Cryogenics Applied to Mass Spectrometric Trace Gas Analysis Alfred Pebler and W. M. Hickam Westinghouse Research Laboratories, Pittsburgh, Pa. 15235 Preconcentration of trace impurities i n inorganic gases by applying a cryogenic freeze-out technique is a convenient way to extend the sensitivity of mass spectrometric analysis into the sub-ppm range. The method can be adapted routinely to a variety of gas systems, examples of which are presented in this paper. These are the analysis of trace impurities in helium, hydrogen, argon/nitrogen mixtures, and high pressure steam. The instrumentation, procedure, and attainable detection limits will be discussed for each of these cases. Further possibilities exist in the analysis of certain air pollutants.
IMPURITIES IN GASES must normally be determined in the presence of a large matrix. Sensitivity thresholds on the order of ppm can be achieved in commercial intermediate resolution mass spectrometers. However, if the impurities in question, such as H2, CO, N2, 0 2 , CO2, HsO, and hydrocarbons, are also part of the residual gases in the inlet system of the mass spectrometer, practical detection limits for these gases are much higher, unless ultrahigh vacuum conditions (
