The electrochemical behavior ofl-cysteine studied at the surface of ferrocenedicarboxylic acid modified carbon paste electrode (FDCMCPE) in aqueous media using cyclic voltammetry, differential pulse voltammetry and double potential step chronoamperometry. It has been found that under optimum condition (pH 8.00) in cyclic voltammetry, the oxidation of l-cysteine occurs at a potential about 200 mV less positive than that of 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 ofl-cysteine showed a linear dependent on the l-cysteine concentration and linear analytical curves were obtained in the ranges of 3.0×10-5 M – 2.2×10-3 M and 1.5×10-5 M – 3.2×10-3 M of l-cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3s) were determined as 2.6×10-5 M and 1.4×10-6 M by CV and DPV methods. This method was also used for the determination ofl-cysteine in patient-blood plasma and some pharmaceutical samples, such as acetylcysteine tablets and aminoplasma serum by using a standard addition method.
