Which hydrogen atom of toluene protonates PAH molecules in (+)-mode APPI MS analysis?

Arif Ahmed, Manik Kumer Ghosh, Myung Chul Choi, Cheol Ho Choi, Sunghwan Kim

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

A previous study (Ahmed, A. et al.; Anal. Chem. 84, 1146-1151(2012) reported that toluene used as a solvent was the proton source for polyaromatic hydrocarbon compounds (PAHs) that were subjected to (+)-mode atmospheric-pressure photoionization. In the current study, the exact position of the hydrogen atom in the toluene molecule (either a methyl hydrogen or an aromatic ring hydrogen) involved in the formation of protonated PAH ions was investigated. Experimental analyses of benzene and anisole demonstrated that although the aromatic hydrogen atom of toluene did not contribute to the formation of protonated anthracene, it did contribute to the formation of protonated acridine. Thermochemical data and quantum mechanical calculations showed that the protonation of anthracene by an aromatic ring hydrogen atom of toluene is endothermic, while protonation by a methyl hydrogen atom is exothermic. However, protonation of acridine by either an aromatic ring hydrogen or a methyl hydrogen atom of toluene is exothermic. The different behavior of acridine and anthracene was attributed to differences in gas-phase basicity. It was concluded that both types of hydrogen in toluene can be used for protonation of PAH compounds, but a methyl hydrogen atom is preferred, especially for non-basic compounds.

Original languageEnglish
Pages (from-to)316-319
Number of pages4
JournalJournal of the American Society for Mass Spectrometry
Volume24
Issue number3
DOIs
StatePublished - Mar 2013

Keywords

  • Atmospheric pressure photo ionization
  • Mechanism
  • Quantum mechanical calculation

Fingerprint

Dive into the research topics of 'Which hydrogen atom of toluene protonates PAH molecules in (+)-mode APPI MS analysis?'. Together they form a unique fingerprint.

Cite this