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 cm
2 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.
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