Discrimination of Isomers of Dichlorobenzene Using Charge Inversion Mass Spectrometry

Chlorinated aromatic compounds are well-known environmental pollutants and their toxicity often depends dramatically on the chlorine substitution pattern within a homological group. Analysis of extremely toxic environmental pollutants such as dioxins requires high sensitivity, typically in the parts-per-trillion (ppt) range. Mass spectrometry (MS), being the most sensitive of analytical methods, has been used for pollutant analysis, but conventional mass spectrometry alone cannot be used for isomer-specific analysis of these toxic chemicals. In this work, we investigated the possibility of discriminating among the isomeric precursors of chlorinated aromatic compounds by charge inversion mass spectrometry using an MS/MS instrument. Charge inversion mass spectra using Cs, K, and Na targets were measured for C6H4Cl2+ ions produced from the ortho-, meta-, and para-isomers of dichlorobenzene (C6H4Cl2). The charge inversion mass spectra were found to display a clear dependence on the nature of the isomeric precursors for each of the targets used. The clear discrimination among the isomers of dichlorobenzene achieved using charge inversion mass spectrometry in the present work indicates that most of the C6H4Cl2+ ions obtained by electron impact retain the structure of the parent molecules, demonstrating the potential utility of this technique for isomer-selective microanalysis of various pollutants.