Collisionally activated dissociation spectra of sodiated peptides and peptide amides

The CAD spectra of the [M + Na]+ ions of a series of peptide free acids and amides have been acquired. The spectra of the sodiated amides were found to differ significantly from those of the sodiated free acids due to absence of the [Bn + Na + OH]+ ions in the spectra of the amides. The abundances of [Yn + Na − H]+ ions, [Wn + Na]+ ions and [Dn + Na]+ ions is increased in the spectra of the sodiated peptides while internal fragments are reduced in abundance. Deuterium labeling shows that the hydrogens lost in the formation of [Yn + Na − H]+ ions and the [An + Na − H]+ ions are non-exchangeable.