Colorimetric determination of ramipril, enalapril maleate and fosinopril in their pharmaceutical formulations

ABSTRACT

Two new spectrophotometric methods were developed for the determination of three angiotensin-converting enzyme inhibitors, namely, ramipril, enalapril maleate and fosinopril. The first method was based on the oxidation of the three drugs by Fe[III] in presence of 1.10-phenanthroline, the formed tris-[Fe-o-phen]complex in acetate buffer and optimum pH was measured at [lambda][max] 510 nm with linear relationship over concentration range from 6-50 micro gml[-1] and molar absorptivity 1.2x10[4] 1 mol[-1]cm[-1] for ramipril and enalapril maleate and 1.8x10[4] 1 mol[-1]cm[-1] for fosinopril. The second method was based on measuring the formed tris -[Fe-bipyridyl]complex in the same condition at [lambda][max] 540 nm with linear relationship in concentration range from 10-54 micro gml[-1] and molar absorptivity of 1.0x10[4] 1 mol[-1]cm[-1] for ramipril, 1.6x10[4] 1 mol[-1]cm[-1] for and enalapril maleate and 1.57x10 [4] mol[-1]cm[-1] for fosinopril. The two methods hold their accuracy and precision well when applied to the determination of the studied drugs in their dosage forms