ENANTIOMERIC SEPARATIONS IN CAPILLARY ZONE ELECTROPHORESIS USING A CHIRAL CROWN-ETHER

Chiral separations of optically active amines using 18-crown-6 tetraca rboxylic acid (18C6H(4)) as pseudo-stationary phase in capillary zone electrophoresis were studied. The buffer composition and pH strongly a ffected the performance of the separation. Although good separations w ere achieved using tertiary (triethylamine) or quaternary amines (tetr amethylammonium) as cationic buffer constituents, with respect to spee d of analysis, separation factor and efficiency, the best results were obtained with Tris. pH was shown to be an important factor for method optimization. Although inclusion complexation of primary amines is en hanced with increasing pH, the difference in the Gibbs free energy of the complexation of D,L-tryptophan was highest at pH 2.5. A synergisti c effect on the resolution of chiral amines was observed when IsC6H(4) and cyclodextrin were dissolved in the same buffer. With this system the enantiomers of noradrenaline could be baseline separated even thou gh neither of the two chiral selectors by itself was able to reserve t he enantiomers. The separation factor depends strongly on the concentr ations of the two selectors. It was demonstrated that simply complexat ion of the cyclodextrin rather than chiral recognition was the basis f or the improved separation.