DESIGN AND CHARACTERIZATION OF GLOW-DISCHARGE DEVICES AS COMPLEMENTARY SOURCES FOR AN ICP MASS-SPECTROMETER

Two types of low cost glow discharge (GD) ion sources have been designed and constructed that can be interfaced to the mass spectrometer of an inductively coupled plasma-mass spectrometry (ICP-MS) system. In one system the cathode (sample) is a central pin and in the second system the cathode (sample) is a disk. This second system is based on the "Grimm" design with a floating restrictor. Either system can be bolted onto the interface system of a SCIEX/Perkin-Elmer ELAN Model 250 or 500 ICP-MS in place of the normal sampling cone. Successful operation requires that the anode of the GD source be biased slightly positive and the shadow stop of the ELAN slightly negative with respect to the grounded skimmer and interface plate. The application of these GD ion sources to the qualitative and quantitative analysis of low alloy steel, stainless steel and brass samples is illustrated. In particular, complexity of GD-MS spectra are assessed with respect to argide and dimer levels. In general the spectra are quite simple with argide levels in the 0.1% to 0.01% range and dimers generally less than 0.01 to 0.001%.