IDENTIFICATION OF TRIMETHYLSILYLATED DIPEPTIDES WITH CHEMICAL IONIZATION MASS-SPECTROMETRY

The chemical ionization (CI) and electron impact (EI) mass spectra were compared for over 40 trimethylsilylated (Me3Si) dipeptides. The dipeptides chosen had all 20 common amino acids represented at amino and carboxyl positions. The CI mass spectra of Me3Si dipeptides typically contain three ions of high abundance used for dipeptide identification: a sequence-determining ion and two molecular weight-determining ions. The intensity of the molecular weight-determining ions relative to that of the ion that characterizes the N-terminal residue (β-cleavage ion) is greater in the CI mode than in the EI mode. Because the available intensity of the β-cleavage ion is similar in both modes, use of the CI mode will extend the lower limit for Me3Si dipeptide identification. © 1979.