The electrochemical behavior of l-cysteine studied at the surface of ferrocenecarboxylic acid modified carbon paste electrode (FCMCPE) in aqueous media using cyclic voltammetry and double step potential chronoamperometry. It has been found that under optimum condition (pH 7.00) in cyclic voltammetry, the oxidation of l-cysteine is occurring at a potential about 580 mV less positive than that an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α and catalytic reaction rate constant, Kh were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of l-cysteine showed a linear dependent on the l-cysteine concentration and linear calibration curves were obtained in the ranges of 10-5 M–10-3 M and 4.1×10-8 M – 3.7×10-5 M of l-cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (2d) were determined as 2.4×10-6 M and 2.5×10-8 M by CV and DPV methods. This method was also examined for determination of l-cysteine in some samples, such as Soya protein powder, serum of human blood by using recovery and standard addition methods.
