Novel thiocyanate-selective membrane sensors based on di-, tetra-, and hexa-imidepyridine ionophores Original Research Article

Potentiometric thiocyanate-selective sensors based on the use of three synthesized di-, tetra-, and hexa-imidepyridine derivatives as novel anionic neutral ionophores in plasticized poly(vinyl chloride) (PVC) membranes are described. The sensors exhibit significantly enhanced response towards thiocyanate ions over the concentration range 5×10−6 to 1.0×10−2 M with a lower detection limit of 0.3 μg ml−1 and slopes ranging from −55.6 to −58.3 mV per decade. Fast and stable response, good reproducibility, long-term stability, applicability over a wide pH range (2–8) and high selectivity for SCN− ion in the presence of 18 common anions are demonstrated. The sensors are used for direct potentiometric measurements of thiocyanate ions over the concentration range 0.2–580 μg ml−1 and for monitoring sequential titration of some metal ions (e.g. Ag+, Tl+, Cu2+, Pb2+) in binary and ternary mixtures. Sequential binding of these metal ions with SCN− ensures share stepwise titration curves with consecutive end point breaks at the equivalent points. Recoveries of 98.5–99.1±0.3% are obtained for metal ion concentrations of 0.06–4 mg ml−1.