New rules concerning the formation of protonated amino acids from protonated dipeptides using the proton affinity order determined from collisionally activated decomposition spectra

The use of the order of the proton affinities of natural α‐amino acids for the explanation of the sequence of dipeptidcs using the collisionally activated decomposition mass spectra of protonated dipeptides ions is discussed. New rules are given concerning the formation of protonated amino acid ions from protonated dipeptide ions using the proton affinity order determined by means of fast atom bombardment tandem mass spectrometry for Gly * M 2 , M 1 * Gly, Leu * M 2 , and M, * Leu systems, where M 1 and M 2 are the N ‐terminal and C ‐terminal sides of the dipeptide, respectively.