PREDICTION OF ARTIFACT PEAK INTENSITY IN LINKED SCANS FOR DISSOCIATIONS OCCURRING IN THE FIRST FIELD-FREE REGION OF SECTOR MASS SPECTROMETERS

Linked scans are commonly used on double-focusing mass spectrometers t o obtain tandem mass spectrometry (MS/MS) spectra. The appearance of a rtifact peaks in linked scan MS/MS spectra from dissociations occurrin g in the first field-free region are a result of poor parent ion resol ution, and they often can complicate the interpretation of the MS/MS s pectra. The kinetic energy release associated with dissociation of ion s of similar m/z to the ''selected'' parent ion is the main factor in determining the intensity of artifact peaks. A means of predicting the intensities of these artifact peaks in product ion and constant neutr al loss scans is presented here. The method requires straightforward c alculations based on Lacey-Macdonald ion intensity diagrams. The exact calculations require knowledge of the kinetic energy release of a par ticular dissociation, the kinetic energy spread of the main beam, and the parent ion and product ion mass-to-charge ratios. Adequate predict ions, however, can be made by assuming a general kinetic energy releas e for any given reaction and a typical instrument energy resolution Th eoretical predictions are in good agreement with experimental data obt ained from the product ion scans of unlabeled and isotopically labeled tirilazad and unlabeled and labeled leucine enkephalin methyl ester. There is also excellent agreement between experiment and theory in the constant neutral loss scans of rubidium bromide clusters. (C) 1997 Am erican Society for Mass Spectrometry.