Enantiomeric separation of local anaesthetic drugs by micellar electrokinetic capillary chromatography with taurodeoxycholate as chiral selector

The enantiomeric separation of local anaesthetic analogues, by means of micellar electrokinetic chromatography (MEKC), using taurodeoxycholate (TDC) both as chiral selector and as surfactant was studied. In this system the analytes are migrating with the micellar phase towards the anode. When a mixed micellar phase between TDC and Brij-35 [polyoxyethylene(23)-dodecanol] was used, the migration direction and migration order of the enantiomers were reversed due to a decreased distribution of the analytes to the micellar phase. The separation time with the mixed micelles is significantly shorter than with neat TDC as the micellar phase. The success of the chiral separation is strongly dependent on the concentration of TDC, there is an optimal concentration of the surfactant for each enantiomer pair in accordance with a proposed theory for the association between the analytes and TDC. In the mixed micellar phase optimum chiral resolution for each analyte was achieved at different ratios of TDC and Brij-35. It is further shown that the affinity of the [S-(+)]-enantiomers for TDC was higher than that of the [R-(-)]-forms.