bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow monitoring of glutamate and aspartate in foods and pharmaceutical products with immobilized bienzyme electrochemical cells
Authors: Palleschi G. , Lavagnini M. G. , Compagnone D. , Bertocchi P. , Moscone D. 
Published: May 2005

AbstractElectrochemical enzyme cells for glutamate and aspartate analysis have been assembled and used in continous‐flow and in flow‐injection analysis. The enzymes, glutamate oxidase (GOD) and aspartate amino‐transferase (AST), were co‐immobilized on an Immobilon Immuno‐affinity membrane, which was placed into a three‐electrode, flow‐through cell. Additional protective membranes were used to reduce the electrochemical interferences and to protect the immobilized enzymes. Thin‐layer and walljet cells were used and compared. Calibration curves for glutamate and aspartate showed a linearity range of 1–500 μmol/L and 10–500 μmol/L respectively. The sensitivity was higher using the flow‐through system with a response time of 2 min. Better reproducibility was achieved using the FIA procedure with a response time of less than 1 min. Glutamate in foodstuffs and asparatate in some pharmaceutical products were analyzed. Results were compared and correlated well with an HPLC procedure.
Anaesthetic lidocaine and dicaine transfer across liquid/liquid interfaces
Authors: Wang Erkang , Yu Zemu , Li Nan 
Published: May 2005

AbstractLidocaine transfer across the water/1,2‐dichloroethane and the water/nitrobenzene interfaces has been investigated by chronopotentiometry with linear current scanning and cyclic voltammetry. The irreversible hydrolysis occurring in the phase transfer of dicaine at the water/nitrobenzene interface is discussed.
Covalent immobilization of DNA onto glassy carbon electrodes
Authors: Millan Kelly M. , Spurmanis Aleksandrs J. , Mikkelsen Susan R. 
Published: May 2005

AbstractDenatured calf thymus deoxyribonucleic acid (DNA) and synthetic poly(dG)poly(dC) have been covalently immobilized onto oxidized glassy carbon electrode surfaces using the water‐soluble carbodiimide, 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide. Immobilized DNA has been detected using the complex Co(bpy) (bpy = 2,2′ ‐bipyridine). This complex has a reversible one‐electron oxidation (Eo′ = 0.33 V versus SHE), binds electrostatically in the minor groove of the DNA double helix, and preconcentrates at the surface of the DNA‐modified electrode prior to a voltammetric scan. Our cyclic voltammetric data indicate that larger Co(bpy) signals are observed at low ionic strength; this is consistent with the larger association constants obtained for the binding of Co(bpy) with calf thymus DNA at low ionic strength. While immobilizations were attempted for four species, poly(dA)poly(dT), native calf thymus DNA, denatured calf thymus DNA, and poly(dG)poly(dC), only the last two species could be successfully immobilized with the carbodiimide procedure; these results show that guanosine and/or cytosine bases will bind covalently to the o‐acylisourea on the glassy carbon surface.
The application of ferrocene‐modified n‐type silicon in glucose biosensors
Authors: Dicks J. M. , Cardosi M. F. , Turner A. P. F. , Karube I. 
Published: May 2005

AbstractThis article describes the application of ferrocene‐modified n‐type silicon electrodes to the anaerobic redox catalysis of glucose oxidase. The electrodes are modified with ferrocene either directly, by using (1,1′‐ferrocenediyl)dichlorosilane, or via an underlying polypyrrole film. Light‐activated catalytic waves are detected in both cases in the presence of glucose oxidase and glucose, thereby demonstrating rapid heterogeneous kinetics between the covalently immobilized mediator and glucose oxidase. A glucose‐sensitive electrode is made by simple adsorption of glucose oxidase from an aqueous buffered solution into the surface film.
Organic‐phase biosensors based on the entrapment of enzymes within poly(ester‐sulfonic acid) coatings
Authors: Wang Joseph , Lin Yuehe , Chen Qiang 
Published: May 2005

