Quantitative bioanalysis of antibody-conjugated payload in monkey plasma using a hybrid immuno-capture LC-MS/MS approach: Assay development, validation, and a case study.

•A novel hybrid approach to quantitatively measure payload conjugated to Ab is reported.•The assay involves immuno-capture, enzyme cleavage and LC–MS/MS analysis of cleaved payload.•Various bioanalytical challenges and solutions were discussed in details for each step.•The assay allowed accurate quantification of conjugated payload for ADC with varying DAR.•The assay was fully validated using a combination of requirements for both LC–MS and LBA methods.