As final products in biotechnological and pharmaceutical industry, the antibodies, protein-based therapeutics, and other recombinant proteins must have their purity and heterogeneity determined. That's because contaminants and modified forms of the product during the production process will drastically alter the biological activity of these proteins. The contaminants and modified forms of the product should be removed to ensure the high purity and then the safety and efficiency of the protein drugs. To successfully evaluate each step of the production system, it is important to develop sensitive and accurate analytical methods for protein purity and homogeneity analysis.