Bioconjugate Characterization: Experts Share Orthogonal Analytical Techniques

Analytical experts Zhengqi Zhang and Lance Cadang have developed orthogonal analytical techniques for characterizing bioconjugates without creating workflow bottlenecks. According to Zhang, Associate Principal Scientist at Merck & Co., his team uses standardized, routine methods such as hydrophobic interaction chromatography ultra-violet (HIC-UV) for drug-to-antibody ratio (DAR), size exclusion chromatography (SEC) for high-molecular-weight species, and imaged capillary isoelectric focusing (icIEF) for charge variants. These methods are used for release and in-process testing.

Decisions about which method to use are based on throughput needs and regulatory risk, with high-resolution mass spectrometry (MS) methods such as SEC-MS, HIC-MS, and RPM reserved for extended characterization, investigations, or regulatory filings. Zhang's team uses a combination of HIC-UV and SEC to estimate the size of material underneath a chromatographic peak.

Cadang, Scientist, Synthetic Molecule Analytical Chemistry at Genentech, adds that his team builds multi-attribute capability into methods from the start. He reserves techniques such as multiangle light scattering (MALS), analytical ultracentrifugation (AUC), and MS for cross-checking high-molecular-weight species at later development stages.