1. Bioprocess Measurements Group, Biomolecular Measurement Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
2. Biomolecular Structure and Function Group, Biomolecular Measurement Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
3. Institute for Bioscience and Biotechnology Research, Rockville, Maryland 20850, United States