Determination of enantiomeric excess using a chiral selective separation mode and polarimetric detection

The quantitative capabilities of a system that combines a chiral selective separation mode with polarimetric detection (CSS/PD) were investigated in terms of the ability to quantitate enantiomeric mixtures even under conditions of poor chromatographic resolution. The laser-based polarimetric detection system can provide a rotational sensitivity on the order of 10 mudeg corresponding to a minimum measurable quantity of 10 ng for a compound with a specific rotation of 100 deg (g/ml)(-1) dm(-1). For the chromatographic studies, peak height and peak area were measured as analytical descriptors of the bimodal response function of this polarimetric detector. Analyses of the dansylated enantiomers of the amino acids phenylalanine, threonine, and valine have shown that chromatographic resolution and specific rotation are important factors affecting the shape of the polarimetric response curve. With CSS/PD, enantiomeric materials can be quantitated at both low and high enantiomeric excess (ee) even at resolutions of 0.3-0.4.