bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ monitoring of peroxodisulfate anion production
Authors: Dalrymple Ian M. , Hitchman Michael L. , Price Denis , Millington J. Peter
Published: May 2005

A direct, continuous method for the measurement of peroxodisulfate anion has been devised and assessed. The approach is based upon the reduction of the anion under mass transfer limiting conditions at an amalgamated copper rotating disk electrode. The preparation of the disk electrode by Hg electroplating was examined in detail in order to generate a reproducible surface. The system was calibrated by demonstrating that the limiting current density for peroxodisulfate reduction was directly proportional to its bulk solution concentration. An electrochemical cell arrangement was then developed to permit the continuous, in situ measurement of peroxodisulfate concentration during electrochemical synthesis.
Voltammetric evidence of adsorption in cadmium(II)‐iodide system at different ionic strengths
Authors: Zelić Marina , Pižeta Ivanka
Published: May 2005

Adsorption 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

An 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

Cysteine, 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

An 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

A 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

The 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

The 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

The 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

Potentials 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

An 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

The 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

Benzoquinone (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

The 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

Electrochemically 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

By 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

Linear 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

Mercury 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

A 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

The 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

We 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

Two 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.
Determination of standard rate constants for electrochemical irreversible processes from linear sweep voltammograms
Authors: Velasco Jaime González
Published: May 2005

A new equation has been deduced from which a direct determination of the standard rate constant from linear sweep voltammograms can be made. Some questions related with the detection limit of irreversibility by means of the linear voltammetric method are also discussed.
An object oriented approach to electroanalytical technique implementation
Authors: Bessant Conrad , Saini Selwayan
Published: May 2005

This work describes the application of object oriented software design to the development of a low cost, functionally versatile, PC‐controlled potentiostat system. The implementation time for the electroanalytical techniques has been drastically reduced within the object oriented environment and it is shown how this approach simplifies the addition of new techniques without recourse to extensive software or hardware redesign. The pertinent aspects to the object oriented technique in the design of the potentiostat software are described in detail and experimental results are presented for chronoamperometry, cyclic voltammetry and square wave voltammetry for the one‐electron transfer compound, potassium hexacyanoferrate(II) in aqueous solution. It is also shown how new electroanalytical techniques based on novel potential‐time waveforms can be rapidly and easily incorporated, and experimental results for the highly sensitive pulsed amperometric detection of glucose in a stirred cell are presented.
Catalytic cathodic stripping voltammetry of 6‐mercaptopurine‐9‐D‐riboside in the presence of nickel ion
Authors: Ion Ana , Bǎnicǎ Florinel Gabriel , Luca Constantin
Published: May 2005

Differential pulse CSV of 6‐mercaptopurine‐9‐D‐riboside (6‐MPR) on a HMDE was investigated at pH about 7 in the presence of nickel ion. According to the value of the accumulation potential. 6‐MPR was preconcentrated either as a mercury compound or an adsorbed nickel complex. During the subsequent cathodic scan, 6‐MPR does catalyze the reduction of nickel ion giving a peak at about −0.8 V (vs. SCE). This peak enables the determination of 6‐MPR at concentrations down to 1 nM with no substantial interference from the heavy metal ions, chloride, alkali metals, complexing agents and only moderate interference by thiols and surface‐active compounds. The best sensitivity and reproducibility were achieved under the following conditions: pH 7.5 (phosphate‐acetate buffer); Ni2+, 1 mM; Eacc = −0.3 V; tacc = 1 to 2 min; scan speed = 20mV/min; pulse interval = 0.2 s.
Adsorption isotherms for atrazine on soils measured by differential pulse polarography
Authors: Vaz Carlos M. P. , Crestana Silvio , Machado Sergio A. Spinola , Mazo Luis Henrique , Avaca Luis Alberto
Published: May 2005

