bluuebunny/crossref_metadata_2025_split huggingface dataset:
Voltammetric evidence of adsorption in cadmium(II)‐iodide system at different ionic strengths
Authors: Zelić Marina , Pižeta Ivanka 
Published: May 2005

AbstractAdsorption of CdI2 on mercury electrodes at three different ionic strengths (1, 4 and 6 mol/L) was studied using differential pulse polarography and square wave voltammetry. As the classical proof of the adsorption is the existence of two peaks, conditions for their simultaneous appearance are investigated. In the optimum concentration range of the surface active species, the effect is highly influenced by the water activity, applied voltammetric technique and the timing parameters of each technique applied. At higher electrolyte concentrations and longer electrolysis times, the main peak becomes more pronounced. At extremly high ionic strengths, however, only the postpeak is to be expected. The region where the two peaks are noticed and characterized is significanty enlarged by means of deconvolution, the resolution enhancement technique.
Evaluation of a new wall‐jet flow‐through cell for commercial ion‐selective electrodes in flow injection potentiometry
Authors: Di Benedetto Lucy Tina , Dimitrakopoulos Telis 
Published: May 2005

AbstractAn improved wall‐jet configuration type flow‐through cell has been developed for use with commercial ion‐selective electrodes (ISEs) and has been evaluated in the flow injection potentiometric (FIP) mode. The flow‐through cell was designed to accommodate commercial ISEs that employ a range of sensing surfaces, including gas‐sensing, liquid polymer membrane and solid‐state based ISEs. Commercial ISEs employed for the evaluation of the flow‐through cell were ammonia, calcium and iodide ion‐selective electrodes. The observed electrode slopes were −58.8 ± 0.9, 25.2 ± 0.5 and −58.3 ± 0.9, mV change / activity decade, respectively, over a wide log‐linear range using a 100 μL sample volume in the FIP mode. Sample throughput rates as fast as 240 injections/h and analytically useful peak height responses can be achieved using injected sample volumes as low as 25 μL with all three types of ISEs.
Voltammetric behavior of cysteine and metallothionein on cobalt(II) tetrasulfonated phthalocyanine modified glassy carbon electrodes
Authors: Limson Janice , Nyokong Tebello 
Published: May 2005

AbstractCysteine, and rat Cd, Zn‐metallothionein (Cd, Zn‐MT) have been studied electrochemically at glassy carbon electrodes modified with cobalt(II) tetrasulfonated phthalocyanine, [CoIITSPc]4−, where Pc(2‐) = phthalocyanine dianion. The electrode was modified by electrodeposition of [CoIITSPc]4−. The anodic currents for the oxidation of cysteine on these electrodes are observed at 0.82 V (vs. Ag/AgCl) in acidic media. The anodic currents for the oxidation of Cd, Zn‐MT are observed at 0.90 V at pH 8.4 (Tris buffer).
Disposable multichannel immunosensors for 2,4‐dichlorophenoxyacetic acid using acetylcholinesterase as an enzyme label
Authors: Kaláb Tomáš , Skládal Petr 
Published: May 2005

AbstractAn improved version of the disposable multichannel immunochemical biosensor for the herbicide 2,4‐dichlorophenoxyacetic acid (2,4‐D) based on a screen‐printed amperometric transducer and monoclonal antibodies (MAb) against 2,4‐D is reported. Entrapment within a thin Nafion film was used for the direct immobilization of MAb at the electrode surface. The amount of the tracer (2,4‐D conjugated to acetylcholinesterase) bound in a competitive immunochemical reaction was determined amperometrically using acetylthiocholine iodide as substrate. The measuring procedure (times of incubation with tracer and substrate, pH, tracer concentration) was optimized. The sensor was able to detect less than 0.01 μg/L of free 2,4‐D in water. One analysis (8 samples) was completed in 30 min (20 min for immunochemical reaction, 5 min incubation with substrate, 5 min measurement). The performance of the immunosensor (two configurations) was evaluated on real samples (tap water) with added 2,4‐D. The determined amounts (mean values 0.097 to 0.105 and 0.89 to 1.13) corresponded well with the added contents of 2,4‐D (0.100 and 1.00 μg/L, respectively).
Square‐wave voltammetric stripping analysis of thallium(III) at a poly(4‐vinylpyridine)/mercury film electrode
Authors: Zen Jyh‐Myng , Wu Jyh‐Way 
Published: May 2005

