A Novel Poly(vinyl chloride) Matrix Membrane Sensor for Batch and Flow-Injection Determinations of Thiocyanate, Cyanide and Some Metal Ions

A poly(vinyl chloride) matrix membrane sensor for the selective determination of thiocyanate has been developed based on the use of copper(II)-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complex (Cu-PADAP) as a novel charged carrier, and o-nitrophenyloctyl ether (o-NPOE) as a solvent mediator. The sensor displays a significantly enhanced response towards SCN− ions over the concentration range 7.0 × 10−6 to 1.0 × 10−2 mol L−1 with a detection limit of 5.6 × 10−6 mol L−1 and a calibration slope of −57.5 ± 0.5 mV decade−1. The sensor exhibits a long life-span, long-term stability, high reproducibility, and a fast response time. The selectivity coefficients of some anions were calculated using the separate solutions method, and found to be in the following order: SCN− > ClO4− > I− > Sal− > NO2− > Br− > NO3− = CH3COO− > Cl− > SO42− = PO43−. The effects of the pH and ionic membrane additives (e.g. tridodecylmethylammonium chloride, TDMAC and potassium tetrakis[bis(3,5-trifluoromethyl)phenyl] borate, KTFPB) were examined. The sensor was used for the determination of SCN− ions in saliva and urine samples collected from some smoker and non-smoker donors. The developed sensor was also applied to determine the cyanide content in electroplating waste water samples after its conversion into thiocyanate. The application of the sensor to monitor the potentiometric titration of Ag+ and Hg2+ using SCN− resulted in sharp inflection breaks at the equivalent points. The data obtained using the proposed sensor correlate very well with results collected using the standard methods of thiocyanate, cyanide and metal analysis.