A tandem mass spectrometry study of trifluoroacetic acid using chemical ionization with methanol and water

Abstract

Mass analyzed ion kinetic energy spectra (MIKES) were scanned for the following ion species generated with water or methanol as reagent gases under chemical ionization conditions: [CF3CO2CH3H]+, [CF3CO2HH]+, [CF2CO2CH3]+, [CF3CO]+, [CF2CO2H]+, [CF3OH2]+ and [CF3OH]+·. Unimolecular decompositions of the [CF3CO2CH3H]+, [CF3CO2H2]+ and [CF3COH2]+ ions were all associated with a dominant loss of an HF molecule. In labeling experiments, an isotopic kinetic effect was evident for the unimolecular loss of HF from the [CF3CO2HD]+ species, in that the intensity of the peak produced by the HF loss exceeded that pertaining to DF loss by a factor of 10. Further unimolecular transitions were found for protonated trifluoroacetic acid at 87 → 67 and 86 → 67. In the MIKE spectrum of [CF2CO2CH3]+ ions derived from protonated trifluoroacetic acid methyl ester, a dish-shaped peak corresponding to 15 kcal/mol kinetic energy release was found for the loss of CO. On introduction of collision gas, additional characteristic product ions were identified, and their compositions were established using deuterium labeled isotopic variants of the parent ions. © 1998 John Wiley & Sons, Ltd.