Stereoselective Separations: Recent Advances in Capillary Electrophoresis and High-Performance Liquid Chromatography

Abstract

In 1848, Louis Pasteur discovered, for the first time, a method to resolve a racemate into its two enantiomers by crystallization (Wainer and Drayer 1993). Since then, this kind of separation has remained a challenging task in analytical chemistry as enantiomers possess identical properties except when in the presence of a chiral handle (plane-polarized light, chiral solvent, chiral reagent, etc.). As Pasteur proposed, enantiomers are separated as diastereomeric derivatives after a chemical reaction with a chiral selector which adds another asymmetric center. Indeed, diastereomers possess different physicalchemical properties which is why the technique of fractional recrystallization remains widely used after so many years (Collet 1989). However, other analytical techniques are now available for enantiomer analysis, which can be divided into two different categories: methods that do not involve separation such as polarimetry, nuclear magnetic resonance, calorimetry and enzymatic techniques, and methods based on separation. In this chapter, only the latter category will be discussed; description of the former may be found in different textbooks (Allenmark 1991; Krustulovic 1989; Wainer and Drayer 1988).