Fluorimetric Determination of Ethionamide in Pharmaceutical Preparations and Biological Fluids

A highly sensitive and specific fluorimetric method was developed for the determination of ethionamide in pharmaceutical preparations and biological fluids (urine and plasma). The proposed method is based on the studyofthequantitativequenchingeffectofethionamideonthenativefluorescenceofeosininacidicmedium due to complex formation. The fluorescence intensity was measured at 536 nm (after excitation at 337 nm). The different experimental parameters affecting the quenching of the native fluorescence of eosin were carefully studied and incorporated into the procedure. Under the described conditions, the method is applicable over the concentration range of 1-8 g/mL with a detection limit of 80 ng/mL. The percentage recoveries for dosage form, spiked urine and plasma were 99.38 0.824, 99.44 1.58 and 99.25 1.15%, respectively. The results obtained were in good agreement with the official methods. A proposal of the reaction pathway is suggested.