A computer program for automatic determination of gases found in an environmental chamber during spacecraft testing is discussed. Program testing is reviewed. The program is being used for the solution of experimental spectra, where the mass spectrometer is used as a contamination monitor by an untrained spectroscopist

Shapiro, H.

English

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138 GODDARD SPACE FLIGHTCENTER
A COMPUTER PROGRAM TO AUTOMATE RESIDUAL
GAS ANALYSIS
n. Shapiro
About five years ago, a need was foreseen for some system that would
automatically determine the gases found in an environmental chamber
during spacecraft testing. At that time, this function was performed by a
skilled chemist reading the output of a mass spectrometer. At best, this is a
time-consuming activity which severely limits the quantity of such scans
that the human operator can analyze. Others also foresaw the need for the
computer processing of such data, and from time to time the literature
would carry a scheme or program to accomplish it. All of these schemes had
drawbacks which, when applied to our needs, were insurmountable. For
example, one scheme required that a library be built using the exact
instrument that would perform the required analysis. Since three different
types of mass spectrometer comprising ten individual instruments are in use
at GSFC, building such libraries is an impossible task.
In 1968, Trombka and Schrnadebeck of GSFC published a least-squares
method for resolving complex pulse height spectra which offered a path to a
solution to our problem. Using their basic concepts and adding a year's
effort, a modification, which is practically a new program, was arrived at.
We have a program today, written in Fortran IV and using a matrix
inversion method, which successfully analyzes mass spectrometer data.
Those aspects of previous programs which were detrimental to our use have
been overcome. A library can be built from any published data, such as
handbooks, textbooks, compendia, or data generated by other instruments.
Results are reasonably good and are understandable in direct proportion to
the quality of the library. Thus, data from the user's instrument itself will
give nearly perfect answers; from good literature values and a typical mass
spectrometer, completely understandable answers; from poor values and
poor data, some answers requiring a preknowledge on the part of the user.
Testing the program was done in the most objective manner. Materials
were prepared, and mass spectrometric data were taken by one group, and
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TECHNOLOGYACCOMPLISHMENTS, 1970 139
these raw data were given to a second group who ran the program.
Unreasonably difficult mixtures of materials were prepared and run, and the
program successfully separated them and printed out a correct analysis each
time (see Table 1).
The program is being utilized currently for the solution of experimental
spectra, where the spectrometer is being used as a contamination monitor
by an untrained spectroscopist.
The ultimate goal is to acquire pushbutton analysis capability. The
program is the most difficult link in the chain of steps necessary to achieve
this goal. Still required is the electronic hardware for taking the signal from
the mass spectrometer, digitizing it, labeling it as to mass number, and
putting it on tape in this fashion so that the program can take over. We have
begun the work on this last phase and are optimistic that next year all mass
spectra can be computer analyzed, and automation will be complete except
for the technician who pushes the button.
Table 1-Computer analysis results.
COMPOUND
ACETIC ACID
ACETONE
CARBON MONOXIDE
ETHANOL
ETHYL ACETATE
3-ETHYL HEXAN E
HYDROGEN CHLORIDE
M ETHAN E
% RELATIVE ABUNDANCE
COMPUTED
15.3 (+_2.0)
64.3 (+_3.9)
3.6 (+_2.2)
11.3 (+1.8)
0.8 (+2.0)
0.4 (+_1.1)
0.1 (+0.7)
3.3 (+1.1)
ACTUAL
15
75
10


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