AbstractA poly(4‐vinylpyridine)/mercury film electrode (PVP/MFE) was used for the determination of trace thallium(III) by square‐wave anodic stripping voltammetry (SWASV). Thallium(III) is preconcentrated onto the PVP/MFE as the anionic forms in chloride medium by the ion‐exchange effect of the PVP. The high solubility of thallium in mercury further facilitates the accumulation effect. Various factors influencing the determination of thallium(III) were thoroughly investigated. This modified electrode displayed good resistance to interferences from surface‐active compounds and common ions and increased sensitivity when used in conjunction with SWASV. In addition, detection can be achieved without deoxygenation and the electrode can be easily renewed. Applicability to various water samples is illustrated.
Effects of pretreatments and modifiers on electrochemical properties of carbon paste electrodes
Authors: Chi Qijin , Göpel Wolfgang , Ruzgas Tautgirdas , Gorton Lo , Heiduschka Peter 
Published: May 2005

AbstractThe electrochemical properties of carbon paste electrodes (CPEs), including unmodified and modified with protein and polycations, were investigated by impedance spectroscopy (IS) using ferricyanide and ferrocene monocarboxylic acid (FcMA) as redox probes. Various electrochemical pretreatments were applied to the unmodified CPE. The heterogeneous charge transfer rate constant of ferro/ferricyanide couple is enhanced by 2 to 10 times compared with that obtained at untreated electrodes. It was found that for ferricyanide the more suitable pretreatments are successive cyclic voltammetric scans, cathodization and a square wave‐like stepping rather than high‐potential anodization. However, the pretreatment only exhibits a slight effect on the kinetics of FcMA. At the CPEs containing modifier, the electron transfer rate of the redox couple depends more on the pH of electrolyte solution if ferro/ferricyanide is used. The results can be explained by the differently charged states of the CPEs that were caused by the protonation or deprotonation of the modifiers in various pH solutions and demonstrate the importance of the electrostatic interaction on the kinetics of the highly polar species such as ferricyanide. The different adsorptive behavior of ferricyanide and FcMA is also discussed.
Quinoprotein glucose dehydrogenase modified carbon paste electrode for the detection of phenolic compounds
Authors: Wollenberger Ulla , Neumann Barbara 
Published: May 2005

AbstractThe development of an amperometric biosensor for the determination of phenolic compounds is described, using quinoprotein glucose dehydrogenase. The enzyme is integrated into carbon paste and its ability to donate electrons to oxidized phenolic compounds during glucose oxidation is exploited. The sensor response is based on electrochemical oxidation of the phenolic compound followed by its enzymatic regeneration when the bulk solution contains glucose and the electrode is potentiostated at +500 mV (vs. Ag/AgCl/0.1 mol/L KCl). As the result of the catalytic analyte regeneration the electrodes offer very sensitive measurements of redox species like p‐aminophenol and hydroquinone and catecholamines such as epinephrine, norepinephrine, and dopamine. The sensor performance is characterized for the different substrates. Highest sensitivity is achieved for p‐aminophenol which could be determined at sub‐nanomolar level.
Electrochemical reduction of secnidazole and its determination in tablets
Authors: Radi A. , El‐Laban S. , El‐Kourashy Abdel‐Ghany 
Published: May 2005

AbstractThe electrochemical reduction of secnidazole has been carried out in aqueous solution in the pH range of 2.0–12.0 by DC polarography, AC polarography and cyclic voltammetry. Two well‐defined reduction waves appear in acidic media, whereas at higher pHs the two waves overlap. The variation of E1/2 or Ep and Ilim or Ip with pH was studied. The diffusion‐controlled nature of the waves was established and the irreversibility of the electrode process was verified by different criteria. The mechanism of reduction was discussed. A method for the detemination of secnidazole by DC polarography at pH 8.5 which allows quantitation over the 1 × 10−5 M‐4 × 10−4 M range was proposed and applied to the determination of secnidazole in tablets. The mean recovery was 99.67% and the relative standard deviation was 0.89%. Excipients did not interfere in the determination.
Solvent dependence of the one‐electron reduction of substituted benzo‐ and naphthoquinones
Authors: Heffner Janell E. , Wigal Carl T. , Moe Owen A. 
Published: May 2005

