PVC Matrix Membrane Sensor for Potentiometric Determination of Triphenyltetrazolium Chloride and Ascorbic Acid

The construction and performance characteristic of a potentiometric PVC membrane sensor for the determination of triphenyltetrazolium chloride (TPTCl) is described. The sensor is based on the use of triphenyltetrazolium (TPT)-tetraphenylborate (TPB) ion pair as ion exchange sites in PVC matrix in presence of dioctylphathalte as plasticizer. The TPT membrane sensor shows a stable, near-Nernestian response for 6×10^-6 - 1×10^-2 M TPTCl at 25 °C over the pH range 3-10 with cationic slope of 57.0 ± 0.5. The lower detection limit is 4×0^-6M and the response time is 10-30 sec. Selectivity coefficients for TPTCl relative to a number of different cations and anions were investigated, which there is negligible interferences. However, iodide, bromide and thiocyanate were interfering. The determination of 2.0- 3340.0 μg/ml of TPTCl in aqueous solutions shows an average recovery of 98.5 % and a mean relative standard deviation of 1.9 at 160μg/ml. The proposed method has been used for indirect potentiometric determination of ascorbic acid in its pharmaceutical formulations which are comparable favorably with those of British pharmacopoeia method. Precipitation titrations involving TPTCl as titrant are monitored with NaTPB using the proposed membrane sensor; the inflection break is about 300 mV.