Differential Pulse Voltammetry Determination of l-Cysteine with Ferrocene-Modified Carbon Paste Electrode

Abstract The preparation of ferrocene-modified carbon paste electrode by incorporation of a mediator into a graphite powder–paraffin oil matrix is described. The suitability of this chemically modified electrode for electrocatalytic oxidation of l-cysteine was studied in buffered solution by cyclic voltammetry and double potential step chronoamperometry. It has been found that, under optimum conditions (pH = 7.00), the oxidation of l-cysteine at the surface of such an electrode occurs at a potential about 500 mV less positive than on an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient α and catalytic reaction rate constant K′h were determined using various electrochemical approaches. The electrocatalytic oxidation peak current of l-cysteine at the surface of this modified electrode was used for determination of l-cysteine by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Linear analytical curves were obtained in the ranges of 10−5 M (= mol dm−3) – 10−3 M and 8.9 × 10−6 M – 2 × 10−4 M of l-cysteine concentration with CV and DPV methods, respectively. The detection limits were determined as 6.5 × 10−6 M and 4.7 × 10−6 M by CV and DPV methods. This method was also examined for determination of l-cysteine in samples, such as Soya protein powder, serum and plasma of human blood, using recovery and standard addition methods.