Achiral selectivity in cyclodextrin-modified capillary electrophoresis

Torus-shaped, circular, and hydrophilic cyclodextrins (CD) have been frequently used in capillary electrophoresis (CE) as buffer modifiers to effect chiral separation of enantiomers of drugs and specialty chemicals. Although less common, both neutral and charged cyclodextrins have also been exploited in CE to optimize the achiral separations of peptides, proteins, small molecules and a variety of positional isomers. Nonionic CDs are only useful for separations of net charged analytes through judicious partitioning of such guest molecules into their hydrophobic cavity of the former. However, they can be used with a surfactant for an effective resolution of neutral solutes as a result of a differential partitioning of such solutes in the micellar and the cyclodextrin-modified buffer phase. Ionic cyclodextrins, particularly, negatively charged derivatives with their own electrophoretic mobilities, increase the separation window and enable better resolution of analytes which weakly complex with or are poorly differentiated by neutral cyclodextrins.