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A novel way of synthesis is developed for the Ba 2 + selective neutral Ionophore 2a: 2,2'-[1,2-phenylenebis(oxyethane-2,1-diyloxy)]bis(N-benzyl-N-phenylacetamide) and its methyl (2b), buthyl (2c), and hexyl (2d) derivatives. Ba 2 + selective electrodes based on Ionophores 2a-d are compared with those with commonly used Ionophore 1: N,N,N',N'-tetracyclohexyl-oxybis(o-phenyleneoxy) diacetamide. It is shown that Ionophores 2a-d, particularly 2b, are superior for measurements of Ba 2 + in the presence of Ca 2 + , and in acidic solutions. Segmented sandwich membrane studies suggest formation of complexes IL 2 2 + for Ba 2 + , Ca 2 + and Mg 2 + ions with Ionophore 2b, while H + ions apparently form complexes H 2 L 2 + . The values of the complex formation constants are consistent with the selectivity coefficients.

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Ion-selective electrodes are described, with membranes tailored for measurements of tetrabutylammonium ions in aqueous and formamide solutions, and for measurements of cesium and calcium ions in the presence of tetrabutylammonium. It is shown that reliable measurements of cesium ions are possible when a correction is introduced for interference from tetrabutylammonium, using Nikolsky selectivity coefficient. A novel membrane composition is described which ensures high selectivity to calcium ions over tetrabutylammonium.