Gas Chromatography - GC Columns > Chiral Stationary Phases > Page 35

Figure 20. The Structure of a - Cyclodextrin

The phenyl-methyl-polysiloxane confers onto the column an intermediate level of polarity so the separations are basically enthalpic due to the dispersive and polar interactions that take place largely with the polymer but also entropic resulting from the chiral selectivity of the cyclodextrins.

 

Derivatization of the base cyclodextrin structure can introduce groups to which only one enantiomer can interact, while the other(s) are partially or wholly entropically hindered from interaction. This increases the differential interaction between the enantiomers and the stationary phase, thus, increasing the separation ratio and hence the resolution.

 

Courtesy of Supelco, Inc.

 

Solute Retention Time (min.)
1. R-N-TFA-Amphetamine 10.12
2. S-N-TFA-Amphetamine 10.86
3. S-N-TFA-Methamphetamine 11.41
4. R-N-TFA-Methamphetamine 11.92
5. d-N-TFA--Pseudoephedrine 13.08
6. l-N-TFA-Pseudoephedrine 13.93