Voltammetric behaviour of clonixin and its differential pulse polarographic determination in tablets

Clonixin, a non-steroid analgesic, can be both reduced at the mercury elect rode and oxidised at the glassy carbon electrode. The anodic response shows well-defined waves in a pH range between pH 2-12. The polarographic respon se shows two irreversible waves or peaks in the range between pH 1-6 shifti ng cathodically when pH increases. Above pH 7.0 all the signals disappeared . The first signal in the dpp mode at pH 1.8 was selected for analytical us e. The polarographic method showed an adequate repeatability, with a CV of 0.7%. The detection and quantification limits were 2.78x10(-6) M and 4.67x1 0(-6) M, respectively. The dpp technique was applied successfully to both t he clonixin uniformity content and composite assay of commercial tablets an d compared with a spectrophotometric technique. Furthermore, pKa calculated by using the 252-nm band pH-dependence was 5.65 +/-0.02, compared with the voltammetric pKa of 6.5.