EFFECT OF NATURE OF PLASTICIZER ON CHARACTERISTICS OF ION-SELECTIVE ELECTRODES REVERSIBLE TO DOUBLY CHARGED INORGANIC ANIONS

Abstract

A study of the effect of the nature of the plasticizer on the characteristics (lower detection limit and selectivity) of electrodes that are reversible to carbonate, hydrogen phosphate, sulfate, selenate, selenite, sulfite, molybdate, tungstate, and thiosulfate ions was carried out. It was found that the membranes of carbonate and hydrophosphate selective electrodes based on quaternary ammonium salts are preferable to plasticize with o-nitrophenyl decyl ether, membranes of sulfate, selenate, selenite-selective electrodes - 1-bromonaphthalene, sulfite, molybdate, tungstate, and thiosulfate selective electrodes - dibutyl phthalate. For sulfate, selenate, and selenite-selective electrodes, there is an improvement in selectivity and a decrease in the detection limit in the series: o-nitrophenyldecyl ether – dibutylphthalate ≈ didecylphthalate ≈ bis (ethylhexyl) sebacinate -1-bromonaphthalene. The replacement of o-nitrophenyldecyl ether with 1-bromonaphthalene leads to a decrease in logKPot for these electrodes by 0.2–1.0 orders of magnitude depending on the interfering ion. The detection limit for sulfate, selenate, and selenite-selective electrodes is reduced by 0.2–0.65 orders of magnitude. For carbonate and hydrogen phosphate selective electrodes from o-nitrophenyldecyl ether to 1-bromonaphthalene, the detection limit decreases, for example, for a carbonate selective electrode by 0.6 orders of magnitude, for a hydrogen phosphate selective electrode by 1 order; the values of logKPot (CO32–, j) decrease by 0.1–0.9 orders of magnitude, and the values of logKPot (HPO42–, j) decrease by 0.6–1.25 orders of magnitude depending on the interfering ion. The results are explained in terms of the theories of Aigen-Denison-Ramzi-Fuoss and Born. The plasticizer that is optimal for carbonate and hydrophosphate selective electrodes has a large dielectric constant ε = 24; for all other electrodes, the optimal plasticizers have lower ε values (ε = 5–6). The use of dibutyl phthalate and 1-bromonaphthalene membranes as plasticizers is consistent with the Aigen-Denison-Ramzi-Fuoss theory, and the use of o-nitrophenyldecyl ether with the Born theory.