Thermal decomposition of phosphorylated peptides in the condensed phase as studied by mass spectrometry

•Detailed temperature dependence of the thermal degradation at 220 °C of phosphorylated peptides in the condensed phase.•Discovery of a site-specific fragmentation during TD only observed in phosphorylated serine peptides.•Mechanistic description of the fragmentation process in phosphorylated serine peptides.

In this study, we expand the knowledge of the thermal decomposition (TD) of biological samples through the investigation of their non-volatile products by mass spectrometry. Specifically, we characterize the temperature dependence of the TD process and the non-volatile TD products of phosphorylated peptides under atmospheric conditions. Peptides with phosphorylated tyrosine, threonine or serine residues were investigated in this study. Results showed that all three tested phosphorylated peptides undergo a dephosphorylation step at temperatures between 200 and 220 °C. In addition, we report on a sequence-specific cleavage in peptides containing a phosphorylated serine amino acid, with the cleavage taking place at the backbone of the nitrogen–alpha carbon (NCα) bond of the phosphorylated serine during the TD process. A mechanistic rationale is presented that accounts for the observation that this cleavage only occurred in phosphorylated serine-containing peptides. Results presented in this study further point to the potential utility of the robust and simple TD process for the rapid preparation of biological samples prior to MS analysis.