The general performance of ten spectrophotometric reagents, namely salicylaldoxime, 2,2′-dipyridyl, dimedone, 8-hydroxyquinoline, dithiooxamide, cupferron, nioxime, 4-methylnioxime, 1,10-phenanthroline hydrate and α-benzoin oxime, as active sensors for Cu2+, Co2+, Ni2+, Cd2+, Fe3+ and Pb2+ ions in a poly(vinyl chloride) membrane electrode system has been assessed using dioctyl phenyl phosphonate as plasticizing solvent mediator. Of the ten ionophores studied, four, namely salicylaldoxime, 2,2′-dipyridyl, dimedone and 8-hydroxyquinoline, showed good response to Pb2+ ions with the working concentration range from 1 × 10–6 to 1 × 10–1 mol dm–3. The best response to Cu2+ ions was shown by electrodes based on 2,2′-dipyridyl, dithiooxamide and cupferron. Although the electrode with 8-hydroxyquinoline as the active sensor responded very well to Fe3+, the complex formed leached into solution. The most promising of the ionophores for the fabrication of Ni2+ ion-selective electrodes were found to be salicylaldoxime and cupferron with linear slopes of 32.9 and 22.5 mV per decade, respectively, from 1 × 10–4 to 3.2 × 10–2 mol dm–3.
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