A New Composition for Co(II)-porphyrin-based Membranes Used in Thiocyanate-selective Electrodes

Abstract: In the present paper, the potentiometric response characteristics of ametalloporphyrin-based electrode in o -nitrophenyloctylether ( o -NPOE) plasticizedpolyvinyl chloride (PVC) membrane are presented for a set of monovalent anions. Asmembrane ionophore, 5,10,15,20-tetrakis-(4-methoxyphenyl)-porphyrin-Co(II)(CoTMeOPP) was used. To establish the optimum composition of the membrane, differentmolar percents of cationic derivative (mol.% relative to ionophore) were used. Electrodesformulated with membranes containing 1 wt.% ionophore, 66 wt.% o -NPOE, 33 wt.% PVC(plasticizer: PVC = 2:1) and the lipophilic cationic derivative (35 mol%) are shown toexhibit high selectivity for thiocyanate with a near-Nernstian slope in the workingconcentration range of 1.0×10 −1 –1.0×10 −5 M, with a good stability in time. Keywords: metalloporphyrins, thiocyanate, anion-selective electrode, near-Nernstian slope. 1. Introduction Substituted meso -tetraarylporphyrins are an interesting class of molecular building blocks owing totheir large size, extended π-system and versatility of metal ion binding.Among a lot of other applications, metalloporphyrins are used as ionophores in solvent / polymericmembrane electrodes. They can induce potentiometric anion selectivity patterns different from the