Electrochemical behavior of quinapril and its determination in pharmaceutical formulations by square-wave voltammetry at a mercury electrode.

The electrochemical behavior of the antihypertensive drug quinapril was investigated at a hanging mercury drop electrode using different voltammetric techniques such as cyclic voltammetry, square-wave voltammetry and chronoamperometry. A simple and sensitive square-wave voltammetric method for the electrochemical analysis of quinapril in its pharmaceutical formulations was developed and validated. The experimental and instrumental parameters affecting the peak current of quinapril were investigated. Various buffers such as Britton Robinson, borate and phosphate buffers at different pH values (3.0-11.0) were examined as supporting electrolyte. The optimum conditions were obtained using Britton Robinson buffer at pH 10.0 and frequency: 50 Hz, scan increment: 4 mV and pulse amplitude: 25 mV. A well-defined peak current was observed at the hanging mercury drop electrode at -1100 mV vs. Ag/AgCl reference electrode. This proposed method was validated by evaluating linearity, sensitivity, repeatability, accuracy, precision, selectivity, recovery, robustness and ruggedness. The linear calibration range was 0.50-8.68 microg mL-' (r = 0.9992). The detection and quantification limits of this method were 0.22 and 0.50 Ctg mL(-1) and intra-day and inter-day precision were between 0.81-4.32% (n = 7), respectively. The developed method was applied successfully for the determination of quinapril in its tablet dosage forms. The average amount of quinapril in tablets was found as 20.26 +/- 0.12 with RSD of 1.60% for 20 mg tabletsand 40.55 +/- 0.23 with RSD of 1.52% for 40 mg tablets.