A critical study of the measurement and calibration of circular dichroism.

Abstract A critical study has been made of circular dichroism (CD) measurements at the wavelengths around 500, 290, and 220 nm. Instruments calibrated at 290 nm with (+)-camphor-10-sulfonic acid gave results for molecular ellipticities [θ] showing deviations up to >30%, at both 220 and 490 nm. Older instruments tended to given higher values of [θ] at 490 nm and lower values at 220 nm, probably due to the age of the Pockel cells. A proposal is made to use d -pantolactone and (+)-tris(ethylenediamine) cobalt (III) iodide monohydrate as calibration standards at 220 and 490 nm, respectively, together with (+)-camphor-10-sulfonic acid at 290 nm.