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Electrode Process (electrode + process)
Selected AbstractsVoltammetric Studies of Parallel Electrode Processes Under Low Ionic Strength Conditions.ELECTROANALYSIS, Issue 7 2006Influence of Convection Abstract It is known that either a very strong enhancement or an almost complete depression of the height of one of two waves can be obtained when two analytes (one appropriately charged and one uncharged) are present in a quiet solution containing no supporting electrolyte. In this paper we examine whether these effects can be extended for solutions with forced convection. Three two-analyte mixtures were examined voltammetrically under conditions of no added supporting electrolyte and added convection. The first mixture (1,1,-ferrocenedimethanol and ferrocenesulfonate anion) changes its total charge from ,1 to +1 after electrooxidation of both components. Under all applied conditions, the introduction of convection caused an increase of both waves without changing the wave height ratio. A similar behavior was observed for the mixture of ferrocene and 1,1,-ferrocenedimethanol. For this system the total charge changes from 0 to +2. A substantial influence of convection on the ratio of two waves was found for the third mixture: ferrocene and ferrocenylmethyltrimethylammonium cation (total charge changes from +1 to +3). For this system the convection strongly depressed the migrational effects. The obtained experimental results were verified with simulations using software MIOTRAS. This software is capable of modeling diffusion, migration, convection and following homogenous reactions. The agreement between experiment and simulations was fairly good. [source] Reagentless Glucose Biosensor Based on the Direct Electrochemistry of Glucose Oxidase on Carbon Nanotube-Modified ElectrodesELECTROANALYSIS, Issue 11 2006Xiliang Luo Abstract The direct electrochemistry of glucose oxidase (GOD) was revealed at a carbon nanotube (CNT)-modified glassy carbon electrode, where the enzyme was immobilized with a chitosan film containing gold nanoparticles. The immobilized GOD displays a pair of redox peaks in pH,7.4 phosphate buffer solutions (PBS) with the formal potential of about ,455,mV (vs. Ag/AgCl) and shows a surface-controlled electrode process. Bioactivity remains good, along with effective catalysis of the reduction of oxygen. In the presence of dissolved oxygen, the reduction peak current decreased gradually with the addition of glucose, which could be used for reagentless detection of glucose with a linear range from 0.04 to 1.0,mM. The proposed glucose biosensor exhibited high sensitivity, good stability and reproducibility, and was also insensitive to common interferences such as ascorbic and uric acid. The excellent performance of the reagentless biosensor is attributed to the effective enhancement of electron transfer between enzyme and electrode surface by CNTs, and the biocompatible environment that the chitosan film containing gold nanoparticles provides for immobilized GOD. [source] The Electrochemical Behavior of ,-Ketoglutarate at the Hanging Mercury Drop Electrode in Acidic Aqueous Solution and Its Practical Application in Environmental and Biological SamplesELECTROANALYSIS, Issue 12 2004Li Yang Abstract The voltammetric behavior of ,-ketoglutarate (,-KG) at the hanging mercury drop electrode (HMDE) has been investigated in acetate buffer solution. Under the optimum experimental conditions (pH,4.5, 0.2,M NaAc-HAc buffer solution), a sensitive reductive wave of ,-KG was obtained by linear scan voltammetry (LSV) and the peak potential was ,1.18,V (vs. SCE), which was an irreversible adsorption wave. The kinetic parameters of the electrode process were ,=0.3 and ks=0.72,1/s. There was a linear relationship between peak current ip, ,-KG and ,-KG concentration in the range of 2×10,6,8×10,4,M ,-KG. The detection limit was 8×10,7,M and the relative standard deviation was 2.0% (C,-KG=8×10,4,M, n=10). Applications of the reductive wave of ,-KG for practical analysis were addressed as follows: (1) It can be used for the quantitative analysis of ,-KG in biological samples and the results agree well with those obtained from the established ultraviolet spectrophotometric method. (2) Utilizing the complexing effect between ,-KG and aluminum, a linear relationship holds between the decrease of peak current of ,-KG ,ip and the added Al concentration C in the range of 5.0×10,6,2.5×10,4,M. The detection limit was 2.2×10,6,M and the relative standard deviation was 3.1% (C=4×10,5,M, n=10). It was successfully applied to the detection of aluminum in water and synthetic biological samples with satisfactory results, which were consistent with those of ICP-AES. (3) It was also applied to study the effect of AlIII on the glutamate dehydrogenase (GDH) activity in the catalytically reaction of ,-KG+NH+NADH,L -glutamate+NAD++H2O by differential pulse polarography (DPP) technique. By monitoring DPP reductive currents of NAD+ and ,-KG, an elementary important result was found that Al could greatly affect the activity of GDH. This study could be attributed to intrinsic understanding of the aluminum's toxicity in enzyme reaction processes. [source] An Electroanalytical Investigation on the Redox Properties of Calcium Antagonist DihydropyridinesELECTROANALYSIS, Issue 10 2003Rosanna Toniolo Abstract The antioxidant capacity of some calcium antagonists and