Chiral separation by cyclodextrin-modified micellar electrokinetic chromatography

Abstract

Chiral separation by micellar electrokinetic chromatography (MEKC), which permits the separation of uncharged or electrically neutral compounds by the electrophoretic technique, was achieved through the addition of cyclodextrins (CDs) to sodium dodecyl sulphate (SDS) micelle solution. In this cyclodextrin-modified MEKC (CD-MEKC), CDs cannot be solubilized to the SDS micelle and migrate with the same velocity as that of the electroosmotic flow. The solutes are distributed among three phases, an aqueous phase, the micelle and the CD. Chiral recognition depended on the type of CD; in particular, γ-CD was effective for the chiral separation in this method. The addition of an organic solvent or a chiral compound such as sodium d-camphor-10-sulphonate or l-menthoxyacetic acid to the SDS micelle solution containing CDs improved the enantioselectivity. The addition of CDs reduced the capacity factors of solutes; in contrast, chiral additives increased them. The resolution was optimized by changing the concentrations of CDs and chiral additives. The chiral separation mechanism is also briefly discussed.