Analytical strategies for the structural elucidation of proline-containing dipeptides by liquid chromatography-electrospray ionization-tandem mass spectrometry

The identification of various proline-containing dipeptides by implementing liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) techniques is a challenging task. The ESI-MS/MS spectra of protonated molecules [M + H](+) display a single dominant product ion, representing the pyrrolidinyl ring (m/z 70.0652). This lack of ESI-MS/MS information leads to unavoidable ambiguity in the structure of the dipeptide. We demonstrate how structural information can be obtained instantaneously through ESI-MS/MS fragmentation of the accompanied sodium adducts [M + Na](+) or alternatively by ESI-MS/MS fragmentation of their carbamate derivatives. Both strategies are based on altering the charge distribution during fragmentation, promoting rich fragmentation patterns and enabling reliable structural elucidation.