Enantiomeric separation by capillary electrophoresis : With special emphasis on the partial filling technique

Abstract: Capillary electrophoresis as a powerful separation technique was employed for resolution of racemic drugs. Taurodeoxycholate (TDC), different cyclodextrins and α1- acid glycoprotein (AGP) were dissolved in the background electrolyte at low pH (3.0 to 4.0 ) as chiral selectors.Enantioresolutions were based on the principle of micellar electrokinetic chromatography, inclusion complexation and affinity interactions between the enantiomers and TDC, cyclodextrins and AGP, respectively.The influence of chiral selector concentration and type, temperature and addition of organic modifiers on enantioselectivity were studied. The temperature was found to be an important factor for regulation of the enantioresolution.In order to avoid UV-absorbance interferences between AGP as a UV-absorbing chiral selector as well as to reduce consumption of chiral selector solution, the partial filling technique (PFT) was employed. The technique was developed and equations describing the feature of the technique as an efficient separation mode in CE was presented. Parameters such as applied plug length (PLapp) and effective plug length (PLeff) were determined. Equations expressing the relation between the PLeff and selectivity and resolution factors were developed.The PFT was used for determination of association constants between AGP as chiral selector and the enantiomers of disopyramide and remoxipride. The association was strongly temperature dependent, and a maximum in binding was observed at 25°C. The PFT was found to be a very convenient approach for measurement of association constants. To verity the above mentioned technique for evaluation of binding constants, the association constants between methyl-β-cyclodextrin and the enantiomers of orciprenaline at different chiral selector concentrations were measured and compared with the data obtained by the conventional technique. The results illustrate the reliability of the system based on the PFT.