Improved spectrometer for gas analysis lessens the intensity problem that occurs in obtaining dispersed ultraviolet radiation. A filter, consisting of a selectively transmitting gas cell, a thin film or mirror, or a predispersing grating, alleviates problems of interference from higher-order spectral lines and from scattered ultraviolet light

Poshchenrieder, W. P.

Samson, J. A. R.

Warneck, P.

English

NASA Technical Reports Server

September 1970	 Brief 70-10402 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Improved Photolonization Mass Spectrometer 
The analytical method of photoionization mass 
spectrometry has been used in the past for research 
in photoionization effects, ionization-potential de-
termination, ion-neutral reactions, and ion-formation 
kinetics. However, practical application of this method 
to the analysis of gases has been severely hampered 
by intensity problems, particularly when monochro-
mators have been employed to obtain dispersed ultra-
violet radiation. The use of a monochromator is, 
nevertheless, essential if one major advantage of the 
photoionization method is to be retained: the ability 
to set the maximum ionization energy extremely ac-
curately, by adjusting the ionizing wavelength. 
A photoionization mass spectrometer has been 
developed which lessens the intensity problem and 
thus increases the potential for application of photo-
ionization mass spectrometry to gas analysis. 
Experiments have shown that sensitivity of the 
technique is limited by interference from higher-order 
spectral lines and from scattered ultraviolet light, 
both of shorter wavelength than desired. Such radi-
ation, inherently generated by the monochromator 
diffraction grating, causes considerable activation of 
molecules with ionization energies above the selected 
maximum photon energy. These problems have been 
greatly reduced by adding a filter to the monochro-
mator. This filter may consist of a selectively trans-
mitting gas cell, a thin film or mirror of selective 
reflectivity, or a predispersing grating. Any of these 
well-known devices, together with a monochromator 
and a mass spectrometer, forms a novel and powerful 
analytical tool. 
In a typical problem such as the analysis of a mix-
ture of nitrogen and carbon monoxide gases, expen-
sive, high-resolution mass spectrometry was formerly 
necessary, since both gases yield a mass peak very
close to M = 28.  Photoionization mass spectrometry 
previously has been able to detect a minimum concen-
tration of only about 0.5% (5000 parts per million) 
carbon monoxide in a nitrogen atmosphere; with the 
addition of an argon gas filter, a concentration of 
less than 100 parts per million of carbon monoxide is 
detectable. Similar improvements have been noted in 
various equivalent cases. 
Notes: 
1. For background information on this innovation 
and on the technique of photoionization mass spec-
trometry, the following documentation may be ob-
tained from the source in Note 2. 
NASA-CR-71210 (N66-19636) 
Physics of Planetary Atmospheres-I V, 
Gas Analysis by Photoionization Mass 
Spectroscopy 
NASA-CR-66100 (N66-27231), 
Development of a Mass Spectrometer 
Employing a Photoionization Source 
The following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: 
NASA-CR-1018 (N68-17329), Improve-
ment and Optimization of a Mass Spec-
trometer Employing a Photoionization 
Source
(continued overleaf) 
-S
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned-rights.
https://ntrs.nasa.gov/search.jsp?R=19700000388 2020-03-17T00:47:59+00:00Z
Patent status: 
This invention is owned by NASA, and a patent
application has been filed. Royalty-free, nonexclusive 
licenses for its commercial use will be granted by
NASA. Inquiries concerning license rights should be
made to NASA, Code GP, Washington, D.C. 20546. 
Source: W.P. Poshchenrieder, J.A.R. Samson, 
and P. Warneck of
GCA Corp.
under contract to
Langley Research Center
(LAR-10180)
[I: 
E 
is 
Brief 70-10402	 Category 04


Improved photoionization mass spectrometer

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