Electrochemical Redox Behavior of Omeprazole Using a Glassy Carbon Electrode

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

SOLID STATE ELECTROCHEMICAL BEHAVIOR of USNIC ACID AT A GLASSY CARBON ELECTRODE

The electrochemical redox behavior of usnic acid, mainly known for its antibiotic activity, has been investigated using cyclic, differential pulse and square wave voltammetry in aqueous electrolyte. These studies were carried out by solid state voltammetry with the solid mechanically attached on the surface of a glassy carbon electrode and at different pH values. Usnic acid did not present any reduction reaction. The pH-dependent electrochemical oxidation occurs in three steps, one electron and one proton irreversible processes, assigned to each of the hydroxyl groups in the molecule. Adsorption of the non-electroactive oxidation product was also observed, blocking the electrode surface. An oxidation mechanism was proposed and electroanalytical methodology was developed to determine usnic acid.

Adsorptive potentiometric stripping analysis of trace tamoxifen at a glassy carbon electrode

A highly sensitive adsorptive stripping procedure for trace measurement of the anticancer drug tamoxifen is described. The method is based on controlled adsorptive accumulation of the drug at an electrochemically treated glassy carbon electrode, followed by chronopotentiometric measurement of the surface species. The chronopotentiometric operation effectively addresses the large background contribution inherent to the glassy carbon electrode to yield a detection limit of 4 x 10(-10) M after 4 min preconcentration. The adsorptive stripping response is evaluated with respect to electrode type and conditioning, accumulation potential and lime, stripping current, pH, drug concentration, potential interferences, and other variables. Applicability to urine samples is illustrated. (C) 1997 Elsevier B.V. B.V.

Decolourization of anthraquinone reactive dye by electrochemical reduction on reticulated glassy carbon electrode

The electrochemistry reduction for the removal of Reactive Blue 4 (RB4) dye from aqueous solution using reticulated glassy carbon electrode is investigated. At pH < 8.0 the anthraquinone group of the RB4 dye are reduced in one cathodic step to hidroquinone after a reversible two-electron process involving a precedent two protons reaction. A stable semiquinone is detected by spectrophotometric technique. At pH > 8.0 the reduction process involves two reversible 2-electron steps, whose species are generated by a protonation equilibrium of anthraquinone group. The results shows that 60% of color removal was obtained after 3 hours of RB4 dye electrolysis at acidic and neutral conditions and only 37% at alkaline conditions. Simultaneously 64% of total organic carbon was removed after electrolysis at pH 2.0.

Modifying glassy carbon (GC) electrodes to confer selectivity for the voltammetric detection of L-cysteine in the presence of DL-homocysteine and glutathione

In this communication we report a proof of concept study of the use of cyclic voltammetry with a polyeugenol-modified glassy carbon (GC) electrode to selectively detect L-cysteine in the presence of both DL-homocysteine and glutathione in perchloric acid. The formation of a polyeugenol-modified gold electrode is also reported for the first time.

Voltammetric sensor for simultaneous determination of p-phenylenediamine and resorcinol in permanent hair dyeing and tap water by composite carbon nanotubes/chitosan modified electrode

p-Phenylenediamine (PPD) and resorcinol (RSN) are hair dye precursors of permanent dyeing more used worldwide. The present work describes a simple and economic voltammetric sensor for simultaneous determination of both components in commercial hair dyeing and tap water at low concentrations. PPD and RSN are oxidized at + 0.17 and + 0.61 V vs. Ag/AgCl at glassy carbon electrode coated by composites of multiwall carbon nanotubes with chitosan (MWNTs-CHT/GCE), which anodic currents density normalized are 10% and 70% higher in relation to the unmodified electrode, respectively. The calibration curve for simultaneous determination of PPD and RSN showed linearity between 0.55 and 21.2 mg L-1 with detection limits of 0.79 and 0.58 mg L-1 to PPD and RSN, respectively. The relative standard deviations found for ten determinations were of 0.73 and 2.35% to 2.70 mg L-1, and 0.87 and 1.08% to 15.96 mg L-1 to PPD and RSN, respectively. The voltammetric sensor was applied to determination of PPD and RSN in tap water and commercial hair dyeing samples and the average recovery for these samples was around 97%. The products generated from PPD and RSN reaction such as was p-quinonediimine and bandrowski base were detected by LC-MS/MS and UV-vis spectrophotometry. (C) 2014 Published by Elsevier B.V.

