Investigation of an enantioselective non-aqueous capillary electrochromatography system applied to the separation of chiral acids

A weak anion-exchange type chiral stationary phase (CSP) based on tert.-but ylcarbamoylquinine as chiral selector and silica as chromatographic support was applied to non-aqueous capillary electrochromatography. The mobile pha ses used consisted of acetonitrile and methanol as organic solvents, and ac etic acid and triethylamine were added as background electrolytes. The infl uence of several experimental parameters (electrolyte concentration, acetic acid-triethylamine ratio, acetonitrile-methanol ratio and temperature) was evaluated in order to obtain improved enantioselectivity and efficiency as well as short run times for the enantiomeric separation of negatively char ged chiral analytes including benzyloxycarbonyl, N-(3,5-dinitrobenzyloxycar bonyl, 9-fluorenylmethoxycarbonyl, benzoyl, acetyl and N-(2,4-dinitrophenyl ) derivatized amino acids and profens. Solvent composition of acetonitrile- methanol (80:20) and enhanced electrolyte concentrations up to 600 mM aceti c acid at a constant acid-base ratio of 100:1 with high applied voltages of -25 kV proved to be optimum regarding short retention times and improved e fficiencies. For example, the enantiomers of Fmoc-Leu could be separated in less than 10 min with a resolution factor of 6.9 and about 100 000 theoret ical plates per meter. (C) 2000 Elsevier Science B.V. All rights reserved.