AbstractThe utility and advantages of the poly(ester‐sulfonic acid) ionomer (Eastman AQ‐55D, Eastman Chemical Products) for entrapping enzymes onto electrodes for organic‐phase biosensing are described. This type of immobilization scheme relies on the stability of Eastman AQ films in various organic solvents. The resulting organic‐phase enzyme elecrodes couple the entrapment of high enzyme loadings with discrimination against anionic interferences, short response times, and a rapid stabilization of the baseline current. The immobilization of the enzymes tyrosinase and horseradish peroxidase (HRP) is evaluated in connection with the biosensing of phenolic and peroxide compounds in acetonitrile solutions. Various conditions of this simple preparation route are explored.
Polarographic and electrochemical studies of some aromatic and heterocyclic nitro compounds: Part V. Polarographic reduction of cyano‐and carboxamido‐nitropyrazoles
Authors: Dumanović D. , Jovanović J. , Marjanović B. , Zuman P. 
Published: May 2005

AbstractReduction of the nitro group in 1‐alkyl‐4‐cyano‐5‐nitropyrazoles follows a pattern similar to that of 1‐alkyl‐5‐nitropyrazoles, involving the sequence H+, e, H+, e, 2e, 2H+. On the other hand, the sequence of proton and electron transfers in the reduction of the nitro group in 1‐alkyl‐3‐nitro‐4‐cyanopyrazoles differs from that in 1‐alkyl‐3‐nitropyrazoles. Similarly, the reductions of 4‐cyano‐3(5) ‐nitropyrazole differs from that of 3(5)‐nitropyrazole, even when both of these reductions are affected by the dissociation of the NH group with pKB = 6.26 and 9.81, respectively. Similarly, the behavior of 1‐alkyl‐4‐carboxamido‐5‐nitropyrazoles resembles that of 1‐alkyl‐5‐nitropyrazoles, but that of 1‐alkyl‐3‐nitro‐4‐carboxamidopyrazoles is different from that of 1‐alkyl‐3‐nitropyrazoles. In 1‐alkyl‐4‐carboxamido‐5‐hydroxylaminopyrazoles, the carboxamido group is reduced in a two‐ and four‐electron process, but the low absolute value of the limiting current of wave i2 indicates the presence of competitive side reactions.
Elucidation of electrochemical reactions using three‐dimensional voltammetry
Authors: Papadopoulos Nikos , Hasiotis Costas , Kokkinidis Giorgos , Papanastasiou Giorgos 
Published: May 2005

AbstractIn this article, we demonstrate that three‐dimensional voltammetry can be used very efficiently as a reversal technique in complicated reactions. Three‐dimensional voltammetry, based on double potential step chronoamperometric data, has been used to obtain information on the reaction products of the electrochemical reduction of 4‐nitroquinoline‐N‐oxide. The study was carried out in aqueous 0.5 M HClO4 solutions on Pt/Bi (upd) electrode.
Alkali and alkaline earth metal ion transfer across the liquid/liquid interface facilitated by ionophore ETH157
Authors: Wang Erkang , Yu Zemu , Qi Deyao , Xu Chengmin 
Published: May 2005

AbstractThe H+, Li+, Na+, K+, Mg2+, Ca2+ and Ba2+ ion transfer across the water/nitrobenzene (NB) and water/1,2‐dichloroethane (DCE) interfaces, facilitated by the ionophore ETH157, has been investigated by cyclic voltammetry (CV). The mechanism of the transfer process has been discussed, and the diffusion coefficients and the stability constants of the complexes formed in the nitrobenzene phase have been determined.
Differential pulse polarographic determination of the artificial sweeteners acesulfame‐K and saccharin in beverages
Authors: Hannisdal Atle , Schrøder Knut H. 
Published: May 2005

