Reducing the Background Level of a Mass-Spectrometric Hollow Cathode Glow Discharge Ion Source

Abstract

Glow discharge mass spectrometry was used for the direct elemental analysis of solids with gas inclusions. The background signal of a glow discharge, which converts the analyte into ions, is higher than the background signals of other plasma sources by several orders of magnitude. The structure and sources of background contamination were analyzed in this work. It was found that hydrocarbon and water impurities, which are adsorbed on the inner surfaces of the discharge chamber, make the major contribution to the background signal of a glow discharge source. A glow discharge plasma licked the walls of the discharge chamber to desorb contaminants. We proposed using a hollow cathode with a holed cap arranged at the vertex. On the appearance of a discharge, a plasma plug is formed in the cathode hole in front of the orifice. This plasma plug prevents a gas flow from the hole to the source chamber. As a result, a gas pressure drop is formed whose magnitude depends on the orifice diameter in the cap.