Charge-transfer complexes of iodine and nonionic surfactants: interpretation and use in the Winkler method

Formation constants (Kc) and molar absorption coefficients (epsilon c) of complexes of iodine and various nonionic surfactants were determined, providing a basis for selection of a surfactant for use in a spectrophotometric modification of the Winkler method. The method of calculation of Kc and epsilon c was extended to include absorption by triiodide at the wavelength of maximum absorbance of the complex. Because the molar absorption coefficients of polyoxyethylene 10 oleyl ether (oleth 10) and polyoxyethylene 23 oleyl ether were significantly greater than those of other surfactants, they are superior candidates for use in the Winkler method. Formation constants could not be correlated with molecular characteristics of the surfactants such as alkyl chain or polyoxyethylene chain length, nor with physical characteristics of iodine-surfactant solutions such as reduction of iodine loss due to volatilization.