A micellar electrokinetic chromatographic method for determination of solubilization isotherms in surfactant micelles.

We have devised a new micellar electrokinetic chromatographic method for determination of the solubilization equilibrium constants of neutral solutes in surfactant micelles as functions of the intramicellar mole fraction of the solute. In this method, the running solution in a capillary and in electrode vessels contains the neutral solute as well as the surfactant micelles, and the injected solution contains the surfactant micelles and the dilute marker compounds for aqueous and micellar phases but not the solute. The mobility of the solute can be measured from a negative peak recorded on the chromatogram. The solute concentration in the capillary is established, and the mobility of the micellar phase incorporating the solute, which depends on the intramicellar mole fraction of the solute, can be measured from the migration time of the micelle marker. These merits enable precise determination of the solubilization isotherms. This method has been used to study the solubilization equilibria of benzene, phenol, and a series of aliphatic ketones in sodium dodecyl sulfate solution, and the validity and effectiveness of this method for quantifying solubilization have been verified.