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

Clonixin, a non-steroid analgesic, can be both reduced at the mercury electrode and oxidised at the glassy carbon electrode. The anodic response shows well-defined waves in a pH range between pH 2-12. The polarographic response shows two irreversible waves or peaks in the range between pH 1-6 shifting 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 use. The polarographic method showed an adequate repeatability, with a CV of 0.7%. The detection and quantification limits were 2.78x10(-6) M and 4.67x10(-6) M, respectively. The dpp technique was applied successfully to both the clonixin uniformity content and composite assay of commercial tablets and 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.