bluuebunny/crossref_metadata_2025_split huggingface dataset:
Complexing properties of polycrownethers: I. Complexation of Na+ and K+ by tribenzo‐15 crown‐5 in MeOH‐DMF Medium
Authors: Lhermet Claude , Morel Jean‐Pierre , Angley Lysiane , Simonet Jacques 
Published: May 2005

AbstractThe complexation of Na+ and K+ cations by the polycyclic ligand tribenzo‐15 crown‐5 is studied in a methanol–dimethylformamide mixture. As opposed to the monomer benzo‐15 crown‐5, this trimer shows a marked selectivity for K+ with respect to Na+. This selectivity is due to the existence of associated farms of the K+ complexes in solution; at high concentration a salt precipitates, which presents a polymeric structure of stoichiometry 3 K+/ 2 trimers.
Adsorptive stripping voltammetry of cobalt and nickel in flow systems at wall‐jet electrodes
Authors: Brett Christopher M. A. , Oliveira Brett Ana Maria C. F. , Pereira Jorge L. C. 
Published: May 2005

AbstractAdsorptive stripping voltammetry of cobalt and nickel in flow systems at wall‐jet mercury thin‐film electrodes has been investigated and assessed. A HEPES biological buffer with sodium perchlorate electrolyte was employed with excess nioxime, or dimethylglyoxime, ligand, and the accumulated complex on the mercury film surface determined by differential pulse reduction. Concentrations down to 1 nM can be routinely measured. Results at the wall‐jet electrode, supported by evidence from LSV and impedance measurements at rotating and stationary electrodes respectively, show the viability of the method.
Adsorption and electrochemical transformations of diphenylcarbazide and diphenylcarbazone on graphite electrodes
Authors: Malakhova Natalia A. , Chernysheva Albina V. , Brainina Khiena Z. 
Published: May 2005

AbstractPotential dependences of the Current and differential double‐layer capacity were used to investigate the processes that take place on a graphite electrode in acidic media containing 1, 5‐diphenylcarbazide (DPCI) and 1, 5‐diphenylcarbazide (DPCO). It is shown that adsorption of the enol form of these compounds on the electrode surface is observed over the potential range of +0.2 to −1.0 V. Over the range of +0.2 to +0.4 V, the adsorbed enol form of the reagents is oxidized, involving formation of radicals to tetrazole salts, which are reduced irreversibly to the starting reagents at a potential lower than −0.2 V. The keto form of diphenylcarbazide is oxidized, omitting the adsorption stage. As the keto form of diphenylcarbazide is oxidized, an uncharged compound (probably a radical or a biradical) is formed.
Vanadium(V) determination through a catalytic polarographic method
Authors: Barrado Enrique , Alvarez Vicente , Pardo Rafael , Batanero Pedro Sánchez 
Published: May 2005

AbstractA method for determining trace level of vanadium(V) has been developed. The reaction is the polarographic reduction of the bromate, catalyzed by this metal ion, in the presence of cupferron, in acetic‐acetate medium. The peak current obtained is proportional to the vanadium(V) concentration between 2.10−8 and 3.10−7 M, with a detection limit of 6.10−9 M. The procedure is very selective and has been successfully applied to a certified steel sample after extraction of iron wit ethyl ether.
Software for interfacing electrochemical instruments to a personal computer
Authors: David FrançOis , Papadopoulos Nikolaos 
Published: May 2005

AbstractA potentiostat and a drop knocker have been interfaced to a Macintosh2 computer, using Labview2 for the programming of the interface. The whole system can perform the functions of a pulse polarograph. Digital storage of the experimental data permits baseline substraction and digital filtering at the end of the experiment.
Soybean meal tissue based membrane bioelectrode for urea
Authors: Deng Jiaqi , Fang Yao , Cai Ronghui 
Published: May 2005

AbstractNovel potentiometric membrane electrodes with high selectivity to urea over the 1.3 × 10−4 − 1.1 × 10−2 M and 4.0 × 10−4 − 1.0 × 10−2 M concentration range were constructed by immobilized soybean meal at a NH3 or CO2 gas‐sensing electrode. The sensor does not require fresh bean tissue so it is not limited by the season of the year. The influence of some experimental parameters, including buffer composition, pH, and immobilization techniques are discussed. The resulting electrode is found to be a viable alternative to the enzyme‐based electrode.
Effects of alternating electric fields on transport through ion exchange membranes
Authors: Irgum Knut , Genborg ÅSa , Glad BÖRje , Gupta Syamasri , Dasgupta Purnendu K. 
Published: May 2005

