Mass Spectrometry in Inorganic Chemistry

10 Automated Data Acquisition and Treatment in Inorganic Mass Spectroscopy R O B E R T J . LOYD and

FRED

E. STAFFORD

Downloaded by CORNELL UNIV on May 17, 2017 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch010

Department of Chemistry and the Materials Research Center, Northwestern University, Evanston, Ill.

Apparatus and

for

handling

systems

for

various are

rapid

mass spectrometry reduction

data

bility,

The

and

data

reported.

throughput,

less stringent and/or

in terms of their variety

of

as in high requirements.

precision,

include resolution

effluents,

the quality

possibly

acquisition

These

time, and errors are greatly

ning time is shortened, increased

of digital

and

of gas chromatograph

as for systems with dling,

aspects

reviewed

as

well

Data

han-

reduced;

run-

of the results

detail,

rapid

informative

is

availa-

presentations.

c a p a c i t y of a mass spectrometer to p r o d u c e i n f o r m a t i o n is f a r greater t h a n that of a n i n d i v i d u a l to receive or r e d u c e i t . T h e n e e d

f o r m o r e d e t a i l e d a n d precise results d e m a n d s that this c a p a c i t y b e u s e d . T h e c a p a c i t y for r a p i d d a t a o u t p u t m u s t b e u s e d w h e n s a m p l e size a n d corrosiveness l i m i t the d u r a t i o n of the e x p e r i m e n t .

R a p i d r e d u c t i o n of

d a t a is p a r t i c u l a r l y i m p o r t a n t i n i n o r g a n i c w o r k w h e r e l o n g s a m p l e p r e p a r a t i o n a n d e x p e r i m e n t a l p r o c e d u r e s are i n v o l v e d — t h e results m u s t b e a v a i l a b l e d u r i n g t h e r u n i n o r d e r that unforeseen p r o b l e m s b e i d e n t i fied a n d r e s o l v e d before the e x p e r i m e n t is t e r m i n a t e d . F o r these reasons a u t o m a t e d d a t a h a n d l i n g t e c h n i q u e s , i n c l u d i n g d i r e c t d i g i t a l a c q u i s i t i o n , c o m p u t e r treatment of d a t a , a n d o n - l i n e c o m p u t e r c o n t r o l of the mass spectrometer are e s p e c i a l l y a t t r a c t i v e . S i n c e F o r t r a n p r o c e d u r e s for c o m p u t a t i o n are e s t a b l i s h e d a n d r e a d i l y accessible, t h e l i m i t i n g step is often the a c q u i s i t i o n of i n f o r m a t i o n d i r e c t l y i n c o m p u t e r c o m p a t i b l e f o r m . T h i s w i l l b e the subject of the present p a p e r . Techniques T h e t e c h n i q u e s c a n b e d i v i d e d into t w o categories—those for r a p i d a c c u m u l a t i o n of l a r g e v o l u m e s of

i n f o r m a t i o n , as i n h i g h r e s o l u t i o n

127

Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

128

MASS

(m/Am

~10

4

S P E C T R O M E T R Y

I N INORGANIC

C H E M I S T R Y

— 10 ) analyses, e s p e c i a l l y o f c h r o m a t o g r a p h effluents, a n d r>

those for l o w flow rates o f i n f o r m a t i o n . H i g h Data Volume Techniques. R a p i d d a t a a c c u m u l a t i o n a n d h a n d l i n g techniques are receiving considerable attention from the various mass spectrometer m a n u f a c t u r e r s , e s p e c i a l l y f o r h i g h r e s o l u t i o n o r g a n i c applications.

F o r t h e spectrometer,

spectra w i t h r e s o l u t i o n o f m/Am

~ 1 0 * s h o w t h a t the o u t p u t o f the secondary electron m u l t i p l i e r c a n b e r e c o r d e d r a p i d l y i n a n a l o g f o r m d i r e c t l y o n m a g n e t i c tape ( 1 3 ) . scan rates are fast e n o u g h t o b e usable f o r gas c h r o m a t o g r a p h

The

effluent

analysis. E q u i p m e n t m u s t b e a v a i l a b l e for subsequent c o n v e r s i o n o f t h e


a n a l o g tape t o c o m p u t e r language.

