bluuebunny/crossref_metadata_2025_split huggingface dataset:
Blank response at glassy carbon electrodes in a flow injection system
Authors: Xu Yan , Halsall H. Brian , Heineman William R. 
Published: May 2005

AbstractThe blank response at glassy carbon electrodes in a flow injection system consists of a transient component and a steady state (residual current) component. The transient response is attributed to nonfaradaic current and faradaic current from the oxidation‐reduction of electroactive surface functional groups on glassy carbon. The magnitude of the transient response was dependent on the potential applied to the electrode, temperature, ionic strength and pH of the injected sample solution, and independent of the flow rate. A linear relationship exists between the transient response and the difference in concentration of ionic species or pH between injected sample and the carrier. A differnce of 0.01 M ionic concentration or 0.04 pH unit between carrier and injected sample could change the transient charge by ca. 0.038 μC/cm2. The shape of the transient response due to pH difference at high positive potential indicates that some changes occur on glassy carbon surface in this potential region.
Cyclic voltammetric study of some calcium antagonist dihydropyridines in aqueous medium
Authors: El Jammal A. , Vire J‐C. , Patriarche G. J. , Palmeiro O. Nieto 
Published: May 2005

AbstractThe electrochemical behavior of several calcium antagonists of the dihydropyridine family has been investigated in aqueous buffered solution using a glassy carbon electrode. Both oxidation of the dihydropyridine ring and the reduction of the nitro or benzoxadiazole moiety are observed using cyclic voltammetry and the shape of the voltammograms depending on the initial scan direction. Each process may interfere with the other. The single reduction peak corresponds to a four‐electron transfer giving rise to the hydroxylamine. Reversing the scan leads to the nitroso derivative, its reversibility depends on the 2‐ or 3‐position of the nitro group. Oxidation of the dihydropyridine ring proceeds through a two‐electron exchange. However, nicardipine, which possesses a dialkylbenzylamine side chain, exhibits two additional peaks; the first due to the methoxylation of the side chain, and the second attributed to the oxidative chlorination of this moiety. Potentials are pH dependent. A general EC mechanism is proposed for the overall process.
Voltammetric detection and analysis of the behavior of diethylstilbestrol oxidation products
Authors: Séquaris Jean‐Marie , Fritz Joan 
Published: May 2005

AbstractPeroxidase‐mediated oxidation of diethylstibestrol (DES), a synthetic estrogen, has been proposed as a pathway in DES‐induced carcinogenicity. However, the transient nature of the DES oxidation product, DES‐quinone (DES‐Q), requires a rapid method such as cyclic voltammetry to study its stability and reactivity. Thus, the irreversible tautomerization of DES‐Q into dienstrol form (Z, Z‐DIES) is described by a two step mechanism. Tautomerization kinetics are studied as a function of pH and temperature. A significant descrease of half‐life for DES‐Q is observed in the presence of the glutathione thiolate form. Furthermore, voltammetric investigations were performed in dimethylformamide to detect the semiquinone radical of DES‐Q, a suspected genotoxic product.
Electro‐oxidative decarboxylation of D‐gluconic acid to D‐arabinose on graphite electrodes
Authors: Pezzatini Giovanni , Wei He , Guidelli Rolando , Pergola Francesco 
Published: May 2005

AbstractA voltammetric investigation of the direct electro‐oxidative decarboxylation of D‐gluconate ion to D‐arabinose on spectroscopic graphite electrode from methanol–water mixtures as well as from aqueous solutions is described. Practically a 100% yield in D‐arabinose and and 80% yield in current were realized. The kinetic behavior points to a rate‐determining release of the first transferring electron from the gluconate anion to the electrode, followed by a cleavage of the C‐1–C‐2 bond and by the resulting decarboxylation.
Theoretical equations for electrochemical processes preceded by concurrent first‐order chemical reactions in DC polarography: Application to the study of the interaction between guanine and diacetyl
Authors: Mellado José Miguel Rodríguez , Montoya Mercedes Ruiz , Galvín Rafael Marín 
Published: May 2005

AbstractTheoretical expressions are derived for electrochemical processes preceded by two concurent first‐order chemical reactions in dc polarography by using both the approximation of convective diffusion under the steady state conditions and the dimensionless differential equations of the Nernst diffusion layer approximation. These equations are formally identical to those obtained for CE and CEC processes, with differences only in the kinetic terms. Study of the interaction between guanine and diacetyl shows the usefulness of these equations. A value of 7 × 104 M is obtained for the formation constant of the adduct guaninediacetyl at 25°C.
Amount adsorbed in adsorption voltammetry. Part 1. Amount adsorbed in the adsorptive accumulation at a symmetric spherical electrode in a stirred solution
Authors: Jin Wenrui , Hou Yongchun , Yan Changtai , Wang Jianyan , Sun Changlin 
Published: May 2005

