Spectrophotometry estimation of captopril in bulk and dosage form

Abstract EN

A simple spectrophotometric method is developed for detemiinatiori of captopril in pure form and pharmaceutical formulations.

The colouiimetric method utilizes 2, 6- dicWoroquinone- 4- chlorimide (DCQ) as a chromogen to be coupled with captopril.

It has been established that captopril reacts with DCQ to form a water-soluble coloured 1 : 1 complex with maximum absorbance at 438 rim.

The colour develops immediately and remains stable for at least three hours.

The optimum conditions for the reaction were investigated and into the procedure.

The validity of the proposed method was tested by analyzing samples of captopril under the optimum experimental conditions employed.

Beer's Law was found to be valid over the concentration range 9.2 x 10-5 - 5.5 x 10-4 M.

The molar absorptivity (e) of the complex was 908.31± 95.91 mol-1 cm-1.

Regression analysis of Beer's plot showed good correlation (R2= 0.9988) and the calibration graph was rectilinear(Y= 0.016 + 908.31 x) with a detection limit of 8 µg ml-1.

The precision of the method was determined on three different concentrations of captopril, The results showed a low standard deviation (RSD%) of 1.66 to 5.68% for captopril concentrations in the range 1.8 x l0-4 - 3.7 x 10-4 M.

The average recovery for two studied commercial tablets (brands A and B) was 97.65 ±1.91%.

and 101.50 ± 1.86%, respectively.

Excipients in commercial tablets and other ingredients in multi-components dosage forms did not influence the absorbance values at the studied wavelength.

The results obtained were sufficiently accurate, reproducible and in accordance with those given by the official method.

The values obtained in dosage forms were specific for the intact drug.

No interference was observed in presence of hydrochlorothiazide, which is co-formulated with captopril.