, Government Printing Office

Washington, D.C., 20402 - Price 25 cents
FOREWORD

The Analytical Chemistry Division was established as

a spearate 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 eight sections encompassing

some JO 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 service analysis or standard reference

material. In addition it is their responsibility to inform

others of their efforts.

Formal publication in scientific periodicals is highly

important. In addition, however, it has been my experience

that informal, annual summaries of progress describing

efforts of the past year can be very valuable in disseminating information. In the future we plan to issue these

summaries for a number of programs. The following is the

second report in this series on progress of the Spark

Source Mass Spectrograph program

In preparing this report, it has been necessary to

make occasional reference to existing commercial equipment.

However, such mention snould in no case be considered as

representing a recommendation or endorsement by the

National Bureau of Standards.

W. Wayne Meinke, Chief

Analytical Chemistry Division

11
TABLE OF CONTENTS

PAGE

1. INTRODUCTION .......... . . . . . . 1

2. INSTRUMENT MODIFICATIONS . . Additional Analyzer Pumping ....... 2

Source Ion Gauge .,.,......,... 6

Cold Finger . . . „ 6

Tantalum Source Parts ......... . 6

Source Apertures ............. 7

3. PLANNED INSTRUMENT MODIFICATIONS ...... 9

4. PROCEDURE FOR SAMPLE ANALYSIS .......

Sample Types ............... 10

Sample Preparation .-......... 10

Running of Sample ............ 11

Plate Development and Handling .<,„„.. 11

Plate Measurement and Data Calculation . . 12

5. EXPERIMENTAL RESULTS ............

Oxygen Isotope Ratios in Al20^ ...... 15

Cartridge Brass ............. 15

Tin NBS 431 to 435 17

LIST OF FIGURES

FIGURE NO.

1. Spark source mass spectrograph . , . . „ 3

2„ Rear view of instrument showing major

vacuum modification .,..„.. ••»• 4

3. Position of major components of mass

spectrograph „.,.. 5

4 Background lines with stainless steel

and tantalum source parts .,.».».« 7

5. Large and small tantalum first and

second apertures ...... ••«... 8

6 Equivalent exposures of Pt with large

and small sized apertures ..,...<> . 9

iii
LIST OF TABLES

TABLE NO, PAGE

1. Isotopic ratios of oxygen in AlpO and

platinum ratios »„».•«. c . . . , . 15

2. Mass spectrographic sensitivity factors

for cartridge brasses C1100 and C1102;

experimental analysis of C1102 ....... 16

3. Comparison of sensitivity factors computed

with and without the use of an internal

standard ,„„.,, ...<>... . „ *, • 18

4 Comparison of experimentally determined

isotope ratios with true values « • • . «.. 1?

5. Sensitivity factors for elements in tin

using As for an internal standard with

an arbitrary sensitivity of 1.000 . . « „ 19

6„ Elemental sensitivity factors in tin

with Sb arbitrarily assigned a sensitivity

factor of 1.000 ..,„....<,. .. 20

IV
SPARK SOURCE MASS SPECTROGRAPH PROGRAM

July 1964 to June 1965

Paul J. Paulsen and Paul E. Branch

ABSTRACT

This report describes the activities of the spark

source mass spectrograph project for the period from

July 1964 through June 1965 . The subjects covered include instrument modifications which resulted in lower

backgrounds , modifications planned for the near future,

an outline of the procedure used in an analysis , a

description of data computation techniques, and experimental results obtained for some NBS standard reference

materials. Photographs of the instrument with its

modifications as well as photographs of the improved

mass spectrum are also included.

1. INTRODUCTION

The radiof requency spark source mass spectrograph has

been shown in the last few years to be a useful tool for the

analysis of solids for elements present down to the parts-perbillion level. Because the elemental sensitivity factors vary

only about one order of magnitude, semi-quantitative analysis

can be obtained without the use of standards. Reports indicate

that with standards ± 20$ accuracy is obtainable. A most important feature of this method of analysis is the absence of

inherent blind spots; in many matrices all elements are detectable at the parts-per-billion level. The blind spots that do

appear come from the matrix itself and in high purity samples

are generally limited to a few elements.

