Indirect spectrophotometric determination of piroxicam and tenoxicam through oxidation with potassium permanganate

Abstract

Three rapid, simple, accurate and selective validated spectrophtometric methods (A, B and C) for the determination of piroxicam (PX) and tenoxicam (TX) in bulk sample and in dosage forms are described. The methods are based on the oxidation of the studied drugs by a known excess of potassium permanganate in sulfuric acid medium and subsequent determination of unreacted oxidant by reacting it with Methylene Blue (Basic Blue 9) dye (method A), Acid Red 27 (Amaranth) dye (method B) and Acid Orange 7 (orange II) dye (method C), in the same medium at a suitable λ_max = 660, 520 and 485 nm, respectively. The reacted oxidant was found to be corresponding to the drug content. Regression analysis of Beer-Lambert plots showed good correlations in the concentration ranges 1.0-8.0, 1.0-9.0 and 1.0-7.2 µg mL^-1 using methods A, B and C, respectively, for PX and 0.3-7.0, 0.3-1.6 and 0.3-2.5 µg mL^-1 using methods A, B and C, respectively, for TX. The stoichiometric ratios for the cited drugs to oxidant were studied. The optimum reaction conditions and other analytical parameters were evaluated. The proposed methods were applied successfully to determine the examined drugs either in pure form or pharmaceutical formulations with good accuracy and precision. The relative standard deviations were ≤ 0.33 with recoveries 98.9-101.7% for PX and ≤ 0.49 with recoveries 99.4-102.0% for TX.

KEY WORDS: Spectrophotometry, Piroxicam assay, Tenoxicam assay, Redox reactions, Dosage forms

Bull. Chem. Soc. Ethiop. 2010, 24(1), 121-126.