Addition of acid in SIMS

The changes in secondary ion mass spectra caused by adding acid into the sample solutions of peptides were investigated. The dependence of spectra on the concentration and amount of acid were systematically measured. The intensity changes of MH+, fragment ions, and total ion current were studied by analyzing the spectra. It was observed that MH+ intensity was significantly increased and the fragmentation was suppressed by the addition of acid. The results obtained suggest that proper amount of acid minimizes the internal energy of MH+, which causes the increase of the stability of MH+ and the reduction of the fragmentation as a result.