Ion-exchange chromatography, capillary isoelectric focusing, and capillary zone electrophoresis coupled to mass spectrometry for charge variant analysis of monoclonal antibodies

Monoclonal antibody (mAb) charge variant analysis, which ensures the quality of biopharmaceuticals, is primarily performed by either cation exchange chromatography (CEX), capillary isoelectric focusing (CIEF), or capillary zone electrophoresis (CZE). Though selectivity is different for all methods, mAb proteoforms can be quantified on the intact level with a low risk of artifacts. Identification and characterization can be performed by mass spectrometry (MS), but coupling is hampered by the use of nonvolatile constituents. Here, we present comparative data and a thorough review of CEX-MS, CIEF-MS, and CZE-MS for the analysis of charge variants on the intact level. The separation of the proteoforms is confirmed by online UV detection with subsequent online MS coupling. Each method was tested for generic use by measuring 10 mAbs with an isoelectric point (pI) of 7.3 to 8.7 without individually adjusting the method parameters for each mAb. The methods and the identified proteoforms are compared among each other as well as to a previously published CZE-MS method on the subunit level. The lysine variant was used to compare the resolution of the different separation methods and showed a high resolving power for all separation methods tested. The different method selectivities were revealed by the monoglycosylation, which was found in the peak of the main variant with CEX and CIEF, while it was separated from the main peak with CZE. In combination with a comprehensive literature review, our results provide a complete overview of the current state of the methods with information on the advantages and limitations of each methodology.