1. National Institute of Metrology, No. 18, Bei San Huan Dong Lu, Chaoyang District, Beijing 100029, China
2. Key Laboratory of Protein and Peptide Drugs, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road,
Chaoyang District, Beijing 100101, China
3. Bioprocess Measurements Group, National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, Maryland 20899, United States