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 sod ium dodecyl sulfate (SDS) improved the resolution of their separation. To investigate the migration behavior of the phthalate esters, we cal culated distribution coefficients in micellar solubilization of the ph thalate 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 literatu re was observed with both SDS solution and methanol mixed solution. Us ing this relationship, the migration times of phthalate esters were es timated 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 p hthalate esters. The enthalpy changes decreased with an increase in th e alkyl chain length of the phthalate esters with both SDS solution an d methanol mixed solution. On the other hand, the trends of the entrop y changes with alkyl chain length were different for the two solutions . These results suggest that the solute-solvent interaction is differe nt for the two solutions.