Wave-Mixing Circular Dichroism Detector for Chiral Liquid Chromatography

Abstract

A circular dichroism (CD) detector based on laser four-wave mixing (FWM) is demonstrated using separate injections of analyte enantiomers onto a standard silica-based microbore high-performance liquid chromatography (HPLC) column. Using the chiral column, a preliminary “detected” mass detection limit of 180 pg is determined inside a laser probe volume of 200 pL, corresponding to a circular dichroism detection limit, ΔA, of 2.2 × 10−5 for (—) camphorquinone. Detection sensitivity levels are dramatically improved when our FWM-CD detector is interfaced to a microbore system due to the lower mobile-phase flow rates and the smaller sample concentrations required for the analysis. Using the microbore column, a preliminary circular dichroism detection limit, ΔA, of 1.6 × 10−6 and a preliminary concentration detection limit of 4.1 × 10−4 M are determined for camphorquinone. This corresponds to a “detected” mass detection limit of 33 pg for the chiral compound. Laser wave mixing offers better detection limits than conventional circular dichroism detection methods and, hence, offers many promising applications.