AbstractThe equation for the amount adsorbed during an adsorptive accumulation at a symmetric spherical electrode in a stirred solution has been derived and discussed under the condition of strong adsorption. When the angular velocity of the solution, ω0, is larger than 64 rad/s and the preconcentration time, ta, is more than 30 s, the equation can be simplified as Γ′(ta) = 4 πkD2/3 r ν−1/6 ω ta c*. The equation has been verified experimentally.
Biosensor for detection of organophosphate and carbamate insecticides
Authors: Marty J‐L , Sode K. , Karube I. 
Published: May 2005

AbstractAn enzyme sensor for the determination of organophosphate and carbamate insecticides is described. The mechanism is based on the coimmobilization and sequential enzymatic reactions of acetylcholinesterase and choline oxidase. The inhibition of acetylcholinesterase is measured as decreased formation of hydrogen peroxide (H2O2) as monitored by a H2O2 sensor. As low as 10 nM paraoxon can be determined with this technique. The long‐term stability of the sensor is two months, when stored at 4°C in phosphate buffer, and one year in a dry state.
A novel batch electrode design for use in stripping potentiometry facilitating medium exchange
Authors: Jagner Daniel , Renman Lars , Wang Yudong 
Published: May 2005

AbstractMedium exchange between electrolysis and stripping steps affords numerous advantages in both voltammetric and potentiometric stripping techniques. A new electrode design for batch mode stripping analysis that allows simple medium exchange under potentiostatic control is described. This is achieved by adherence of a drop of sample to a glass tube containing a glassy‐carbon disc working electrode and a porous ceramic plug, which is in liquid contact with the inner solution in which the reference and counter electrodes are situated. The electrode can be used both for manual operation and for an automated system with a sample changer. Its use is demonstrated in the constant‐current stripping potentiometry determination of the dimethylglyoxime complexes of nickel(II) and cobalt(II) after medium exchange with stripping in 5 M CaCl2, thus avoiding interferences from dissolved oxygen and excessive amounts of zinc(II).
Considerations of the pH dependence of hydrous oxide films formed on iridium by voltammetric cycling
Authors: Hitchman Michael L. , Ramanathan Subramaniam 
Published: May 2005

AbstractThe electrochemical behavior and the analytical utility of hydrous oxide films, formed on iridium by voltammetric cycling, have been studied by evaluating the dependence of the apparent Standard Electrode Potential (E°′) and the ratio of protons to electrons (p/e) participating in the potential determining equilibria on the charge storage capacity. A model based on electron exchange involving protons in solution and conductive sites on the hydrous oxide surface is proposed and it is shown that an increase in population of the conductive sites can be correlated with an enhancement in proton exchange capacity. The influence of the pretreatment is shown to be an important factor in determining both E°′ and p/e. The implications of these results for the use of hydrous iridium oxide electrodes as potentiometric pH sensors are considered.
Reverse pulse voltammetry with waiting period at conventional disk electrodes: Theory
Authors: Stojek Zbigniew , Jaworski Aleksander 
Published: May 2005

AbstractRegeneration of the initial concentrations at a solid, stationary disk electrode after each reverse pulse in the reverse pulse voltammetry simplifies interpretation of the experimental data but requires modification of the waveform. The modification examined in this work involved inserting a waiting period after each reverse pulse at the potential where the initial concentrations could be reproduced. For conventional disk sizes and a wide range of τ, which is the sum of generating time and pulse time, the minimum length of the waiting time was found theoretically to be 12τ.
The anodic dissolution of dental amalgams studied with abrasive stripping voltammetry
Authors: Scholz Fritz , Rabi Fazil , Müller Wolf‐Dieter 
Published: May 2005

AbstractThe recently described technique abrasive stripping voltammetry was used to study the corrosion behavior of five commercial dental amalgams. Abrasive stripping voltammetry of these amalgams reveals details of the anodic dissolution of the alloys that are not accessible by other methods. Systematic studies of SnHg alloys, SnAg alloys, and dental amalgams lead to a method that allows the identification of the γ2‐phase in dental amalgams. It can be shown that the non‐γ2 amalgams have a higher stability than γ2‐containing amalgams only in solutions of very low complexation ability. In cases of more aggressive solutions such as lemon juice, non‐γ2 and conventional amalgams exhibit identical behavior during the anodic oxidation.
LCEC of underivatized polypeptides and proteins at copper electrodes
Authors: Luo Peifang , Baldwin Richard P. 
Published: May 2005

