Application of potassium ferricyanide in the spectrophotometric determination of captopril

A novel method for the determination of captopril by spectrophotometer is described in this paper. The experiment is based on the fact that Fe(Ⅲ) is reduced to Fe(Ⅱ) by captopril, then the in situ formed Fe(Ⅱ) reacts with potassium ferricyanide to give the soluble prussian blue at pH 4.00, and its maximal adsorption wavelength (λ_max) is 735 nm. Good linear relationship is obtained between the absorbance and the concentration of captopril in the wide range of 0.05-20 μg/mL. The linear regression equation is A=-0.04314+0.11423C (μg/mL) with a correlation coefficient R=0.9998. The detection limit (3σ/k) is 0.04 μg/mL, the molar absorption coefficient is 2.5×10⁴ L/mol cm. By mensurating the absorbance of soluble prussian blue, the indirect determination of captopril can be obtained. This method has been successfully applied to determination of captopril in pharmaceutical samples.Analytical results obtained are satisfactory.