High‐efficient characterization of complex protein drugs by imaged capillary isoelectric focusing with high‐resolution ampholytes

Abstract A carrier ampholyte is a molecule containing both acid and base functionality that is critical for imaged capillary isoelectric focusing. The quality of an imaged capillary isoelectric focusing separation for protein charge variants’ characterization is highly dependent on attributes of the carrier ampholytes used including baseline signal, linearity of the pH gradient, pI discrimination, and consistency between manufactured lots. AESlytes are a high‐resolution carrier ampholyte series that have been developed for the high‐resolution and selective characterization of diverse and complex protein drugs including diverse fusion proteins, antibody‐drug‐conjugate, bi‐specific antibodies, and viral proteins. While routine commercial ampholytes usually cannot solve such challenges, AESlytes demonstrate a reduction in baseline noise and distinguishably increased consistency between lots as compared to other commercial ampholytes. Here we apply AESlytes for the imaged capillary isoelectric focusing separation of several commercial fusion proteins and biosimilars with excellent repeatability. In addition, AESlytes with narrow‐range pH were employed directly coupled to a mass spectrometer for optimizing the separation resolutions allowing more reliable and accurate protein charge variant identification. Our study demonstrates that innovative high‐resolution carrier ampholytes as critical reagents play an essential role in high‐performance imaged capillary isoelectric focussing and tandem mass spectrometry analysis the routinely commercial ampholytes cannot achieve, especially for extremely complex protein drugs.