MIGRATION BEHAVIOR OF PHTHALATE-ESTERS IN MICELLAR ELECTROKINETIC CHROMATOGRAPHY WITH OR WITHOUT ADDED METHANOL

Selected phthalate esters including priority pollutants were analyzed by micellar electrokinetic chromatography (MEKC). Addition of methanol (20%, v/v) to aqueous migration buffer solution containing 0.05 M sodium dodecyl sulfate (SDS) improved the resolution of their separation. To investigate the migration behavior of the phthalate esters, we calculated distribution coefficients in micellar solubilization of the phthalate esters from the analytical data of MEKC. A linear relationship between the logarithms of the measured distribution coefficients and those of octanol-water partition coefficients reported in the literature was observed with both SDS solution and methanol mixed solution. Using this relationship, the migration times of phthalate esters were estimated from their octanol-water partition coefficients. Enthalpy and entropy changes resulting from their micellar solubilization were also evaluated in order to investigate the distribution mechanism of the phthalate esters. The enthalpy changes decreased with an increase in the alkyl chain length of the phthalate esters with both SDS solution and methanol mixed solution. On the other hand, the trends of the entropy changes with alkyl chain length were different for the two solutions. These results suggest that the solute-solvent interaction is different for the two solutions.