Determination of label efficiency and label degree of critical reagents by LC-MS and native MS

Degree of labeling and label efficiency are key factors for optimal characterization of critical reagents that are used in ligand binding assays. Here, three case studies are shown demonstrating how liquid chromatogra-phy-mass spectrometry (LC-MS) was utilized to characterize critical reagents using three unique methodologies. Critical reagent batches were prepared for LC-MS analysis by use of: 20 mM dithiothreitol (DTT) (Case 1), rapid PNGaseF (Case 2), and a mobile phase diluent (Case 3). LC-MS was run at three different MS method conditions in each troubleshooting case specific for reduced IgG, intact IgG, and native LC-MS, respectively. Specified LC-MS methods based on sample type and configuration elucidated clear MS profiles, allowing for degree of labeling and label efficiencies to be calculated. Ultimately the LC-MS analyses were fine-tuned for critical reagent charac-terization, and practices for analyzing similar reagents in the future can be established.