The photodetachment-modulated pulsed electron capture detector. Iodide- and bromide-specific detection for the trace analysis of halocarbon mixtures. Photodetachment cross sections of the halides

Abstract

The use of photodetachment (PD) of electrons from negative ions in a pulsed electron capture detector (ECD) is described. Sensitive responses to halogenated hydrocarbons that produce either I/sup -/, Br/sup -/, or Cl/sup -/ upon electron capture can be created by passing a chopped light beam through the ECD and amplifying the modulated component of the ECD signal. By use of a relatively simple light source system, including an arc lamp and a high-throughput monochromator, the photodetachment-modulated (PDM) pulsed ECD can be made to respond selectively and sensitively to iodine-containing hydrocarbons alone or to iodine- and bromine-containing hydrocarbons in the presence of chlorinated hydrocarbons. This capability is shown to be useful in the trace analysis of a complex mixture of halogenated hydrocarbons by gas chromatography. Simultaneous with this PDM response, a normal ECD response is also obtained. The ratio of the modulated and normal responses thereby obtained during a single chromatogram provides an indication, along with the chromatographic retention time, of the identity of the analyte. The detection limit of the iodide/bromide-specific mode of the PDM-ECD to CH/sub 2/I is shown to be competitive with that of the normal mode of the pulsed ECD.