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Four simple, sensitive and accurate spectrophotometric methods have been developed for the determination of some calcium channel blockers: Amlodipine besylate (ADB), Diltiazem hydrochloride (DTZ) and Verapamil hydrochloride (VPM) in pharmaceutical formulations. These methods based on formation ion pair complexes with Sulfochlorophenol-S (SCPS), Bromopyrogallol red (BPR), Eriochromecyanine- R (ECC) and Pyrocatechol violet (PCV) in acidic medium. The colored products are extracted with chloroform and measured spectrophoto- metrically at 462, 600, 440 and 442 for ECC, SCPS, BPR and PCV, respectively. Beer’s low was obeyed in the concentration range, for ECC: 25 - 175 μg·ml-1, 50 - 150 μg·ml-1 or 100 - 250 μg·ml-1, for SCPS: 300 - 800 μg·ml-1, 200 - 700 μg·ml-1 or 100 - 550 μg·ml-1, for BPR: 50 - 400 μg·ml-1, 200 - 700 μg·ml-1 or 200 - 700 μg·ml-1 for VPM, DTZ or ADB, respectively and for PCV: 50 - 250 μg·ml-1 for VPM or 200 - 500 μg·ml-1 for DTZ with molar absorptivity, for ECC: 2.2 × 104, 2.1 × 104, 1.6 × 104 L·mol-1·cm-1, for SCPS: 3.8 × 103, 5.6 × 103, 8.1 × 103 L·mol-1·cm-1, for BPR: 11 × 103, 4.8 × 103, 6.9 × 103 L·mol-1·cm-1 for VPM, DTZ or ADB, respectively and for PCV: 19.5 × 103 L·mol-1·cm-1 for VPM and 6.6 × 103 L·mol-1·cm-1 for DTZ and relative standard deviation, for ECC: 0.76%, 0.86%, 0.46%, for SCPS: 0.94%, 0.96%, 0.86%, for BPR: 0.96%, 0.95%, 0.55% for VPM, DTZ or ADB, respectively and for PCV: 0.81% for VPM and 0.65% for DTZ. These methods have been successfully applied for the assay of drug in pharmaceutical formulations. No interference was observed from common pharmaceutical adjuvants. Statistical comparison of the results with the reference method shows excellent agreement and indicates no significant difference in accuracy and precision. </p

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Spectrophotometric determination of some calcium channel blockers using Sulfochlorophenol-S, Bromopyrogallol red, Eriochromecyanine-R and Pyrocatechoil violet