one calcium agonist 1,4-dihydropyridines (DHPs) was evaluated by a competitive kinetic procedure. With the exception of Amlodipine, all the calcium antagonist DHPs display an unambiguous antioxidant capacity, while for the calcium agonist DHP (Bay K 8644) no measurable reactivity towards peroxyl radicals could be detected. The finding was corroborated by an electroanalytical investigation of the redox properties of DHPs compounds to get an insight about both the thermodynamic constraints of their oxidation process and reaction pattern. The oxidation potentials decrease with both antioxidant capacity and increasing basic character, thus suggesting the relevance of the electron density on the DHP ring. For all the compounds investigated, the overall oxidation process takes place through a primary one-electron step accompanied by a fast proton release and the formation of a neutral radical undergoing a second much easier one-electron step. The protonated form of the parent pyridine derivative is thus generated as the final product. This pattern is relevant for the antioxidant effect, since the radical intermediate is much more prone to be oxidized than to be reduced, thus fully preventing the propagation of the oxidative chain reaction. In the case of calcium antagonist DHPs, the above release of protons complicates the overall oxidation process by introducing a parasitic side reaction where a coupling between protons and the starting species takes place. This DHP self-protonation subtracts part of the original species from the electrode process because the parent cationic species is no longer electroactive. Conversely, the calcium agonist DHP, which is more difficult to be oxidized, turned out to be such a weak base as to be unable to undergo the self-protonation reaction. The combined effect of oxidation potentials and proton binding capacity of DHPs is a key element for the redox transition, which could support their antioxidant effect and should be considered to some extent in accounting for the calcium antagonist vs calcium agonist effect. [source] Voltammetric determination of parthenolide in spiked human plasma and urinePHYTOCHEMICAL ANALYSIS, Issue 4 2001F. Belal Abstract The voltammetric behaviour of parthenolide, a biologically active sesquiterpene lactone, was studied using direct current (DCt), alternating current and differential-pulse polarography (DPP). Parthenolide developed well-defined cathodic waves over the whole pH range in Britton,Robinson buffers. At pH 10 the diffusion current constant was 3.54,±,0.08 (± standard deviation; n,=,8). The current vs concentration plots were rectilinear over the range 4,36 and 1,28,µg/mL in the DCt and DPP modes, respectively, with a minimum detectability of 0.06,µg/mL (about 1,×,10,7,M) using the latter technique. The waves were characterised as being diffusion controlled, although adsorption phenomenon played a limited role in the electrode process. The described analytical method was applied to the determination of parthenolide in spiked human urine and plasma; the percentage recoveries were 95.72,±,0.22 and 94.0,±,0.13 (± standard deviation; n,=,9), respectively. Copyright © 2001 John Wiley & Sons, Ltd. [source] Dramatic Effects of Ionic Liquid on Platinum Electrode Surface and Electron-Transfer Rates of meso -TetraphenylporphyrinsELECTROANALYSIS, Issue 12 2006Afsaneh Safavi Abstract The effect of addition of a room temperature ionic liquid, 1-butyl-3-methyl imidazolium hexafluorophosphate [bmim][PF6], on the electrochemical behavior of different free-base para-substituted meso -tetraphenylporphyrins in dichloromethane solution has been studied using cyclic voltammetric technique. It has been found that the ionic liquid has the ability to regenerate platinum electrode surface and improves the reversibility of electrode processes. This has been true for the case of all the porphyrins studied. [source] Electrochemistry at High Pressures: A ReviewELECTROANALYSIS, Issue 10 2004Debora Giovanelli Abstract High pressure electrochemical studies are potentially dangerous and less immediately implemented than conventional investigations. Technical obstacles related to properties of the working electrode material, preparation of its surface, availability of suitable reference electrodes, and the need for specially designed high pressure equipment and cells may account for the relative lack of experimental data on electrochemistry at high pressures. However, despite the stringent requirements for system and equipment stability, significant developments have been made in recent years and the combination of electrochemical methods with high hydrostatic pressure has provided useful insights into the thermodynamics, kinetics, and other physico-chemical characteristics of a wide range of redox reactions. In addition to fundamental information, high pressure electrochemistry has also lead to a better understanding of a variety of processes under non-classical conditions with potential applications in today's industrial environment from extraction and electrosynthesis in supercritical fluids to measurement of the pH at the bottom of the ocean. The purpose of this article is to detail the experimental pressurizing apparatus for electroanalytical measurements at high pressures and to review the relevant literature on the effect of pressure on electrode processes and on the properties of aqueous electrolyte solutions. [source] | ||||||||||