During the past year work with the spark source mass spectrograph in our laboratory has been in three general categories,

a. Semi-quantitative analysis of high purity materials

for elements present to the 100 ppb level.

b. Obtaining quantitative information on elemental sensitivities and instrument operation by studying standard samples.

c. Modifying the instrument in order to improve detection

capabilities

.

While the analysis of high purity materials could be considered to be primarily a service function, it in fact has

generated part of the problems studied in b and in one way or

another was the prime factor in all instrument modifications.
The quantitative studies using known samples are being

made in order to build a base of information for use in future

analysis. To the present, this work has resulted primarily in

the development of methods of sample and data handling., and

has indicated to what extent data obtained at high concentration can be used at lower concentrations. However , its most

important aspect has been in the general improvement in the

competence level of the technique.

All instrument modifications were made in order to improve

the detection limits, not by increasing instrument sensitivity,

but by removing interferences. The interferences arose from

lines at specific masses caused by instrument background gases

and source parts, general plate background, from poor vacuum,

and too broad matrix lines.

The instrument used for these studies is a Consolidated

Electrodynamics Corporation (CEC) No. 21-110 lot 4 1/2 as shown

in figures 1 and 2*, The 200-liter per second ion pump on the

electric sector (figure 2) was added two years ago to replace

the oil diffusion pump supplied by CEC. The other items labeled in the figure were added this last year and will be described later.

2. INSTRUMENT MODIFICATIONS

A. Additional Analyzer Pumping

Poor vacuum in the electric and magnetic sectors of the

instrument degrades sensitivity of analysis in two ways, both

being directly proportional to the pressure in the system.

Ions undergoing a change in charge upon collision with gas

molecules between the magnetic and electric sectors will

appear as discrete lines on the photographic plate masking

specific masses. Due to the low probability of collisions at

the vacuum level normally 'obtained, these lines are seen only

for the matrix element at levels corresponding to a few parts

per million.

Causing more interference are ions undergoing change of

charge on collision with gas molecules in the magnetic sector.

These ions cause a continuous background darkening of the

In order to specify the procedures and equipment modifications adequately, 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.
Figure 1, Spark source mass spectrograph.

photographic plate , which is darkest near the major peaks

,

namely the lines of plus one, two, three, etc., charged matrix

ions. Normal operation of the RF spark in the source, which

is separately pumped, causes pressures well into the 10-b torr

region which in turn significantly raises the pressure in the

electric and magnetic analyzer sections. To eliminate this

pressure rise in the electric and magnetic sections and the

resulting increase in background, a combination titanium

sublimation pump and ion pump was installed on the drift tube

connecting the source to the electric sector. The pumping

capacity of this unit is about 400 liters per second.
Figure 2. Rear view of instrument showing major vacuum

modification. A. New pumping port. B. Titanium sublimation chamber. C. 100-liter per

second ion pump. D. 200-liter per second ion

pump. E Liquid nitrogen cold finger.

No pressure rises are now detectable in the analyzer section

upon sparking This position and the pumping capacity were

selected in anticipation of the future addition of a pump on

the magnetic sector. See figure 2 and 5B in figure j5.

4
10 II

ELECTRIC

SECTOR

MAGNETIC

SECTOR

1. SAMPLE ELECTRODES

2. FIRST APERTURE

3. SECOND APERTURE

4. OBJECT SLIT

5. ELECTRIC SECTOR ENTRANCE SLIT

5A. 200 L/S ION PUMP

5B. NEW PUMPING PORT- 400 L/S

6. ELECTRIC SECTOR EXIT SLIT

7. MAGNET SHUNT

8. BEAM MONITOR ELECTRODES

9. ENERGY RESOLVING SLIT

10. PHOTOGRAPHIC PLATE MASK

11. FUTURE MAGNET PUMPING SYSTEM

Figure 3. Diagram showing position of major components

of mass spectrograph.

