Electron capture ion mobility spectrometry for the selective detection of chlorinated and brominated species after capillary gas chromatography

Abstract

This paper reports the first investigation of electron capture ion mobility spectrometry as a detection method for capillary gas chromatography. In previous work with negative ion mobility detection after gas chromatography, the principal reactant ion species were 02-or hydrated 02due to the presence of oxygen in the drift gas.These molecular reactant ions have a mobility similar to chloride and bromide ions, which are the principal product ions formed by most halogenated organics via dissociative ion-molecule reactions. Oxygenated reactant ions thus interfere with the selective detection of chloride and bromide product ions. A recently described ion mobility detector design efficiently eliminated ambient impurities, including oxygen, from infiltrating the ionization region of the detector; consequently, in the negative mode of operation, the ionization species with N2 drift gas were thermalized electrons.Therma1ized electrons have a high mobility and their drifl time occupies a region of the ion mobility spectrum not occupied by chloride, bromide, or other product ions. The result was improved selectivity for halogenated organics which ionize by dissociative electron capture.This was demonstrated by the selective detection of 4,4'-dibromobiphenyl from the components of a polychlorinated biphenyl mixture (Aroclor 1248).