This work describes the electrochemical behavior of captopril (CAP-SH), on glassy carbon in the presence of 4,4-biphenol, using cyclic voltammetry as a diagnostic technique. The results indicate a complicated catalytic system. Cyclic voltammetry and liner sweep voltammetry were used to characterize the electrochemical properties of 4,4-biphenol and to investigate its electrocatalytic effect on the CAP-SH oxidation. The diffusion coefficient of CAP-SH and the catalytic rate constant of the reaction of 4,4-diphenoquinone with CAP-SH was also estimated using digital simulation method. The other kinetic parameters of this process were calculated at various pHs. The dependence of peak currents on pH, concentration and the potential scan rate was investigated. A linear calibration curve was obtained in the concentration range of captopril of 25–300 μM, with a limit of detection of 3.34 μM. The relative standard deviation (R.S.D%) for 6 replicate measurements of captopril (100 μM) was 1.92%. The method was developed for the determination of captopril in tablet and plasma samples with satisfactory results