TO X AXIS OF X-Y RECORDER, COMPUTER,etc..

RANGE

/

1.35 V

R

f

R ZERO

SLI DEW I RE/ SHAFT

Figure 1. Retransmitting slidewire circuit used to encode shaft positions. Breaking connection 1-2 and connecting 1-3 may give a more convenient zeroing arrangement T h e mass s p e c t r o g r a p h offers the p o s s i b i l i t y of i n t e g r a t i n g a l l o f t h e i o n intensities s i m u l t a n e o u s l y o n the p l a t e a n d o f t r a n s l a t i n g the p l a t e p a r a l l e l t o the slit t o o b t a i n a t i m e - r e s o l v e d mass s p e c t r u m . T h e d a t a h a n d l i n g p r o b l e m becomes one o f c a l i b r a t i n g a n d r a p i d l y d i g i t i z i n g the vast a m o u n t o f i n f o r m a t i o n ( a b o u t 10° readings o f o p t i c a l d e n s i t y p e r s p e c t r u m p r o d u c e d b y the m i c r o d e n s i t o m e t e r u s e d t o r e a d the p l a t e s ) , l o c a t i n g t h e peaks, i d e n t i f y i n g o v e r l a p p e d ( b l e n d e d ) peaks, a n d c o m p u t i n g t h e masses to o n e p a r t i n a b o u t 10 . S u b s t a n t i a l progress has b e e n r e p o r t e d i n a u t o 5

m a t i n g microdensitometers, i n w r i t i n g computer programs, a n d i n devisi n g p a r t i c u l a r l y i n f o r m a t i v e w a y s t o present the i n f o r m a t i o n ( J , 2, 3 , 5, 7, 8, 11, 13, 16,. 18, 20). T h e s u b s t a n t i a l c a p i t a l i n v e s t m e n t i n v o l v e d l i m i t s the a v a i l a b i l i t y o f s u c h f a c i l i t i e s . Lower Volume Techniques. I n m a n y other experiments, the a v a i l a b l e i o n intensities are so s m a l l that measurements m u s t b e m a d e o v e r l o n g e r


10.

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Data

129

Acquisition

p e r i o d s of t i m e to o b t a i n u s a b l e signal-to-noise r a t i o . h u m a n a c q u i s i t i o n a n d treatment, this i n f o r m a t i o n

W h i l e fast f o r

flow

still may

be

h a n d l e d easily b y a p p a r a t u s that is b e c o m i n g r e a d i l y a v a i l a b l e to e v e r y laboratory. Shaft Encoding: Ionization Efficiency Curves. V a r i o u s a p p l i c a t i o n s r e q u i r e e n c o d i n g of a shaft p o s i t i o n . W h i l e d i g i t a l shaft encoders are a v a i l a b l e , t h e y are u s u a l l y p r o h i b i t i v e i n p r i c e . A s i m p l e s o l u t i o n w h i c h n e e d n o t sacrifice a c c u r a c y is to use a r e t r a n s m i t t i n g s l i d e w i r e a n d t h e c i r c u i t s h o w n i n F i g u r e 1. T h i s a p p a r a t u s w i l l generate a n a n a l o g s i g n a l p r o p o r t i o n a l to t h e


p o s i t i o n of a n y c o n t r o l shaft. S u c h a c i r c u i t has b e e n u s e d i n o u r l a b o r a t o r y f o r the past t w o years to r e c o r d i o n i z a t i o n efficiency curves.

The

r a n g e a n d zero controls w e r e selected to p e r m i t a n y 10-volt segment of i o n i z i n g e l e c t r o n energy to give f u l l scale deflection o n the X - a x i s of a 10 m i l l i v o l t X - Y recorder.

T h e t i m e constant of the entire c i r c u i t , c o m -

p r i s i n g the electron voltage r e g u l a t o r , detector, a n d r e c o r d e r w a s l a r g e enough that a small t i m i n g motor ( A . W . H a y d o n C o . , W a t e r b u r y , C o n n . , 1 / 6 o r 1 / 3 0 r . p . m . ) w a s u s e d to generate a r e p r o d u c i b l e sweep.

