Migration behaviour and selectivity of dichlorophenols in micellar electrokinetic capillary chromatography - Influence of micelle concentration and buffer pH

The migration behaviour and selectivity of isomeric dichlorophenols (DCPs) were investigated with micellar electrokinetic capillary chromatography (MECC) and sodium dodecyl sulfate (SDS) as an anionic surfactant in a phosphate-borate buffer solution. The electrophoretic mobility of each solute as a function of the micelle concentration at six pH values from 6.00 to 8.51 was measured and the influence of the concentration of micelles in the range 0-40 mM on the migration behaviour and selectivity of the isomeric species was examined. The results indicate that these properties were greatly influenced by the micelle concentration and by the buffer pH, and varied continuously in the vicinity of the critical micelle concentration (cmc). The influences of micellar concentration and pH correlate at low SDS concentrations when the solute is partially dissociated. An inversion point, at which a reversal of the migration order of 2,5-DCP, 2,3-DCP, 2,4-DCP and 3,4-DCP occurred, was observed in plots of the mobility as a function of the SDS concentration at a given pH. As the SDS concentration was increased, the influence of micelle concentration was enhanced, accompanied by a decreased influence of pH. Based on the magnitude of the binding constants of these solutes with the micelles, the migration order of dichlorophenols in MECC was rationalized. A comparison of the migration behaviour and selectivity of dichlorophenols in MECC and capillary zone electrophoresis (CZE) was made. The cmc and binding constants of six isomeric dichlorophenols with micelles are reported.