On‐target deuteration for peptide sequencing by laser mass spectrometry

Hydrogen–deuterium exchange was evaluated as a tool for sequence analysis of peptides by matrix‐assisted laser desorption–ionization utilizing post‐source decay (PSD‐MALDI). The number of exchangeable hydrogens (EH) of precursor ions and product ions can be determined from the mass difference between ion signals originating from the deuterated and the non‐deuterated form of a peptide, resulting in a second dimension of structural information. The reliability of sequence determination by combinatorial algorithms or pattern recognition techniques is considerably increased by employng this ‘EH spectroscopy.’ On‐target deuteration is a simple preparatory step which can be performed reversibly with the already mass‐analysed sample within a few minutes and without consumption of additional sample material. The efficiency of hydrogen–deuterium exchange with this technique is about 98.5%. In addition to supporting sequence analysis, deuteration can be used to investigate fundamental fragmentation mechanisms of peptides in PSD‐MALDI. Inconsistencies with expected fragmentation pathways have been found for fragments a1–a3 of substance P.