AbstractTransport of permitted and Donnas‐forbidden ions as well as neutral solutes through ion exchange membranes have been investigated in continuous flow‐through configurations in the presence and absence of an alternating electrical field (0.05–100 kHz, 0–40 V p‐p). There is no discernible effect on the transport rate of forbidden ions and neutral solutes but very significant increases in steady state transmembrane transport occur for permitted ions. At least for cation exchangers, an increase in effective ion exchange capacity also appears to occur in the presence of the field. These effects are ascribed to the greater kinetic energy of the ions exposed to the alternating field and thus to the higher effective thermodynamic temperature the ions experience.
Adsorptive stripping voltammetry of chromium 1,5‐diphenylcarbazonate
Authors: Malakhova Natalia A. , Chernysheva Albina V. , Brainina Khiena Z. 
Published: May 2005

AbstractElectrochemical transformations of chromium 1,5‐diphenylcarbazonate (the complex), absorbed on the surface of a graphite electrode from a solution of 0.15 M sulfuric acid, were studied. The complex was synthesized by mixing acetone solutions of CrCl3·6H2O and diphenylcarbazone, as well as aqueous solutions of K2Cr2O7 and aqueous acetone solutions of diphenylcarbazide. The complex is absorbed on the electrode over the potential interval 0.55–0.30 V when the circuit is open. In the presence of diphenylcarbazide this interval narrows considerably as a result of competing absorption. Electrochemical reduction of the complex proceeds in stages, with formation of a chromium‐containing radical as an intermediate product that is subsequently reduced to diphenylcarbazide, with chromium(III) released to the solution. Absorbed complex is electrochemically oxidized in one stage mainly, with diphenylcarbadiazone formed as the main product.
Electroanalytical studies of chlorophylls and their determination
Authors: Wang Naixing , Di Pingping , Yu Tangdi , Chen Jianmin , Deng Jiaqi 
Published: May 2005

AbstractThe differential pulse polarographic behavior and quantitation of chlorophylls have been investigated. The detection limit is 2.4 × 10−7 M. The kinetics of the photolytic reaction of chlorophylls has been explored. Some kinetic parameters of the reaction system and the possibilities of a path for the photolytic reaction of chlorophylls have been measured and established. This reaction shows zero order kinetics with a rate constant of 3.3 × 10−6 mol · dm−3 · hr−1; with the help of the Arrnhenius relation, the activation energies of this reaction were determined. The method was successfully applied to the determination of chlorophylls in toothpaste and several kinds of green leaves.
Improved method for the determination of surfactants in fresh waters based on suppression of polarographic oxygen maximum
Authors: Bednarkiewicz Ewa 
Published: May 2005

AbstractMeasurements of the first kind of polarographic maximum current as a function of DME drop time allowed determination of the surfactants activity in natural fresh waters by means of standard addition techniques. In this way, the results of determination became independent of sample composition changes (over a reasonable range). The reported method expands an upper detection limit of determinations of surfactants, without dilution of the sample, up to 1 mg dm−3. Samples with higher content of surfactants were diluted with 0.001 mol dm−3 KCl solution of small and known amounts of surface active contaminants. The optimum range of electrical conductivity of the solution for recording the well‐developed oxygen maximum is attained because of dilution. It was found that surfactant activity for three types of drinking waters varied from 1 to 4 mg dm−3.
Determination of sulfur dioxide in white wines by flow injection with electrochemical detection
Authors: Cardwell Terence J. , Cattrall Robert W. , Nan Chen Guo , Iles Peter J. , Hamilton Ian C. , Scollary Geoffrey R. 
Published: May 2005

AbstractThe determination of sulfur dioxide in wines by flow injection analysis is described. The method is based on a dual electrochemical system, the upstream electrode being a coulometric electrode that eliminates interferences prior to the detection of the analyte at an amperometric electrode. At least 30 wine samples per hour can be determined by this procedure, and the results for free and total sulfur dioxide concentration in white wines compare favorably with those obtained by the standard aspiration‐oxidation, method.
Novel solvent systems for the preparation of phase‐inversion cellulose acetate size exclusion membranes: Voltammetric investigations
Authors: Kuhn Lance S. , Weber Stephen G. 
Published: May 2005