AbstractA fast differential pulse polarographic method for the determination of the artificial sweeteners acesulfame‐K and saccharin in beverages has been developed. Polarograms of the sweeteners are recorded directly in a supporting electrolyte containing 0.1 M NaCl (5.8 g/L) and 0.004 M tetrabutyl ammonium iodide (1.5 g/L). The pH of the supporting electrolyte is adjusted to 1.9 with concentrated HCl. The results are found to be in good agreement with high performance liquid chromatography (HPLC) results.
Biocatalysis and electrocatalysis at carbon paste electrodes doped by diaphorase‐methylene green and diaphorase‐meldola blue
Authors: Kulys Juozas , Gleixner Gerd , Schuhmann Wolfgang , Schmidt Hanns‐Ludwig 
Published: May 2005

AbstractThe electrocatalytical oxidation of dihydronicotinamide adenine dinucleotide (NADH) and ascorbic acid was investigated on carbon paste (CP) electrodes doped by diaphorase and the mediators methylene green (MG) and meldola blue (MaB). Bioelectrocatalytical oxidation of NADH proceeds at the potential 0–0.25 V versus saturated calomel electrode (SCE). Km(app), Imax, and sensitivity were 0.9 and 3.6 mM, 1.4 and 6.7 μA, and 0.20 and 0.24 mA mM−1 cm−2 for MaB‐ and MG‐doped CP electrodes, respectively. The biocatalytical process of NADH oxidation is not sensitive to oxygen, and optimum activity is at pH 7.3. The nonenzymatic electrocatalytical oxidation of NADH and ascorbic acid on CP electrodes doped by mediators proceeds at the same potential, and the efficiency of NADH oxidation was 50% in comparison to the biocatalytical process. Ascorbate oxidase immobilized on graphite powder was used to increase the selectivity of the electrocatalytical system of NADH oxidation over the electrochemical oxidation of ascorbic acid.
Voltammetric assay of thrombin adsorbed on the carbon paste electrode
Authors: Randriamanazaka H. N. , Nigretto J. M. 
Published: May 2005

AbstractAn electrochemical procedure to assay a protease adsorbed on a carbon paste electrode (CPE) is described. In the conformation described, the catalysis is induced by thrombin, an enzyme of the blood coagulation system. The kinetics are followed for increasing intervals of time, by monitoring with the modified enzyme electrode an electrogenic redox probe (either p‐nitroaniline or p‐aminodiphenylamine) released via amidolysis from a specific peptide substrate contained in the solution. Analysis of the voltammetric current response as a function of time showed that the Lineweaver‐Burk type treatment could apply, in good agreement with theoretical predictions. From the experimental data, the heterogeneous catalytic rate and the apparent Michaelis constant were deduced. The global kinetics were satisfactorily interpretated in terms of a competition existing between catalysis and transport of the substrate toward the electrode.
Fundamentals and limitations for the application of the carbon paste electroactive electrode in the electroanalysis of solids
Authors: Gruner Wolfgang , Kunath Jürgen , Kalnishevskaja Ljubov N. , Posokin Juri V. , Brainina Khjena Z. 
Published: May 2005

AbstractExperimental conditions for the qualitative and quantitative application of the carbon paste electroactive electrode (CPEE) in the analysis of powders and pulverizable materials are demonstrated for two substances (Cu and TiC) with different reaction schemes in sulfuric acid. The selection of the carbon powder, the type and content of the organic binder, and the paste preparation was done with respect to homogeneity and reproducibility. The influence of the size and shape of the sample particles as well as of the graphite particles on the analytical result is discussed.
Voltammetric reaction of the sulfide/disulfide system with oxygen at mercury electrodes
Authors: Fedurco Milan , Veselá Věra , Heyrovský Michael 
Published: May 2005

AbstractOn the voltammetric curve in the potential range where the first step of the reduction of oxygen at the hanging mercury drop electrode is inhibited by a surfactant, the presence of cystine or other disulfides in the solution produces a reduction peak, the height of which is greatly enhanced by oxygen.
Benzoquinone‐mediated glucose/glucose oxidase reaction at pyrolytic graphite electrode
Authors: Murthy A. Surya N. , Anita  
Published: May 2005