Differential pulse polarography was used to study the adsorption of atrazine on three tropical soils with different compositions regarding organic matter, clay, silt and sand. The corresponding Freundlich isotherms were determined and the calculated adsorption coefficients, KF, were 4.4, 9.9 and 5.2 mL g−1 for Pindorama, Monte Alegre and Ribeirão Preto soils, respectively. These values are in good agreement with previous reports. A comparison between the results obtained by differential pulse polarography and by gas chromatography was also performed showing that both techniques yield very similar isotherms.
Chronopotentiometric stripping of DNA at mercury electrodes
Authors: Paleček Emil , Tomschik Miroslav , Staňková Veronika , Havran Luděk
Published: May 2005

Denatured (single‐stranded, ss) and native (double‐stranded, ds) DNAs were studied by constant current chronopotentiometric stripping analysis (CPSA) at a hanging mercury drop electrode (HMDE). In agreement with the previous voltammetric studies at neutral pH values ssDNA produced CPS cathodic peak CA (due to reduction of cytosine and adenine) and anodic peak G (due to oxidation of the guanine reduction product) at dt/dE against E curves. The same peaks produced by dsDNA were substantially smaller. Differences in heights (areas) of peaks G and CA produced by ss and dsDNAs at partial and full electrode coverage are compared and discussed. Using CPSA a well‐developed and symmetrical peak CA was obtained at low DNA concentrations compared to a poorly measurable inflection produced by differential pulse or linear sweep voltammetries under the same conditions. The CPS peak CA can be used also in adsorptive transfer stripping (AdTS, medium exchange) experiments. In the previous AdTS voltammetric measurements only peak G was exploited while the voltammetric peak CA was poorly defined to be of any use in combination with DNA‐modified electrodes. CPS peaks were measured in the presence and in absence of air. It was shown that in the presence of air peak CA is enhanced while peak G decreased. We compared the CPSA of ssDNA at the mercury and carbon paste electrodes (CPE). The CPS peak G (obtained with HMDE) seems to be the best choice for the electrochemical determination of DNA in highly diluted solution. With 10 min adsorptive preconcentration a detection limit below 20 ng of ssDNA per mL was obtained at HMDE. At CPE the limit of detection (of the same ssDNA) was at least two‐fold higher.
Poly(4‐vinylpyridine)‐coated chemically modified electrode for the detection of uric acid in the presence of a high concentration of ascorbic acid
Authors: Zen Jyh‐Myng , Chen Yao‐Jung , Hsu Chi‐Teng , Ting Yuan‐Shih
Published: May 2005

A poly(4‐vinylpyridine)‐coated carbon paste electrode (PVP/CPE) was developed for the selective determination of uric acid (UA) in the presence of ascorbic acid (AA) by square wave voltammetry. The oxidation of UA at carbon‐based electrodes in acidic solutions suffers from interference from AA which can be oxidized at a potential close to that of UA. Due to the very distinct ability of AA and UA to form hydrogen bonds with PVP, the overlapped oxidation potentials of AA and UA can be separated. Linear calibration plots are obtained over the 0–9 μM and 10–30 μM in pH 1.1 buffer solution with slopes (μA/μM) and correlation coefficients of 3.6, 0.9992 and 7.5, 0.9989, respectively. The detection limit (3σ) is 0.2 μM. The acceptable tolerance of concentration of AA for the determination of 20 μM UA is at least as high as 0.1 mM. The practical analytical utility is illustrated by selective measurements of UA in human urine without any preliminary treatment.
Development of NOx gas sensors based on nitrate‐selective polypyrrole electrodes
Authors: Hernández Emily C. , Mortensen Charles , Bachas Leonidas G.
Published: May 2005

