Mass Spectrometric Monitoring of Fragments of Organic Compounds in a Double-Flow Glow Discharge Cell

摘要

A simple glow discharge (GD) mass spectrometer was constructed to study the decomposition of trace organic vapor in ambient air in the glow discharge plasma under various discharge conditions. The organic sample was diluted with air and then introduced into a glow discharge cell composed of a grounded stainless-steel cathode tube and an anode tube outside the cathode. The sample flow was reversed from the cathode tube to the space between cathode and anode to form a double flow to increase the residence time of the sample in the plasma. Ions formed in the plasma were extracted by differential pumping to a quadrupole mass analyzer. Mass spectra for several organic compounds were obtained to elucidate what species were formed during the decomposition of these compounds in the plasma. The signal intensity of the GD mass spectrometer was closely related to the pressure of the interface region. The relative intensity of the fragmented ions depended strongly on the discharge current rather than on the sampling flow rate. In most cases, except at high concentrations, no parent molecular peaks were observed which indicated complete fragmentation of the molecule.