Determination of protein charge variants with (imaged) capillary isoelectric focusing and capillary zone electrophoresis

Biopharmaceuticals are increasingly present in pharmaceutical therapy. These highly complex molecules are still challenging for development and quality control. Charge heterogeneity is next to size heterogeneity, glycan analysis, or peptide mapping one main aspect of their thorough characterization. This review focuses on the charge-based analysis of biopharmaceuticals through CE. An overview is given about the three separation techniques cIEF, imaged cIEF and CZE for the analyses of charge variants, emphasizing assays and their precision. Especially the developments in the experimental conditions have been given a high priority: sample preparation, capillary properties, anolytes and catholytes, carrier ampholytes, sacrificing agents, solubility enhancement, isoelectric point marker, mobilization techniques, and detection modes have been discussed. CIEF shows a particularly high heterogeneity in its methods. Therefore, a design space is suggested that states the most important adjustable parameters and their range. This enables an adequate design of experiments for individual sample separations, in order to accelerate and simplify method developments.