Pharma Focus Asia

Spectrophotometric determination of Ethionamide in Pharmaceuticals using Folin-Ciocalteu reagent and Iron (III)-Ferricyanide as Chromogenic Agents

Authors: Nagib A.S. Qaraha, Kanakapura Basavaiaha, Sameer A.M. Abdulrahman


Two simple and sensitive spectrophotometric methods are described for the determination of ethionamide (ETM) in pure drug and tablets. The first method is based on the reduction of Folin-Ciocalteu (F-C) reagent by ETM in sodium carbonate medium to form a blue coloured complex, which was measured at 760 nm (Molybdenum-tungsten blue method). In the second method (Prussian blue method), iron (III) was reduced to iron (II) by ETM in HCl medium, the iron (II) formed was complexed with ferricyanide, and the resulting Prussian blue also measured at 760 nm. The absorbance measured in each case was related to ETM concentration. The experimental conditions were carefully studied and optimized. Beer's law was obeyed in the concentration ranges of 1–40 and 0.2–4.0 μg/ml with Molybdenum-tungsten blue method and Prussian blue method, respectively, with corresponding molar absorptivity values of 5.72 × 103 and 3.18 × 104 l/( The limits of detection (LOD) and quantification (LOQ) were 0.09 and 0.27 μg/ml (Molybdenum-tungsten blue method) and 0.01 and 0.04 μg/ml (Prussian blue method). Within-day and between-day relative standard deviations (%RSD) at three different concentration levels were <3%, and the respective relative errors (%RE) were ≤ 2% implying good accuracy and precision of the methods. The proposed methods were successfully applied to the determination of ETM in bulk powder and tablets, and the results demonstrated that the methods were as accurate and precise as the official method.


Ethionamide; Folin-Ciocalteu reagent; Iron (III); Ferricyanide; Spectrophotometry; Pharmaceuticals

Citation: Nagib A.S. Qaraha, Kanakapura Basavaiaha, Sameer A.M. Abdulrahman Spectrophotometric determination of Ethionamide in Pharmaceuticals using Folin-Ciocalteu reagent and Iron (III)-Ferricyanide as Chromogenic Agents

Received: 27 March 2016, Revised: 27 June 2016, Accepted: 19 July 2016, Available online: 31 August 2016

Copyright: © 2016 Elsevier B.V. or its licensors or contributors. Open Access funded by Taibah University


The spectrophotometric methods described in this article were found to be simple without involving any critical experimental variable compared to most reported methods. The methods were demonstrated to be both accurate and precise besides being robust and rugged. Both systems have wide linear dynamic ranges of applicability, and the Prussian blue method with an ? value of 3.18 × 104 l mol−1 cm−1 is the most sensitive one ever reported for ETM (Table 6). The reference method [4] requires scrupulously anhydrous medium for accurate end point detection, besides generating a large quantity of organic solvent as waste. This creates the problem of waste disposal, and hence it is not a green method further, the reference method is applicable to macro scale (300 mg drug per trial). In contrast, the proposed methods seldom employ organic solvents, and applicable over micro scale (μg/ml). These advantages coupled with the use of cheap and readily available chemicals and simple instrumentation, make the methods suitable for use in quantity control laboratories of developing and under developed countries which would ill-afford the expensive techniques like HPLC and others.


The gift sample of Ethionamide by Panacea Biotec Ltd. is gratefully acknowledged. Prof. K. Basavaiah wishes to thank the University Grants Commission, New Delhi. India, for the award of BSR faculty fellowship. The first author is thankful to the UGC New Delhi, India for financial assistance through Junior Research Fellowship.

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