Enantioseparation of local anaesthetic drugs by capillary zone electrophoresis with cyclodextrins as chiral selectors using a partial filling technique.

The enantiomers of prilocaine were successfully resolved with alpha-cyclodextrin, and those of mepivacaine and bupivacaine, with methyl-beta-cyclodextrin as chiral selectors, by means of capillary zone electrophoresis (CZE) employing a partial filling technique. By this separation mode, a discontinous separation zone is formed in the capillary. Prior to application of the actual drug substance, the capillary is partially filled with the separation solution. During the enantioseparation both ends of the capillary are dipped into the running buffer solution, i.e., without chiral selector. The consumption of chiral selector is thus very low, less than a microliter per run. The repeatibility of the electrophoretic mobility of the enantiomers was better than 1.2% relative standard deviation (RSD). The effect of the length of the separation zone on the resolution of the enantiomers was studied. The application time of the chiral selector, instead of the selector concentration, was varied in order to improve and regulate the enantioresolution and reduce consumption of the chiral selector as much as possible. It was found that the enantioseparations were directly affected by the length of the separation zone, and there was a minimal plug length where complete enantioresolution was achieved.