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ISRN Analytical Chemistry
Volume 2014 (2014), Article ID 717019, 11 pages
Research Article

Redox-Reaction Based Spectrophotometric Assay of Isoniazid in Pharmaceuticals

Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore 570 006, India

Received 21 January 2014; Accepted 25 February 2014; Published 22 April 2014

Academic Editors: B. N. Barman, G. Drochioiu, J. V. Garcia Mateo, B. Rittich, and A. Szemik-Hojniak

Copyright © 2014 N. Swamy et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Two spectrophotometric methods are described for the determination of isoniazid (INH) in pharmaceuticals. In the first method (FCR method), INH is reacted with Folin-Ciocalteu reagent in Na2CO3 medium and the resulting blue colored chromogen measured at 760 nm. Iron(II), formed as a result of reaction between INH and iron(III), is made to react with ferricyanide, and the resulting Prussian blue is measured at 760 nm, basing the second method (FFC method). The conditions for better performance are optimized. Beer’s law is obeyed in the concentration ranges 0.5–10 and 0.2–3.0 μg mL−1 for FCR method and FFC methods, respectively, with corresponding molar absorptivity values of and  L mol−1 cm−1. The methods are validated for accuracy, precision, LOD, LOQ, robustness, and ruggedness as per the current ICH guidelines. The validated methods were successfully applied to quantify INH in its commercial formulation with satisfactory results; hence the methods are suitable for isoniazid determination in bulk drugs and pharmaceuticals.