A nitrate‐selective polypyrrole‐based electrode was used in the development of NOx sensor. The nitrate‐selective film was prepared by electropolymerizing pyrrole in presence of a nitrate salt. This resulted in a film that responded to nitrate in buffered media with near‐Nernstian slopes and excellent reproducibility. This electrode was incorporated into a gas‐sensing arrangement where it was immersed in a buffered compartment and separated from an acidified sample solution by a gas‐permeable membrane. Additions of nitrite to the acidified solution resulted in the production of NOx, which can cross the gas‐pemeable membrane into the buffered internal filling solution where it is trapped as nitrate and sensed by the nitrate‐selective polypyrrole electrode. This sensor arrangement resulted in detection limits in the μM range and had excellent selectivity characteristics.
Amperometric sensing of ammonia in aqueous solutions using a polyaniline‐modified electrode in flow injection systems
Authors: Trojanowicz Marek , vel Krawczyk Tadeusz Krawczyński , Zmorzyńska Małgorzata , Campanella Luigi
Published: May 2005

Platinum electrode modified with polyaniline by electropolymerization exhibits amperometric sensitivity to nonprotonated ammonia in aqueous solutions in the anodic range of potentials. Sensitivity of response depends mostly on the kind of doping anions used and the polarization potential applied during measurements. This detection can be utilized for design of amperometric biosensors for urea.
Detection of DNA hybridization using self‐assembled bilayer lipid membranes (BLMs)
Authors: Siontorou Christina G. , Nikolelis Dimitrios P. , Piunno Paul A. E. , Krull Ulrich J.
Published: May 2005

The present work reports the use of self assembled bilayer lipid membranes supported on the surface of a metal (s‐BLMs) as transducers for the direct electrochemical monitoring of DNA hybridization. Characterized oligomers based on single stranded deoxyribonucleic acid (ssDNA) thymidylic acid icosanucleotides that were terminated with C16 (dT20‐C16) and deoxyadenylic acid icosanucleotides (dA20) were used for the hybridization procedure at the lipid membrane surface. The decrease of the ion conductivity observed during the hybridization procedure is indicative of the formation of the duplex, which may subsequently be excluded from the membrane. The incorporation of nucleic acids into the lipid matrix was investigated by differential scanning calorimetric (DSC) experiments. The present simple electrochemical biosensor for monitoring of DNA hybridization was regenerable for multiple cycles of application. This approach provides low detection limits for DNA (a few hundreds of fmol), fast response times (on the order of a few minutes), mild conditions of hybridization and capability of analyzing small volumes of sample.
Electropolymerization of pyrrole‐2‐carboxylic acid and 4,4′‐dihydroxybenzophenone on platinum electrodes. Applications to assemble novel glucose sensors
Authors: Curulli A. , Palleschi G.
Published: May 2005

The electropolymerization of pyrrole‐2‐carboxylic acid (PY‐2‐COOH) and of 4,4′‐dihydroxybenzophenone (DHB) has been carried out on Pt electrodes by scanning the potential from +0.4 V to + 1.4 V (vs. SCE) for PY‐2‐COOH and from 0.0 V to + 0.8 V (vs. SCE) for DHB, at scan rate of 2–5 mV/s, in phosphate buffer (PBS) pH 8. To test the permselectivity of these polymers, cyclic voltammograms of H2O2, ascorbic acid (AA), uric acid (UA) and acetaminophen (APAP) were carried out and results were compared with those obtained at the bare electrode. The electropolymerization in the presence of glucose oxidase was also carried out. The probes were then tested as glucose sensors. Glucose was detected, by amperometric measurements at +0.6 V (vs. SCE). The linear response to glucose was in the range 7 × 10−6‐1.8 × 10−3 mol/L, for the sensor prepared with PPY‐2‐COOH and 4 × 10−6 −2 × 10−3 mol/L, for the sensor prepared with PDHB. The detection limit was 5 × 10−6 mol/L. for PPY‐2‐COOH and 2 × 10−6 mol/L for PDHB. The response time of both polymers was 3–5 s. The stability of the electropolymerized films and the glucose probes was evaluated, in storage and operational conditions The glucose probes, stored in buffer at 4°C when not in use, showed a residual enzyme activity of 50%, after about two months.
Sensor–analyte interaction kinetics as a metal speciation criterion
Authors: Labuda Ján , Bučková Miriam , Halamová L'udmila
Published: May 2005

