DETERMINATION OF COLLISION-INDUCED DISSOCIATION MECHANISMS AND CROSS-SECTIONS IN ORGANOPHOSPHORUS COMPOUNDS BY ATMOSPHERIC-PRESSURE IONIZATION TANDEM MASS-SPECTROMETRY

Nineteen organophosphorus compounds (OPCs) of the generic classes (dia lkyl alkyl'-phosphonates (twelve compounds) and tri-alkyl phosphates ( seven compounds) were investigated by atmospheric pressure ionization (API) tandem mass spectrometry (MS/MS). All OPCs showed consistent and comparable collision-induced dissociation (CID) pathways allowing for a generalized scheme for dissociation. When the alkyl groups are equa l to or larger than ethyl, CID mechanisms are dominated by McLafferty rearrangements and neutral losses are stable molecules in all cases ex cept cleavage of P-C or O-C bonds to form alkyl fragment ions. CID cro ss-sections for the OPCs were determined with excellent reproducibilit y and a good correlation was found with a simple model. Inferences wit h respect to ionic structures were made from observed trends in the cr oss-section measurements. Limitations in API-MS/MS instruments of this design are found in the energy distribution of the ionization and ion sampling events.