Practical hints for peptide sequencing by soft ionization methods.

Practical hints are summarized for the investigation of peptides by soft ionization methods based on liquid secondary ion mass spectrometry. The method aims: to purify the sample; to force a peptide to the surface by ion pair formation; to recover the sample used for mass spectral analysis; to distinguish between Lys and Gln by derivatization; to spot amino acids in the low mass region; and to improve sequence information by use of peptide fragments, not described previously.