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 to obtain tandem mass spectrometry (MS/MS) spectra. The appearance of artifact peaks in linked scan MS/MS spectra from dissociations occurring in the first field-free region are a result of poor parent ion resolution, and they often can complicate the interpretation of the MS/MS spectra. The kinetic energy release associated with dissociation of ions 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 neutral loss scans is presented here. The method requires straightforward calculations based on Lacey-Macdonaldion intensity diagrams. The exact calculations require knowledge of the kinetic energy release of a particular dissociation, the kinetic energy spread of the main beam, and the parent ion and product ion mass-to-charge ratios. Adequate predictions, however, can be made by assuming a general kinetic energy release for any given reaction and a typical instrument energy resolution. Theoretical predictions are in good agreement with experimental data obtained 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.