Charge inversion spectra of the [M − H]− ions of Di- and polypeptides analyzed by fast atom bombardment mass spectrometry

The [M − H]− ions of a series of dipeptides, containing glycine at the N-terminal, and polypeptides have been generated by fast atom bombardment using an alkaline glycerol/water matrix, and their charge inversion spectra obtained using helium as the collision gas. The results presented indicate that the general features of the charge inversion spectra of these molecules are significantly different from the collisional activation spectra of the positively ([M + H]+) and negatively ([M – H]−) charged species. Whereas the collisional activation spectra of positively and negatively charged ions contain sequence information, the charge inversion spectra are very sensitive to the radicals present in the amino acids and can be used to determine the composition of the peptides.