Capillary electrophoresis of herbicides. II. Evaluation of alkylglucoside chiral surfactants in the enantiomeric separation of phenoxy acid herbicides

Two chiral alkylglucoside surfactants, namely n-octyl-(OG) and n-nonyl-β-D-glucopyranoside (NG), were evaluated in the enantiomeric separation of phenoxy acid herbicides. The enantiomeric resolution could be manipulated readily by adjusting the surfactant concentration, ionic strength, pH and separation temperature. The optimum surfactant concentration needed for maximum enantiomeric resolution varied among the different analytes and was an inverse function of the hydrophobicity of the phenoxy acid herbicides, with the most hydrophobic solute requiring less surfactant concentration for attaining a baseline enantiomeric resolution. Due to the ionic nature of the phenoxy acid herbicides, increasing the pH of the running electrolytes increased the degree of ionization of the acidic herbicides thus decreasing their association with the chiral micelles and in turn their enantiomeric resolution. Increasing the ionic strength seems to enhance both the solubilization of the solute in the micelle and the chiral interaction of the solute with the micelle with a net increase in enantiomeric resolution. Performing the separation at a sub-ambient temperature favoured an enhanced solute-micelle association and improved enantiomeric resolution.