Quantitation and on-line concentration of enantiomers in open-tubular capillary electrochromatography

The feasibility of open-tubular capillary electrochromatography (OTCEC) wit h UV detector for quantitation of enantiomers is explored, and a simple on- line sample concentration method to improve detection sensitivity of negati vely charged enantiomers more than 1000-fold is described. With a capillary of 25 mum ID, the limits of detection (LODs) for absolute concentration an d for enantiomeric ratio are 10(-6) M and 0.6-0.8% (signal-to-noise ratio S /N = 10). Good linearity and reproducibility are observed. The detection se nsitivity is enhanced by combination with field-enhanced sample injection ( FES[). A water plug is introduced hydrodynamically into the capillary inlet end and then the sample solution prepared with water is introduced with el ectrokinetic injection. With this concentration technique, the LOD for abso lute concentration is reduced to a 10(-9) m level. On the other hand, due t o the peak-sharpening eff ect of FES], the LOD for enantiomeric ratio for t he first-eluted enantiomer is significantly improved, being 0.3%. Effects o f the injection conditions, such as length of water plug, buffer concentrat ion, injection voltage, and injection time on the enrichment efficiency are investigated. Online concentration of a racemic compound with two chiral c enters is demonstrated.