Electrochemical investigations of diclofenac at edge plane pyrolytic graphite electrode and its determination in human urine

Voltammetric investigations of diclofenac are described using square wave voltammetry (SWV) at edge plane pyrolytic graphite sensor (EPPG). The oxidation of diclofenac occurred in a single, well-defined, pH dependent peak. The currents increase linearly with diclofenac concentrations in the range 10–1000 nM. Controlled potential electrolysis has been carried out and the product of oxidation has been characterized as 5-hydroxydiclofenac using 1H NMR. The oxidation process was found to involve 2e, 2H+ and a tentative mechanism for the oxidation of diclofenac has also been suggested. The oxidation peak is used to determine the concentration of diclofenac and detection limit and sensitivity of the proposed method are 6.2 × 10−9 M and 69 nA nM−1 respectively. The suitability of the present method was proved by the determination of diclofenac in pharmaceutical formulations and real urine samples obtained from patients undergoing treatment with diclofenac. The interfering effect of common coexisting metabolites in urine has also been reported. The method is simple, reliable and precise and involves inexpensive instrumentation with good stability and reproducibility.