Factors affecting the separation of mandelic acid enantiomers by capillary electrophoresis

Summary

The separation of the optical isomers of mandelic acid by capillary electrophoresis using γ-cyclodextrin as a chiral selector is presented. The mobility of the enantiomers can be regulated by adjustment of the pH, the concentration of the chiral selector and by the molarity and the temperature of the buffer. Different organic modifiers can either increase or decrease resolution. The importance of the nature of the electrolyte is evidenced by the fact that acceptable enantioseparation has only been achieved using phosphate buffer. The factors affecting the mobility are discussed. A simple equation describing the apparent mobility of the analytes in buffers containing cyclodextrins is presented. The equilibrium constant for the inclusion complex formation of mandelic acid with γ-cyclodextrin was found to be 2.8 M⁻¹ for D-mandelic acid and 2.4 M⁻¹ for the L-enantiomer.