Rapid titrimetric and spectrophotometric determination of frusemide (furosemide) in formulations using bromate-bromide mixture and methyl orange

Two methods based on titrimetric and spectrophotometric techniques using bromate-bromide mixture and methyl orange as reagents are described for the determination of frusemide in bulk drug and formulations. In titrimetry, an acidified solution of frusemide is titrated directly with bromate-bromide mixture using methyl orange as indicator. Spectrophotometry entails adding a fixed and known amount of bromate-bromide mixture to an acidified solution of drug and determination of the residual bromine by reacting with a fixed amount of methyl orange and measuring the absorbance at 520 nm. The amount of bromine reacted corresponds to drug content. The quantification in titrimetry is based on a 1:0.333 reaction stoichiometry (Frusemide: KBrO3) and the method is applicable over 2-20 mg range. In spectrophotometry, the calibration graph is found to be linear over 0.25-3.50 µg mL-1 range with a molar absorptivity of 6.11104 L mol-1 cm-1 and a Sandell sensitivity of 5.18 ng cm-2. The limits of detection and quantification are calculated to be 0.07 µg mL-1 and 0.24 µg mL-1, respectively. The statistical evaluation of the methods was examined by determining the intra-day and inter-day precision. The methods were applied to the determination of frusemide in tablets and the results were found to agree well with the declared amounts. The accuracy and reliability of the proposed methods were further ascertained by parallel determination by a reference method and by recovery studies using standard addition technique