Titrimetric and modified spectrophotometric methods for determination of Amlodipine besylate using Bromate Bromide mixture and two dyes. Il Farmaco

ABSTRACT: One direct titrimetric method and two indirect spectrophotometric methods for the determination of amlodipine besylate (ADB) are described. The methods use bromate-bromide mixture and two-dyes, namely Methyl Orange and Indigo Carmine, as reagents. In titrimetry (Method A), an acidified solution of ADB is titrated directly with bromate-bromide mixture using methyl orange as an indicator. Spectrophotometry involves the addition of known excess of bromate-bromide mixture to an acidified solution of ADB and the determination of the residual bromine based on its ability to bleach the dyes Methyl Orange (Method B) or Indigo Carmine (Method C) quantitatively. Titrimetry allows the determination of 1-10 mg of ADB, whereas spectrophotometry is applicable over the concentration ranges of 0.5-3.0 µg ml-1 and 1.25-12.50 µg ml-1 for method B, and method C, respectively. Method B with a calculated molar absorptivity of 6.56 x 104 l mol-1 cm-1, is the most sensitive method ever developed for ADB. The limits of detection and quantification are reported for both the spectrophotometric methods. The methods described could usefully be applied to routine quality control of tablets containing ADB. No interference was observed from common pharmaceutical adjuvants. Statistical comparison of the results with the reference method shows an excellent agreement, and indicates no significant difference in accuracy and precision. The reliability of the methods has been ascertained by recovery studies