Despite the early successes with the polysiloxane based stationary phases carrying peptide chiral selection agents, the chiral selectors used in contemporary chiral GC are largely cyclodextrin based. The cyclodextrins are produced by the partial degradation of starch followed by the enzymatic coupling of the glucose units into crystalline, homogeneous toroidal structures of different molecular size. Three of the most widely characterized are the alpha-, beta- and gamma-cyclodextrins and have been shown to contain 6 (cyclohexamylose), 7 (cycloheptamylose) and 8 (cyclooctamylose) glucose units, respectively. These cyclic, chiral, torus shaped macromolecules contain the D(+)-glucose residues bonded through a-(1-4)glycosidic linkages.

Courtesy of ASTEC Inc.

Figure 26. The Molecular Structure of a, b, and g Cyclodextrins