B„ Source Ion Gauge . Gases in the source cause background lines to appear

for 02; 0, N2 ; N, C,2> C, C02 ^ CO and hydrocarbons. In

general most of the unit masses from ~$2 on down have

interfering lines at the parts per million level

originating from source gases. In order to minimize gas*

background lines an ion gauge was mounted on the source

chamber to monitor source pressures so as to insure an

adequate vacuum before an analysis was attempted An

overnight pumping after sample loading gives source

pressures of 1 x 10'"' torr; with a six hour baking (overnight^ of the source region at 110° C 3 a pressure of 1 to 2

x 10~*o is obtained. However , even with baking ^ pressures

of midrange 10"*° are obtained upon first sparking of the

sample during an analysis.
C. Cold Finger . A liquid nitrogen cold finger was added to the source

housing (figure 2) in order to remove hydrocarbon lines

from the source background. The hydrocarbons originate

from the oil diffusion pump used to pump the source. If

liquid nitrogen is added soon after source pumping is

started (with pressures of low 10"-3 to high 10 ) pressure

drops of 5-to-10 fold are observed; if added to a well

pumped source (low 10~") the pressure drops less than 50^.

Without liquid nitrogen a well pumped source shows hydrocarbon lines equivalent to 1 ppm Fe in the iron region of

the spectrum. With liquid nitrogen in the source cold

finger the lines are removed to below 0.1 ppm Fe} our

present detection limits.

D. Tantalum Source Parts . Analysis of several materials having five-nines and

six-nines purity indicated the presence of iron, nickel

and chromium at levels too high to be credible. Since the

entire instrument and specifically the source parts are

made of stainless steel it was assumed that these lines

represented instrument background. Since lines on the

plate can only be formed for ions leaving the source with

the full accelerating voltage these lines must originate

from limited regions within the source.

In order to locate the source of background the most

suspect parts of the source were replaced stepwise with

parts fabricated from either aluminum or tantalum while

noting the apparent iron, chromium, and nickel content of

a high purity platinum sample. In this manner it was found

that the background was due to the sample holding Jaws,

the first aperture (No. 2 in figure 3) and the second

aperture (No. 3 in figure 3) of the source slit system.

To meet this problem these stainless steel parts were

replaced with tantalum parts. The instrument background

now- contains masses l8l (Ta+

), 182 (TalT1"), 197 (Ta0+

), which interferes with gold 197 at approximately the 1 ppm

level), and 213 (Ta0+2 ). This background causes little

difficulty in that tantalum is unlikely to be present in

most samples, and if suspected the sample may be rerun

using stainless steel parts. The stainless steel background appears to be removed from the spectra at our

present limits of detection. However, a few tenths parts

per million iron has been found in all high purity samples

run using the tantalum parts and it is not known whether

this represents true contaminants or some residual

instrument background.
Shown in

purity copper

f orementioned

steel parts,

lines show up

parts and are

Figure 4 are two equal exposures for a high

sample. The upper one was made using the

tantalum parts, the lower one with stainless

The iron, nickel, and chromium background

at more than 10 ppm with stainless steel

totally absent with tantalum parts.

t

58

Ni +i

56

Fe +I 52

Cr +I

tantalum

stainless

steel

Figure 4. Background lines with stainless steel

and tantalum source parts.

E„ Source Apertures . In most high purity materials a likely impurity is an

element of one unit higher and/or one unit lower Z number.

Thus finding one ppm of these impurities may involve

detecting a line only a few ma&s units away from the matrix

line which is a million times as intense. In this

situation high resolution and low background at the matrix

lines are of prime importance.

A comparison was made between the spectra for a

standard size second aperture (No. 3> figure 3)j which is

a rectangular opening, and one of half its length. The

shorter aperture resulted in narrower matrix lines for

equal exposures. Other experiments with combinations of

first and second aperture sizes resulted in the selection

of a first aperture of a 1/8-in. diameter hole (as compared

to 1/4-in, as supplied by CEC) and a second aperture 0,040

in. by 0.068 in, (as compared to 0.040 in. by O.I87 in, as

supplied by CEC), This combination reduces the average ion

current through the instrument by a factor of 2 to 3 and

thus longer times are required to make the exposures.