AbstractConstant potential amperometric detection of underivatized polypeptides and proteins can be carried out at metallic copper electrodes. When coupled with liquid chromatography, this approach provides a sensitive and selective method of analysis for these compounds. Two different detection mechanisms can be employed: a neutral pH, low potential oxidation process attributed to enhanced dissolution of the electrode by peptide species capable of forming soluble Cu(II) complexes and a high pH, high potential electrocatalytic oxidation of the analytes. Of the two approaches, the latter process was found to be more attractive for LCEC applications as it was useful for a wider range of peptides and proteins and gave substantially larger currents and lower detection limits. The compounds exhibiting useful electrocatalytic response at the copper electrode ranged from oligopeptides such as enkephalins and bradykinin to very large proteins such as glucose oxidase (F.W. 160,000) and catalase (F.W. 240,000). The response was not dependent on the presence of tyrosine, tryptophan, or cysteine amino acid units and was shown to be compatible with both ion‐exchange and reverse‐phase separation schemes.
Convection independent detection with voltammetric single microdisk electrodes
Authors: Matysik Frank‐Michael , Emons Hendrik 
Published: May 2005

AbstractA new cell construction for voltammetric investigations at microdisk electrodes in flowing solutions is described. A platinum microdisk electrode can be arranged inside a small tube facing the flowing solution. Systematic investigations were carried out with electrodes ranging from 0.7 μM to 114 μm in diameter. It is demonstrated that the voltammetric response for continuous flow detection, as well as for flow injection measurements, does not depend on convection if the disk diameter of the electrode is equal to 0.7 μm. In addition, detection limits for the determination of ferrocene in continuously flowing acetonitrile solutions and under flow injection conditions were determined at electrodes with various diameters.
Renewable alcohol biosensors based on alcohol‐dehydrogenase/nicotinamide‐adenine‐dinucleotide graphite epoxy electrodes
Authors: Wang Joseph , Gonzalez‐Romero Elisa , Ozsoz Mehmet 
Published: May 2005

AbstractAlcohol dehydrogenase (ADH) and nicotinamide adenine dinucleotide (NAD+) have been incorporated within rigid graphite epoxy matrices to yield renewable (by polishing) alcohol sensors. The enzyme and cofactor retain their bioactivity on confinement in the graphite epoxy, with the oxidation current of the NADH formed serving as the response. Because of the intimate contact between the biocatalytic and sensing sites, the reagentless sensor produces steady‐state signals within 15–30s. The influence of various experimental variables is explored for optimum analytical performance. Common polishing procedures are used to regenerate fresh bioactive surfaces.
Simultaneous flow injection analysis of L‐lactate and L‐malate in wine based on the use of enzyme reactors
Authors: Yoshioka Shuichi , Ukeda Hiroyuki , Matsumoto Kiyoshi , Osajima Yutaka 
Published: May 2005

AbstractThe simultaneous determination of L‐malate and L‐lactate, by enzyme‐supported flow injection analysis (FIA), was developed using two enzyme reactors in parallel and a single oxygen electrode. NADH formed in the reaction of malate dehydrogenase (MDH) was regenerated to NAD+ with dissolved oxygen, using vitamin K3 and diaphorase (DI). L‐Lactate was determined using the enzyme lactate oxidase (LOD). When sample solutions were simultaneously injected into the two reactors (the MDH‐DI‐reactor and the LOD‐reactor) with a controlied residence time, a “train” of two peaks corresponding to L‐lactate and L‐malate were seen in the FIA‐gram. The peak currents were linearly related to the L‐malate and L‐lactate concentration in the range 0.05–1.2 mM and 0.01–0.5 mM, respectively. The present system was applied to the determination of L‐lactate and L‐malate in wine. The results showed good agreement with those obtained using a conventional method (F‐kit method), suggesting that this system may be applicable to the monitoring of malo‐lactic fermentation during wine production.
The use of the reference element method for stripping voltammetric analysis of natural waters
Authors: Brainina Khiena Z. , Vilchinskaya Elena A. , Khanina Rosa M. , Kalnishevskaya Lyubov N. 
Published: May 2005

