A comparative study of the enantiomeric separation of labeled amino acids with cyclodextrins and mixed micelles in capillary electrophoresis

Enantiomeric separations of fluorescently labeled amino acids are studied by capillary electrophoresis (CE) under a novel variety of experimental conditions. Three different labels are evaluated using two different additives: cyclodextrins (beta- and gamma-) and a dual surfactant system of sodium dodecyl sulfate and sodium taurodeoxycholate. Fluorescein-5-isothiocyanate is the best label to use in this cyclodextrin-based system, and dansyl chloride is the best label to use in this dual surfactant system. Possible limitations for separation of the enantiomers using the mixed micelle system include the fact that there is little interaction of the solute with the surfactants, the negative charge of the solute is limiting the separation window of the system, and the amount of the chiral phase available for partitioning is limited. The separations using cyclodextrins as a chiral selector show that the label affects migration order of the enantiomers, and the cyclodextrins are very effective in separating numerous enantiomers. Overall, cyclodextrins are the better buffer additive for CE use, and the dual surfactant systems, including sodium taurodeoxycholate, offer future promise.