Dependence of benzyl alcohol loss onC‐terminal amino acid in tandem mass spectrometry ofN‐protected tripeptides

The effect of the basicity and chain length of the C ‐terminal amino acid on the fragmentation of N ‐protected tripeptides was investigated with a hybrid tandem instrument. Positive‐ion unimolecular decomposition and colisionally activated decomposition studies on the [M + H] + ions of a series of N ‐benzyloxycarbonyl (Cbz or Z)‐protected tripeptides, Cbz–Gly–Leu–Xxx–OMe and Cbz–Gly–Pro–Xxx–OMe, where Xxx = Arg, Lys, Orn, Gln and Glu, indicate that substitution of leucine with proline at the second position in the tripeptides facilitates the loss of benzyl alcohol (108 u) from the precursor. Additionally, higher gas‐phase basicity and longer chain length of the C ‐terminal side‐chain group promote the formation of the [M + H – 108] + ion.