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

Abstract

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.