APTD of phospho- and sulfopeptides
Phospho- and sulfopeptides were subjected to atmospheric pressure thermal dissociation (APTD), which was effected by passing peptide ions generated by electrosonic spray ionization (ESSI) through a heated coiled metal tube. Sequence informative fragment ions including a-, b-, c-, and y-types of ions were observed with increased relative intensities under APTD compared with collision-induced dissociation (CID), performed inside the ion trap. A certain degree of preservation of phosphate and sulfate ester moieties was observed for some fragments ions under APTD. The neutral fragments generated outside the mass spectrometer provided rich and complementary sequence information to that provided by the fragment ions directly obtained from APTD.
Mass spectra of a sulfopeptide (FDMWGT-sY-DQE) showing (a) negative ion mode APTD and (b) neutral species generated from negative ion mode APTD and ionized by API in the positive ion mode [-+] NRI.