Determination of association constants of cyclodextrin-nonionic surfactant inclusion complexes by a partition coefficient method

The partition behavior of isotopic labeled nonionic surfactants between carbon tetrachloride and an aqueous solution containing beta-cyclodextrin (beta-CD) was studied with a liquid scintillation counting technique. The association constants of the inclusion complexes were determined at different temperatures. It was found that the nonionic surfactants form 1 : 1 inclusion complexes with beta-CD. The results demonstrated that the smaller the HLB values of the nonionic surfactants, the greater the association constants with beta-CD, and that for the same surfactant the association constant is higher at lower temperatures.