AbstractNovel solvent systems have been developed for the casting of size exclusion electrode modifications by the phase‐inversion process. Solvent systems studied were (solvent/nonsolvent): pyridine/2‐octanol, pyridine/cyclohexanol, acetone/2‐octanol, tetrahydrofuran/aqueous Mg(ClO4)2, and tetrahydrofuran/toluene. These were compared to modifications made from the solvent system acetone/aqueous Mg(ClO4)2. The membranes were cast onto Pt microelectrodes embedded in glass. Cyclic voltammograms were recorded once per min after immersing the membrane‐modified electrode into a solution containing an electroactive species. Modified electrode response time to a concentration perturbation is correlated with the percent nonsolvent and percent polymer in the casting solution. The magnitude of the current from a solution of a 1500 dalton polyethylene glycol ferrocene carboxylate ester solute, and good casting reproducibility. This formulation is recommended for permselective coating applications; applications to biosensors are envisioned.
Electrocatalysis at hydrogenase or cytochrorme C3‐modified glassy carbon electrodes
Authors: Bianco Pierre , Haiadjian Jean 
Published: May 2005

AbstractThe immobilization of two redox proteins, hydrogenase and cytochrome c3 extracted from Desulfovibrio desulfurifcans sulfate‐reducing bacterium, on glassy carbon electrodes modified via carbodiimide procedure is reported. The catalytic activity at the hydrogenase‐modified glassy carbon electrode is detected in the presence of methylviologen, which acts as a shuttle between immobilized hydrogenase and the electrode surface. The effect of experimental parameters (e.g., methylviologen concentration or pH) on the catalytic activity is examined; maximum activity is observed at pH 9.5. Catalytic activity is also detected when methylviologen is replaced by cytochrome c3, which is the physiological partner of hydrogenase. The cytochrome C3‐modified glassy carbon does not yield a stable electrochemical response due to cytochrome c3 reconformation at the electrode surface.
Polarographic determination of some pesticides containing nitro group: Application to a study of adsorption on lignin
Authors: Rupp Elinore , Zhong Qiping , Zuman Petr 
Published: May 2005

AbstractThe polarographic method proved suitable for investigation of adsorption of acifluorfen (I) (5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2′‐nitrobenzoic acid) on lignin. Polarographic reduction of acifluorfen in aqueous buffers (pH < 7) is complicated by adsorption of the reduction product. In acidic media the reduction of the protonated hydroxylamino group occurs at such positive potentials that only a single six‐electron wave is observed. In buffers containing 33% (w/w) ethanol the effects of the adsorption are eliminated and the reduction of the hydroxylamino group occurs at more negative potentials, so that one four‐electron and one two‐electron wave are observed. Splitting of the four‐electron wave at pH > 7 is attributed to a decrease in protonation rate of the reduction intermediate. Unsubstituted p‐nitrophenyl phenyl ether (II) shows an analogous behavior. Reduction wave of the nitro group can be used for determination of aciflurofen (I), fluorodifen (III), oxyfluorfen (IV), and bifenox (V) in the 1 × 10−5 to 5 × 10−4 M range. Adsorption of acifluorfen depends on the nature of the lignin and pH.
Determination of tetramethrin by adsorptive stripping with square wave voltammetry
Authors: Hernández P. , Galán‐Estella F. , Hernández L. 
Published: May 2005

AbstractThe present work reports on an adsorptive stripping voltammetric procedure for the determination of tetramethrin. The best conditions found were pH 4 in 0.2 mol/L acetic acid/acetate buffer solution, and accumulation potential of −0.5 V (vs. Ag/AgCl electrode), an accumulation time of 60 s, frequency 120 Hz, step potential (Es) 2 mV. Under these conditions, determination limits of 1.7 ng/mL−1 (8.5 10−9 M) are achieved.
Phase‐selective alternating current adsorptive stripping voltammetry of folic acid on a mercury thin‐film electrode
Authors: del Pozo José Amez , García Agustín Costa , Miranda Ordieres Arturo J. , Blanco Paulino Tuñón 
Published: May 2005

AbstractOptimum conditions for the mercury electrodeposition onto glassy carbon electrodes and the optimum alternating current (AC) adsorptive stripping signals of folic acid (vitamin B12) were found. The film was characterized by electron microscopy and the results obtained in the analysis of the vitamin were compared with those previously reported using conventional mercury electrodes (static or hanging). The mercury thin film electrode (MTFE) has shown more sensitive signals for folic acid with good performance and reproducibility. A detection limit down to 10−12 M could be reached by using 300 s accumulation time.
Voltammetric determination of the titrable acidity of milk using a platinum microelectrode
Authors: Daniele Salvatore , Baldo M. Antonietta , Ugo Paolo 
Published: May 2005

