ORIGIN OF PRODUCT IONS IN THE MS MS SPECTRA OF PEPTIDES IN A QUADRUPOLE ION-TRAP/

Stored waveform inverse Fourier transform and double resonance techniq ues have been used in conjunction with a quadrupole ion trap to study the dissociation patterns of peptide ions. These experiments provide i nsight into the origin of individual product ions in an MS/MS spectrum . Results show for a series of leucine enkephalin analogues with five amino acid residues that the b(4) ion is the main product ion through which many other product ions arise. It was also observed that the per centage of the a(4) product ions that are formed directly from the pro tonated molecule (M+H)(+) depends on the nature of the fourth amino ac id residue. in addition, it was determined that in the peptides studie d here lower series b ions (e.g., b(3)) arise from direct dissociation of higher series b ions (e.g., b(4)) only about 50% of the time. (C) 1998 American Society for Mass Spectrometry.