Fragmentation pathways and mechanisms of aromatic compounds in atmospheric pressure studied by GC-DMS and DMS-MS

Differential mobility spectrometry (DMS) is a highly sensitive sensing technology capable of selecting and detecting ions based on the difference between ion mobility at high and low electric field. The combination of a micro-fabricated DMS with gas chromatography (GC) has allowed extensive investigation of the ion chemistry and collisionally induced dissociation (CID) of diaryl molecules on a millisecond timescale at temperatures up to 130 degrees C. DMS-pre-filtered time-of-flight mass spectrometry (DMS-MS) has been used to verify the chemical composition of the ion species resolved by GC-DMS. This work focuses on the fragmentation of diaryl compounds, including diphenyl methane (DPM) and bibenzy] (BB), using information from the DMS and DMS-MS spectra of a series of aromatic compounds. Density functional theory calculations have been used to investigate the geometry and the energy along the reaction coordinate for the loss of benzene from DPM-H+ and BB-H+ for comparison with GC-DMS and DMS-MS experimental results and with previously reported chemical ionization MS. DPM-H+ is observed to undergo field-induced fragmentation in the DMS to produce C7H7+(Bz(+)) and unobserved neutral benzene with a low energy barrier. In contrast, BB-H+ fragments to C8H9+ and benzene with a higher energy barrier. Calculated barriers and experimental results are in qualitative agreement. Depletion of the ionized fragments in favor of ion-neutral clusters was also observed at higher concentrations. It is suggested that CID in DMS can further enhance DMS analytical performance. (C) 2007 Elsevier B.V. All rights reserved.