pH-ISEs with an expanded measuring range based on calix[4]arenes: specific features of the behaviour and description of the electrode response.
This article contains a description of pH-ISEs with plasticised PVC membranes that contain calix[4]arene or p-tertbutylcalix[4]arene as an ionophore and tetradecylammonum nitrate taken in a subequivalent amount relative to calyxarene as an ionic additive. It has been discovered that real ISEs have an extraordinarily wide measuring range which is about 1.5-2 pH units wider then the measuring range of tridecylamine-based ISEs under the same conditions. Just as in the case of amine-type neutral carriers-based pH-ISEs, the upper detection limit depends on the concentration and lipophilicity of anions and the lower limit, on the concentration and lipophilicity of cations present in the sample solution. A simple quantitative description of the electrode response and the detection limits of such ISEs is suggested which is based on inclusion of extraction equilibria at the membrane/solution interface for two limiting cases: complete dissociation and strong association of ions in the membrane. Interface equilibria constants that occur in the acid and alkali media are estimated experimentally in model extraction systems. Characteristics of the ISEs calculated with use of the estimated constants agree satisfactorily with those measured experimentally. Probable reasons of the expansion of the measuring range of the ISEs considered in comparison with ISEs based on amine-type neutral carriers are discussed.
Egorov
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Sin'kevich
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