Systematic approach to the treatment of enantiomeric separations in capillary electrophoresis and liquid chromatography .3. A binding constant-retention factor relationship and effects of acetonitrile on the chiral separation of tioconazole

In previous chiral CE work on the separation of tioconazole enantiomers by P-cyclodextrin, the mode of action of alcohols as organic modifiers has been elucidated. Using acetonitrile, an increase in the organic modifier concentration in the range 0-15% (v/v) is found to cause twice the decrease in the value of the host-guest binding constant in comparison to methanol. With both modifiers, the selectivity (alpha=1.23) is the same across the full solvent composition range, consistent with action via alteration in solvent affinity for the free analyte. A unified treatment linking binding constants in CE and retention (capacity) factors in LC is developed for the case where 1:1 binding between selector and analyte occurs. This is parameterised for cyclodextrins as mobile phase additives in CE and chiral stationary phase selectors in LC. Reasonable agreement is found between the observed and calculated relationship between LC and CE results for tioconazole binding to beta-cyclodextrin in water-organic cosolvent mixtures. This suggests that CE may be used for the optimization of the same separation in LC, allowing method development time in LC to be substantially decreased using data gathered in CE experiments.