Spectrophotometric method for the determination of nifedipine with 4-(methylamino)phenol and potassium dichromate

A new simple, sensitive and reproducible spectrophotometric method for the determination of nifedipine in pure and dosage forms has been proposed. It is based on the reduction of nifedipine with Zn/NH₄Cl, followed by coupling with N-methyl-1,4-benzoquinoneimine - the oxidation product of 4-(methylamino)phenol, to give a chromophore which absorbed maximally at 525 nm. The experimental conditions were optimised and Beer's law was obeyed over the concentration range of 5-175 μg ml^-1. The molar absorptivity, detection limit, recovery and RSD were found to be 1.9×10³ l mol^-1 cm^-1, 1.1 μg ml^-1, 99.7-100.5% and 0.3-0.8%, respectively. The proposed method was compared favourably with the official B.P. method.