Trace Analysis and Fundamental Studies by Plasma Chromatography

Abstract

The plasma chromatograph uses an ion-molecule reactor coupled with an ion-drift spectrometer to produce plasmagram patterns of positive and negative ionic complexes of a trace constituent in a gas. Using an air carrier gas the reactant ions (H₂0) _nH⁺ and (H₂0) _n0₂ are created to undergo ion-molecule reactions with trace organic molecules. The resulting plasmagrams are characteristic of the organic molecules, their concentration and reactivity. Organic compounds studied include salicylaldehyde, benzoic acid, acetophenone, naphthalene, and the polychlorinated biphenyls. Using a nitrogen carrier gas, thermal electrons are the only negative reactant species present, and a trace sample compound will undergo reactions such as occur in the gas chromatographic electron-capture detector, permitting a study of basic characteristics of this detector. Negative plasmagrams show only a strong halogen ion peak for many halogenated benzene compounds, providing experimental evidence of dissociative electron capture. The effect of the simultaneous presence of other electron-capturing species such as air in the carrier gas for the electron-capture detector on sensitivity and linearity is shown by plasmagrams.