AbstractPotentials for the one‐electron reduction of a series of substituted benzo‐ and naphthoquinones were measured in 10 aprotic solvents by cyclic voltammetry and used to construct Hammett plots. Hammett reaction constants, ρ, were determined in each solvent and used as indicators of the solvent‐mediated stabilization of the charged radical‐anion product of the reduction reaction. Correlations of Hammett ρ values with solvent parameters suggest that the Lewis acidity of the solvent, in particular the solvent's ability to donate a partially positive proton, is a consistent predictor of the degree of charge stabilization of the quinone radical anion. Other mechanisms of charge stabilization, including solvent–solute charge transfer complexes and dipole–dipole interactions involving the molecular dipole moment (or an induced dipole moment) of the solvent, were found to be inconsistent predictors of the effect of solvent on one‐electron quinone reduction in aprotic media.
Simultaneous determination of mercury and arsenic by anodic stripping voltammetry
Authors: Viltchinskaia E. A. , Zeigman L. L. , Garcia D. M. , Santos P. F. 
Published: May 2005

AbstractAn electrochemical method for the simultaneous determinations of HgII concentration and total AsIII and AsV concentration has been developed. The method does not require the additional preliminary step of the chemical reduction of AsV to AsIII, or oxidation of AsIII to AsV before stripping analysis takes place. Also, the method for the simultaneous determination of HgII concentration and AsIII concentration is described. Measurements were performed in 0.1 M HCl using a gold‐plated graphite electrode as sensor. Detection limits for both methods are below 0.4 ppb. Relative standard deviation did not exceed 15%. The possible interference by other trace metals was investigated. Analyses of natural water and industrial solutions were made using proposed methods and AAS. The t‐test demonstrates that there was no significant difference between the results obtained with these methods. Proposed methods decrease the time of analysis because concentrations of the HgII and arsenic ions were measured simultaneously. Also, the removal of the additional step of chemical reduction of AsV to AsIII or oxidation of AsIII to AsV decreases analysis time, and also reduces the chance of contamination due to the use of additional reagents.
Direct electron transfer reaction of glucose oxidase at bare silver electrodes and its application in analysis
Authors: Wen Zhihui , Ye Baoxian , Zhou Xingyao 
Published: May 2005

AbstractThe direct electron transfer reaction of glucose oxidase (GOx) at a bare silver electrode is verified. The electron transfer number n = 2, electron transfer coefficient α = 0.45 and rate constant of the electrochemical reaction Ks = 0.1 s−1 are obtained. This communication presents a multimolecular adsorption model to explain the properties of the direct electron reaction between GOx and bare silver electrodes. The residual valence force may be an important factor to ensure a direct electron transfer reaction on the bare electrode. On the basis of the experimental fact that only biologically active GOx exhibits electrochemical activity in solution, a facile analytical method for analyzing the active GOx concentration is developed. The results determined correspond very well to that of a spectrometric method.
Electrocatalytic oxidation of ascorbic acid using benzoquinone as a mediator
Authors: Murthy A. Surya N. , Sharma Jyotsna 
Published: May 2005

AbstractBenzoquinone (BQ) in solution catalyses the electrochemical oxidation of ascorbic acid (AH2) at basal plane graphite (BPG) electrode. The overpotential for AH2 decreases by 120 mV at pH 7.3 in presence of BQ as compared to the potential without BQ. A simultaneous increase in anodic current in the cyclic voltammogram of BQ as a function of AH2 forms the basis of a sensor for AH2. The kinetics for the reaction between AH2 and BQ have been determined by cyclic voltammetric data.
Advances in electrochemical immunosensors
Authors: Skládal Petr 
Published: May 2005

AbstractThe developments in the field of electrochemical immunosensors and immunoassays are reviewed. The enzyme labels suitable for amperometric, potentiometric and conductimetric detection are mentioned. Indirect immunosensors (i.e., that involving enzymatic or electroactive labels) use either heterogeneous or homogeneous formats. Immunoelectrodes are based on conventional electrodes, semiconductor devices are represented by ISFETs and light addressable potentiometric sensors (LAPS). Direct label‐free monitoring of immunoreactions is demonstrated on capacitance systems and pulsed detection using polypyrrole‐modified electrodes. The approaches to regeneration of sensing surfaces are discussed. Examples are given on applications of electrochemical immunodevices in clinical medicine and in environmental monitoring.
Patterned self‐assembled alkanethiolate monolayers on gold. Patterning and imaging by means of scanning electrochemical microscopy
Authors: Wittstock Gunther , Hesse Ronald , Schuhmann Wolfgang 
Published: May 2005

