Thiocyanate selective sensor based on tripodal zinc complex for direct determination of thiocyanate in biological samples

A potentiometric thiocyanate-selective sensor based on the use of zinc-tris(N-tert-butyl-2-thioimidazolyl)hydroborate complex [Ttt-Bu–Zn] as a neutral carrier for a thiocyanate-selective electrode is reported. Effect of various plasticizers viz., o-nitrophenyloctyl ether (o-NPOE), dioctylphthalate (DOP), dibutylphthalate (DBP), benzylacetate (BA), and anion excluder, hexadecyltrimethylammonium bromide (HTAB), with Ttt-Bu–Zn complex in poly (vinyl chloride) (PVC) were studied. The best performance was obtained with a membrane composition of DOP:PVC:Ttt-Bu–Zn:HTAB percent ratio (w/w) of 60:33:5:2. The sensor exhibits significantly enhanced selectivity toward thiocyanate ions over the concentration range 6.3 × 10−7 to 1.0 × 10−2 M with a lower detection limit of 3.16 × 10−7 M and a Nernstian slope of 59.4 ± 1.1 mV decade−1. Influences of the membrane composition, pH, and possible interfering anions were investigated on the response properties of the electrode. Fast and stable response, good reproducibility, long-term stability, applicability over a wide pH range (3.5–9.0) are demonstrated. The sensor has a response time of 14 s and can be used for at least 45 days without any considerable divergence in their potential response. The proposed electrode shows fairly good discrimination of thiocyanate from several inorganic and organic anions. It was successfully applied to direct determination of thiocyanate within physiological fluids and environmental samples.