Spectrophotometric determination of etodolac in pure form and pharmaceutical formulations

Background: Etodolac (ETD) is a non-steroidal anti-inflamatory antirheumatic drug. A survey of the literature reveals that there is no method available for the determination of ETD in pure form and pharmaceutical formulations by oxidation-reduction reactions. Results: We describe three simple, sensitive and reproducible spectrophotometric assays (A-C) for the determination of etodolac in pure form and in pharmaceutical formulations. Methods A and B are based on the oxidation of etodolac by Fe(3+) in the presence of o-phenanthroline (o-phen) or bipyridyl (bipy). The formation of the tris-complex on reaction with Fe(3+)-o-phen and/or Fe(3+)-bipy mixtures in acetate buffer solution at optimum pH was demonstrated at 510 and 520 nm with ophen and bipy. Method C is based on the oxidation of etodolac by Fe(3+) in acidic medium, and the subsequent interaction of iron(II) with ferricyanide to form Prussian blue, with the product exhibiting an absorption maximum at 726 nm. The concentration ranges are 0.5-8, 1.0-10 and 2-18 mu g mL(-1) respectively for methods A, B and C. For more accurate analysis, Ringbom optimum concentration ranges were calculated, in addition to molar absorptivity, Sandell sensitivity, detection and quantification limits. Conclusion: Our methods were successfully applied to the determination of etodolac in bulk and pharmaceutical formulations without any interference from common excipients. The relative standard deviations were <= 0.76\%, with recoveries of 99.87\%-100.21\%.