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 × 10-3 mol L-1 FeCl3 and 3.04 × 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 4.60 × 10–6–5.06 × 10–5 mol L-1; detection limit is 1.99 × 10–7 mol L-1. The proposed method has been validated; the mean recovery ranges from 99.8–101.4% 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 conventional spectrophotometric method. The experimental true bias of all samples is lower than ± 2.0%. The proposed method has been applied to the determination of captopril in bulk and dosage forms.Razvijena je jednostavna osjetljiva kinetička spektrofotometrijska metoda za određivanje kaptoprila. Metoda se temelji na redukciji Fe(III) u Fe(II) koji zatim s kalijevim fericijanidom daje plavo obojeni produkt. Nastajanje produkta praćeno je spektrofotometrijski na valnoj duljini 730 nm. Optimalne koncentracije FeCl3 i potassium ferricyanida bile su 1,23 × 10-3 mol L-1, odnosno 3,04 × 10-4 mol L-1. Početna brzina upotrebljena je za izradu baždarnog pravca. Linearnost je postignuta u koncentracijskom području od 4,60 × 10–6 do 5,06 × 10–5 mol L-1; granica detekcije bila je 1,99 × 10–7 mol L-1. Predložena metoda je validirana. Srednja vrijednost analitičkog povrata iznosila je 99,8–101,4% uz RSD < 2%. Uobičajeni ekscipiensi nisu smetali određivanju. Ispitivanja hipoteze točke i intervala potvrdila su da nema značajne razlike između predložene metode i opisane spektrofotometrijske metode. Stvarna eksperimentalna pogreška za sve uzorke bila je manja od ± 2%. Opisana metoda primijenjena je za određivanje kaptoprila kao čiste supstancije i u ljekovitom pripravku
