Evaluation of an icIEF‐MS system for comparable charge variant analysis of biotherapeutics with rapid peak identification by mass spectrometry

Protein therapeutics are usually produced in heterogeneous forms during bioproduction and bioprocessing. Heterogeneity results from post‐translational modifications that can yield charge variants and require characterization throughout product development and manufacturing. Isoelectric focusing (IEF) with UV detection is one of the most common methods to evaluate protein charge heterogeneity in the biopharmaceutical industry. To identify charge variant peaks, a new imaged microfluidic chip‐based isoelectric focusing (icIEF) system coupled directly to mass spectrometry was recently reported. Bridging is required to demonstrate comparability between existing and new technology. As such, here we demonstrate the comparability of the pI value measurement and relative charge species distributions between the icIEF‐MS system and the control data from a frequently utilized methodology in the biopharmaceutical industry for several blinded development‐phase biopharmaceutical monoclonal antibodies across a wide pI range of 7.3–9.0. Hyphenation of the icIEF system with mass spectrometry enabled direct and detailed structural determination of a test molecule, with masses suggesting acidic and basic shifts are caused by sialic acid additions and the presence of unprocessed lysine residues. In addition, MS analysis further identified several low‐abundance glycoforms. The icIEF‐MS system provides sample quantification, characterization, and identification of mAb proteoforms without sacrificing icIEF quantification comparability or speed.