Traditional bioanalysis supporting pharmacokinetic assessments involves monitoring surrogate analytes (peptides or payload) via targeted bottom-up based approach. With recent advances in high-resolution mass spectrometers (HRMS), we can measure the macromolecule directly at intact level, which reveals biotransformation previously not observed in traditional LC-MRM (liquid chromatography-multiple reaction monitoring) approach. In this intact approach, ADCs are enriched from plasma matrix with immunocapture, and followed by elution from beads before LC-MS (liquid chromatography-mass spectrometry) analysis. For drug-toantibody ratio (DAR) of 8 cysteine-conjugated ADCs used in this study, since interchain disulfide bonds were repurposed as conjugation sites, light chain (LC) and heavy chain (HC) would dissociate in acid elution before analysis on LC-HRMS (liquid chromatography-high resolution mass spectrometry).