Investigation and Optimization of Titrimetric and Spectrophotometric Methods for the Assay of Flunarizine Dihydrochloride Using in Situ Bromine.

Three indirect methods for the assay of flunarizine dihydrochloride (FNH) in bulk drug and commercial formulation based on titrimetric and spectrophotometric techniques using bromate-bromide mixture are described. In titrimetry, a measured excess of bromate-bromide mixture is added to an acidified solution of FNH and the unreacted bromine is determined iodometrically (method A). Spectrophotometry involves the addition of a known excess of bromate-bromide mixture to FNH in acid medium followed by estimation of unreacted bromine by its reaction with excess iodide and the liberated iodine (I₃⁻) is either measured at 370 nm (method B) or liberated iodine reacted with starch followed by the measurement of the blue colored starch-iodide complex at 575 run (method C). Titrimetric method is applicable over the range 4.5-30.0 mg FNH (method A), and the reaction stoichiometry is found to be 1:2 (FNH:KBrO₃). The spectrophotometric methods are applicable over the concentration ranges 0.8-16.0 µg/mL and 0.4-8.0 µg/mL FNH for method B and method C, respectively. The molar absorptivities are calculated to be 2.83 x 10⁴ and 4.96 x 10⁴ L mol⁻¹cm⁻¹ for method B and method C, respectively, and the corresponding Sandell sensitivity values are 0.0168 and 0.0096 µg cm⁻². The proposed methods have been applied successfully for the determination of FNH in pure form and in its dosage form and the results were compared with those of a literature method by applying the Student's t-test and F-test.