Novel thiocyanate-selective membrane sensor based on crown ether-cetyltrimethyl ammonium thiocyanate ion-pair as a suitable ionophore

Abstract

A potentiometric thiocyanate-selective sensor based on the use of crown ether-cetyltrimethyl ammonium-thiocyanate (CCT) as a neutral carrier for a thiocyanate-selective electrode is reported. The electrode was prepared by coating the membrane solution containing PVC, plasticizer, and carrier on the surface of graphite electrode. Influences of the membrane composition, pH, and possible interfering anions were investigated on the response properties of the electrode. The sensor exhibits significantly enhanced response toward thiocyanate ions over the concentration range 1 × 10 −6 to 1.0 × 10 −1 M with a lower detection limit of 0.03 μg ml −1 and a slope of −57.6 mV decade −1. Fast and stable response, good reproducibility, long-term stability, applicability over a wide pH range (3.8–9.2) are demonstrated. The sensor has a response time of ≤20 s and can be used for at least 6 weeks without any considerable divergence in their potential response. The proposed electrode shows fairly good discrimination of thiocyanate from several inorganic and organic anions. The sensor is used for direct potentiometric measurements of thiocyanate ions over the concentration range 0.06–5800 μg ml −1 and for monitoring sequential titration of some metal ions (e.g. Ag +, Cu +, Pb 2+) in binary and ternary mixtures. Sequential binding of these metal ions with SCN − ensures sharp stepwise titration curves with consecutive end point breaks at the equivalent points.