AbstractElectrochemically induced localized desorption of self‐assembled dodecylthiolate monolayers from a macroscopic Au electrode was performed using a scanning electrochemical microscope (SECM). The microelectrode of the SECM is operated as auxiliary electrode and moved in close proximity to the monolayer‐covered gold surface, thereby restricting electrochemical reactions occurring at the macroscopic gold surface to a region perpendicular beneath the auxiliary microelectrode. Subsequently, the obtained laterally‐structured monolayers have been imaged using the feedback mode of the SECM. High feedback currents occur over regions from which the alkanethiolate monolayer was locally desorbed while low currents are measured over the intact layer. The electrochemically induced desorption of alkanethiolate monolayers was laterally restricted to regions which are approximately 2–3 times larger in diameter than the diameter of the microelectrode used in the desorption step. The desorption protocol has been optimized to obtain renewed gold surfaces of defined geometry. First evidence was obtained that re‐adsorption of functionalized thiols onto these renewed and laterally structured gold surfaces, which are surrounded by the densely packed nonfunctionalized monolayer, may open routes for the fabrication of miniaturized integrated sensors and sensor arrays.
Characterization of the effects of varying the pH and monomer concentrations of poly(oxyphenylene) insulating films on carbon fiber electrodes
Authors: MacTaylor Christine E. , Ewing Andrew G. 
Published: May 2005

AbstractBy varying the conditions of an electrodeposition solution containing phenol and 2‐allylphenol, thin poly(oxyphenylene) films can be formed. These films have been used to insulate flame‐etched carbon fiber electrodes to produce smaller electrode tip diameters. Experiments have been performed to test both the insulating properties and the film thickness of this poly(oxyphenylene) copolymer at pH 5.0, 7.0, and 9.0. The effects of monomer concentration on the polymer insulation integrity and film thickness have also been investigated. These experiments show that a decrease in pH results in thinner insulating films. It is also shown that monomer concentration can be decreased to 12 mM phenol/18 mM 2‐allylphenol without causing an appreciable change in the insulating properties of the copolymer film; however, as the concentration is decreased, the pH appears to have less influence on the copolymer thickness.
Electrochemical determination of thiosulfate in seawater in the presence of elemental sulfur and sulfide
Authors: Ciglenečki Irena , Ćosović Božena 
Published: May 2005

AbstractLinear sweep voltammetry (LSV) has been used for the direct determination of thiosulfate in the mixture with other sulfur species (sulfide, elemental sulfur) in 0.5 M NaCl/3 × 10−2 M NaHCO3, pH 8.3 as supporting electrolyte and in natural seawater samples. The determination is based on anodic depolarization reaction between sulfur and the mercury electrode. Investigations were carried out over wide concentration ranges, from 10−8 to 10−4 M of sulfide and 10−6 to 10−4 M of thiosulfate in the solution. In seawater conditions (pH 8.3) thiosulfate displays a voltammetric peak at about −0.15 V, and sulfide and/or elemental sulfur between −0.6 and −0.7 V (vs. Ag/AgCl). Based on the appearance of the voltammetric peaks of thiosulfate and sulfide at different potentials, and using different experimental conditions, i.e., accumulation at different starting potentials [E = 0 or E = −0.2 V (vs. Ag/AgCl)], a method for the direct determination of thiosulfate and sulfide in the mixture has been proposed. The direct method of thiosulfate determination in seawater can be used if the concentrations of sulfide are lower than 5 × 10−5 M. Higher concentrations of sulfide have to be decreased by acidifying and degassing the sample to prevent interferences. The method was applied for the analysis of sulfur species in marine samples from anoxic environment.
Iron determination in osteoblast‐like cell culture medium by adsorptive cathodic stripping voltammetry with a mercury microelectrode
Authors: Morais Simone , Carvalho Graça Simõnes , Sousa João Paulo 
Published: May 2005

AbstractMercury film microelectrodes were used to determine iron in osteoblast‐like cell culture medium by performing adsorptive cathodic stripping voltammetry in the presence of catechol. The optimized analytical conditions are a catechol concentration of 5.00 × 10−4 mol L−1, pH 8.0 and a collection potential of −1.80 V which eliminates the copper interference. The reoxidation period was limited to the time between switching to −0.10 V and scanning up to the metal peak (ca. −0.40 V). The limit of detection obtained for a 30 s collection time was 1.93 × 10−8 mol L−1 iron. The results achieved by this procedure and using the square‐wave voltammetry technique are accurate and precise. Biological assays were performed to evaluate the mineralization process.
A photo‐cured coated wire potassium ion‐selective electrode for use in flow injection potentiometry
Authors: Alexander Peter W. , Dimitrakopoulos Telis , Hibbert D. Brynn 
Published: May 2005

