1. host cell protein analysis During the process of protein production and purification, such as recombinant proteins, some host cell proteins (HCPs) may still remain in the protein sample, which poses potential risks in the clinical application. Even though purification systems are well- developed and optimized, trace of HCPs still may still remain in the protein products. Any residual HCP, even low levels, can potentially compromise the safety and efficacy of biopharmaceuticals. Contamination of HCPs can cause allergic response in patients. Hence, it is crucial to analyze the percentage of HCPs in the purified protein products.