SELECTIVITY IN CAPILLARY ELECTROPHORESIS - APPLICATION TO CHIRAL SEPARATIONS WITH CYCLODEXTRINS

In order to accurately evaluate the performances of any electrolyte me dium, a clear concept of selectivity in capillary electrophoresis and related electroseparation techniques is proposed. Selectivity is defin ed as the ratio of the affinity factors of both analytes for a separat ing agent (phase, pseudophase, or complexing agent present in the back ground electrolyte). When in the presence of a complexing agent and if only 1:1 complexation occurs, selectivity corresponds to the ratio of the apparent binding constants and is independent of the concentratio n of the complexing agent. This concept is illustrated through the sep arations of neutral and anionic enantiomers in the presence of a catio nic cyclodextrin, the mono(6-amino-6-deoxy)-beta-cyclodextrin, as a ch iral complexing agent. The values obtained for different pairs of enan tiomers are discussed with regard to the functional groups that distin guish them. When the analytes have the same mobilities in free solutio n and in their complexed form, then the resolution equation developed in micellar electrokinetic chromatography may be applied and optimum c onditions (affinity factors, chiral agent concentration) can be predic ted.