Application of oxidants to the spectrophotometric determination of amlodipine besylate in pharmaceutical formulations

Three new spectrophotometric methods for the determination of amlodipine besylate have been proposed. The first two methods, i.e. A and B, are based on the oxidation of the drug with Fe(III) and the estimation of Fe(II) produced after chelation with either 1,10-phenanthroline or 2,2′-bipyridyl at 500 and 515 nm, respectively. The Beer's law was obeyed in the concentration ranges of 2-10 and 4-14 μg ml ^-1 with molar absorptivity of 2.9 × 10 ⁴ and 2.7 × 10 ⁴ l mol ^-1 cm ^-1 for methods A and B, respectively. The third procedure depends on the interaction of amlodipine besylate with ammonium heptamolybdate tetrahydrate, which resulted in the formation of molybdenum blue (λ _max 825 nm). The linear dynamic range and the molar absorptivity values were found to be 15-59 μg ml ^-1 and 1.8 × 10 ⁴ l mol ^-1 cm ^-1, respectively. The results of the proposed procedures were validated statistically and compared with those obtained by the reference method. The proposed methods were applied successfully to the determination of amlodipine besylate in commercial tablets.