A general approach to the determination of metal speciation based on the initial reaction rate of the (bio)chemical sensor‐metal complex interaction is reported. The kinetic lability of the copper complexes with glycine, salicylic acid, humic acid, cysteine, thiourea and EDTA has been evaluated according to criteria based on the calculated and experimentally obtained rate constants for the accumulation of copper ions on a carbon paste electrode modified by the cation exchange resin Dowex 50W‐X8. Anodic stripping voltammetry was used for the copper quantification.
Voltammetric behavior of nitroimidazoles at a DNA‐biosensor
Authors: Brett Ana Maria Oliveira , Serrano Sílvia H. P. , Gutz Ivano , La‐Scalea Mauro A. , Cruz Maria Luiza
Published: May 2005

The newly developed DNA‐biosensor is a very promising tool for the investigation and study of the action of drugs specifically designed to interact with DNA. In this work the electrochemical reduction of nitroimidazole drugs was studied in the presence of DNA immobilized onto the surface of a glassy carbon electrode. This enabled preconcentration of the drug onto the electrode surface, which was then electrochemically reduced to the corresponding hydroxylamine which followed by reoxidation give the nitroso compound and subsequently an azoxycompound. Moreover, as the target of the nitroimidazole action was the DNA, the damage caused to DNA on the electrode surface by areduction product of this drug could be detected in situ.
Evaluation of copper‐based electrodes for the analysis of aminoglycoside antibiotics by CE‐EC
Authors: Voegel Phillip D. , Baldwin Richard P.
Published: May 2005

Aminoglycoside antibiotics including gentamicin, bekanamycin, tobramycin, lincomycin, neomycin, kanamycin, and ribostamycin have been determined by CE‐EC with copper clectrodes. Both copper wall‐jet electrodes (WJEs) and copper on‐capillary electrodes (OCEs) were evaluated. The OCEs provided μM detection limits, superior stability and reproducibility (2–3% relative standard deviation in oxidation current), and a simple instrumental set‐up without the need for capillary/electrode alignment. The analytical capabilities of the Cu‐OCE were examined, following the optimization of CE conditions, for the seven aminoglycosides above; and the practical utility of this approach was demonstrated through the determination of aminoglycoside antibiotics in three pharmaceutical preparations.
A bienzyme sensor for the determination of hypoxanthine and inosine
Authors: Hu Shengshui , Liu Chung‐Chiun
Published: May 2005

A biosensor for the detection of hypoxanthine (Hx) and inosine (HxR) has been developed by the coimmobilization of nucleoside phosphorylase (NP) and xanthine oxidase (XO) on a chemically modified electrode, which uses a glassy carbon electrode coated with a Nafion ‐ paraquat film. This sensor responds to Hx and HxR in the presence of phosphate, and it responds only to Hx in the absence of phosphate (borate buffer as medium). The sensor measurement is based on the oxygen consumed due to the enzymatic reaction involving xanthine oxidase which is immobilized on the electrode surface. In this study, the experimental parameters are optimized and the linear relationships between the decreased currents and the concentrations of both Hx and HxR in the range of 1 × 10−6‐2 × 10−4M are obtained. This biosensor exhibits a high degree of sensitivity and can be used for the assay for Hx and HxR in fish meat or other biological samples.
What makes the anodic stripping voltammetry of mercury at a trace level possible?
Authors: Lovrić Milivoj , Scholz Fritz
Published: May 2005

For thermodynamic reasons it is impossible to describe the anodic stripping voltammetry (ASV) of mercury at concentrations below 10−7 mol/L as involving a simple deposition and dissolution of metallic mercury. That follows from the finite solubility of elemental mercury in water at ambient temperature. Instead, it is a more or less strong adsorption of mercury atoms on the electrode surface which makes ASV possible. At these low concentrations, the atomic mercury in the solution can no longer be neglected. A theoretical description for staircase cyclic voltammetry of the reaction Hg ⇌ Hg ⇌ Hg + 2e− has been developed and it is discussed with respect to the ASV of mercury. The adsorption of atomic mercury is considered for the case of different electrode materials and adsorption constants have been estimated from underpotential deposition peaks. The distribution of the following mercury species is given for different electrode potentials and total mercury concentrations: Hg, Hg2+, Hg, Hg and Hg.
Conducting phenylenevinylene blends as electrode materials in LC amperometric detection
Authors: Staes E. , Nagels L. J. , Verreyt G. , Jacobs S. , Bao Y. , Geise H. J.
Published: May 2005

