Comparing differentiation of xylene isomers by electronic ionization, chemical ionization and self-ion/molecule reactions and the first observation of methyne addition ions for xylene isomers in self-ion/molecule reactions for non-nitrogenated compounds.

This study presents the self-ion/molecule reaction (SIMR) spectra of three xylene isomers, and proposes an approach to differentiating them based on observed differences in relative abundances of ions formed by SIMR in an internal source ion trap instrument. It also demonstrates the applicability of SIMR for isomer discrimination, which is better than electron ionization (EI) and dimethyl ether chemical ionization (DME CI) in an ion trap mass spectrometer (ITMS) since no CI reagent, metal ions or internal standards are required to perform SIMR. The merits of the new method for distinguishing isomers are that it is simple, rapid and economic. To date, methyne addition products ([M+13](+) ions) have been observed for several nitrogenated compounds including aza-crown ethers, aniline and dopamine from SIMR in the ITMS. The xylene isomers are, however, the first three non-nitrogenated compounds that have been shown to produce the methyne addition ions in SIMR. Copyright 2003 John Wiley & Sons, Ltd.