The Selectivity Characteristics of Surfactant Ion-sensitive Nitrobenzene-membrane Electrode

Abstract

Abstract The selectivity coefficients of nitrobenzene-membrane electrode containing dodecyltrimethylammonium dodecyl sulfate as an ion exchanger were determined. For a homologous series of surfactant ions, the logarithm of the selectivity coefficient was found to increase linearly with increasing hydrocarbon chain length. The selectivity sequence for anionic surfactant ions with the same alkyl chain length became alkyl-benzenesulfonate ion>alkyl sulfate ion>>alkanesulfonate ion, while that for cationic ones became alkyltrimethyl-ammonium ion≈1-alkylpyridinium ion>>alkylammonium ion. These results can reasonably be interpreted in terms of the partition coefficient of surfactant ion between aqueous and membrane phases. A tentative estimation based on the theory of liquid-membrane electrode led to −2900 J mol−1 for the standard free energy of transfer of a methylene group from water to nitrobenzene.