A novel amperometric electrode based on a conducting polymer is presented and its properties are compared with those of a glassy carbon electrode. The electrode material was made by mixing 2,5‐dimethoxy‐1,4‐bis[2‐(3,4,5‐trimethoxy‐phenyl)ethenyl]benzene with iodine and polycarbonate. The blend was coated on a glassy carbon electrode by evaporation from a chloroform solution. Catecholamines were used as test substances in LC and FIA measurements. They were oxidized at a potential of +0.7 V (vs. SCE). The electrode exhibited a linear response for injected concentrations from 2.5 × 10−6M to 2.5 × 10−3M. It had a response time of 1.2 s and a coulometric efficiency of 0.74% at a linear flow rate of 1 mL/min. The electrode material is stable for several months under normal operating conditions. Hydrodynamic voltammograms showed E1/2 values shifted by approximately 100 mV as compared to glassy carbon. The novel redox‐conducting coating is proposed as an alternative material for the development of enzyme electrodes and chemically modified electrodes.
Voltammetric study of nimesulide and its differential pulse polarographic determination in pharmaceuticals
Authors: Álvarez‐Lueje A. , Vásquez P. , Núñez‐Vergara L. J. , Squella J. A.
Published: May 2005

Nimesulide, N‐(4‐nitro‐2‐phenoxyphenyl)methanesulfonamide is an antiinflamatory analgesic agent that is both reducible at the mercury electrode and oxidizable at the glassy carbon electrode. Nimesulide in hydroalcoholic solution, presents cathodic response in a wide range of pH (2–12), both, by differential pulse and tast polarography techniques. The obtained results show only one main well‐defined peak or wave in all the pH range studied. This peak (or wave) corresponds to the nitro group reduction in position 4. The voltammetric oxidation shows one well‐resolved signal in all the pH range studied. This anodic signal could be attributed to the methylsulfonamide group oxidation. For analytical purposes, a very well resolved diffusion controlled differential pulse polarographic peak obtained at pH 7 was selected. This peak was used to develop a new method for the determination of nimesulide in pharmaceutical dosage forms. The recovery study (104.8% with a RSD of 1.3%) shows that the method is sufficiently accurate and precise to be applied in the individual tablet assay of commercial samples.
Spontaneous assembly of the inclusion complexes of viologen‐attached alkanethiols and α‐, β‐cyclodextrin on gold electrode
Authors: Yan Juchao , Dong Shaojun
Published: May 2005

Electroactive self‐assembled monolayers (SAMs) with well‐defined electrochemical responses were prepared by spontaneous assembly of the inclusion complexes (CD/C8VCωSH) of viologen‐attached alkanethiols (C8VCωSH) and α‐ and β‐cyclodextrin (CD). They were characterized by X‐ray photoelectron spectroscopy and cyclic voltammetry. The results demonstrate that the chemisorption process of CD/C8VCωSH on gold substrate occurs through S–Au bonds, and that the redox sites in SAMs of CD/C8VCωSH are in a much more uniform environment than those in SAMs of C8VCωSH.
Simultaneous adsorptive stripping voltammetric measurements of trace chromium, uranium, and iron in the presence of cupferron
Authors: Wang Joseph , Lu Jianmin , Luo Denbai , Wang Jianyan , Tian Baomin
Published: May 2005

