DILUTED VERSUS UNDILUTED CYCLODEXTRIN DERIVATIVES IN CAPILLARY GAS-CHROMATOGRAPHY AND THE EFFECT OF LINEAR CARRIER GAS VELOCITY, COLUMN TEMPERATURE, AND LENGTH ON ENANTIOMER SEPARATION

The effect of dilution of the chiral stationary phase octakis(3-O-butyryl-2,6-di-O-pentyl)-gamma-cyclodextrin in the achiral polysiloxane OV-1701 on the separation factor was investigated over a wide concentration range. The loss in enantioselectivity was only negligible down to a dilution of 50 % (w/w), since the separation factor vs. concentration curves levels off at higher concentrations. Because of the strong temperature dependence of the separation factors, the properties of short columns (10 m and 4.5 m) were evaluated. These short columns, which allow operation at low temperatures and lead to enhanced separation factors were found to be appropriate for the separations of simple mixtures, because the gain in selectivity exceeded the loss in separation efficiency. For complex mixtures, the higher efficiencies of columns of at least 25 m in length were still necessary. A plot of In alpha vs. 1/T did not yield straight lines, but showed a significant curvature, leading to considerable relative errors if thermodynamic data were derived from these plots.