Peptide purity assignment for antibody quantification by combining isotope dilution mass spectrometry and liquid chromatography

Peptide purity assignment is necessary for quantification of antibody. Recently, isotope dilution mass spectrometry (IDMS) has been proposed as a primary method for an accurate antibody measurement with traceability. When using the IDMS method, antibodies are measured using their signature peptide as the calibration standard. Therefore, the purity assignments of their signature peptide are essential for the standardization and harmonization of the antibody measurement. In this study, SI-traceable purity assignments of the signature peptides of an antibody were investigated by combining the IDMS and high performance liquid chromatography (HPLC) method. The final purity was calculated from the mass fraction of the total peptide determined by IDMS and the relative fraction of the target peptide determined by HPLC. The uncertainty was evaluated within the 95% confidence range. These peptides with the certified purity value can also be used for the quantification of antibodies for SARS-CoV-2.