Spectrophotometric Assay of Ethionamide in Pharmaceuticals Using Picric Acid and Iodine as Charge-Transfer Complexing Agents

Author(s): Swamy N* and Prashanth K.N

Abstract: Two simple, rapid and sensitive spectrophotometric methods are described for the determination of ethionamide (ETN) in bulk drug and tablets. The methods are based on the reaction of ETN as n-donor with –acceptor iodine (method A) and -acceptor, picric acid (method B) in chloroform. The resultant charge-transfer complexes were measured at 400 nm for iodine (method A) and at 420 nm for picric acid (method B). Different variables affecting the reaction were studied and optimized. Under the optimum reaction conditions linear relationships with good correlation coefficients were found between absorbance and concentration of ETN in the ranges, 1-20 and 2-45 μg mL-1, for method A and method B, respectively. The limits of detection (LOD) and quantification (LOQ) were: 0.24 and 0.73 μg mL-1 (method A), and 0.96 and 2.92 μg mL-1 (method B). A Job’s plot of absorbance versus the molar ratio of ETN to each of the acceptors under consideration indicated 1:1 (donor: acceptor) ratio. The methods were validated for accuracy, precision, selectivity, robustness and ruggedness. The proposed methods were applied successfully to the determination of ETN in tablets with good accuracy and precision and without interference from common additives. The results compared favorably with those of the official method.

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