Gas Chromatography

Chiral gas chromatography (GC) has emerged as an extremely efficient and sensitive method for the determination of the enantiomeric purity of chiral drugs. In addition, it is now possible to effect preparative separations of volatile racemic compounds. The main limitation of this technique is that the sample needs to be readily vaporized without decomposition. However, there are a number of advantages to the use of chiral GC such as the ability to analyze multicomponent mixtures of enantiomers and to separate the enantiomers away from trace contaminants. It is possible to extend the detection of enantiomeric impurities down to the picogram level enabling the reliable determination of ee to levels >99.9%.

Chiral GC relies on the use of a CSP of high enantiomeric purity to effect resolution of mixtures of enantiomers.

5.6.3 Capillary Electrophoresis

This relatively new method of enantioseparation involves the use of capillary electromigration techniques. In common with chiral GC and HPLC the origin of the enantioseparation lies in the noncovalent intermolecular interactions between the analyte and the chiral selector and is not based on electrophoretic mobility, as enantiomers possess the same charge densities. Capillary electrophoresis is usually carried out with bare silica capillaries. For this reason the chiral selector is added to the electrolyte in order to form diastereomeric complexes with the analyte thereby effecting chiral discrimination. In common with HPLC a number of chiral selectors have been used to effect enanti-oseparation such as cyclodextrins, polysaccharides, macrocyclic antibiotics, and proteins.

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