In the development and production of protein biologics, charge isomers of the target protein can arise due to Post-Translational Modifications (PTMs) and degradation. Biopharmaceutical groups rely on Capillary IsoElectric Focusing (cIEF) and imaged cIEF (icIEF) to quantify the charge isomers present. Characterizing biological charge isomers is useful for many life cycle stages including cell line selection, stability studies, formulation, and processing control but this characterization requires the proteins to be separated into individual charge fractions with enough purity for downstream assays.

Further, the direct coupling of icIEF to a Mass Spectrometer (MS) for characterization would streamline the characterization process significantly. 

AES has developed the CEInfinite preparative icIEF system and proprietary Whole Column Image Detection (WCID) separation cartridges for fractionation and online coupling of icIEF to MS. WCID allows for real-time observation of the separation focusing (icIEF) as well as the subsequent mobilization process to isolate the charge isomer peaks. During pressure mobilization, an electric field keeps the samples in the separation capillary focused. The separation capillary has a larger Inner Diameter (ID) and the transfer capillary has a smaller ID. Hence, this difference greatly minimizes the remixing of separated protein isomers as they travel away from the cartridge.