Figure 5 shows tantalum parts in the large and small sized

apertures. The upper disks are the first apertures and

the lower disks are the second apertures; the latter are

tantalum inserts fitting into the stainless steel "top hat"

shown on the right. (The inserts resulted from the

conversion from stainless steel to tantalum apertures as

previously discussed)

7
/'

Figure 5. Large and small tantalum first and second

apertures.

Figure 6 shows the plus-one platinum line of two

exposures of 1.00 x 10-° coulombs (1/10 the possible

maximum exposure) made on the same sample of 99+$ Pt.

The exposure labeled "small" used a 1/8-in. diameter first

aperture and a 0.068-in. long second aperture* The one

labeled "large" used a 1/4-in. first aperture and a O.I87-

in. long second aperture. The greatly improved line widths

A A A A A

small apertures

large apertures

Pt TaH

+

Ta+

Figure 6. Equivalent exposures of Pt with large

and small sized apertures.

8
from the small sized apertures are limited to major peaks

of the matrix material (Pt), with low concentration impurity

lines having essentially the same line width for both

aperture sizes. The matrix line widths increase with an

increase in exposure for both aperture sizes. However, ten

times as heavy an exposure is necessary for the small

aperture in order to obtain the same line width as with the

large aperture.

3. PLAJMEB INSTRUMENT MODIFICATIONS

Within the next year we plan to replace our present

15- kV ion accelerator with one capable of operating at 16,

20, and 24 kV. When operated at 24 kV the sensitivity of

detection for the instrument should be four times that

obtained at 15 'KV. This CEG conversion also includes a

new electric sector power supply and in addition requires

acquisition of a new source capable of handling 24 kV, At

the same time wider slits will be installed throughout the

instrument to give an increase in sensitivity of a factor

of three. This conversion will result in a loss of

resolution from our present 1 part in 2500 to 1 part in

2000. The combination of higher accelerating voltage and

wider slits should result in a 12-fold increase in detection

sensitivity. There will also be, however, an increase in

background from ions scattered by gas molecules in the

magnet as discussed previously. Additional pumping at the

magnet such as shown in figure 3> at No. 11 will be needed

to lower this background. The additional pumping will not

be added until after the effectiveness of the change in

accelerating voltage and slits widths has been evaluated.

In those areas of the mass range where our present

background is below the threshold of detection for the

plate, the increased background will have little if any

effect in reducing the 12-fold increase in sensitivity.

Where the background is presently detectable, the increased

background will partially but not completely cancel the

increased sensitivity.
4, PROCEDURE FOR SAMPLE ANALYSIS

A. Sample Types , The R. F. spark source should be capable of running

any type solid with a vapor pressure less than 1 x 10""7

torr at room temperature. Our actual experience has been

with solid conductors , and with insulators using a

conducting, counter electrode. Present plans call for a

study in the future of conducting and insulating powders

pelletized with ultra pure carbon powder.

B. S amp 1 e Prep arat i on . Preparation depends on sample size and the type of

information desired from the analysis. Identification of

the major components in micron sized particles can be

obtained by mounting them on the tips of ultra pure

electrodes and sparking. However, surface contamination

on the electrodes must be removed prior to mounting.

The ideal sample consists of two electrodes 1/2 in.

long with a diameter between 0.020 and 0.050 in. Larger

diameters up to 1/8 in. can be handled, but efficiency of

ion collection drops off at larger sizes due to

projections of the sample lying between the point where

sparking occurs and the source slit. All samples must be

etched just before loading into the instrument in order

to remove contaminations introduced in machining and

handling.

