Fundamental aspects of chiral separations by capillary electrophoresis

A review is presented that surveys the basic theory of direct separation of enantiomers by capillary electrophoretic (CE) techniques. These separations are based on the formation of diastereomeric complexes between the enantiomeric analytes and a chiral selector added to the electrolyte solution. The review covers a comprehensive treatment of the equations needed for optimization of selectivity coefficients, resolution and analysis time in the zone electrophoretic mode. In this context, it takes into account combined equilibria of complexation and protonation/deprotonation as well as complexation and paritition into micelles. On the basis of these equations, the benefits of charged selectors and the optimization potential inherent to pH tuning can be documented. In addition, the review deals with some basic aspects of chiral isoelectric focusing and briefly discusses indirect enantioseparation. In a subsequent section a survey is given on particularfeatures of the various types of chiral selectors. Finally, the recent developments in preparative enantioseparation in continuous free-flow system and by use of isoelectric membranes are discussed.