Determination of ethionamide in pharmaceutical by spectrophotometry via oxidation reaction with potassium iodate

Abstract

Two new spectrophotometric methods are described for the determination of ethionamide (ETM) in pure and tablet forms. Method A is based on the oxidation of ETM by KIO₃ in H₂SO₄ medium, and the in situ generated iodine is extracted into chloroform and measured at 520 nm. In method B, the same iodine is complexed with starch and the intense blue coloured complex is measured at 580 nm. Different variables affecting the reactions were carefully studies and optimized. Beer's law is obeyed in the concentration ranges of 20-400 and 5-125 µg mL^-1 with method A and method B, respectively, with the respective molar absorptivity (ɛ) values of 4.04×10² and 1.39×10³ L mol^-1 cm^-1. The Sandell sensitivity values were calculated to be 0.4113 and 0.1193 µg mL^-1. The limits detection (LOD) and quantification (LOQ) were calculated to be 0.85 and 2.56 µg mL^-1 for method A and 0.27 and 0.81 µg mL^-1 for method B. The intraday and interday precision expressed as relative standard deviation (%RSD) were found to be in the range 1.46 to 2.32 %. The accuracy expressed as relative error (%RE) was better than 2.35%. The methods were also found to be robust and rugged as found from low values of RSD. The methods were applied to the determination of ETM in tablets and no interference was observed from common tablet excipients.