Enantiomer separation by nonaqueous and aqueous capillary electrochromatography on cyclodextrin stationary phases

Native beta- and gamma -cyclodextrin bound to silica (ChiraDex-beta and Chi raDex-gamma) were packed into capillaries and used for enantiomer separatio n by capillary electrochromatography (CEC) under aqueous and nonaqueous con ditions. Negatively charged analytes (dansyl-amino acids) were resolved int o their enantiomers by nonaqueous CEC (NA-CEC). The addition of a small amo unt of water to the nonaqueous mobile phase enhanced the enantioselectivity but increased the elution time. The choice of the background electrolyte ( BGE) determined the direction of the electroosmotic flow (EOF). With 2-(N-m orpholino) ethanesulfonic acid (MES) or triethylammonium acetate (TEAA) as BGE an inverse EOF (anodic EOF) was observed while with phosphate a cathodi c EOF was found. The apparent pH (pH*), the concentration of the BGE, and t he nature of the mobile phase strongly influenced the elution time, the the oretical plate number and the chiral separation factor of racemic analytes.