A comparison of keV atom bombardment mass spectra of peptides obtained with a two-sector mass spectrometer with those from a four-sector tandem mass spectrometer

Abstract

The information content of the conventional fast (keV) atom bombardment (FAB) mass spectra of six peptides, substance P, des-Arg 1substance P. Fibrinopeptide A, des-Arg 16fibrinopeptide A, oxidized somatostatin, and reduced somatostatin, ranging in molecular weight from 1190.6 to 1638.7 is compared with that of the corresponding spectra measured by a high-performance (four-sector) tandem mass spectrometer after collision-induced decomposition (CID). The CID spectra exhibit distinct peaks corresponding to extended series of sequence characteristic ions free of the chemical background and contribution of the matrix which makes the weak fragment ion signals in conventional FAB mass spectra so difficult to interpret. The presence of arginine, a strongly basic amino acid, in either the N-terminal or C-terminal position is reflected in the dominance of characteristic N-terminal and C-terminal fragment ions. The resolving power of the first of the two mass spectrometers is clearly sufficient to permit the recording of separate CID spectra of oxidized and reduced somatostatin in a mixture.