Potentiometric determination of oxybutynin hydrochloride in pharmaceutical formulations at modified carbon paste electrodes
A new potentiometric sensitive and selective modified carbon paste (MCPE) electrodes based on phosphotungestic acid (PTA), sodium tetraphenyl borate (NaTPB), phosphomolybdic acid (PMA) or ammonium reineckate (RN) ion pairing agents for determination of (Ox.HCl) were developed. The proposed electrodes have a Nernstian slope values of 58.50±0.71, 58.71±1.20, 54.80±1.30 and 59.20±0.70 mV decade-1for electrodes modified with 20, 10, 5 and 10 mg of Ox-TPB (electrode I), Ox-RN (electrode II), Ox-PMA (electrode III) and Ox-PTA (electrode IV) ion pairs, respectively, with a dynamic drug concentration range at 25 (C was 1.0x10-5 - 1.0x10-2 mole L-1 with detection limit of 1.0× 10-5 mol L-1. The response of MCPEs were pH independent in the range 2.0-6.0 with a fast response time of 10 s for electrode I and 12 s for electrodes II-IV. The MCPEs showed a relatively long life time of 36 days. A pure and pharmaceutical formulation of Ox.HCl was quantified using calibration and standard addition methods and the obtained results agreed with that of the official HPLC method. Validation parameters were optimized according to ICH recommendations.
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