Equilibrium dialysis of barbituric acids up to high concentrations of aqueous sodium alkylsulfonate solutions

The partition coefficient K of four barbituric acids has been determined by the equilibrium dialysis method in aqueous solutions of sodium alkylsulfonate at 25°C. The results obtained from dilute solutions to 0.3 M surfactant concentration are compared with solubility data for the same systems. The K values as deduced from Langmuir or Freundlich isotherms decrease with increasing surfactant concentration. The detergent used was an impure commercial product of known composition, which could be considered as a mixed surfactant. The change of partition coefficient with surfactant concentration as obtained from equilibrium dialysis experiments has been interpreted by assuming a continuous change of micelle composition.