Selectivity in Capillary Electrophoresis:  Application to Chiral Separations with Cyclodextrins

Abstract

In order to accurately evaluate the performances of any electrolyte medium, a clear concept of selectivity in capillary electrophoresis and related electroseparation techniques is proposed. Selectivity is defined as the ratio of the affinity factors of both analytes for a separating agent (phase, pseudophase, or complexing agent present in the background 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 concentration of the complexing agent. This concept is illustrated through the separations of neutral and anionic enantiomers in the presence of a cationic cyclodextrin, the mono(6-amino-6-deoxy)-β-cyclodextrin, as a chiral complexing agent. The values obtained for different pairs of enantiomers are discussed with regard to the functional groups that distinguish them. When the analytes have the same mobilities in free solution and in their complexed form, then the resolution equation developed in micellar electrokinetic chromatography may be applied and optimum conditions (affinity factors, chiral agent concentration) can be predicted.

A family of single‐isomer positively charged cyclodextrins as chiral selectors for capillary electrophoresis: Mono‐6A‐butylammonium‐6A‐deoxy‐β‐cyclodextrin tosylate

“…Other examples on the use of singleisomer positively charged b-CDs in chiral CE have been published in literature [22][23][24][25][26].…”

Chiral capillary electrophoretic separation of amino acids derivatized with 9‐fluorenylmethylchloroformate using mixed chiral selectors of β‐cyclodextrin and sodium taurodeoxycholate

“…According to literature [13,17,23,24] and Eq. (1), the mobility difference of a pair of enantiomers, Dm, is the most critical to obtain chiral resolution.…”

“…Fillet et al [13,17] proposed that the mobility difference between a pair of enantiomers, Dm, was enlarged by the addition of a second chiral selector, which acted in a cooperative way. Slightly differently, Leliever et al [23] suggested a concept of intrinsic selectivity for binary CD, which was originally defined as the ratio of the affinity factors of the enantiomers for a single chiral selector [24]. Both of the concepts are undoubtedly helpful for better understanding of the improvement of separation selectivity in dual chiral selector systems.…”

Comparison of charged cyclodextrin derivatives for the chiral separation of atropisomeric polychlorinated biphenyls by capillary electrophoresis

“…The cationic CD b-CD-NH 2 used is a basic CD, which has one of its primary hydroxyl groups substituted by an amine function. This CD has an estimated pK a of 8.2, then at acid pH this CD is positively ionized [15]. On the other hand, at pH lower or equal to 2 the electroosmotic flow (EOF) is suppressed [45] and the neutral analytes investigated, without self-electrophoretic mobility, only will migrate to the detector when they are complexed with the charged CD.…”