PHARMACEUTICAL ANALYSIS Spectrophotometric Determination of Risedronate and Etidronate in Pharmaceutical Formulations via the Molybdovanadate Method Mohamed I. Walash, Mohamed E.-S. Metwally, Manal I. Eid, and Rania N. El-Shaheny Department of Analytical Chemistry, Faculty of Pharmacy, University of Mansoura, Mansoura, Egypt Abstract: An accurate and sensitive spectrophotometric method was developed for the determination of risedronate and etidronate in pharmaceuticals. The method was based on oxidation of the studied drugs with potassium persulfate and reaction of the generated orthophosphate ions with molybdovanadate reagent. The produced yellow phosphovanadomolybdate complex was measured at 313 nm. The method was rectilinear in the ranges 0.5–10 and 0.5–8 mg=mL with detection limits of 0.087 and 0.122 mg=mL for risedronate and etidronate, respec- tively. The method was applied for the determination of the studied drugs in their tablets, and the results agreed with those obtained by the comparison methods. Keywords: Etidronate, molybdovanadate, risedronate, spectrophotometry INTRODUCTION Risedronate sodium, (I), is sodium trihydrogen [1-hydroxy-2-(3-pyridyl) ethylidene] diphosphonate, and etidronate disodium, (II), is disodium dihydrogen (1-hydroxyethylidene) diphosphonate (Scheme 1). Both Received 3 December 2008; accepted 15 April 2009. Address correspondence to Manal I. Eid, Department of Analytical Chemis- try, Faculty of Pharmacy, University of Mansoura, 35516 Mansoura, Egypt. E-mail: manal_eid@yahoo.com Analytical Letters, 42: 1571–1587, 2009 Copyright # Taylor & Francis Group, LLC ISSN: 0003-2719 print=1532-236X online DOI: 10.1080/00032710902993795 1571