With

m o d e r a t e l y intense i o n currents, a p p e a r a n c e potentials c o u l d b e

repro-

d u c e d to 0.04 e. v. F o r a w e a k i o n c u r r e n t of a b o u t 40 ions p e r s e c o n d f u l l scale, a r e c o r d i n g is s h o w n i n F i g u r e 2. It w a s p r o d u c e d i n a b o u t 20 m i n u t e s of easy w o r k c o m p a r e d w i t h a h a r d h o u r for m a n u a l processing. A

buffer m e m o r y ,

a time averaging computer

( t h a t of N o r t h e r n

Scientific C o r p . , M a d i s o n , W i s e , is p a r t i c u l a r l y s u i t a b l e because of f a c i l e m e m o r y a d d r e s s i n g ) , or a s m a l l c o n t r o l c o m p u t e r m i g h t b e s u b s t i t u t e d f o r t h e X - Y recorder.

Such units can provide in-place time averaging

as w e l l as i n p u t for a large, c e n t r a l c o m p u t e r .

A n on-line computer for

a u t o m a t e d d e t e r m i n a t i o n of a p p e a r a n c e potentials also is r e p o r t e d

(12).

Direct Recording of Low Resolution Spectra. A p p a r a t u s is a v a i l a b l e commercially

from

Non

Linear

Systems

(Del

Mar, Calif.)

(19).

D u r i n g a l o w r e s o l u t i o n scan, b o t h the v a r y i n g i o n - a c c e l e r a t i n g voltage a n d the i o n i n t e n s i t y are d i g i t i z e d a n d r e c o r d e d . calculated b y computer. m/e

250 is r e p o r t e d

(10).

T h e mass s p e c t r u m is

M a s s a c c u r a c y of better t h a n 1 / 4

a.m.u. at

F o r magnetic scanning instruments, both

N u c l i d e C o r p . (State C o l l e g e , P a . ) a n d V a r i a n Associates C a l i f . ) h a v e a n n o u n c e d n e w , h i g h a c c u r a c y gaussmeters.

(Palo Alto,

O f additional

interest is u s i n g t w o H a l l effect probes i n series s u c h t h a t a s i g n a l p r o p o r t i o n a l to the m a g n e t i c field s q u a r e d , a n d l i n e a r w i t h mass is p r o d u c e d . Averaging and Digitization of Ion Currents. I n m a n y aspects of the mass spectrometry of h i g h t e m p e r a t u r e systems or of r e a c t i v e i n t e r m e d i ates, the i o n intensities are s u c h that the c u r r e n t at e a c h p e a k m u s t b e a v e r a g e d o v e r a p e r i o d of t i m e d u r i n g w h i c h the spectrometer


settings

130

MASS

m u s t r e m a i n constant.


I N

INORGANIC

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A n integrating digital voltmeter ( D V M )

(Vidar

C o r p . , M o u n t a i n v i e w , C a l i f . , M o d e l 500) c o u l d not b e u s e d to measure the electrometer

o u t p u t d i r e c t l y because the i n t e g r a t i o n p e r i o d of

20

msec, is too short f o r the s m a l l i o n currents a v a i l a b l e . C o n s e q u e n t l y t h e system of F i g u r e 3 w a s b u i l t . T h e integrator c i r c u i t is s h o w n i n F i g u r e 4; u s i n g the h i g h q u a l i t y o p e r a t i o n a l a m p l i f i e r makes it easy to construct.


12r-

10

111

12

13

Nominal e l e c t r o n e n e r g y , Courtesy S. M .

14 e.v. Schildcrout

Figure 2. Automatically recorded ionization efficiency curve for the metastable process Ni(CO) ~* NiCO + CO: ion intensity vs. ionizing electron energy in e.v. Scan rate, 1 /3 volt per minute; maximum ion intensity shown corresponds to about 40 ions per second. The graininess of the low resistance retransmitting slide wire needed to match the recorder available causes the curve to look as if it is composed of a series of vertical lines +

2

+


10.

