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 (dialkyl 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 equal to or larger than ethyl, CID mechanisms are dominated by McLafferty rearrangements and neutral losses are stable molecules in all cases except cleavage of PC or OC bonds to form alkyl fragment ions. CID cross‐sections for the OPCs were determined with excellent reproducibility and a good correlation was found with a simple model. Inferences with respect to ionic structures were made from observed trends in the cross‐section measurements. Limitations in API‐MS/MS instruments of this design are found in the energy distribution of the ionization and ion sampling events.