Abstract-The influence of the electronic and steric effects of the p-OCH 3 , p-Cl, and o-NHCOC(CH 3 ) 3 substituents in the phenyl rings of Co(III) tetraphenylporphyrinates as well as that of the introduction of the axial nitrogen-containing ligand (dodecylimidazole) on the anionic selectivity of the membranes has been studied. It has been stated that the substitution at the phenyl cycles of the porphyrin had no significant influence on the anionic selectivity of the membrane, whereas the introduction of the axial nitrogen-containing ligand reduced the membrane specificity, the selectivity series approaching the classical Hofmeister series. All the studied electrodes have exhibited the enhanced (as compared to the Hofmeister series) selectivity towards nitrite, hydrocarbonate, and hydrophosphate anions.Keywords: porphyrinate, cobalt, axial ligand, ion-selective electrode, selectivity, sorption Development of ions-selective electrodes has been currently directed mainly on the detailed investigation of the selectivity and mechanism of the electrode reactions in order to extend the range of the practical application of ion-selective electrodes in the clinical practice and environmental studies.Various anion-exchangers (salts of quaternary ammonium, phosphonium, and arsonium bases, triphenylmethane dyes, and phenanthroline metal complexes) serve as the membrane-active component of the anion-selective electrodes. The selectivity of membranes based on the quaternary ammonium salts is determined by the solvation energy of the corresponding anions, the latter being arranged in the Hofmeister series according to this parameter [1]:2-> HPO 4 2-.The selectivity with respect to anions can be altered as compared to the Hofmeister series in the case of the selective interactions of the active membrane components with dissolved anions. Examples of such selectivity modifiers include certain lipophilic derivatives of В 12 vitamin and the structurally similar metal porphyrinates [2-6], the latter being of undoubtful interest for development of ion-selective membranes [7][8][9][10].Upon formation of metal complexes with synthetic porphyrins, the metal ion is inserted in the cavity of the macrocyclic ligand and is strongly bound to the donor atoms of the latter. The porphyrinates properties are largely determined by the incorporation of the metal ion into the conjugated electronic system of the macrocycle and the possibility of interaction with additional axial ligands.In this work we pioneered in study of the membranes containing the electrode-active thiocyanate salts of Co(III) porphyrinates. For the sake of comparison, we included the complex 1 based on mesotetraphenylporphin into consideration (The Hammett constant of the substituents in the phenyl ring σ H ≡ 0); the effect of the substitution at the phenyl groups were studied using the complexes of meso-tetra(p-methoxyphenyl)porphin 2 (σ p-OMe -0.25), meso-tetra(p-chlorophenyl)porphin 3 (σ p-Cl 0.23), and meso-tetra(o-pivalamidophenyl)porphin 4. Compounds 5 and 6 were similar ...
