Electrochemical Reduction Using Glassy Carbon Electrode in Aqueous Medium of a Potential Anti-Chagas Drug: NFOH

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

Antineoplasic Drug Methotrexate Redox Mechanism Using a Glassy Carbon Electrode

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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.

Electrochemical Behavior of a Glassy Carbon Electrode Chemically Modified with Nickel Pentacyanonitrosylferrate in Presence of Sulfur Compounds

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

Poly(glutamic acid) nanofibre modified glassy carbon electrode: Characterization by atomic force microscopy, voltammetry and electrochemical impedance

Glassy carbon electrodes (GCE) were modified with poly(glutamic acid) acid films prepared using three different procedures: glutamic acid monomer electropolymerization (MONO), evaporation of poly(glutamic acid) (PAG) and evaporation of a mixture of poly(glutamic acid)/glutaraldehyde (PAG/GLU). All three films showed good adherence to the electrode surface. The performance of the modified GCE was investigated by cyclic voltammetry and differential pulse voltammetry, and the films were characterized by atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). The three poly(glutamic acid) modified GCEs were tested using the electrochemical oxidation of ascorbic acid and a decrease of the overpotential and the improvement of the oxidation peak current was observed. The PAG modified electrode surfaces gave the best results. AFM morphological images showed a polymeric network film formed by well-defined nanofibres that may undergo extensive swelling in solution, allowing an easier electron transfer and higher oxidation peaks. (C) 2007 Elsevier Ltd. All rights reserved.

Electrochemical behavior of a glassy-carbon electrode chemically modified with cadmium pentacyanonitrosylferrate in the presence of tetrahydrothiophene

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

Electrooxidation of sulfide by cobalt pentacyanonitrosylferrate film on glassy carbon electrode by cyclic voltammetry

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

Electrochemical reduction of nitroprusside on a glassy carbon electrode modified by poly-L-lysine films

The present work describes the preparation and characterization of polyelectrolyte coatings of poly-L-lysine (PLL) to modify a glassy carbon electrode and its application to the pre-accumulation of nitroprusside (NP). The effects of the coating on the electrochemical reduction of NP were investigated. The performance of the modified electrode indicates that the drug can be immobilized by electrostatic interaction and the voltammetric signal monitored at all pH values in the range of 2-12. The strong interaction between NP and PLL stabilizes the complex on the electrode surface and minimizes the chemical reaction of lost CN- ions as a subsequent reaction of electron transfer, which could improve the action mechanism of NP.

Electrochemical reduction and determination of Cibacron Blue F3GA at poly-L-lysine modified glassy carbon electrode

The oxidation of a reactive dye, Cibacron Blue F3GA, CB, (C.I. 61211), widely used in the textile industries to color natural fibers, was studied by electrochemical techniques. The oxidation on glassy carbon electrode occurs in two steps at 2.0 < pH < 10 involving one electron transfer each to the amine group leading to the imide derivative. Stable films of poly-L-lysine (PLL) in the presence of glutaraldehyde (GA) 97.5%:2.5% on glassy carbon electrode can be used to detect low levels of dye using its oxidation peak at +0.75V by voltammetry. Linear calibration graphs were obtained for the CB reactive dye, from 1.0 X 10(-6) to 1.0 X 10(-5) mol L-1 in B-R buffer, pH 2.0, using a pre-concentration off-line during 10 min. The detection limit (3 sigma/slope) was calculated to be 4.5 X 10(-8) mol L-1. Films of PLL can readily be applied for the determination of CB dye bearing aminoanthraquinone as chromophore and chlorotriazinyl as reactive group at concentrations at least 100 times lesser than using a glassy carbon electrode without modification. The method described was applied for the determination of CB dye in tap water and raw water collected from the municipal treatment plant with a recovery of 89.2% +/- 5.4 and 88.0% +/- 6.5, respectively. (c) 2005 Elsevier Ltd. All rights reserved.

Application of a glassy carbon electrode modified with poly(glutamic acid) in caffeic acid determination

Glassy carbon electrodes were coated with films of poly( glutamic acid) ( PG), and the modified electrode proved to be very effective in the oxidation of caffeic acid. The performance of the film was also tested with ascorbic acid, coumaric acid, ferulic acid, sinapic acid and chlorogenic acid. At pH 5.6, all the hydroxycinnamic acids yield a higher peak current intensity when oxidized after incorporation in the PG-modified electrode, and only the oxidation of ascorbic acid exhibits overpotential reduction. At pH 3.5 only caffeic and chlorogenic acid are incorporated in the modified electrode and exhibit a well-defined oxidation wave at +0.51 V and +0.48 V, which is the base for their determination. Linear calibration graphs were obtained from 9 x 10(-6) mol L-1 to 4 x 10(-5) mol L-1 caffeic acid by linear voltammetric scan and from 4 x 10(-6) mol L-1 to 3 x 10(-5) mol L-1 by square wave voltammetric scan. The method was successfully applied to the determination of caffeic acid in red wine samples without interference from other hydroxycinnamic acids or ascorbic acid.

Determination of iodide and idoxuridine at a glutaraldehyde-cross-linked poly-L-lysine modified glassy carbon electrode

The detection limit (about 0.017 mu g mL(-1)) for voltammetric determination of iodide (peak at +0.87 V vs. Ag/AgCl at pH 2) at a glutaraldehyde-cross-linked poly-L-lysine modified glassy carbon electrode involving oxidation to iodine was found to be several orders of magnitude lower than that for the voltammetric determination on a bare glassy carbon electrode. This method was applied successfully to the determination of iodide in two medicinal formulations. Idoxuridine was determined indirectly at the same electrode by accumulating it first at -0.8 V vs. Ag/AgCl. At this potential the C-I bond in the adsorbed idoxuridine is reduced giving iodide, which is then determined at the modified electrode. The method was successfully applied to the determination of idoxuridine in a urine sample.

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.

Voltammetric determination of ethyl acetate in ethanol fuel using a Fe 3+/Nafion®-coated glassy carbon electrode

A voltammetric method for the determination of ethyl acetate in ethanol fuel using a Fe3+/Nafion®-coated glassy carbon electrode (GCE) is proposed. The ethyl acetate present in the ethanol fuel was previously converted to acetohydroxamic acid via pretreatment with hydroxylamine chloride. The acetohydroxamic acid promptly reacted with the iron (III) present in the film, producing iron (III) acetohydroxamate, which presents a well-defined voltammetric peak current at -0.02 V. Optimization of the voltammetric parameters for the cyclic, linear sweep, square wave, and differential pulse modalities was carried out for this chemically-modified electrode. Square wave voltammetry afforded the best response for acetohydroxamic acid detection. The analytical curve for this species was linear from 9 to 100 μmol L 1 according to the following equation: ip (μA) = 0.27 + 2.55Cacetohydroxamic acid (μmol L 1), with linear correlation coefficient equal to 0.993. The technique presented limit of detection equal to 5.3 μmol L 1 and quantification limit of 17.6 μmol L 1. The proposed method was compared to the official method of ethyl acetate analysis (Gas Chromatography), and a satisfactory correlation was found between these techniques. © 2012 Elsevier Ltd. All rights reserved.