Cobalt hexacyanoferrate/graphene nanocomposite – Application for the electrocatalytic oxidation and amperometric determination of captopril

A nanocomposite of cobalt hexacyanoferrate/reduced graphene oxide was synthesized by a facile precipitation route. The nanocomposite morphology was characterized by scanning electron microscopy. A nanocomposite-modified carbon paste electrode was then fabricated and its redox behavior was characterized. In the voltammograms of the modified electrode recorded in phosphate buffer solution, pH 7.4, two quasi-reversible redox transitions appeared related to the Co(II)/Co(III) and Fe(II)/Fe(III) transitions. The diffusion of the counter cation into the nanocomposite and the charge transfer kinetics across the electrode/electrolyte interface were studied. The modified electrode showed an efficient electrocatalytic activity toward the electrooxidation of captopril. In the presence of captopril, the anodic peak current of the Fe(II)/Fe(III) transition increased and the cathodic one decreased, while, the peak currents of the Co(II)/Co(III) transition remained almost constant. This indicates that captopril was oxidized on the modified electrode surface through a surface mediated electron transfer (an electrocatalytic reaction). The catalytic rate constant and the electron transfer coefficient for the electrooxidation process and the captopril diffusion coefficient were reported. A sensitive and time-saving amperometric method was developed for the analysis of captopril. Based on the developed method, captopril was determined with a detection limit of 0.331 μM. The proposed amperometric method was also applied to the analysis of captopril in tablets.