MODELING OF GLOW-DISCHARGE SOURCES WITH FLAT AND PIN CATHODES AND IMPLICATIONS FOR MASS-SPECTROMETRIC ANALYSIS

A set of three-dimensional models for a direct current glow discharge in argon, developed previously in our group, is applied to analytical glow discharge cells with either flat or pin-type cathodes. Among othe r quantities, the densities of the plasma species are calculated and c ompared for these two cathode shapes. A comparison is also made for th e computed argon and sputtered cathode (copper) ion currents leaving t he glow discharge cell and entering the mass spectrometer, because thi s is of major interest from the analytical point of view. Finally, for the pin cell, the influence of sampling distance (i.e., distance betw een cathode pin and exit slit to the mass spectrometer) on the calcula ted plasma quantities is investigated. (C) 1997 American Society for M ass Spectrometry.