An illustration of the contamination problem was a

tantalum sample cut using a spark erosion machine and

then vapor degr eased with trichloroethylene. Despite the

use of new oil and the cleaning of the machine just before

this job, the mass spectrum showed over a dozen elements

above the 10-ppm level as well as hydrocarbons. This list

of elements could well have been a list of materials pre- viously cut with the machine. The tantalum sample was then

removed from the instrument, etched for approximately 30

seconds in a 50-50 HF and HN0, mixture, and rinsed in

distilled water. Upon rerunning the sample, all the

elements previously seen were not detected at the 1-ppm

level,

C. Running of Sample

Since increases in R.F. pulse lengths, pulse repetition rates, and voltages will all increase the power

to the sample and hence its temperature, it was decided to

maintain all of these factors constant during an analysis

10
in order to avoid the change in instrument bias which might

result from such temperature changes. The gap between the

sample electrodes is maintained at maximum possible

separation while sparking since it has been shown that, for

a constant total exposure, intensity of the plus one ion

(and the plus two) changes markedly with gap width, and the

ratio of the one to two is more reproducible with a wide

gap. The surface of the sample is presparked for an

exposure of 1 x 10 coulomb in order to condition the

electrodes and to remove surface contamination. A

comparison of this exposure to one of equal intensity

selected from the set of succeeding exposures identifies

the surface contaminants. Experience indicates that a

thorough prespark will reduce surface contaminants only 10

to 100 fold. For analysis of alloys where duplicate

exposures are made at several exposure levels, exposures

are alternated between the high and low levels.

D » Plate Development and Handling . Plates are presently being developed using Ilford

caustic hydroquinone for 2 and 1/2 minutes at 68 P.

Ilford ID-19 and Kodak D-19 have also been used However,

no systematic studies on the optimum developer and

conditions of development have been undertaken .or are

anticipated.

Ilford Q-2 photographic plates are ordered only during

the winter months and are stored at 0°F in order to prevent

heat fogging during shipment and storage of the plates. It

is necessary, however, to allow the plates to warm up to

room temperature before loading and pumping them. It was

recently discovered that a longstanding, elusive but

characteristic pattern of plate fogging has been caused by

loading cold plates into the vacuum system. The fogging

arises from the fast removal of condensed water from the

cold plate emulsion upon pumping.

E . Plate Measurement and Data Calculation . For measuring peak absorption of line images the

microphotometer is adjusted for Ofo absorption at the

clearest portion of the plate and 100$ absorption for no

light. Plate calibration curves can be obtained with

methods analogous to those used in emission spectroscopy.

However, there are two important differences between

photometry of plates used in mass spectroscopy and those

generally used in emission spectroscopy. First, the

maximum darkening of the mass spectrographic plate gives

approximately 90% absorption while the emission

spectrographic plate has a maximum darkening of essentially

11
100$ absorption. Thus a plot of the Seidel function values

for $ absorption vs, log exposure, which gives a straight

line calibration curve for emission spectroscopy, will

give a line which curves asymptotic-ally to the Seidel value

corresponding to 90$ absorption for a mass spectrographic

plate. Secondly the maximum line darkening on a mass

spectrographic plate varies from 80 to 9°$ between high and

low mass, with the lower mass ions giving the darker lines.

Thus the Seidel plots for high and low mass ions will

curve off to different values at the 100$ absorption end

of the plot. Under these conditions no single calibration

curve will serve for all lines on the plate.

If the percent absorption values obtained from the

microphotometer for various masses are multiplied by a

"stretch" factor of 100 divided by percent absorption at

maximum darkening for that mass, one obtains percent

absorption values from zero to 100 which will give a

straight line calibration curve fitting all masses on a

plate* At present, calibration curves are obtained using

log intensity vs. probability function values of the

stretched percent absorption. The "curve" is assumed to

be a straight line and the slope of this line is calculated

from the percent absorption values and the known ratio of

isotopes for an element. Normally data for the slope are

pooled for at least three different elements, each with a

half dozen pairs of lines whose absorption values range

from 10 to 90$. Because of the high scatter in the data

from which comparisons must be made it has &ot been

determined whether the probability function presently

used or the Seidel function from emission spectroscopy

will give the closest fit to a straight line calibration

curve.

Once the slope of the calibration curve is found this

information plus peak heights, peak backgrounds, and peak

stretch values are fed by a Teletype unit into a computer

in which the following operations are performed:

1. Calculates peak intensity and peak background

values from $ absorption, and subtracts to find net

intensity,

2. Averages net intensity values for the duplicate

exposures.

