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.