AbstractAn internal standard method is proposed in the stripping analysis of natural waters. The method consists of the introduction into the sample solution of a reference element and subsequent calculation of the concentration of several elements by the increase in the analytical signal from the reference element. Criteria of the reference element selection are given. Calculated proportionality factors k obtained with the use of solutions simulating sea and river waters under the same experimental conditions can be applied to the determination of copper(II), lead(II), and cadmium(II) in natural waters. The use of the internal standard method allows one to substantially shorten the time of analysis (3–5 minutes instead of 30–50 minutes) and to improve accuracy and reproducibility of the analytical data.
Bombyx mori silk fibroin‐based immobilization method for preparation of urea electrode
Authors: Fang Yao , Shao Zhengzhong , Deng Jiaqi , Yu Tongyin 
Published: May 2005

AbstractA novel method for enzyme immobilization was developed. This system represents the first successful use of silk fibroin (obtained directly from Living Bombyx mori) as immobilization materials for the construction of an urea electrode. It is based on the structural transition of the silk fibroin membrane from α‐helix and random coil to antiparallel β‐sheet. Operational conditions and response characteristics of the resulting urea electrode were investigated, including immersion time, pH, buffer, response time, calibration curve, recovery, thermal stability, and lifetime.
Voltammetric study of cadmium complexation in halogenide mixtures of high ionic strength
Authors: Zelić Marina , Branica Marko 
Published: May 2005

AbstractCadmium complexation in chloride‐bromide and chloride‐iodide mixtures of a high ionic strength (I = 4 mol/L) was studied by polarographic/voltammetric methods. In the first case, statistically expected formation constants of mixed‐ligand complexes were confirmed. The presence of iodide ions, however, makes interpretation of the experimental data more difficult because the electrode process becomes complex. In addition to CdI2, which is a well‐known surface‐active species, CdClaI2a− seems to be adsorbed at the mercury surface.
Fast pulsed amperometric detection at noble metal electrodes: A study of oxide formation and dissolution kinetics at gold in 0.1 M NaOH
Authors: Roberts Richard , Johnson Dennis C. 
Published: May 2005

AbstractThe anodic charge (qa) for oxide formation, obtained by potential‐step chronocoulometry at a Au minidisk electrode, is nearly a linear function of log (t/ms) for t = ca. 3–30 ms with a slope proportional to the applied overpotential for oxide formation. It was demonstrated that, contrary to popular opinion based on voltammetric observation at slow scan rates (ϕ), the anodic current for oxide formation obtained using a linear potential‐scan waveform is not a linear function of ϕ at large values of ϕ. It was also demonstrated that a reverse potential‐step waveform can be used to interrupt the rapid oxide growth and, perhaps, inhibit the conversion of the hydrous oxide (AuOH) to the inert oxide (AuO). This result has probable significance for decreasing the background current during anodic pulsed amperometric detection of amines and sulfur compounds whose oxidation mechanisms are believed catalyzed by AuOH but not by AuO. The cathodic charge (qc) for oxide dissolution is approximately a linear function of t with a slope that is proportional to the applied potential.
Stripping measurements of hydrogen peroxide based on biocatalytic accumulation at mediatorless peroxidase/carbon paste electrodes
Authors: Wang Joseph , Ciszewski Aleksander , Naser Najih 
Published: May 2005

AbstractBiocatalytic accumulation, followed by chronoamperometric detection, is shown to greatly enhance the sensitivity of mediatorless biosensing of hydrogen peroxide at horseradish peroxidase (HRP)/carbon paste bioelectrodes. The mixed carbon paste, with its close proximity between the biocatalytic and graphite sensing sites, promotes the mediatorless accumulation of the oxidized form of HRP. Hence, a 28‐fold enhancement of the response for 10 μM hydrogen peroxide is obtained following 3‐minute preconcentration. The relative standard deviation (surface‐to‐surface) at the 10 μM level is 3.3%. The effect of experimental variables, such as the preconcentration time, measuring potential, or paste composition, are explored. Analogous observations are reported for tissue (horseradish root)‐based carbon pastes, for mediated HRP detection, and for monitoring of organic peroxides. Future prospects of the bioamplification approach are discussed.
Polarographic and electrochemical studies of some aromatic and heterocyclic nitro compounds, part I: General mechanistic aspects
Authors: Zuman Petr , Fijalek Zbigniew , Dumanovic Dragica , Sužnjević Desanka 
Published: May 2005

