LINE AND IN-SITU QUANTIFICATION OF GAS-MIXTURES BY MATRIX INTERVAL ALGEBRA ASSISTED QUADRUPOLE MASS-SPECTROMETRY

A novel, efficient technique to identify and quantify complex gas mixt ures is described. This approach can be applied on line and in situ an d is extendible to samples with reactive and thermally labile species. Complex hydrocarbon mixtures are prepared in test experiments by irra diating frozen methane targets with 9 MeV alpha particles in an ultrah igh vacuum chamber and releasing them during successive heating of the solid samples from 10 to 293 K after each ion bombardment. A quadrupo le mass spectrometer monitors time-dependent ion currents of selected m/z values, which are proportional to partial pressures in the case of a nonoverlapping fragmentation pattern. Predominantly, parent molecul es and fragments of different molecular species add to a specific mit value, i.e., C2H4+, N-2(+), and CO+ contribute to m/z=28. Programmed m /z ratios are chosen to result in an inhomogeneous system of linear eq uations including the measured ion current (right-hand vector), partia l pressures (unknown quantity), and the calibration factors of fragmen ts of individual gases determined in separate experiments. Since all q uantities are provided with experimental errors, matrix interval algeb ra, i.e., an IBM high accuracy arithmetic subroutine defining experime ntal uncertainties as intervals, is incorporated in the computations t o extract individual, calibrated components of complex gas mixtures. T his proceeding enables the quantitative sampling of calibrated hydroca rbons, and, especially, H-2 and D-2 without further time-consuming pre separation devices on line and in situ, hence justifying the use of th is approach in space missions to elucidate the chemical composition of , e.g., planetary atmospheres without payload wasting gas chromatograp hs. (C) 1995 American Institute of Physics.