Collision-induced fragmentation pathways including odd-electron ion formation from desorption electrospray ionisation generated protonated and deprotonated drugs derived from tandem accurate mass spectrometry

The rapid desorption electrospray ionisation (DESI) of some small molecules and their fragmentation using a triple‐quadrupole and a hybrid quadrupole time‐of‐flight mass spectrometer (Q‐ToF) have been investigated. Various scanning modes have been employed using the triple‐quadrupole instrument to elucidate fragmentation pathways for the product ions observed in the collision‐induced dissociation (CID) spectra. Together with accurate mass tandem mass spectrometry (MS/MS) measurements performed on the hybrid Q‐ToF mass spectrometer, unequivocal product ion identification and fragmentation pathways were determined for deprotonated metoclopramide and protonated aspirin, caffeine and nicotine. Ion structures and fragmentation pathway mechanisms have been proposed and compared with previously published data. The necessity for elevated resolution for the differentiation of isobaric ions are discussed. Copyright © 2006 John Wiley & Sons, Ltd.