AbstractComparing reduction potentials of aromatic nitro compounds with those of corresponding nitroso compounds, by studying shifts of half‐wave and peak potentials with pH and by following the decrease of limiting current in buffered 35% DMF‐water mixtures, the sequence of protons and electrons in the four‐electron reduction step was proved to be: H+, e, H+, e, 2e, 2H+. Arylhydroxylamines formed in the four‐electron reduction of nitro compounds can be protonated and further reduced, they can undergo dehydration (provided that the dehydration product is stable), they can undergo chemical reactions with intermediates of the reduction of the nitro group, like ArNO\documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\mathop 2\limits^.} $\end{document}, they can be electrooxidized to nitrosobenzenes (which can undergo chemical reactions) or they can react with carbonyl groups when present. Stabilization of the dehydrated form can occur in quinonemethide (nifedipine) or in some quinone‐like heterocyclic derivatives. Side reactions of ArNHOH and ArNO are demonstrated by smaller peaks in CV and by controlled potential electrolysis. Reactions of ArNHOH with carbonyl groups were observed by formation of new waves of nitrones in the reduction of nitrobenzenaldehydes.
Polarographic and electrochemical studies of some aromatic and heterocyclic nitro compounds, part III: Electroreduction of mono‐ and dinitropyrazoles and ‐imidazoles
Authors: Dumanović D. , Jovanović J. , Sužnjević D. , Erceg M. , Zuman P. 
Published: May 2005

AbstractThe reduction of mono‐ and dinitropyrazoles and of nitroimidazoles follows the general pattern of reduction of aromatic nitro compounds: The nitro group is reduced in a four‐electron step to a hydroxylamino group and the protonated form of the hydroxylamino group is—in the lower pH range—further reduced to an amine. This reduction differs from that of nitrobenzenes in participation of a second hydrogen ion probably involved in protonation of the heterocyclic ring. This second proton is for nitroimidazoles transferred before the uptake of the first electron, for nitropyrazoles probably after this uptake. The transfer of the second electron is indicated to be the potential determining step. The two sequences are H+, H+, e, H+, e, 2e, H+ and H+, e, H+, H+, e, 2e, H+, respectively. For nitropyrazoles and nitroimidazoles without an alkyl substituent on the ring nitrogen, the reduction process is further complicated by the dissociation of the NH‐group in the heterocyclic ring. For 1‐alkyl‐5‐nitroimidazoles, for 4(5)‐nitroimidazole and for N‐unsubstituted‐4‐ and 3(5)‐ nitropyrazoles (but not for 2‐nitroimidazoles, 1‐alkyl‐4‐nitroimidazoles and 1‐alkylnitropyrazoles) the hydroxylamino derivative formed in the first four‐electron step undergoes a base catalyzed dehydration yielding a quinone‐like ketimine. Easy reduction of this species results in alkaline solutions in a limiting current which is significantly higher than corresponds to a four‐electron and limits to a six‐electron reduction. Such dehydration reactions occur considerably faster for dihydroxylamino derivatives formed in the reduction of dinitropyrazoles resulting in two waves with total transfer of up to 12 electrons.
Polarographic and electrochemical studies of some aromatic and heterocyclic nitro compounds, part IV: Polarographic reduction of 2‐alkylnitroimidazoles and aminonitroimidazoles
Authors: Dumanović D. , Jovanović J. , Sužnjević D. , Erceg M. , Zuman P. 
Published: May 2005

Abstract1, 2‐Dialkyl‐4‐nitroimidazoles are reduced between pH 0 and 13 in a four‐electron wave. The resulting arylhydroxylamine is stable and in acidic media reduced further to the amine. 1,2‐Dialkyl‐5‐nitroimidazoles and 2‐alkyl‐4(5)‐nitroimidazoles are reduced in alkaline media with the number of electrons approaching six. The hydroxylamine derivative formed in these reductions can be dehydrated and yields an easily reducible, quinone‐like ketimine. The rate of the dehydration governs the heights of the first step and is base catalyzed. The sequence of electron and proton transfers for 2‐ alkylsubstituted nitroimidazoles is the same as that observed for corresponding desalkyl compounds.1‐Alkyl‐4‐amino‐5‐nitroimidazoles, as well as 1‐alkyl‐4‐nitro‐5‐aminoimidazoles, are reduced in a single wave, the height of which approaches that of a six‐electron process. The dehydration of the hydroxylamino derivative is favored, probably due to an internal base catalysis. The shifts of half‐wave potentials with pH differ principally from those of all other nitroimidazoles and indicate the predominant role of the amino group in the proton transfer.