Thiocyanate: selective membrane electrode based on macrotricyclic binuclear Cu(II)–Schiff base complex

Abstract

A highly selective PVC membrane electrode was prepared for thiocyanate (SCN−) determination, based on macrotricyclic binuclear Cu(II)–Schiff base complex as an ionophore. The novel macrotricyclic compound (cryptand) was synthesized by condensation of 4,4′-diamino-dibenzo-18-crown-6 with bis(4-formyl phenyl)terephthalate under high-dilution condition and the structure was confirmed by FT-IR, 1H NMR,13C NMR and MS studies. The Cu(II) complex of the compound was prepared and was examined for use as anion-selective electrode as a carrier which displays an anti-Hofmeister selectivity sequence in following order: SCN− > ClO4 − > NO3 − > CN− > I− > CO3 2− > NO2 − > Br− > Cl− > SO4 2− with a preference for thiocyanate ion over many common anions. The electrode has a linear dynamic range between 1.0 × 10−7 and 1.0 × 10−1 M, with a Nernstian slope of −58.9 mV decade−1 and detection limit of 3.1 × 10−8 M. The working pH range of the sensor was found be in the range of 3.0–8.0. It exhibits a fast response time of 20 s and has a lifetime of about 2 months. Application of the electrode for determination of thiocyanate in waste water samples and in human urine samples have also been demonstrated.