Objective:Protein content determination is one of the most important quality control aspects for biotherapeutics,for instance Interferon α 2a(IFN α 2a).The accuracy of protein content determination provides not only the quality control base for specific activity and filling of the biotherapeutics,but also an important reference data for stability evaluation,residual impurities control and other physiochemical properties identification.Currently,commercially available kits for total protein content determination provide bovine or human serum albumin as assay standard substance.However,systematic errors will be introduced to the test results inevitably due to the differences in amino acid composition between IFN α 2a and serum albumin standard substance.Although some of the manufactures applied IFN αt 2a itself as reference substance for protein content determination in the internal release control,the traceability background is not clear for the assigned protein content——they could not explain how they assigned protein content for the first batch of internal reference substance exactly.Recent years with the booming of the similar biotherapeutic products(SBP)including IFN α 2a,more and more guidelines and regulations require a head to head thoroughly comparative study between similar biotherapeutic products(SBP)and reference biotherapeutic product(RBP).Therefore,to develop a homogeneous standard substance for IFN α 2a protein content determination with clear traceability background will contribute to the IFN α 2a quality control as well as the head to head comparative study.