Analytical Sciences

Abstract − Analytical Sciences, 22(9), 1213 (2006).

Electrocatalytic Oxidation and Highly Selective Voltammetric Determination of L-Cysteine at the Surface of a 1-[4-(Ferrocenyl ethynyl)phenyl]-1-ethanone Modified Carbon Paste Electrode
Electroanalytical Chemistry Research Laboratory, Department of Chemistry, Faculty of Basic Science, Mazandaran University, Babolsar, Iran
A carbon paste electrode (CPE) chemically modified with 1-[4-(ferrocenyl ethynyl)phenyl]-1-ethanone (4-FEPEMCPE) was employed to study the electrocatalytic oxidation of L-cysteine using cyclic voltammetry, differential pulse voltammetry and double potential step chronoamperometry as diagnostic techniques. The diffusion coefficient (D = 7.863 × 10-6 cm2 s-1) of L-cysteine was also estimated using chronoamperometry. The electron-transfer coefficient, α (= 0.40), for L-cysteine at the surface of 4-FEPEMCPE was determined using cyclic voltammetry technique. It was found that under an optimum pH (= 7.00), the oxidation of L-cysteine at the surface of such an electrode occurred at a potential of about 350 mV less positive than that of an unmodified CPE. The catalytic oxidation peak currents represented a linear dependence on the L-cysteine concentration. Linear analytical curves were obtained in the ranges of 9.0 × 10-5 - 4.9 × 10-3 M and 2.0 × 10-5 - 2.8 × 10-3 M of L-cysteine with correlation coefficients of 0.9981 and 0.9982 in cyclic voltammetry and differential pulse voltammetry, respectively. The detection limits (2 σ) were determined to be 9.9 × 10-6 M and 5 × 10-6 M with cyclic voltammetry and differential pulse voltammetry, respectively. The influences of twenty other amino acids, such as glutamine, L-glutamic acid, L-glysine, L-histidine, L-isoleucine, L-leucine, L-arginine hydrochloride, L-aspargine, L-aspartic acid, S-carboxy methyl-L-cysteine, L-methionine, L-phenyl alanine, L-proline, L-serine, L-threonine, L-cystine, cysteamine and gluthathione, on the current response of the sensor were examined. The obtained results did not show any influence on the analytical signal of L-cysteine by these amino acids (except for cysteamine). The method was also used for the selective determination of L-cysteine in patient-blood plasma and some pharmaceutical preparations by using standard addition method.