Characterization of therapeutic mAb charge heterogeneity by iCIEF coupled to mass spectrometry (iCIEF–MS)

Imaged capillary isoelectric focusing (iCIEF) has emerged as an important technique for therapeutic monoclonal antibody (mAb) charge heterogeneity analysis in the biopharmaceutical context, providing imaged detection and quantitation by UV without a mobilization step. Besides quantitation, the characterization of separated charge variants ideally directly by online electrospray ionization–mass spectrometry (ESI–MS) is crucial to ensure product quality, safety, and efficacy. Straightforward direct iCIEF–MS coupling combining high separation efficiency and quantitative results of iCIEF with the characterization power of MS enables deep characterization of mAb charge variants. A short technical setup and optimized methodical parameters (30 nl/min mobilization rate, 2%–4% ampholyte concentration, 0.5–2 mg/ml sample concentration) allow successful mAb charge variant peak assignment from iCIEF to MS. Despite a loss of separation resolution during the transfer, separated intact mAb charge variants, including deamidation as well as major and minor glycoforms even from low abundant charge variants, could be characterized by online ESI–MS with high precision. The presented setup provides a large potential for mAb charge heterogeneity characterization in biopharmaceutical applications.