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Benzene as a selective chemical ionization reagent gas
Author(s) -
Allgood Charles,
Lin Yi,
Ma YeeChung,
Munson Burnaby
Publication year - 1990
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210251003
Subject(s) - chemistry , ion , chemical ionization , reagent , proton , molecule , mass spectrum , analytical chemistry (journal) , proton affinity , benzene , ionization , organic chemistry , protonation , physics , quantum mechanics
Dilute mixtures of C 6 H 6 or C 6 D 6 in He provide abundant [C 6 H 6 ] +· or [C 6 D 6 ] +· ions and small amounts of [C 6 H 7 ] + or [C 6 D 7 ] + ions as chemical ionization (CI) reagent ions. The C 6 H 6 or C 6 D 6 CI spectra of alkylbenzenes and alkylanilines contain predominantly M +· ions from reactions of [C 6 H 6 ] +· or [C 6 D 6 ] +· and small amounts of MH + or MD + ions from reactions of [C 6 H 7 ] + or [C 6 D 7 ] + . Benzene CI spectra of aliphatic amines contain M +· , fragment ions and sample‐size‐dependent MH + ions from sample ion‐sample molecules reactions. The C 6 D 6 CI spectra of substituted pyridines contain M +· and MD + ions in different ratios depending on the substituent (which alters the ionization energy of the substituted pyridine), as well as sample‐size‐dependent MH + ions from sample ion‐sample molecule reactions. Two mechanisms are observed for the formation of MD + ions: proton transfer from [C 6 D 6 ] +· or charge transfer from [C 6 D 6 ] +· to give M +· , followed by deuteron transfer from C 6 D 6 to M +· . The mechanisms of reactions were established by ion cyclotron resonance (ICR) experiments. Proton transfer from [C 6 H 6 ] +· or [C 6 D 6 ] +· is rapid only for compounds for which proton transfer is exothermic and charge transfer is endothermic. For compounds for which both charge transfer and proton transfer are exothermic, charge transfer is the almost exclusive reaction.