A sensitive kinetic spectrophotometric method for the determination of captopril in bulk and dosage forms

A simple and sensitive kinetic spectrophotometric method has been developed. The method is based on the reduction of Fe(III) with captopril. Fe(II) then reacts with potassium ferricyanide, resulting in the formation of a blue product. The reaction is followed spectrophotometrically by measuring the rate of change of absorbance at 730 nm. Thus, 1.23 x 10(-3) mol L(-1) FeCl3 and 3.04 x 10(-4) mol L(-1) potassium ferricyanide were used as optimum values for maximum concentration of captopril in the calibration graph. The initial rate is utilized for constructing the calibration graph, which was found to be linear in the range from 4.60 x 10(-6) to 5.06 x 10(-5) mol L(-1); detection limit is 1.99 x 10(-7) mol L(-1). The proposed method has been validated; the mean recovery ranges from 99.8 to 101.4% with RSD < 2%. Common excipients do not interfere with the determination. The point and interval hypotheses tests have been performed and confirmed that there is no significant difference between the proposed method and the conventional spectrophotometric method. The experimental true bias of all samples is lower than +/- 2%. The proposed method has been applied to the determination of captopril in bulk and dosage forms.