Titrimetric and spectrophotometric assay of felodipine in tablets using bromate–bromide, Methyl Orange and Indigo Carmine reagents

Three new methods based on titrimetric and spectrophotometric tech- niques are described for the determination of felodipine (FLD) in the bulk drug and in tablets using a bromate-bromide mixture and two dyes, Methyl Orange and In- digo Carmine. In the titrimetric method (method A), the drug solution was treated with a measured excess of the bromate-bromide mixture in acid medium, and after the reaction was judged to be complete, the unreacted bromine was determined iodo- metrically. The two spectrophotometric methods are based on the bromination of the drug with a known excess of the bromate-bromide mixture under acidic conditions followed by the estimation of the surplus bromine by reaction with either Methyl Or- ange (Method B) or Indigo Carmine (Method C), and measuring the absorbance at 520 nm or 610 nm, respectively. In all the methods, the amount of reacted bromine corresponds to the drug content. The titrimetric procedure is applicable for between 6-15 mg and the reaction stoichiometry was found to be 1:1 (drug: BrO3-). The sys- tems obey Beer's law between 0.12 - 0.87 gm l-1 and 0.5 -6 .0 gm l-1 for methods B and C, respectively. The limits of detection and quantification are reported for both the spectrophotometric methods. The methods could usefully be applied to rou- tine quality control of pharmaceutical formulations containing FLD. Statistical comparison of the results with the reference method shows excellent agreement and indicates no significant difference in accuracy and precision.