DESTRUCTION OF HALOGENATED METHANES BY NON-ELECTRON CAPTURE PROCESSES WITHIN AN ELECTRON CAPTURE DETECTOR

摘要

The rates of destruction of 8 halogenated methanes by processes other than dissociative electron capture (EC) reactions have been measured within an ionization cell for which conditions are identical to those existing within an electron capture detector (ECD) for gas chromatography (GC). It is shown that additional destructive processes are distinctly operative for CCl4 and CBrCl3, but not for CH2Br2, CH3I, CHBr3, CHFBr2, CF2Br2, and CHCl3. In these measurements, CFCl3 serves as a reference compound for which no extra-EC destruction with an ECD is assumed. This assumption is based on previous uses of CFCl3 as a reference compound in related studies and on additional measurements provided in the present study. It is shown that the most likely mechanism for the extra-EC destruction of CCl4 is a reaction of this compound on the walls of the ion source which have been chemically activated by the deposition of gas phase free radicals. The rate of this wall-assisted destruction of CCl4 is increased with use of lower temperatures and approaches unit efficiency upon wall collisions at room temperature. The implications of these results for the quantitative analysis of halogenated compounds by the ECD are discussed.