The biotransformation of ADCs may not only impact their pharmacological profiles, but also may pose challenges for their quantification in study samples. One common workflow for determining the concentrations of total antibody and ADCs is ligand binding assay. In this context, understanding the biotransformation of ADCs provides insight into appropriate selection of capture and detection reagents that may not be impacted by a given biotransformation for enrichment and subsequent quantitative analysis. Another widely used approach is monitoring the surrogate analyte to represent ADC concentration through LC-multiple reaction monitoring mass spectrometry (LC-MRM-MS). In many established quantitative intact ADC assays, the payload itself serves as a surrogate analyte after enzymatic or chemical release from the antibody. However, most potential biotransformation on payload would result in mass to charge (m/z) and retention time (RT) mismatch with the pre-specified values. Both cases could lead to the inaccurate quantification of ADC, compromising the correct characterization of its pharmacokinetics (PK) profiles.