Enantioselective capillary electrophoresis of amino acid derivatives on cyclodextrin evaluation of structure-resolution relationships

Abstract

In this work a strategy for enantioselective separations of α-amino acid derivatives in cyclodextrin (CD)-modified capillary zone electrophoresis (CZE) is presented and the effects of various experimental parameters such as temperature, pH, applied voltage and the use of organic modifiers (methanol, tert.-butyl methyl ether, carnitin) have been studied in detail. For the modification of α-amino acids, also helpful in order to improve sensitivity by UV or fluorescence detection, well known derivatives such as dinitrobenzoyl, dinitrophenyl, dimethylaminonaphtylsulfonyl, car☐ybenzyl and 9-fluorenylmethoxycarbonyl and the new 6-aminoquinolyl-N-hydroxysuccinimidilcarbamoyl derivatives have been prepared, and the chiral derivatives have been tested with respect to their resolvability in CZE using different cyclodextrins (α-, β-, γ-CDs and CD derivatives) as chiral additives to the electrophoretic buffer system. In general the selector-selectand interactions could be improved by using amino acid derivatives containing nitro- or dimethylamino groups in combination with extended (methylated or hydroxypropylated) CDs. Further enhancement of enantiomeric resolution was achieved by the addition of organic modifiers and/or lowering the temperature down to 5°C. At temperatures above 40°C a non-linear relationship of the decrease of resolution as function of 1/T was noticed.