AbstractA platinum microelectrode with a radius of 12.5 μm was employed for determining the acidity of crude bovine milk samples by voltammetric titration. Solutions of sodium hydroxide and of several acids of different strengths were used as titrants. The relative standard deviation (RSD) was within 3%, regardless of the type of titrant agent employed. The data found with this approach were compared with those obtained by the classical methods commonly employed for the determination of the titrable acidity of milk.
An amperometric solid‐state sensor for Nitrogen dioxide based on a solid polymer electrolyte
Authors: Opekar František 
Published: May 2005

AbstractA new sensor is described consisting of a Nafion membrane to which a very fine gold square grid indicator electrode is mechanically pressed. A platinum counter and a Pt/air reference electrode are prepared on the membrane using a chemical plating method. Nitrogen dioxide was determined in air by reduction at −0.3V vs. Pt/air electrode (0.75 V vs. SHE). The response dependence on the NO2 concentration was linear, with a sensitivity of 59 nA.ppm−1 (42% rel. humidity). The time constant and the time required to attain 95% of the steady ‐state response were 2.2 and 10 s, respectively. The response was independent of the air flow rate, but increased linearly with increasing relative humidity. The sensor sensitivity decreased with time–the longer the sensor was in contact with NO2. The decrease amounted to ca. 5% per 24 hours during constant exposure to NO2. The indicator electrode can be reactivated by cyclic polarization. On the basis of the sensitivity attained, the indicator electrode can be considered as an array of microband electrodes.
Voltammetric investigations of copper processes in the presence of oxygen
Authors: Krznarić Damir , Plavšić Marta , Ćosović Božena 
Published: May 2005

AbstractThe redox processes of copper ions were studied by alternating current (ac) voltammetry and cyclic voltammetry in 0.5 M NaCl and NaClO4 solutions. The studies were performed at different pH values in the presence of atmospheric oxygen or by the addition of H2O2 to the process. In the case of copper ions in NaCl solution both in the presence of atmospheric oxygen and added H2O2, a catalytic current was observed. With cyclic voltammetry the current was in the cathodic direction in spite of having an anodic sweep. The key factor is the presence of chloride ions as in the NaClO4 solution; the observed catalytic current peaks are much smaller. The mechanism for the observed redox processes of copper is proposed.
Characterization of uranyl‐monoperoxo species in 0.7 mol L−1 LiCIO4
Authors: Djogic Renata , Branica Marko 
Published: May 2005

AbstractAccording to the calculations, in the presence of equimolar concentrations of uranyl‐ion and hydrogen peroxide at 5 < pH < 7, the predominant species is UO2O complex. Spectro‐photometrically, it has been confirmed in the bulk of the solution giving the apparent concentration stability constant K
= 2 × 105 mol−1 L. Electrochemically, normal, differential pulse polarography and cyclic voltammetry at DME and HMDE are used to elucidate the reduction scheme of the uranyl‐monoperoxo complex.
Homogeneous catalysis of electrochemical reactions. Channel electrode voltammetry and the EC′ mechanism
Authors: Compton Richard G. , Fisher Adrian C. , Spackman R. Anthony 
Published: May 2005

AbstractThe shape of the current–voltage curves at a channel electrode have been calculated for the various situations of the catalytic (EC′) mechanism. In particular the halfwave potential and limiting current are found to be highly sensitive to the solution‐flow rate and to the concentrations of the mediator and substrate employed. These observations provide a ready method of unambiguously characterizing the different pathways.
Electrochemical oxidation of L‐ascorbic acid at the graphite electrode and its monitoring by a thick‐film graphite sensor assembly
Authors: Xing Xuekun , Tan Thiam‐Chye , Shao Meijun , Liu Chung‐Chiun 
Published: May 2005

AbstractThe experimental results obtained in this study show that a thick‐film graphite sensor assembly (with a Pt counter and an Ag/AgCl reference electrode) can be conveniently fabricated by the photolithographic and screen‐print metallization techniques. This sensor has been successfully employed for quantitatively determining L‐ascorbic acid concentration in aqueous solutions with reasonably good reproducibility. This sensor provides the possibility of developing a miniature size practical device for detecting ascorbic acid in biochemical processing, such as in food and drug production. The mechanistic aspects of the oxidation of L‐ascorbic acid on optical pyrolytic graphite electrodes were further studied with a rotating OPG disk electrode in two different electrolyte solutions. It was found that the oxidation of L‐ascorbic acid is more favored in pH = 7 solutions than in pH = 1 solutions although a common 2‐electron transfer pathway is applied in both cases.
Polarographic studies and measurements of nitrite in cobalt(II)—thiocyanate—ascorbic acid solution
Authors: Li Peibiao , Zhao Zaofan , Gao Zhiqiang 
Published: May 2005

