The Mechanism of Chromatographic Retention - Chiral Chromatography > Chiral Polysiloxane Stationary Phases > Page 70

The primary hydroxyl groups are located at the base of the torus on the C6 atoms. As these hydroxyl groups are free to rotate, they partially block the base aperture. The size of the cavity increases with increasing number of glucose units (figure 33).

Chiral selectivity can be exploited in LC by either adding a chirally active component to the mobile phase or the stationary phase. but chirally modified stationary phases are the more common. There are five general types of stationary phase in common use in LC. The first type is the protein based stationary phase. These were the first to be developed and are usually natural proteins bonded to a silica matrix. They contain a large number of chiral centers and interact selectively with small molecular weight solutes. Although there are specific interactive sites that provide the chiral selectivity, the majority of the molecule contributes to general retention.

Courtesy of Supelco

Figure 33 A Molecular Model of Cyclodextrin