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Data

Acquisition

131

T h e p r e c i s i o n t i m e r is a preset counter set to c o u n t the 60-herz l i n e f r e q u e n c y for 1/4, 1 / 2 , 1, o r 2 m i n u t e s . S e v e r a l advantages accrue f r o m this apparatus. T h e u n i f o r m i t y o f r e c o r d i n g the intensities a n d o f t i m e a v e r a g i n g are s i g n i f i c a n t l y i m p r o v e d over a v e r a g i n g b y eye.

D a t a r e d u c t i o n is less tedious, a n d t h e t i m e

r e q u i r e d is r e d u c e d b y about 2 5 % .


Multiplier Electrometer

Grid Electrometer

Integrator

Integrator

2 Pen Recorder

Τ imer

A

Digital Voltmeter Figure 3. Direct digital data output system. The timer is a preset counter that activates the relays shown in Figure 4. Line frequency is counted M a n u a l t r a n s c r i p t i o n o f the d a t a , w i t h its consequent errors, w a s e l i m i n a t e d b y e n c o d i n g

delays a n d

t h e v a r i o u s spectrometer

controls,

a u t o m a t i c a l l y s c a n n i n g the v a r i o u s d a t a stations, a n d w r i t i n g t h e i n f o r m a t i o n w i t h a 12-line p a r a l l e l e n t r y tape perforator.

T h e mechanics of

the C o m p u t i n g C e n t e r n o w m a k e i t d e s i r a b l e t o use o n e o f the i n c r e m e n t a l m a g n e t i c recorders that are b e c o m i n g a v a i l a b l e at l o w cost. T h e system comprises t h e f o l l o w i n g : ( 1 ) D i g i t a l e n c o d i n g o f s u c h i d e n t i f i c a t i o n m a t e r i a l as mass o r date. ( 2 ) D i g i t a l e n c o d i n g o f s u c h i n s t r u m e n t settings as i n p u t resistor, electrometer ranges, a n d emission c u r r e n t as w e l l as t i m e . ( 3 ) A n a l o g - t o - d i g i t a l c o n v e r s i o n of t h e r m o c o u p l e readings, elec trometer o u t p u t , shaft e n c o d e r o u t p u t . ( 4 ) S c a n n i n g a n d " w r i t i n g " the p r e c e d i n g sources o f i n f o r m a t i o n w i t h the d e s i r e d a m o u t of operator i n t e r v e n t i o n . T h e i d e n t i f i c a t i o n m a t e r i a l is entered d i r e c t l y onto the tape b y means of a selector s w i t c h a n d 12 b a n k s o f f o u r - p o l e w a f e r switches p r o v i d i n g b i n a r y c o d e d d e c i m a l ( B C D ) output.

I n s t r u m e n t settings also are e n

c o d e d s i m p l y b y c o u p l i n g t h e a p p r o p r i a t e c o n t r o l shafts t o f o u r - p o l e w a f e r switches that p r o d u c e signals c o r r e s p o n d i n g to 0 t h r o u g h 9 i n B C D


132

MASS

output.


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A n a l o g - t o - d i g i t a l c o n v e r s i o n i n a l l cases is a c c o m p l i s h e d

with

the D V M . T h e heart of the system is t h e scanner w h i c h presents e a c h of t h e a n a l o g signals to the D V M i n u n v a r y i n g sequence.

A possible

i n v o l v i n g a c o m m e r c i a l scanner, a n d a n I B M ( P o u g h k e e p s i e , c a r d p u n c h is d e s c r i b e d elsewhere

(4).

system Ν.

Y.)

T h e present u n i t w a s b u i l t t o

h a v e f a c i l e e n t r y of s p e c i a l c o n t r o l i n f o r m a t i o n ( E r r o r , E n d of D a t a Subset, etc. ) a n d a series of i n t e r l o c k s to m i n i m i z e operator error.

