Host cell proteins (HCPs) in biopharmaceuticals must be controlled in the downstream process (DSP) of antibody production, since it has critical influence on product quality. Generally, the majority of HCPs in harvested cell culture fluid are removed during the affinity step using Protein A chromatography resin, and the remaining HCPs are remove in the polishing step by a combination of ion-exchange chromatography, hydrophobic interaction chromatography, etc. Thus, identification of remaining HCPs after Protein A affinity chromatography process can work as…