AbstractIn view of the high reversibility of the p‐benzoquinone/hydroquinone couple at a pyrolytic graphite (PG) electrode (compared to platinum or carbon paste electrodes) the glucose‐glucose oxidase (GOD)‐benzoquinone coupled reaction was examined on a pyrolytic graphite surface in homogeneous solution and kinetic data obtained.
Tensammetric techniques for electroanalysis
Authors: Lukaszewski Zenon 
Published: May 2005

AbstractThe following tensammetric schemes, alternating current (ac) polarography of fundamental harmonic and second harmonic, phase‐sensitive ac, square wave tensammetry, differential pulse and normal pulse tensammetry, Kalousek commutator technique, derivative chronopotentiometry, and several other techniques, are reviewed. Thermodynamic background and kinetic limitations of tensammetric analytical signals are discussed. Special attention is given to the behavior of mixtures and to the consequences of association of the analyte as well as to applications of different tensammetric techniques.
On the adsorption voltammetry of the boron‐Beryllon III system: Part I. Determination of boron in plants and soils
Authors: Jin Wenrui , Jiao Kui , Metzner H. 
Published: May 2005

AbstractA very sensitive electrochemical adsorptive voltammetric procedure for trace measurements of boron(III) in plants and soils is described. The complex of boron(III) with Beryllon III is adsorbed on a dropping mercury electrode (DME) with a long lifetime, and the reduction current of the accumulated complex is measured by linear sweep voltammetry. In order to form the boron(III) complex with Beryllon III, it is necessary to boil the solution for 15 minutes. The electrochemical behavior of the complex is explored. The size of the complex peak, which appears at a position between two peaks of reduction of the ligand, is proportional to the boron concentration. Optimum experimental conditions include 0.05 M HOAc/0.25 M NaOAc as supporting electrolyte, 1 × 10−4 M Beryllon III, solution pH 4.4, and an initial potential of −0.30 V (versus SCE). The linear range of the determination of boron is 4 × 10−5 −1 × 10−5 M. The relative standard error of the method is 0.76% for 3 × 10−6 M boron (III) and 3.4% for 6 × 10−7 M boron (III), respectively.
On the adsorption voltammetry of the boron‐Beryllon III system: Part II. Mechanism of the electrochemical reduction of Beryllon III and its complex with B(III) in acetate buffer
Authors: Jin Wenrui , Jiao Kui , Metzner H. 
Published: May 2005

AbstractThe adsorptive and voltammetric characteristics of Beryllon III and its complex with B(III) at a mercury electrode have been investigated in acetate buffer. The adsorption phenomena were observed by sampled dc polarography, normal pulse polarography, linear sweep voltammetry, and drop time curve measurement. It was found that (1) the reactant was an azo‐group in Beryllon III or its complex with B(III) adsorbed on the surface of the mercury electrode; (2) for reduction of Beryllon III, the product was a hydrazo compound and it was also adsorbed on the surface of the electrode; two electrons and two protons were irreversibly transferred in the overall reaction and the apparent transfer coefficient αn (= 1.8) was measured experimentally; the irreversible electron transfer was followed by a chemical reaction; (3) for reduction of Beryllon III complex with B(III), the product was a hydrazo compound; two electrons and two protons were transferred reversibly in the reaction; the hydrazo compound was desorbed from the surface of the electrode, and the reversible electron transfer was followed by a chemical reaction.
A square‐wave voltammetry of Europium(III)‐humic acid complex
Authors: Mlakar M. , Branica M. 
Published: May 2005

AbstractThe reduction process of Europium(III) in the presence of humic acid was investigated by squarewave (SW) voltammetry. The Eu(III)‐humate complex is reduced reversibly, and both the reactant and product of the redox reaction are adsorbed at the electrode surface. The relationship between the properties of the SW response and the parameters of a charge transfer and of the excitation signal are discussed. The SW voltammograms of the Eu‐humate complex are analyzed according to the theoretical predictions.
Simplified treatment of differential pulse polarography
Authors: Fatouros N. , Krulic D. , Rouelle F. , Champagne G. Y. 
Published: May 2005