The

o p e r a t i o n of this u n i t is s h o w n i n T a b l e I. T h e scanner is a c t i v a t e d b y C o n t r o l a. T h i s causes a s p e c i a l p u n c h o n the tape w h i c h the c o m p u t e r is p r o g r a m m e d to i n t e r p r e t as "start n e w subset of d a t a . " T h r e e s u c h Downloaded by CORNELL UNIV on May 17, 2017 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch010

p u n c h e s are c o d e d to m e a n "start n e w p a g e or n e w set of d a t a , " a n d five s u c h p u n c h e s m e a n " e n d of r u n . " P r e s s i n g this b u t t o n also readies the scanner to start C y c l e I. T h e first step of the c y c l e is to r e a d "preset" i n f o r m a t i o n set m a n u a l l y o n the 12 w a f e r switches. S u c h i n f o r m a t i o n i n c l u d e s the i o n mass, e l e c t r o n energy, etc.

A selector s w i t c h o n the perforator chooses

between

the "preset" or the " e x t e r n a l " i n f o r m a t i o n a n d is i n t e r l o c k e d so that step I A c a n b e p e r f o r m e d o n l y i f it is i n the correct p o s i t i o n . S i m i l a r l y , I B a n d I C are i n t e r l o c k e d w i t h the " e x t e r n a l " p o s i t i o n . I n the " e x t e r n a l " p o s i t i o n , three channels accept o u t p u t f r o m a d i g i t a l c l o c k ; f o u r m o r e channels a c c e p t i n f o r m a t i o n f r o m the encoders f o r t h e secondary electron m u l t i p l i e r o u t p u t resistance, m u l t i p l i e r electrometer range setting, " g r i d " ( u n m u l t i p l i e d i o n c u r r e n t ) electrometer r a n g e set t i n g , a n d i o n i z i n g electron emission regulator setting. A n e i g h t h c h a n n e l accepts the d i g i t a l v o l t m e t e r ( D V M ) range, a n d f o u r m o r e a c c e p t t h e D V M r e a d i n g itself. T h e D V M p o l a r i t y s i g n a l is not u s e d . I n p o s i t i o n I B , the D V M reads either a t h e r m o c o u p l e a t t a c h e d to a K n u d s e n c e l l , a n a u t o m a t i c o p t i c a l p y r o m e t e r o u t p u t if a v a i l a b l e , or a shaft e n c o d e r ( F i g u r e 1 ) a t t a c h e d to the s l i d e w i r e of a m a n u a l o p t i c a l pyrometer. T h e scanner is a d v a n c e d to p o s i t i o n I C . T h e operator t h e n measures the i o n c u r r e n t u s i n g the integrators. If v i s u a l o b s e r v a t i o n of the s t r i p c h a r t r e c o r d i n g indicates that the measurement is satisfactory, C o n t r o l c ( p e r f o r m C y c l e I I ) is a c t i v a t e d a n d the t w o integrator outputs r e c o r d e d . T h i s c y c l e m a y b e r e p e a t e d as m a n y times as d e s i r e d . S h o u l d a n error be m a d e , C o n t r o l d causes a p u n c h w h i c h is p r o g r a m m e d to m a k e the c o m p u t e r d i s r e g a r d the p r e c e d i n g t w o frames of i n f o r m a t i o n c o r r e s p o n d i n g to the p r e c e d i n g steps I I . 1 a n d II.2. W h e n the a p p r o p r i a t e n u m b e r of readings has b e e n t a k e n , C o n t r o l a is p u s h e d one, three, or five times, a n d the scanner is set to a c c e p t i n f o r m a t i o n for the next mass peak, the next set of peaks, or to e n d the r u n respectively.


10.

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A N D S T A F F O R D

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Acquisition

133

|] Reset OPEN

INTEGRATOR

{Γ

»

- ^ K Z >

CLOSED 100

Input CLOSED jj

OPEN

L,

INPUT

Φ

Π

3

ι

—

OUTPUT


4.64M

Figure 4. Integrator circuit simply constructed using a high qual ity operational amplifier. This circuit affords more precision than the pen recorder. The operational amplifier is a Philbrick Re searches, Inc. (Dedham, Mass.), Model SP-2A; a Keithley Instru ments, Inc. (Clevefond, Ohio), Model 300 also seems suitable Table I. Cycle I A. B. C.

