Steps Toward Full Wavelength Range Calibration for Circular Dichroism Spectroscopy

Abstract

Circular dichroism (CD) measurements are important for the characterization of higher-order molecular structure in the biopharmaceutical industry. Comparing CD measurements between laboratories has been difficult. To reduce CD measurement uncertainty, good laboratory practice requires the measurement of cell path length. NIST has recently launched Standard Reference Material (SRM) 2082 for path length using absorbance intensity at 280 nm. Most CD instruments simultaneously measure both CD and absorbance spectra. Far ultraviolet measurements of CD spectra are usually made in cells with path lengths appropriate to the intended use of SRM 2082. One of the components of this standard, L-tryptophan, is chiral and could also be used as a reference material for CD intensity at 223 nm. However, the shape of the CD spectrum over many wavelengths is often used to describe the higher-order structure of biopharmaceuticals suggesting we need a more encompassing method. We will describe our efforts to develop a method to calibrate a CD instrument across the full wavelength range of the measured spectrum using SRM 2082.