Determination of phosphorus in biodiesel using 1:12 phosphomolybdic modified electrode by cyclic voltammetry

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Preconcentration of rutin at a poly glutamic acid modified electrode and its determination by square wave voltammetry

The voltammetric determination of rutin in 0.04 mol l(-1) B-R buffer (pH 4.0) by square wave voltammograms (+0.41 V vs. Ag/AgCl(sat.)) at a poly glutamic acid modified glassy carbon electrode was found to be several orders of magnitude lower than that on a bare glassy carbon electrode. Rutin can be preconcentrated on the films of poly glutamic acid and presented linear relationship from concentration of 7 x 10(-7) to 1 x 10(-5) mol l(-1) in 0.04 mol l(-1) B-R buffer pH 4.0. The method was successfully applied to the determination of rutin in pharmaceutical formulation without any pretreatment.

Electrooxidation and determination of dopamine using a Nafion (R)-cobalt hexacyanoferrate film modified electrode

The electrocatalysis of dopamine has been studied using a cobalt hexacyanoferrate film (CoHCFe)-modified glassy carbon electrode. Using a rotating disk CoHCFe-modified electrode, the reaction rate constant for dopamine was found to be 3.5 x 105 cm(3) mol(-1) s(-1) at a concentration of 5.0 x 10(-5) mol L-1. When a Nafion (R) film is applied to the CoHCFe-modified electrode surface a high selectivity for the determination of dopamine over ascorbic acid was obtained. The analytical curve for dopamine presented linear dependence over the concentration range from 1.2 x 10(-5) to 5.0 x 10(-4) mol L-1 with a slope of 23.5 mA mol(-1) L and a linear correlation coefficient of 0.999. The detection limit of this method was 8.9 x 10(-6) mol L-1 and the relative standard deviation for five measurements of 2.5 x 10(-4) mol L-1 dopamine was 0.58%.

Potentiometric determination of phosphorus in biodiesel using chemically modified electrode with cobalt film

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Modification of glassy carbon electrodes with a poly-L-lysine/glutaraldehyde film

A film of poly-L-lysine (PLL) adheres better to the surface of a glassy carbon electrode when the PLL is partially cross-linked by means of glutaraldehyde. A film composition of 97.5% PLL/2.5% glutaraldehyde gives good adhesion and retains the anionic exchange capability of the PLL. The performance of the film was tested with hexacyanoferrate(III) using electrochemical and nonelectrochemical accumulation.

Modificação de eletrodos de carbono vítreo e nanotubos de Ti/TiO2 com aspirinato de cobre (II) para detecção eletroquímica e redução fotoeletrocatalítica de íons nitrito

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Voltammetric sensor for amoxicillin determination in human urine using polyglutamic acid/glutaraldehyde film

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Application of voltammetric technique to the analysis of indanthrene dye in alkaline solution

The Indanthrene Olive Green B (C.I. Vat Green 3; C.I. 69500), VG3 dye, a vat dye bearing an anthraquinonoid group and a ketonic group, can be detected by differential pulse voltammetry in alkaline solution using glassy carbon electrode. on the adsorbed form the dyes are reduced into three cathodic steps at -0.54 V, -0.65 V and -0.93 V vs Ag/AgCl. The leuco form generated after previous electrolysis at controlled potential of -1 V can be detected by voltammetry due to its reoxidation peak at -0.08 V. An analytical method is proposed for determining the vat dye using modified glassy carbon electrode by electrochemical activation in alkaline medium. Linear relationship was observed between l(Pu) vs concentration from I X 10(-5) mol L-1 to 6.0 X 10(-4) mol L-1. The detection limit was calculated to be 9.3 X 10(-6) mol L-1. (c) 2005 Elsevier Ltd. All rights reserved.

Determination of the relative contribution of phenolic antioxidants in orange juice by voltammetric methods

The electrochemical oxidation of caffeic, chlorogenic, sinapic, ferulic and p-coumaric acids was investigated by cyclic voltammetry on acetate buffer pH 5.6 on glassy carbon electrode and modified glassy carbon electrode. According to their voltammetric behavior, the antioxidant activity of these phenolic acids was evaluated and the results pointed to the following sequence: caffeic acid (E-a = +0.31 V) > chlorogenic acid (+ 0.38 V) > sinapic acid (+ 0.45 V) > ferulic acid (+ 0.53 V) >p-coumaric acid (+ 0.73 V). The results were confirmed by DPPH test, which evidenced the strongest antiradical activity for compounds possessing the cathecol moiety (caffeic and chlorogenic acids). Linear calibration graphs were obtained for their determination at concentrations from 1 x 10(-4) to 1 x 10(-3) mol L-1. The method was applied to orange juice. Selectivity was illustrated by the analysis of caffeic and chlorogenic acids electrodeposited on a glassy carbon electrode previously modified by electrochemical activation in the presence of ascorbic acid. (C) 2003 Elsevier B.V. All rights reserved.