Page 207 - Chiral Separation Techniques

Chiral Separation Techniques: A Practical Approach, Second, completely revised and updated edition
Edited by G. Subramanian
Copyright © 2001 Wiley-VCH Verlag GmbH
ISBNs: 3-527-29875-4 (Hardcover); 3-527-60036-1 (Electronic)
7 Chiral Derivatization Chromatography

Michael Schulte

7.1 Introduction

Discrimination between the enantiomers of a racemic mixture is a complex task in
analytical sciences. Because enantiomers differ only in their structural orientation,
and not in their physico-chemical properties, separation can only be achieved within
an environment which is unichiral. Unichiral means that a counterpart of the race-
mate to be separated consists of a pure enantiomeric form, or shows at least enrich-
ment in one isomeric form. Discrimination or separation can be performed by a wide
variety of adsorption techniques, e.g. chromatography in different modes and elec-
trophoresis. As explained above, the enantioseparation of a racemate requires a non-
racemic counterpart, and this can be presented in three different ways:

1. As a unichiral template which is used as a stationary phase itself, or which is
bonded to a solid support (silica particles or fused silica capillaries).
2. As a unichiral additive which is mixed with the racemate of interest to form non-
covalent diastereomeric complexes which can be distinguished by achiral tech-
niques.
3. As a unichiral group which reacts with the racemate to form diastereomeric
molecules which can be separated by achiral adsorption processes.
This chapter will focus on topic 3, which is normally regarded to be chiral deriva-
tization chromatography, but will also cover other topics that might be considered
when applying derivatization techniques. The goal for the separation of the race-
mates may be their analysis or their preparation. Both topics will be covered in this
chapter.