Isomeric glycopeptides can also be differentiated by UVPD, as demonstrated for the glycopeptide TMSIPT (Figure ). This bis-glycosylated peptide has three glycosites (two Thr and one Ser) and several glycoforms are possible. Figure depicts the UVPD spectra acquired for the 2+ charge state of the six amino acid peptide with a total glycan composition of HexNAc(3)Hex (1). Based on the fragment ions generated by UVPD, Byonic identified the glycosites as S3 and T6 occupied by (1) GalNAcGlcNAcGal and GalNAc and (2) GalNAcGlcNAc and GalNAcGal, respectively. An array of fragment ions was produced for the peptide, in addition to a few corresponding to the peptide sequence without any glycan contributions in the lower m/z range. The dominant ions in the higher m/z range matched both peptide and glycan ions. Diagnostic ions that were crucial to characterizing these two glycoforms were the y2 ion (in Figure ) and the b4 ions identified in both Figure and S9b. The y2 ion in confirms a single GalNAc positioned at T6 and the two b4 ions that have a difference of 162.05 Da, corresponding to galactose, indicating that the spectrum in Figure contains a core 2 glycan and the spectrum in Figure contains a core 3 glycan at position S3.