title: 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.
abstract: 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 x 10(-6) cm2 s(-1)) of L-cysteine was also estimated using chronoamperometry. The electron-transfer coefficient, alpha (= 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 x 10(-5) - 4.9 x 10(-3) M and 2.0 x 10(-5) - 2.8 x 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 sigma) were determined to be 9.9 x 10(-6) M and 5 x 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.
authors.affiliation: Electroanalytical Chemistry Research Laboratory, Department of Chemistry, Faculty of Basic Science, Mazandaran University, Babolsar, Iran.
authors.forename: Jahan-Bakhsh
authors.initials: JB
authors.lastname: Raoof
authors.forename: Reza
authors.initials: R
authors.lastname: Ojani
authors.forename: Hadi
authors.initials: H
authors.lastname: Beitollahi
authors.forename: Rahman
authors.initials: R
authors.lastname: Hosseinzadeh
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D002244:Carbon / Q000032:analysis / Q000737:chemistry; D002384:Catalysis; D003545:Cysteine / Q000032:analysis* / Q000737:chemistry; D004563:Electrochemistry / Q000379:methods*; D004566:Electrodes; D005296:Ferrous Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry; D004364:Pharmaceutical Preparations; D011199:Potentiometry / Q000379:methods
chemical_list: C520373:1-(4-(ferrocenyl ethynyl)phenyl)-1-ethanone; D000596:Amino Acids; D005296:Ferrous Compounds; D004364:Pharmaceutical Preparations; D002244:Carbon; D003545:Cysteine; D010100:Oxygen