CHARGED AND UNCHARGED CYCLODEXTRINS AS CHIRAL SELECTORS IN CAPILLARY ELECTROPHORESIS

Chargeable cyclodextrins (CD's) offer new possibilities for the separation of enantiomers in capillary electrophoresis. Carboxymethylated, carboxyethylated, and succinylated beta-cyclodextrin were used in these experiments in two different modes. At low pH (< pH 4) all carboxylic functions were protonated and the CD's behaved as ''quasi stationary phases''. At high pH (> pH 5), deprotonation of the carboxylic functions lead to mobility of the negatively charged chiral selectors themselves. They acted then as micellar-like systems which can be described as ''moving stationary phases''. Under these conditions the separation of uncharged enantiomers was possible. Additionally the capability of these cyclodextrins as ion-pairing agents for the separation of enantiomers with positive charges has also been investigated. Employing the same cyclodextrin in the charged and the uncharged modes (at high or low pH) the migration order of the enantiomers could be reversed.