Operation of the Scanner" for Direct Tape O u t p u t

Record "preset" information ( interlocked ). Read with D V M a n d record "thermocouple" station. Activate C y c l e II. h

Cycle II 1. 2. 3.

(a) Read with D V M a n d (b) print integrator 1 output. (a) Read with D V M and (b) print integrator 2 output. Hold.

Controls a. b. c. d.

G o to C y c l eI.,A . Advance i n C y c l e I. Perform C y c l e II. Error.

The scanner comprises two counting rings—Silicon Controlled Rectifiers. Cycle I can be initiated only if the perforator interlock is activated, and if Control a is pushed. It advances one step at a time. Cycle II has five steps and once activated is advanced through all steps back to " H o l d " by an R - C timing network. Additional steps might be added to permit "shutter position," electron energy, gaussmeter reading, etc. to be recorded. Clare Corp. HGSM-1016, bistable, single pole mercury relays are used for switching. See text. Circuits may be obtained from "Motorola Semiconductor Circuits Manual," Motorola, Inc., Phoenix, Arizona, 1964. tt

6

0


134

MASS


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E a c h of t h e t i m e steps I I . l a n d II.2 are r e p e a t e d , the five channels of i n f o r m a t i o n r e p r e s e n t i n g the e n c o d e r positions a n d the D V M range are r e c o r d e d .

T h e c o m p u t e r is p r o g r a m m e d to scan these a n d p r i n t out

a s p e c i a l s i g n a l i f a n y one s h o u l d change w i t h i n a p a r t i c u l a r subset of d a t a . T h i s has p r o v e d u s e f u l i n s p o t t i n g operator or r e c o r d e r errors. A s a result of this system, almost a l l m a n u a l treatment is e l i m i n a t e d a n d the C D C 3400 c o m p u t e r reduces i n one m i n u t e of r u n n i n g t i m e d a t a t h a t p r e v i o u s l y r e q u i r e d 100 m a n hours s i m p l y to o b t a i n a t a b l e of i o n intensities. T h e s e intensities are p r o v i d e d i n t a b u l a r f o r m a n d o n p u n c h e d cards, a n d m u s t b e c o m p a r e d

w i t h the o r i g i n a l s t r i p chart r e c o r d i n g

b e c a u s e of v a r i o u s i n s t r u m e n t a l a n d operator errors.

(Such

comparson


is r e l a t i v e l y fast b u t n e e d not b e d o n e i m m e d i a t e l y i f r o u g h results are n e e d e d d u r i n g a r u n . ) T h e cards are c o r r e c t e d a n d reprocessed to m a k e a n y necessary c a l c u l a t i o n s a n d to present the results i n a v a r i e t y of potentially informative ways. A p a r t f r o m the o b v i o u s

t i m e s a v i n g a n d the m o r e t h o r o u g h d a t a

treatment, there are other benefits. O p e r a t o r fatigue is d i m i n i s h e d , p r o b a b l y because of t h e r h y t h m i m p o s e d

by

the apparatus.

T h e r e is a

t e n d e n c y to take m o r e d a t a . M o s t i m p o r t a n t , the results are a v a i l a b l e soon e n o u g h to b e u s e d for p l a n n i n g the r e m a i n d e r of the r u n a n d thus p e r m i t the w o r k e r to take a m o r e efficient role i n d e s i g n i n g his e x p e r i m e n t . O n - l i n e C o m p u t e r C o n t r o l . T h e v a r i o u s steps as w e l l as the decisions described above under Computer Compatible Output can and have 8) b e e n p e r f o r m e d b y a s m a l l , o n - l i n e c o n t r o l c o m p u t e r .

(7,

Such an instru-

m e n t w o u l d c o m p l e t e l y r e p l a c e b o t h the scanner a n d d a t a - w r i t e r i n the system d e s c r i b e d above, as w e l l as a n y t i m e a v e r a g i n g c o m p u t e r .

New

units w i t h i n c r e a s i n g m e m o r y c a p a c i t y a n d d e c r e a s i n g cost are c o n t i n u a l l y b e c o m i n g a v a i l a b l e ; t h e i r cost m a y b e l o w e r t h a n t h a t of t h e s c a n n e r / t i m e a v e r a g i n g systems.

