Simultaneous separation and enantioresolution of racemic local anesthetic drugs by capillary zone electrophoresis with Tween 20 and methyl-beta-cyclodextrin as selectors, employing a double plug technique

A new approach for simultaneous chiral and achiral separations by capillary zone electrophoresis is described. Two adjacent selector plugs, consisting of Tween 20 as an achiral and methyl-beta-cyclodextrin (CD) as a chiral se lector, are employed and four related local anesthetics are used as model c ompounds. The principles of the partial filling technique, whereby the capi llary is filled with the chiral selector solution followed by the micellar solution at different plug lengths and concentrations, prior to application of the solutes, was employed. During the run both capillary ends were dipp ed in a simple buffer, i.e., one without additives. The two separation medi a worked independently without any interaction. Separation of the solutes a nd their enantiomers was regulated by adjusting both the concentration and plug length (PL) of the micellar solution in the capillary, employing methy l beta-CD as chiral selector either at 38 or 76 mM, The solutes were separa ted on the basis of their affinity towards the micellar phase before they r eached the methyl-beta-CD plug for enantioseparation. In the absence of the micellar plug, the enantiomers of prilocaine overlapped those of bupivacai ne. The solutes and their enantiomers were completely separated by employin g two adjacent plugs consisting of 100 mM Tween 20 solution (PL approximate to 10 cm) and methyl-beta-CD solution at either 38 or 76 mM (PL approximat e to 30 cm).