Electrocatalytic oxidation of cysteine by quinizarine at glassy carbon electrode

Cyclic voltammetry, chronoamperometry and rotating disk electrode voltammetry were used to investigate the electrochemical behavior of cysteine at glassy carbon electrode modified with quinizarine. The modified electrode showed high electrocatalytic activity toward cysteine; the current was enhanced significantly relative to the situation prevailing when a bare glassy carbon electrode was used. The electrocatalytic process was highly dependent on the pH of the supporting electrolyte. The kinetics parameters of this process were calculated, the apparent electron transfer rate constant ks and α (charge transfer coefficient between glassy carbon electrode and quinizarine) were 4.44 s−1 and 0.66, respectively. The experimental parameters were optimized and the mechanism of the catalytic process was discussed. The differential pulse voltammetry response of the modified glassy carbon electrode was linear against the concentration of cysteine in the range of 8.0 × 10−7 to 1.0 × 10−5 M. The limit of detection was found to be 1.6 × 10−7 M.