Chiral GC Columns by Derivative Type

Chiral capillary GC columns are manufactured using derivatized cyclodextrin stationary phases, either neat or after being doped at controlled percentages into a polysiloxane carrier. Cyclodextrins are macromolecules composed of 6 or more D(+)-glucose residues bonded through α-glycosidic linkages, and are classified according to the number of glucose residues they contain: α-cyclodextrins contain 6 residues, β-cyclodextrins contain 7 residues, and gγ-cyclodextrins contain 8 residues. The fact that there are three different size cyclodextrins (α-, β-, and γ-) allows for the separation of a wide variety of different sized analytes. The configuration of these macromolecules results in a structure that includes a cavity, the size of which increases with the increasing number of glucose residues. The mouth of the cavity has a larger circumference than the base.

Positions of dervitives on the CD structure:

The primary hydroxyl groups at the 6-positions of each glucose residue extend below the macromolecule. Because they are free to rotate, they partially block the base. The secondary hydroxyl groups at the 2,3-positions of each glucose residue extend above the macromolecule. All hydroxyl groups, whether at the 2,3,6-positions, can be selectively modified with a derivative to impart unique physical properties and inclusion selectivities. Without derivatization, no enantiomeric selectivity is exhibited.

Selectivity of these phases is a function of the derivative, the degree of derivatization, the position of the derivative on the cyclodextrin, whether the derivatized cyclodextrin is used neat or doped into a polysiloxane, and if doped, at what percentage. These phases are stable, high boiling liquids, and make effective stationary phases for gas-liquid chromatography.