A rapid cIEF–ESI–MS/MS method for host cell protein analysis of a recombinant human monoclonal antibody

A rapid and reproducible system that couples capillary isoelectric focusing to a high-resolution mass spectrometer was developed for on-line analysis and identification of protein digests. Magnetic microsphere-based immobilized trypsin was used for protein digestion to reduce the digestion time to 10 min, with a total analysis time of 4 h. A three-protein-mixture (myoglobin, BSA, cytochrome c) with a molarity ratio of 1:10:50 was successfully digested and identified. This system was also used to analyze host cell protein impurities in a recombinant humanized monoclonal antibody product in which the sample was product-depleted using affinity capture on protein A/protein L columns prior to analysis. A database search identified 37 host cell proteins with peptide and protein identity probability greater than 0.9.