I n a d d i t i o n , t h e y c a n p r o v i d e buffer m e m o r y for a

central, shared-time computer

and can continually monitor

i n l e t t e m p e r a t u r e , etc., for p o s s i b l y a b n o r m a l c o n d i t i o n s .

pressure,

Convenient

p r o g r a m m i n g p e r m i t s a n y of a w i d e v a r i e t y of sequences to b e d e s i g n e d a n d i n t e r c h a n g e d as necessary.

F o r t r a n packages are a v a i l a b l e o n m a n y

units. I n a system o p e r a t i n g for i s o t o p i c analyses, o n l y m o d e r a t e r e s o l u t i o n a n d a r e l a t i v e l y n a r r o w mass range are r e q u i r e d (7,8).

A gauss meter

is u s e d to o b t a i n a mass i n d i c a t i o n , a n d the c o m p u t e r is p r o g r a m m e d to i d e n t i f y a n d r e c o r d o n l y the t o p of the peak.

E l e c t r o m e t e r ranges are

c o m p u t e r c o n t r o l l e d b y means of relays. T h e c o m p u t e r also decides w h e n e n o u g h scans o v e r the s p e c t r u m h a v e b e e n m a d e to o b t a i n preselected r e p r o d u c i b i l i t y l i m i t s . T h e n e w h i g h a c c u r a c y gauss meters m e n t i o n e d p r e v i o u s l y m a y i m p r o v e p e r f o r m a n c e w h e r e w i d e r mass ranges a c c u r a c y are d e s i r e d .


and/or

10.

L O Y D

A N D

STAFFORD

Automated

Data

Acquisition

135

P r o g r a m s a n d interfaces d e v e l o p e d (6) t o enable a s m a l l P D P c o m p u t e r ( D i g i t a l E q u i p m e n t C o r p . , M a y n a r d , M a s s . ) to c o n t r o l a f o u r - c i r c l e x - r a y diffractometer s h o u l d b e r e a d i l y a d a p t a b l e to the mass spectrometer. T h e p r o g r a m s d e v e l o p e d i n c l u d e those f o r p r e l i m i n a r y scans t o find s i g nificant intensities i n a n e w system, a n d a r o u t i n e to m a x i m i z e i n t e n s i t y o n t h e detector.

S u c h a m a x i m i z a t i o n r o u t i n e is essential i n cases, as

i m p l i e d elsewhere (17) f o r a s i m p l e i n o r g a n i c system, w h e r e t h e gauss m e t e r does n o t give a sufficiently accurate i n d i c a t i o n of mass. A system f o r o n - l i n e c o m p u t e r c o n t r o l l e d a n d processed d e t e r m i n a t i o n o f a p p e a r a n c e potentials b y the r e t a r d i n g p o t e n t i a l difference m e t h o d has b e e n r e p o r t e d

(12).

(RPD)

D a t a reduction using a shared time


c o m p u t e r also is r e p o r t e d ( 9 ) . Conclusion V a r i o u s systems w i t h d i f f e r i n g c a p a b i l i t i e s h a v e b e e n

described.

U s i n g o n e or several of these has g r e a t l y i m p r o v e d t h e q u a l i t y of i n f o r m a t i o n a v a i l a b l e f r o m t h e mass spectrometer.

P r e c i s i o n is i n c r e a s e d b y

i n c r e a s e d s y s t e m a t i c i t y a n d b y r e d u c i n g h u m a n error. creased also b y i n - p l a c e t i m e a v e r a g i n g .

