A TANDEM MASS-SPECTROMETRY STUDY OF TRIFLUOROACETIC-ACID USING CHEMICAL-IONIZATION WITH METHANOL AND WATER

Mass analyzed ion kinetic energy spectra (MIKES) were scanned for the following ion species generated with water or methanol as reagent gase s under chemical ionization conditions: [CF3CO2CH3H](+), [CF3CO2HH](+) , [CF2CO2CH3](+), [CF3CO](+), [CF2CO2H](+), [CF3OH2](+) and [CF3OH](+. ). Unimolecular decompositions of the [CF3CO2CH3H](+), [CF3CO2H2](+) a nd [CF3COH2](+) ions were all. associated with a dominant loss of an H F molecule. In labeling experiments, an isotopic kinetic effect was ev ident for the unimolecular loss of HF from the [CF3CO2HD](+) species, in that the intensity of the peak produced by the HF loss exceeded tha t pertaining to DF loss by a factor of 10. Further unimolecular transi tions were found for protonated trifluoroacetic acid at 87 --> 67 and 86 --> 67. In the MIKE spectrum of [CF2CO2CH3]+ ions derived from prot onated trifluoroacetic acid methyl ester, a dish-shaped peak correspon ding to 15 kcal/mol kinetic energy release was found for the loss of C O. On introduction of collision gas, additional characteristic product ions were identified, and their compositions were established using d euterium labeled isotopic variants of the parent ions. (C) 1998 John W iley & Sons, Ltd.