Spectrophotometric Determination of Furosemide in Pharmaceuticals Using Permanganate

Based on the reduction of permanganate by furosemide (FUR) in either acidic or basic medium, two simple, sensitive and cost-effective methods were proposed for the determination of FUR in bulk drug and in formulations. In method A, FUR was treated with a measured excess of permanganate in acid medium and the unreacted oxidant was measured at 550 nm, whereas in method B the reaction was carried out in alkaline medium and the resulting manganate was measured at 610 nm. In method A, the amount of permanganate reacted corresponds to the FUR content and the absorbance was found to decrease linearly with the concentration; while in method B, the absorbance increases with concentration. Under optimum conditions, working ranges was 3.0-24.0 μg ml-1 and 1.25-20.0 μg ml-1 by method A and method B, respectively. The calculated molar absorptivities are 9.06 * 10^3 and 1.36 * 10^4 L mol-1 cm-1 for method A and method B, respectively, with corresponding Sandell sensitivity values of 0.0365 and 0.0243 μg cm-2. The limits of detection (LOD) and quantification (LOQ) have also been reported. Accuracy and precision for the assay were determined by calculating the intra-day and inter-day at three concentration levels; the intra-day RSD was 2.7% and the accuracy was better than 2.8% (RE). The methods were successfully applied to the determination of FUR in tablets and injections dosage forms; either in monopreparations of FUR or in combination with amiloride HCl. The results tallied well with the label claim and were statistically compared with those of a reference method by applying the Student fs t-test and F-test. The accuracy was further ascertained from placebo and synthetic mixture analysis and also from spike-recovery method.