Qualification and application of a liquid chromatography–quadrupole time‐of‐flight mass spectrometric method for the determination of trastuzumab in rat plasma

An liquid chromatography-quadrupole time-of-flight (QqTOF) mass spectrometric method was developed for the determination of humanized or human monoclonal antibodies in rat plasma at the early drug discovery stage. Trastuzumab was used as a model monoclonal antibody. The method consisted of immunoprecipitation followed by tryptic digestion for sample preparation and LC-TOF-MS/MS analysis of specific signature peptides in the positive ion mode using electrospray ionization for analysis. A stable isotope-labeled signature peptide was also used as internal standard. A quadratic regression (weighted 1/concentration(2) ), with an equation y = ax(2) + bx + c, was used to fit calibration curves over the concentration range of 0.500-100 µg/mL for trastuzumab. Samples from a pharmacokinetic study in rat were analyzed by this qualified LC-TOF-MS/MS method and concentrations were compared with those generated by enzyme linked immunosorbent assays method. The LC-TOF-MS/MS method was accurate and precise, with quantitative results comparable with those of ELISA. The qualification run met the acceptance criteria of ±25% accuracy and precision values for quality control samples. Within-run accuracy ranged from 1.53 to 9.20% with precision values ≤10.29%. This LC-TOF-MS/MS method approach could be used as a complementary method for humanized or human monoclonal antibodies at the early drug discovery stage.