P r e c i s i o n is i n -

A l a r g e v o l u m e of significant

i n f o r m a t i o n i n v a r i o u s p o t e n t i a l l y i n f o r m a t i v e forms is m a d e a v a i l a b l e r a p i d l y , a n d i t b e c o m e s possible to m o r e effectively s t u d y gas c h r o m a t o g r a p h effluent, a n d corrosive, u n s t a b l e , o r o t h e r w i s e t r a n s i t o r y systems. Results b e c o m e a v a i l a b l e w h i l e t h e e x p e r i m e n t is i n progress, p e r m i t t i n g t h e u n e x p e c t e d t o b e i d e n t i f i e d r a p i d l y , a n d p e r t i n e n t modifications of t h e e x p e r i m e n t to b e m a d e . Acknowledgments M u c h of t h e c a p i t a l e q u i p m e n t f o r this project w a s a c q u i r e d f o r u s at m i n i m u m cost as "excess" o r as gifts b y J o s e p h D o w n e y of t h e N o r t h w e s t e r n U n i v e r s i t y P u r c h a s i n g D e p a r t m e n t . T h e extensive c o l l a b o r a t i o n of James B . B r u c e , J o h n E . F e d y s k i , G e o r g e A . Pressley, J r . , S a r a J . Steck, J o a n C . K a y e , a n d P a m e l a M . B r o w e r e of great v a l u e . V o g e l b a c k C o m p u t i n g C e n t e r ( N o r t h w e s t e r n U n i v e r s i t y ) a n d its staff, e s p e c i a l l y J . R i c h ard Walston, provided both a i d a n d computing time.

W e gratefully

appreciate support from the Northwestern University Materials Research Center, T h e University, a n d the A t o m i c E n e r g y Commission, Document COO-1147-12. Literature

Cited

(1) Biemann, K., Bommer, P., Desiderio, D. M., McMurray, W. J., Advan. Mass Spectrometry, Proc. Conf., 3rd, Paris, 1964, 639 (Pub. 1966).



136

MASS


I N INORGANIC

C H E M I S T R Y

(2) Biemann, K., Bommer, P., Desiderio, D. M., McMurray, W. J., Tetra hedron Letters 1964, 1725. (3) Biemann, K., Bommer, P., Desiderio, D. M., McMurray, W. J., Tetra hedron Letters 1965, 647. (4) Brown, E. R., Smith, D. E., DeFord, D. D., Anal. Chem. 38, 1130 (1966). (5) Burlingame, A. L., Advan. Mass Spectrometry, Proc. Conf., 3rd, Paris, 1964, 701 (Pub. 1966). (6) Busing, W. R., Woody, J. W., Roseberry, R. T. (private communication). (7) Cook, H. D., Barker, F. B., Hudgens, J. E., 5th Natl. Meeting Soc. Appl. Spectr., Chicago, June 13-17, 1966, Abst. 202. (8) Cook, H . D., Barker, F. B., Hudgens, J. E., Conf. Mass Spectr. Allied Topics, 13th, St. Louis, 1965, p. 220. (9) Hogan, P. J., DeLaeter, R. J., J. Sci. Inst. 43, 662 (1966). (10) Howard, H. E., Anal. Chem. 38, 946 (1966). (11) Kohl, D. Α., Dissertation, Indiana Univ., Dec., 1966, pp. 62 ff. (12) Martignoni, P., Morgan, R. L., Cason, C., Rev. Sci. Inst. 36, 1783 (1965). (13) McLafferty, F. W., Science, 151, 641 (1966). (14) McMurray, W. J., Greene, Β. N., Lipsky, S. R., Anal. Chem. 38, 1194 (1966). (15) Merrit, Charles, Jr., Issenberg, I., Bazinet, M. L., Green, Β. N., Merron, T. O., Murray, J. G., Anal. Chem. 37, 1037 (1965). (16) Olsen, R. W., Conf. Mass Spectr. and Allied Topics, 13th, St. Louis, 1965, p. 191. (17) Stafford, F. E., Pressley, G. Α., Baylis, A. B., ADVAN. CHEM. SER. 72,

137 (1967). (18) Steinhaus, D. W., Engelman, R., Jr., Briscoe, W. L., U. S. At. Energy Comm. LA 3100 (1964). (19) Thomason, Ε. M., Anal. Chem. 35, 2155 (1963). (20) Venkataraghavan, R., McLafferty, F. W., Amy, J. W., Anal. Chem. 39, 178, 278 (1967). RECEIVED

October 5, 1966.


Mass Spectrometry in Inorganic Chemistry

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