3* Calculates standard deviations (cr),

4. Rejects data differing 2cr from average and recalculates a new average intensity.

12
5. Calculates the ratio of the net Intensity of each

line measured to an "internal standard" line from the same

exposure.

6. Repeats steps 2, 3, and 4 for ratios calculated in

.5.

For an average plate involving the analysis of a

dozen elements in an alloy there are approximately 2^0

peaks used to compute the results. The total time

necessary with the computer calculation of this amount of

data is 3 hours for punching tapes,, 3 hours of Teletype

time , and under 100 seconds of actual computer time

Twenty-eight hundred separate steps of addition,

multiplication, squaring, etc., would be necessary to make

the same calculations by hand. The use of the computer

results in a saving of approximately two man days per plate,

but more important is the drastic reduction of number of

errors made in the calculations.

The average peak intensities and/or ratios of

intensities thus calculated can be used with the isotopic

abundances of the mass line measured and the relative

sensitivity factors for each element to calculate the

concentration of each element in the sample. When a

standard sample is run, as is the case for most of the data

contained in this report, the certified elemental

concentrations are combined with the forementioned data to

calculate relative elemental sensitivity factors

The use of an internal standard has been adopted in

these determinations of sensitivity factors in order to

correct for some of the intensity fluctuations which are

common to all lines. This includes fluctuations caused

by errors in the measurement of total exposure, changes in

the ratio of plus one to plus two ions, and changes in

peak width. The effectiveness of the internal standard

method is shown by the lower percent standard deviation*

in the ratio of peak intensities, as compared to the percent

standard deviation in the peak intensities for a given

set of data.

Up to the present all data have been based upon the

maximum intensity for the plus one charge state of each

element, A more reliable method of analysis would be to

Percent standard and deviation = coefficient of variation

= — X 100, where a is the standard deviation and x is the

x

3 average of the results used to determine a. 13
measure the total number of ions for each element which

hit the photographic plate. To do this would require

the summation of the peak areas over all the charge states

of an element. Summation of all charge states is

necessary because the distribution of ions among the charge

states is dependent upon non-reproducible sparking

conditions in the source. Peak areas must be measured

instead of maximum intensities since peak widths and

shapes are not constant. Peak shapes are irregular at

low percent absorption and in regions of the plate where

perfect focus is unobtainable. Peak widths change with

source operating conditions and position on the

photographic plate.

The extension of our present technique by measuring

the percent absorption at 10 uniformly spaced positions

across the peak, and a summation of the calculated

intensities to give a peak area would not be of practical

value because of the overwhelming increase in the number

of calculations necessary per plate. In the future 3 data

will be computed from the product of maximum peak

intensity times the peak width at half intensity. This

product is a good approximation to peak area, but it is

sensitive to irregularities in the peak shapes.

5. EXPERIMENTAL RESULTS

A. Oxygen Isotope Ratios in A1P 0^.

The oxygen isotope ratios in a sample of A^O-x in rod

•form were measured in order to determine the feasibility

of using the spark source mass spectrograph to analyze

for oxygen 18 in a diffusion-exchange experiment with

AI2O-2 and enriched oxygen. By the use of a counterelectrode of platinum and a short piece of A^O^ it was

possible to obtain a satisfactory ion beam from this

insulator. The isotopes of platinum were used to determine

the plate calibration curve by the method described

previously.

Table 1 shows the results for oxygen isotope ratios

as well as some platinum ratios which were included to

indicate the accuracy of the calibration curve.

It was concluded that the errors in the oxygen ratio

determinations by this method were too large to be of

practical value for the diffusion-exchange experiments.

