Sequeince‐ion studies in peptides: The generation of C″ ions

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Abstract
The mechanism for the formation of C″-type ions from protonated peptides, produced under conditions of fast-atom bombardment and rollisional activation was investigated. Comparison of the tandem mass spectra of the [M + H]+ ions of a model peptide and the corresponding [Md + D]+ ions, in which all exchangeable hydrogens are replaced with deuterium, revealed that neither the carboxylic hydrogen not a hydrogen from a nitrogen atom is involved in the process of migration of a hydrogen which leads to the formation of Cn″-type ions. The most feasible position from which the transferred hydrogen originates is that at the first C-atom in the side-chain of the adjacent ainino acid.