A novel microchip‐based imaged CIEF‐MS system for comprehensive characterization and identification of biopharmaceutical charge variants

A microfluidic system has been designed that integrates both imaged capillary isoelectric focusing (iCIEF) separations and downstream MS detection into a single assay. Along with the construction of novel instrumentation and an innovative microfluidic chip, conversion to MS‐compatible separation reagents has also been established. Incorporation of 280 nm absorbance iCIEF‐MS analysis not only permits photometric quantitation of separated charge isoforms but also facilitates the direct monitoring of analyte focusing and mobilization in real‐time. The outcome of this effort is a device with the unique ability to allow for both the characterization and identification of protein charge and mass isoforms in under 15 min. Acquisition, quantitation, and identification of highly resolved intact mAb charge isoforms along with their critical N‐linked glycan pairs clearly demonstrate analytical utility of our innovative system. In total, 33 separate molecular features were characterized by the iCIEF‐MS system representing a dramatic increase in the ability to monitor multiple intact mAb critical quality attributes in a single comprehensive assay. Unlike previously reported CIEF‐MS results, relatively high ampholyte concentrations, of up to 4% v/v, were employed without impacting MS sensitivity, observed to be on the order of 1% composition.