Original Articles
Nagib Qarah and Kanakapura Bas
Abstract
Two simple, sensitive, selective, rapid and reproducible visible spectrophotometric methods are presented for the determination of ethionamide (ETM) in bulk and dosage forms by employing two sulphonthalein dyes: bromophenol blue (BPB method) and bromothymol blue (BTB) as chromogenic agents. . The methods are based on the formation of intensely yellow colored ion-pair complexes upon the reaction of the drug with the cited dyes in chloroform medium. The 1:1 (drug:dye) complexes formed were spectrophotometrically measured at 450 nm with both the dyes without involving the extraction step. Optimization of the experimental conditions is described. Beer’s law is obeyed in the concentration ranges of 0.4-10 and 0.5-14 μg mL-1 for BPB method and BTB method , respectively, with corresponding molar absorptivity values of 1.86×104 and 1.39×104 L mol-1 cm-1. The calculated limits detection (LOD) and quantification (LOQ) were 0.03and 0.09 μg mL-1(with BPB) and 0.05 and1.15 (with BTB). The suitability of the methods for the quantitative determination of ETM was proved by validation in accordance with the requirements of the ICH guidelines. The coefficients of variation were <1.5 % for intra-day and <2.0 % interday analysis, and the accuracy expressed as relative error were< 2.0%. The methods were applied to the determination of ETM in tablets and the results agreed well with the label claim and those obtained by the reference method. The accuracy of the methods was ascertained by recovery study via standard-addition procedure. The possible reaction pathway is also discussed