AbstractA potassium ion selective electrode (ISE) is reported based on the epoxyacrylate polymer prepared from o‐nitrophenyl octyl ether as the plasticizer and 2,2′‐bis [3,4‐(15‐crown‐5‐)‐2‐nitrophenylcarbamoxymethyl]tetradecane (BME‐44) as the ionophore. Several different electrodes were studied by photo‐curing different membranes onto a silver wire (0.8 mm i.d.), and the response characteristics were evaluated. The membranes prepared exhibited strong adhesion to the metal substrate and showed improved mechanical strength compared to poly(vinyl chloride)‐based membranes. The sensor exhibited Nernstian response over a log‐linear range of between 0.01 mM and 100 mM, and was selective against the common interfering ions. Fast response reaching 90% of steady‐state value in 5 s makes this sensor applicable for flow injection potentiometry measurements. The potassium ISE allows for accurate determinations of potassium in various water samples by flow injection potentiometry.
Highly sensitive cyclic voltammograms of 4‐aminodiphenylamine obtained by a porous carbon felt electrode and estimation of the hydrolysis rate constant of its quinonediimine state at a neutral pH
Authors: Uchiyama Shunichi , Hasebe Yasushi , Maeda Yuji , Yoshida Yasuhiko 
Published: May 2005

AbstractThe measurement of reversible redox waves of very low concentrations of 4‐aminodiphenylamine and 4‐hydroxydiphenylamine (below 1 × 10−5 M) were carried out by using a porous carbon felt electrode. The high sensitivity of the porous carbon felt electrode may be based on the surface affinity to both compounds, resulting in accumulation. Reversible redox waves of 4‐hydroxydiphenylamine appeared during the multicyclic voltammograms of 1 × 10−5 M 4‐aminodiphenylamine at a neutral pH solution when a porous carbon felt electrode is used, although the glassy carbon electrode did not show the distinct redox waves. The hydrolysis rate constants of the quinonediimine state of 4‐aminodiphenylamine at neutral pH range have not been measured due to its low solubility. The hydrolysis rate constants of the quinonediimine state of 4‐aminodiphenylamine at neutral pH are measured by the decrease and increase rates of 4‐aminodiphenylamine and 4‐hydroxydiphenylamine, respectively, using cyclic voltammetry The first order rate constant of hydrolysis of the quinonediimine state at pH 7.0 was found to be 9.1 × 10−5 s−1 and did not significantly depend on the proton concentration in a neutral pH range.
Electrochemical study of interactions between DNA and viologen‐thiol self‐assembled monolayers
Authors: Li Jinghong , Cheng Guangjin , Dong Shaojun 
Published: May 2005

AbstractWe investigated the binding characteristics of double‐stranded DNA to self‐assembled monolayers (SAMs) containing viologen groups formed on the surface of gold electrodes via Au–S bonds. The positive charged and hydrophobic surfaces of the viologen SAMs modified gold electrodes are suitable to bind strongly with DNA, whose interactions to solution DNA and adsorbed DNA both lead to positive shifts (22.5 mV and 65 mV, respectively) in the first redox potential of viologen centers, indicating that the main interaction is from a hydrophobic interaction. Meanwhile, the binding of DNA strongly affects the kinetics of electron transfer of the viologen group so that the separation of anodic and cathodic peak potentials becomes larger and the heterogeneous electron transfer constant becomes smaller.
Electrochemistry of vanadium hexacyanoferrate film
Authors: Liu Changwei , Dong Shaojun 
Published: May 2005

AbstractTwo stable redox couples, accompanying clear color switches between yellow, green and blue, can be observed when the VHCF‐coated film platinum electrodes are cyclic potential scanned in 3.6 M H2SO4 and 0.2 M K2SO4 electrolyte solution. Electrochemical results and in situ Fourier transfer infrared (FT‐IR) spectroscopy demonstrate that the redox reaction of the electroactive iron sites is related to the first redox couple (E1/2 = 0.81 V) while the second redox couple (E1/2 = 1.01 V) is due to the redox reactions of the electroactive vanadyl ions. Under the proper conditions, such as in high acidic solutions or thin films (deposition time is less than 2 min) and so on, the third redox couple (E1/2 = 0.89–0.94 V) can be observed on the cyclic voltammograms, which originates from the redox reactions of the interstitial vanadyl ions. This electrochemical reaction mechanism is investigated by in situ probe beam deflection technique, exchange of K+ ions accompanies with redox reaction of the iron sites, but for redox reaction of the vanadyl ions, both H+ ions, K+ ions and water molecules are involved.