Calculation of organic solute and surfactant activities from solubilization data

Vapor pressure methods developed in our laboratory have produced highly precise solubilization data relating to the interaction of volatile organic compounds with nonvolatile solutes, including ionic surfactants in aqueous solution. By using a computational method similar to one developed previously we can infer the change in activity of the surfactant from solubilization isotherms. The technique, employing a form of the Gibbs-Duhem equation, yields values of the surfactant activity or monomer concentration, independent of any particular mass action model. Results show that surfactant activities inferred from benzene vapor pressure data for aqueous solutions of sodium n-octylsulfate are nearly equal to those calculated previously with a mass-action model. New activity coefficient results (obtained by vapor pressure and vapor pressure osmometry methods) are reported for both the organic solute and the surfactant in several systems containing organic compounds dissolved in aqueous n-hexadecylpyridinium chloride.