A mass isolation device selects a precursor ion of a sample that has been digested using a protease. A first fragmentation device fragments the precursor ion using collision-induced dissociation (CID), and the resulting product ions are analyzed using a mass analyzer producing a CID spectrum. A list of theoretical candidate glycopeptide sequences is determined from CID spectrum. The mass isolation device again selects the precursor ion of the sample. A second fragmentation device fragments the precursor ion using electron-based dissociation (ExD), and the resulting product ions are analyzed using the mass analyzer producing a CID spectrum. For each sequence of the list, the sequence is computationally fragmented, producing theoretical fragments, mass-to-charge ratio (m/z) values are calculated for the theoretical fragments, and the sequence is scored using c and z fragment matching rules. The highest scoring sequence is identified as a peptide sequence of a glycopeptide of the sample.
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