Effect of matrix modification by strong mineral acids on the positive fast atom bombardment mass spectra of peptides

We report an investigation of the effect of the addition of strong mineral acids to the most commonly used matrices for fast atom bombardment mass spectrometry of peptides. Among the acids tested we found that perchloric acid has a beneficial effect on: (i) the sensitivity, (ii) the stability of quasi-molecular ion signals. Furthermore, in the presence of basic residues, ions related to perchlorate adducts are present. These further signals may be useful in differentiating peptides containing lysine from those containing the isobaric glutamine.