Spectrophotometric and High Performance Liquid Chromatographic Determination of Amlodipine Besylate in Pharmaceuticals

Two rapid assay procedures based on visible spectrophotometry and high performance liquid chromatography (HPLC) have been developed for the determination of amlodipine besylate (ADB) in pharmaceutical formulations. Spectrophotometric method is based on the bromination of ADB with a known excess of bromate-bromide mixture in acid medium followed by the determination of surplus bromine by reacting with Metanil Yellow and measuring the absorbance at 530 nm. The HPLC determination was carried out on a reversed phase C 18 column using 0.1% orthophosphoric acid (pH 3): acetonitrile (20:80) at a flow rate of 1.0 ml min with UV-detection at 238 nm. In the spectrophotometric method, the absorbance is found to increase linearly with increasing concentration of ADB, which is corroborated by the calculated correlation coefficient of 0.9975. The system obeys Beer’s law for 1.25-7.50 μg ml ADB with a molar absorptivity of 2.51 x 10 l molcm and a Sandell sensitivity of 16.37 ng cm. The limits of detection and quantification are calculated to be 0.17 and 0.56 μg ml, respectively. In the HPLC method, a rectilinear relationship was observed between 7.55 – 241.6 μg ml ADB with a detection limit of 1.51 μg ml and a quantification limit of 3.02 μg ml. The statistical evaluation of the methods was examined by determining intra-day and inter-day precision. The methods, when applied to the determination of ADB in tablets, gave satisfactory results. Accuracy and reliability of the proposed methods were further ascertained by parallel determination by the reference method and by recovery studies.