PARENT ION RESOLUTION IN LINKED SCANS FOR DISSOCIATIONS OCCURRING IN THE FIRST FIELD-FREE REGION OF SECTOR MASS SPECTROMETERS

A frequently employed means of studying reactions of ions under high e nergy collisional activation conditions involves linked scanning a dou ble-focusing mass spectrometer to detect product ions formed in the fi rst field-free region. Experiments have demonstrated that the effectiv e resolution of the parent ion varies during the course of a product i on scan, and this variation is attributed to the kinetic energy releas ed during dissociation. Carefully generated Lacey-Macdonald ion intens ity diagrams accurately reflect the dissociation events occurring in v arious regions of sector mass spectrometers. Consideration of such dia grams leads to an understanding of the noted phenomena and allows: the derivation of an expression for the effective parent ion resolution. Furthermore, the approach predicts that parent ion resolution varies d uring constant neutral loss scans and that the relatively poor resolut ion (and its variation) can provide particularly misleading data. Resu lts from product ion scans with stable isotope-labeled compounds and c onstant neutral loss scans with rubidium bromide and stable isotope-la beled peptide derivatives were consistent with the theoretical predict ions. (C) 1997 American Society for Mass Spectrometry.