Evidence for a mechanism that involves secondary electron capture in the liquid secondary ionization mass spectrometry beam-induced dehalogenation of organic compounds.

The effect of the analyte electron affinity on the liquid secondary ionization mass spectrometry beam-induced dehalogenation of simple bromoaromatic compounds in a glycerol matrix was investigated. The results show a definite trend of decreasing dehalogenation with increasing analyte electron affinity. At high analyte electron affinity (≥ 1.0 eV), no dehalogenation was observed. These results are consistent with electrochemical and pulse radiolysis studies where one electron reduction was shown to be responsible for dehalogenation. A chloroaromatic compound with high electron affinity, 4-(4-chloro-benzoyl)pyridine, exhibited reduction by hydrogen addition but not dehalogenation. The radiation chemistry of alcohols was used to elaborate a scheme of the reactive species generated in the glycerol matrix by kiloelectronvolt particle bombardment. The possible role of those species in reduction processes such as dehalogenation was evaluated. The observation that dehalogenation decreases with analyte electron affinity is mechanistically consistent with the proposition that secondary electron production is an intrinsic part of the bombardment process.