Ruthenium Hexacyanoferrate (III) Modified Glassy Carbon Electrode for Determination of Captopril

A glassy carbon electrode modified with a ruthenium (III) hexacyanoferrate film was investigated for the determination of captopril in pharmaceutical formulations. The RuOHCF film was deposited on the surface of the electrode after applying 50 successive cycles and subsequent stabilization in a mixture of NaNO3 0.50 mol L-1 + HCl 0.050 mol L-1 used as supporting electrolyte. The main processes responsible for the redox electrode response are attributed to the system RuII/RuIII/RuIV, and appeared at -0.080, 0.86 and 1.01 V (vs. SCE). The redox process at -.080V was selected for the determination of captopril in the present study, once it provided higher sensibility and occurs in a lower potential than the other ones which can prevent interferences. The experimental parameters used in the determination of the analyte, using differential pulse voltammetry were optimized: pulse amplitude: 50 mV, scan rate: 5 mV s(-1) and potential window: -0.5 to 0.2 V (vs. SCE). The analytical application of the sensor in real samples demonstrated a linear range between 0.060 and 0.80 mu mol L-1 (r=0.998) with a detection limit of 0.047 mmol L-1. A mechanism based on co-precipitation of captopril and the Ru (III) complex in the film is presented once the signal of the RuII/III redox couple decreases with increasing the analyte concentration. Recoveries of 99 to 100% were achieved in pharmaceutical samples and the proposed procedure agreed with the HPLC official method within 95% confidence level, according to the t-Student test.