The errors are believed to have been caused by differences

in peak widths and background lines at masses 17 and 18

16^+ , „ 16~+ 0H and Ho . 14
Table 1„ Isotopic ratios of oxygen in AlpCU

and platinum ratios. ^

Experimental True Error

value value

Oxygen 16/17 2010 ±20$ 2667 b

25f*

Oxygen l6/l8 299 ±17^ 488 38^

Oxygen 17/18 0.151 + 7 A<?o O.183 170

Platinum 196/198 3.65 ±11$ 3.51 4 o 0$

Platinum 195/198 5.03 ±12$ 4.69 7.3$

Platinum 194/I96 1.35 ± 6.7^ 1*30 2 3^

, Difference expressed in percent

Percent standard deviation.

B« Cartridge Brass.

Analyzed samples have been run primarily to determine

if sensitivity factors determined at high concentration

levels can be applied at low levels. A secondary purpose

is to have sensitivity factors available for various

matrices for semiquantitative analysis , and to see if the

sensitivity factor of a given element changes with matrix.

The sensitivity factors reported are per unit weight (not

atomic) and have been determined using peak heights but

not peak widths. These are preliminary results from

sparking a single loading of each sample. The final

results will be based on three sets of duplicate analyses , each with new sample electrodes, for all the standards in

this series, C1100, CHOI, C1102.

In Table 2 are shown the sensitivity factors of

samples C1100 and C1102 determined for each element using

an internal standard of lead (sensitivity factor of lead - 1.000). In addition, the data from C1102 were combined

with the sensitivity factors determined for C1100 to

calculate an analysis of C1102* The NBS certified analysis

of C1102 is included for comparison. The inherent

difficulty in using one element for an internal standard

is that erroneous results for it in either the standard

sample or the "unknown" sample will cause a constant error

for all the elements in the "unknown" sample. This effect

is probably the cause of the consistently low results

determined for C1102.

15
Table 2. Mass spectrographic sensitivity factors

for NBS cartridge brasses C1100 and C1102j

experimental analysis of C1102.

Sensitivity factors

C1100

Pb 1.00

Al 40

P 27

Fe 3.08

Mn o c 6o

Ni 1.98

As 5.0

Ag 1.09

Cd 4.5

Sn 1.16

Sb 2.1

Te 2.4

Bi 0.90

C1102

l o 000

(11)?

2.2

0.37

1.4

3.7

1.01

3.15

1.2

1.8

0.8'D

Analysis of C1102

Experimental

value

NBS certified

value

Weight percent Weight percent

0.00019

.0078

. 0028

.0037

.0029

.00093

.0031

.0063

O 0045

. 00047

0.0007

.011

O 0045

o 005

.004

.0010

.0045

«006

o005

.0005

C. Tin NBS 431 to 435 . During the analysis of a high purity tin sample it

became necessary to determine the sensitivity factors of

several elements found in the tin in order to give

qualitative data. The NBS tin standards 431 through 435

contained the elements of interest. When sensitivity

factors for both 431 and 435 were obtained^ conflicting

results showed up for copper , one of the elements of

interest. It was decided therefore to determine the

sensitivity factors for as many elements as practical in

the whole series to see if other elements acted in the

same way. In general when going from 431 to 435 there is

a 20-fold decrease in elemental concentrations. The data

represents multiple exposures on a single plate from a single pair of sample electrodes. During the period when

this data was collected considerable trouble was

encountered with uneven fogging of the plates as discussed

previously.

Table 3 lists the percent standard deviation of peak

intensities and the percent standard deviation in the ratio

of peak intensity to the intensity of the arsenic peak on

the same exposure. The lower deviations for the ratio

values indicate the effectiveness of the "internal

standard" in moderating intensity fluctuations. The

16
Table 3. Comparison of sensitivity factors computed with

and without the use of an internal standard.

Precision Calculat;ed

of measur ements sensitivity factors

Intensity Ratio From ratio From intensity

Cu 63 20$a 8.6^a 2.23 2.2}

Cu 65 21 7.2 2 21 2.23

Zn 66 52 26 20,1 20.2

Zn 67 23 16 20.5 20.5

Zn 68 31 26 19.3 19.3

As 75 17 — 1.000 1.000

Sb 121 20 6.3 0.365 0.367

Sb 123 20 12 .377 .377

Pb 207 20 14 .594 .593

Pb 208 21 10 .601 O 6o4

Bi 209 26 13 .876 .888

aPercent standard deviation.

sensitivity factors _, however 3 indicate that it makes

little difference whether average intensities or peak

ratios are used in the calculation.