The ligand cupferron is used for the simultaneous adsorptive stripping voltammetric measurements of several trace metals. Experimental variables affecting such multielement capability, including the cupferron concentration, adsorption time or metal concentration are explored. Adequate resolution is demonstrated for up to five metals (FeIII, UVI, CrVI, VV, and BiIII), present at the ppb concentration level. Possible changes in peak heights, associated with competition for the complexing ligand and/or coadsorption effects, are explored. Different concentration ratios of the mixture components can be tolerated. Applicability to groundwater or river‐water samples is illustrated.
A novel amperometric transducer design for needle‐type implantable biosensor applications
Authors: Yang Qingling , Atanasov Plamen , Wilkins Ebtisam
Published: May 2005

A novel transducer design is proposed based on a electrocatalyst for hydrogen peroxide oxidation (platinum black) electrodeposited on the inner wall of a stainless steel needle which serves as a working electrode, and an external Ag/AgCI reference/counter electrode. Electropolymerized 1,3‐diaminobenezene (1,3‐phenylenediamine) is employed as a protective layer for the platinum black as well as an interference eliminating layer. This configuration uses the Pt electrocatalyst in its most active dispersed form and ensures good mechanical ruggedness and protection of the catalytic and biological components. The design also provides the possibility to obtain high enzyme loading and hence an extended sensor life‐time. Two types of glucose sensors were constructed based on this novel design concept. The enzyme (glucose oxidase) was immobilized either in a hydrophilic gel matrix inside the needle body (i) or cross‐linked on the inner needle surface (ii). Cellulose triacetate, polycarbonate, and Nafior were used as external diffusion control layers, which extended the linear range of the sensor response to over 25 mM glucose. These biosensors demonstrated diminished response to interferences from oxidizable compounds present in body fluids and a life time of at least three months.
Catalytic behavior of osmium(II), rhodium(III) and ruthenium(II) Phthalocyanines towards the electrooxidation of cysteine on glassy carbon electrodes
Authors: Sekota Mantoa , Nyokong Tebello
Published: May 2005

Glassy carbon electrodes (GCE's) modified with phthalocyanine complexes of Rh, Ru and Os are employed for the catalytic oxidation of cysteine. When cyanide and dimethylsulfoxide (DMSO) are used as axial ligands giving (DMSO)(Cl)RhIIIPc, [(CN)2RhIIIPc]−, (DMSO)2OsPcII, and [(DMSO)2Ru(II)Pc]·2DMSO complexes, the peak currents for the oxidation of cysteine increase after each scan, indicating an increase in the catalytic activity of the electrode with repetitive scanning. This improvement in the catalytic activity of the GCE after the first scan is attributed to the formation of dimeric π cation radical species at the electrode surface.
Determination of gold by anodic stripping voltammetry with carbon fiber ultramicroelectrodes
Authors: Alarnes‐Varela Gabriel , Costa‐García Agustín
Published: May 2005

Carbon fiber ultramicroelectrodes have been used in anodic stripping voltammetry (ASV) of trace gold. The advantageous characteristics of ultramicroelectrodes combined with ASV resulted in a fast, selective, sensitive and reproducible method. An electrochemical pretreatment was necessary for analytical determinations. The combination of supporting electrolyte (HCl 0.1 M) and electrodeposition potential (0.0 V) gave a high selectivity. A calibration plot from 1.00 × 10−8 M to 1.60 × 10−6 M (r = 0.9994) was achieved with a detection limit of 5.94 × 10−9 M and a relative standard deviation (RSD) of 2.87% at 3.0 × 10−7 M. AgI, CuII, PbII and HgII metals in the concentration of 1.00 × 10−6 M were not found to interfere with the ASV of gold (3.00 × 10−7 M) when carried out under optimum conditions. The procedure was applied to the determination of gold in two tap water synthetic samples.
Determination of thioglycolic acid and cysteine in hair‐treatment products at ceramic carbon composite electrodes
Authors: Wang Lai‐Hao , Chen Zong‐Shion
Published: May 2005

Ceramic carbon composite electrodes, prepared by incorporating ceramic powders with carbon paste matrices, are shown to facilitate the oxidation of thiol compounds. These electrooxidation processes are applied for the detection of cysteine and thioglycolic acid in hair‐treatment products.