AbstractThe expression for the current of differential pulse polarography (DPP), in the case of reversible systems, has been established using the diffusion layer model without resolving the diffusion equations. Criteria for the reversibility of the electrochemical reaction, inherent to DPP, are also discussed.
A comparative spectroelectrochemical study of the electrosorption of benzonitrile and benzylcyanide on a silver electrode
Authors: Holze Rudolf 
Published: May 2005

AbstractThe electrosorption of benzonitrile (BN) and benzylcyanide (BC) on a polycrystalline silver electrode from aqueous electrolyte solutions was studied with surface‐enhanced Raman spectroscopy (SERS). Spectra, obtained with the potential of the electrode within a potential range where, according to simultaneously performed cyclic voltammetry, solely adsorption occurs, showed bands clearly attributable to molecules adsorbed on the silver electrode. The results imply both end‐on adsorption via the nitrile group and edge‐on orientation, depending mostly upon the composition of the supporting electrolyte solution.
Polarographic behavior and determination of some S‐triazine herbicides
Authors: Ignjatović Ljubiša M. , Marković Dragan A. , Veselinović Dragan S. , Bešić Borislav R. 
Published: May 2005

AbstractThe possibility for differential pulse polarography (DPP) determination of S‐triazine has been shown and compared with gas‐chromatographic (GC) measurements. Good agreement was found between GC and DPP measurements in analyzing 20 samples of industrial wastewater. It was found, using controlled potential coulometry (CPC), that four electrons take part in electrochemical reduction steps. On the basis of this and polarographic measurements, the mechanism of electrochemical reduction of S‐triazine was postulated.
Bilayer lipid membranes for electrochemical sensing
Authors: Nikolelis Dimitrios P. , Krull Ulrich J. 
Published: May 2005

AbstractBilayer lipid membranes (BLMs) are described as selective and sensitive electrochemical transducers for inorganic ions and organic species. The electrostatic properties of BLMs, which are significant in controlling ion permeation processes, and the possible mechanisms for signal generation are presented herein. Operation of a BLM‐based transducer hinges on a selective interaction between analyte in aqueous solution and membrane‐embedded receptors; as a result, the electrostatic fields and/or the physical phase structure of the membrane alters, leading to an analytical signal (most commonly conductivity changes) which can be related to the analyte concentration. Examples of electrochemical sensors based on this principle and efforts to stabilize these bilayer membranes are presented in this review article.
Nafion‐crown ether modified carbon fiber electrodes: New microbiosensors for detection of neurotransmitters in vitro and in vivo
Authors: Baumeyer Thomas , Dittrich JÜRgen , Crespi Francesco 
Published: May 2005

AbstractBased on experience in in vivo voltammetry with Nafion carbon fiber electrode coated (CFE), a new kind of modification, was developed based on mixing Nafion and crown ether (dibenzo‐18‐crown‐6) solutions. Nafion‐crown ether electrodes (NA‐CRO‐CFEs) offer higher sensitivity to dopamine than Nafion‐CFEs. The improvement of detection limit is caused by enrichment of the neurotransmitter in polymermembrane by interaction of oxygen atoms of the crown ether and the positively charged amino group of catecholamine. With NA‐CRO‐CFEs one is able to detect dopamine and serotonin in physiological basal concentrations in vitro and in vivo without overlapping of oxidation peaks of ascorbic acid or metabolites. Identification of in vivo peaks is discussed with in vitro and in vivo experiments.
Graphite‐teflon enzyme electrode
Authors: Wang Joseph , Reviejo A. Julio , Angnes Lucio 
Published: May 2005