Table 4 lists the

same data used for tab

with the true value,

calibration curve fits

should represent only

plate and errors in re

indicate that the phot

the accuracy of analys

isotope ratios determined from the

le 3 for various elements together

The differences indicate how well the

the plate. The standard deviations

the nonunif ormity in the photographic

ading the plate absorption. The data

ographic plate will ultimately limit

is to a 3 to 5 percent error.

Table 4. Comparison of experimentally deter:

isotope ratios with true values

True Experimental

Isotopes ratio

2.235

ratio

Cu 63/65 2.249 ± 4.6^

Zn 66/68 1.498 1.554 ± 2.3

Zn 67/68 0.2213 0,2131* 2.1

Cd 110/111 .9718 .9844* 3.8

Sb 121/123 1.339 1.309 ± 9o0

Pb 207/208 0.4321 0.4258* 7.6

Percent standard deviation.

17
Listed in Table 5 are all the sensitivity factors

determined for the series 4j51 through 435. Only on number

4^1 was a duplicate determination made. Arsenic , the

arbitrarily chosen internal standard, has been assigned a

sensitivity factor of 1.000 for all samples. Copper has a

sensitivity factor which increases with a decrease in

concentration (431 to 435) while the sensitivity of zinc

decreases with a decrease in concentration. All other

elements show no trends with a change in concentration.

Excluding copper and zinc the maximum deviation of the

sensitivity factors from the average is less than +45 and

-44 percent.

Table 5. Sensitivity factors for elements in tin

using As for an internal standard with

an arbitrary sensitivity of 1.000,

Cu Zn As Cd Sb Eb Bi Ag

431 A 1.81 21,,1 1.,000 3,56 0,290 0.388 0.454

4^1 B 1.09 16,,7 1<,000 2.38 .214 .294 .450 0.348

Average 1.45 18,.9 1,,000 2.97 .253 .341 .452 .348

432 2.21 24,.5 1,,000 4.77 .465 .726 .984 ,657

433 2.27 19, 3 1,,000 4.60 371 .584 ,847 .599

4^4 3.91 11, 5 1<,000 6.74 .471 .804 1.10 .661

435 5.37 5,,02 1,

1,

,000

000

4.23

4.66

,426

.391

.463

.584

.636

.804 —

Average ,566

Maximum deviation +45$ +20$ +38$ +37$ +17$

from the average -36 -36 -41 -44 -39

Since the choice of arsenic as the internal standard

was completely arbitrary and since it was also noted that

the sensitivity of antimony followed the changes in the other

elements 3 all the data in table 5 were recalculated with

respect to antimony. This was done by simply dividing the

sensitivity factors in each row by the value for antimony.

The results of this conversion are shown in Table 6.

Copper and zinc still show the same trends, but now the

maximum deviations from the average sensitivity factors are

less than 25$, if only one piece of arsenic data is omitted.

18
Table 6. Elemental sensitivity factors in tin

with Sb arbitrarily assigned a sensitivity factor of 1.000.

Cu Zn As Cd Sb Pb Bi Ag

451 A 6.23 72.7 3.45 12.3 1.000 1.18 lo56

4^1 B 5.09 78.0 4.67 11.1 1.000 1*37 2.10 1.63

Average 5-66 75.3 4.06 Hc7 l o 000 1.27 1.83 1.63

4;52 4.75 52.7 2.15 10.2 1.000 1.56 2.04 1.41

433 6.12 52.0 2.695 12.4 1.000 1.57 2 28 l 6l

4;34 8.30 24.4 2.12 14 C 3 1.000 1.71 2o33 1.40

+35 12.6 11.8 2.35 9.96 l o 000 1.09 1.49 —

Average 2.67 11.7 1.000 1.44 1.99 1.51

Maximum deviat ion +52$ +22$ +19$ +17$ +8fo

from the average -21 -15 -24 -25 -7*3

19


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