Potentiometric Sensors for the Determination of Valdecoxib in Pharmaceutical Preparation

Valdecoxib (VALD) selective electrodes based on VALD-5,6-diamino-2-thiouracil hydrochloride (DTUH) (VALD-DTUH) ion pair in PVC matrix membrane were constructed. The plasticizers used were dibutylphthalate (DBP) (Electrode B) tri-n-butylphosphate (TBP) (electrode C), or dioctylphthalate (DOP) (electrode) A. The electrodes gave the linear range between 6.0×10⁻⁶-17.9×10⁻³, 2.5×10⁻⁵–8.3×10⁻³M, M and 2.5×10⁻⁶–2.0×10⁻²M respectively. The slopes for linear range ranged from 39.29 to 58.76mV/decade with correlation coefficients lying between 0.997, 0.989 and 0.999 respectively. The best detection limit was 1.50×10⁻⁶M for the electrode based on DOP. Selectivity coefficients of VALD related to a number of interfering cation and some organic compounds and excipients were studied using matched potential method (MPM(, and there were negligible interference caused by most of the investigated species. The pH and life time of the electrodes were also studied. The direct determination of VALD shows an average recovery of (100.08-100.61 and 99.75-101.00)% and a mean relative standard deviation of (2.70-0.61 and 2.39-0.56)% for sensor A and B respectively. The results obtained by determination of VALD in tablets using the proposed sensors which comparable favorably with those obtained by spectrophotometric method. Validation of the method shows the suitability of the electrodes for the determination of VALD in pharmaceutical formulation.