AbstractThe fabrication and performance of graphite‐Teflon‐enzyme electrodes are described. The new bulk‐modified composite enzyme electrodes couple the advantages of renewable (polishable) surfaces, mechanical rigidity, fast response, and favorable signal‐to‐noise characteristics. The new fabrication strategy is illustrated for the immobilization of horseradish peroxidase and glucose oxidase, in connection with measurements of peroxide species and glucose, respectively. The incorporation of a ferrocene mediator to yield a reagentless device is also illustrated. Flow injection measurements of hydrogen peroxide with the graphite‐Teflon‐peroxidase detector are carried out at 120 samples/hour, to yield a detection limit of 2.5 × 10−6 M and a relative standard deviation of 2%. Applicability to organic‐phase biosensing is illustrated.
Determination of manganese using the method of electrochemical enrichment
Authors: Stara V. , Kopanica M. 
Published: May 2005

AbstractManganese was determined by differential pulse voltammetry in pre‐enriched solution. The metal was first deposited on the surface of a hanging mercury drop electrode by electrolysis, and after a short oxidation interval, the reformed manganese(II) ions were determined by differential pulse cathodic polarization scan. The detection limit (with 120 seconds deposition) was 2 μg L−1. The only interfering element was cobalt (when present at tenfold concentration excess). Compared with conventional stripping voltammetry the described method has a lower detection limit value, and the analysis is performed during a shorter time interval. The proposed method was applied for the determination of manganese in natural waters.
Electrochemical reduction and oxidation of two cephalosporin antibiotics: Ceftriaxone (rocephin) and cefoperazone (cefobid)
Authors: El‐Maali Nagwa Abo , Ali Azza M. M. , Ghandour Mahmoud A. 
Published: May 2005

AbstractTwo cephalosporin antibiotic derivatives, ceftriaxone (CFRX) and cefoperazone (CFPZ), have been studied by direct current, differential pulse polarography (DPP), and cyclic voltammetry. Both give rise to two irreversible two‐electron reduction steps. The characteristics of the corresponding electrode reactions are discussed. The electrooxidation of both drugs was also studied at the carbon paste electrode (CPE). Both drugs give rise to one oxidation peak at about +1.05 V vs. SCE (pH 1.6, phosphate buffer solution). Optimum pH ranges for the determination of these drugs at the CPE are also given. Linear calibration plots were obtained over the concentration ranges 0.49 to 99 μg/mL and 0.66 to 534 μg/mL for CFRX and CFPZ, respectively. Detection limits of 2.5 ng/mL and 0.13 μg/mL for CFRX and CFPZ, respectively, were readily achieved.
Determination of adenine by chronopotentiometric stripping analysis with nafion‐modified electrode
Authors: Litong Jin , Shenghui Liu , Zhuping Bai , Yuzhi Fang 
Published: May 2005

AbstractThe determination of adenine by chronopotentiometric stripping analysis with Nafion‐modified electrode is reported. Various conditions for the determination of adenine were explored. In the Britton‐Robinson (BR) buffer solution (pH 3.3), preconcentration was carried out at −0.2 V (vs. SCE) for 90 seconds by chronopotentiometric stripping analysis. The peak height was proportional to the adenine concentration between 2.5 × 10−7 and 8.0 × 10−6 mol/L. For 10 repetitive measurements, the relative standard deviation for 5 × 10−6 mol/L, adenine was 2.2%. The method was fairly free of interference, and the results of real samples were satisfactory.
Voltammetric waveshapes measured in flowing systems: Mass transport‐limited tafel analysis of some nonsimple systems
Authors: Compton Richard G. , Fisher Adrian C. , Sanders Giles H. W. 
Published: May 2005

AbstractAnalytical theory is presented which allows rigorous mass transport‐corrected Tafel analysis for the reversible electrode processes (1) 2B ⇄ A2 + 2e− and (2) B2 ⇄ 2A + 2e− occurring at electrodes in flowing systems. Predictions are compared with the conclusions of numerical finite‐difference modelling for both wall‐jet and channel flow cell geometries. Exceillent agreement is found.