AbstractIn the cobalt(II)—thiocyanate—ascorbic acid solution (pH = 2.0), nitrite can form a ternary complex (CoSCNNO)+, which can be reduced at mercury electrode to −0.59 V (vs. SCE). The wave can be used for the polarographic determination of traces of nitrite in the concentration range of 1 × 10−8 −8 × 10−7 M (single sweep polarography), 1 × 10−7 −4 × 10−5 M (differential pulse polarography). or 1.5 × 10−6 −2 × 10−4 M (direct current polarography). The mechanism of the electrode process is studied by linear sweep voltammetry, DC polarography, cyclic voltammetry, double‐step chronocoulometry, and controlled potential coulometry. The polarographic wave is ascribed to the reduction of nitrogen monoxide in the complex to hydroxyamine. The procedure is used for the direct determination of nitrite in various real samples.
Determination of several catechols on bare and polymer coated glassy carbon electrode
Authors: Heiduschka Peter , Dittrich Jürgen 
Published: May 2005

AbstractGlassy carbon electrodes were coated with a copolymer of styrene and maleic acid anhydride. The voltammetric behavior of catechol, ascorbic acid, dopamine, and DOPAC was examined at both bare and coated electrode using cyclic voltammetry and modified differential pulse voltammetry. Electrochemical pretreatment increased peak current of catechol and its derivatives; the polymer coating caused significant decrease of peak currents and shift of peak potentials. The signal of ascorbic acid is greatly suppressed, while that of DOPAC disappears even after polymer coating.
Catalytic polarographic detection of disulfides following liquid chromatography
Authors: Nagashima Kunio , Kamaya Minori , Ishii Eizen 
Published: May 2005

AbstractFour kinds of disulfides in organic compounds were sensitively detected in NH4OH‐NH4Cl (0.2 M)‐Co2+ (5 × 10−4 M) solution by differential‐pulse polarography. This detection mechanism was based on the Brdicka reaction. A new flow‐through cell (on‐detector reactor) was used to combine the polarographic detection with high‐performance liquid chromatography. The detection limit for dithioglycolic acid was 1 × 10−4 M using 10 μl samples.
Evaluation of nafion as media for glucose oxidase immobilization for the development of an amperometric glucose biosensor
Authors: Fortier Guy , Vaillancourt Marc , Bélanger Daniel 
Published: May 2005

AbstractA novel glucose biosensor has been prepared by deposition of a mixture containing glucose oxidase dissolved in water and Nafion dissolved in methanol at the surface of a platinum disk electrode. Glucose concentration is evaiuated by measuring the amperometric current corresponding to hydrogen peroxide electrooxidation at 0.7 V vs. SCE. The addition of glucose oxidase to Nafion resulted in a Nafion‐glucose oxidase film that was more permeable to anionic species than Nafion alone. The calibration curve for glucose is linear from 5 μM up to about 10 mM. In oxygen‐saturated solution, the linear range extended to 15 mM. The optimum pH for the assay was found to be 5.5. The enzyme is not stabilized against temperature deactivation when it is immobilized in Nafion. The Pt/Nafion‐glucose oxidase electrodes showed good stability when stored dry at room temperature with 80% of the initial response retained after 250 days.
An electrochemical assay for tissue plasminogen activator (t‐PA)
Authors: Cardosi Marco , Ho Wah On , Athey Dale , McNeil Calum 
Published: May 2005

AbstractAn electrochemical assay for tissue plasminogen activator (t‐PA) is described. The activity of t‐PA is measured in a coupled assay following the amidolytic cleavage of a synthetic tripeptide by the enzyme plasmin. The released electroactive label, p‐aminophenol, is detected anodically either at a glassy carbon indicator electrode or at a platinized activated carbon electrode in a specially constructed perspex cell. Calibration plot data for t‐PA are presented for buffered samples using the perspex block‐type cell. The limit of detection for t‐PA in this assay is 0.25 IU/ml. In addition, the assay format is adapted to yield kinetic information using repetitive square wave voltammetry as the mode of detection.