Homogeneous Electrocatalytic Oxidation and Voltammetric Determination of L-Cysteine by 1,1'-Ferrocenedicarboxylic Acid at Glassy Carbon Electrode

The homogeneous electrocatalytic oxidation of L-cysteine by 1,1'-Ferrocenedicarboxylic acid (FDC) as a redox mediator was studied in aqueous medium at the surface of a glassy carbon electrode (GCE) using cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV) methods. It was found that in the presence of FDC at pH 6.0, the mediated oxidation peak current of L-cysteine is maximum and the oxidation overpotential of L-cysteine decreases about 450 mV. The diffusion coefficient of L-cysteine and catalytic reaction rate constant were also determined using chronoamperometry. The experimental results showed that the electrocatalytic oxidation peak current of L-cysteine is proportional to the concentration of L-cysteine. The calibration plot for L-cysteine was found to be linear in the ranges of 6.0x10(-5) M-2.0x10(-3) M and 2.0x10(-5) M-5.0x10(-4) M by CV and DPV, respectively. The detection limits (S/N=3) were determined as 3.6x10(-5) M and 9.8x10(-6) M using CV and DPV methods, respectively. Finally, the proposed voltammetric method was used for the determination of L-cysteine in water samples by standard addition method.