Analysis of oxidative modification of VWF A2 peptide by LC-ESI-MS/MS. (A) Reconstructed ion chromatograms extracted from the mass window corresponding to the expected mass/charge (m/z) ratios of the oxidized and unoxidized tryptic fragments. Note the almost complete disappearance of the m/z = 1088.7 peak with HOCl treatment and appearance of a peak with m/z = 1096.7. The increase in 8 atomic mass units in the doubly charged ion is consistent with the addition of 1 oxygen atom to the peptide. (B) MS/MS spectrum of nonoxidized peptide (m/z = 1088.7, doubly charged ion). (C) MS/MS spectrum of oxidized peptide at 75μM HOCl (m/z 1096.7, doubly charged ion). Note that the methionine residue in the oxidized peptide gained 16 atomic mass units.