Collision-induced dissociation of some protonated peptides with and without mass selection

Collision-induced dissociation (CID) of several protonated peptides formed by positive-ion electrospray (ES+) and by Cs+ fast-ion bombardment are reported. The CID spectra of ions formed by the first ionization method were effected at elevated extraction cone voltages within the ion source of a single quadrupole instrument, while linked-fields-scan measurements at constant B/E of ions formed by the latter technique were performed within the collision cell of a trisector instrument. For molecular masses below 1000 Da, the two sets of spectra yielded identical sequencing information; however, for higher molecular masses the similarity was less evident. This divergence between the two sets of measurements is partially attributed to dominant doubly charged ions and less efficient dissociation of sodium adduct ions at elevated cone voltages.