Control of the elution order of enantiomers by light irradiation using azobenzene-modified chiral stationary phases in micro liquid chromatography

Abstract

In micro liquid chromatography, a method for the reversible control of the elution order of enantiomers by light irradiation was developed. Two photo-responsive chiral stationary phases (CSP(1) and CSP(2)) with an azobenzene moiety were prepared using D- and L-valine, respectively. The prepared stationary phases were continuously packed into a UV-permeable polymer-coated fused-silica capillary tubing (100 μm, i.d.) with 20 cm of length, respectively, and used as a micro column. When 3,5-dinitrobenzoyl-D,L-leucine isopropyl ester and 3,5-dinitrobenzoyl-D,L- alanine methyl ester were used as test samples, the samples were eluted in the order D-form and L-form, after UV light was irradiated to only the part of CSP(1) in the column. Continuously, when UV light was irradiated to the part of CSP(2) after visible light was irradiated to the CSP(1), the elution order became L-form and D-form. It could be seen that a reversible change in the retention order was caused by the reduction of the enantio-selectivity of the stationary phase by UV light irradiation.