DIRECT AND INDIRECT CHIRAL SEPARATION OF AMINO-ACIDS BY CAPILLARY ELECTROPHORESIS

Two approaches to the chiral separation of racemic mixtures of amino acids by means of capillary electrophoresis have been evaluated. These were indirect separation of diastereomers formed by derivatization with (+)- or (-)-1-(9-fluorenyl)ethyl chloroformate and direct chiral separation after derivatization with 9-fluorenylmethyl chloroformate. Separation conditions were optimized by the application of a full factorial design. For indirect separation, concentration of sodium dodecyl sulphate (SDS) and pH were the most important separation variables, and for direct separation, concentration of isopropanol (IPA), beta-cyclodextrin and SDS were the most prominent factors affecting separation. The presence of IPA was a prerequisite for chiral recognition. With regard to selectivity, efficiency, analysis time and ease of method development the best results were provided by the indirect method. It should be noted, however, that the success of this approach is based on the availability of a derivatization reagent in high optical purity.