Fig. 4

LC/MS total ion current chromatograms of trypsin digested trastuzumab reference material vs. Protein G isolated endogenous human serum IgG pools. Sequence determination of tryptic peptides selected for quantification was achieved by LC–MS/MS. Peptides selected for quantification of Asn (N) deamidation, Asp (D) isomerization, and Met (M) oxidation are marked with arrows. Analytical quantification data are summarized in Table 4