On line and in situ quantification of gas mixtures by matrix interval algebra assisted quadrupole mass spectrometry

Abstract

A novel, efficient technique to identify and quantify complex gas mixtures is described. This approach can be applied on line and in situ and is extendible to samples with reactive and thermally labile species. Complex hydrocarbon mixtures are prepared in test experiments by irradiating frozen methane targets with 9 MeV α particles in an ultrahigh vacuum chamber and releasing them during successive heating of the solid samples from 10 to 293 K after each ion bombardment. A quadrupole 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 molecules and fragments of different molecular species add to a specific m/z value, i.e., C2H+4, N+2, and CO+ contribute to m/z=28. Programmed m/z ratios are chosen to result in an inhomogeneous system of linear equations including the measured ion current (right-hand vector), partial pressures (unknown quantity), and the calibration factors of fragments of individual gases determined in separate experiments. Since all quantities are provided with experimental errors, matrix interval algebra, i.e., an IBM high accuracy arithmetic subroutine defining experimental uncertainties as intervals, is incorporated in the computations to extract individual, calibrated components of complex gas mixtures. This proceeding enables the quantitative sampling of calibrated hydrocarbons, and, especially, H2 and D2 without further time-consuming preseparation devices on line and in situ, hence justifying the use of this approach in space missions to elucidate the chemical composition of, e.g., planetary atmospheres without payload wasting gas chromatographs.