Experimental test of absorption flattening correction for circular dichroism of particle suspensions.

There are well established theoretical models for correction for absorption flattening of circular dichroism (CD) measurements on particle suspensions. However, these have not been directly tested experimentally. We describe a test system with the chiral tris(ethylenediamine)Co(III) complex dissolved in water trapped inside sephadex particles, suspended in 1-butanol. Independent measurements of particle size distribution, volume fraction, and the absorbance of the suspension are used to calculate the required CD correction. The corrected CD signal is found to agree rather well with that for the same amount of Co-complex dispersed uniformly throughout the sample cell. This holds for different particle volume fractions and Co-complex concentrations inside the particles. The correction seems to work despite a substantial scattering contribution to the absorbance, which is not considered in the theoretical models.