bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synergistic electrochemical and chemical modification of carbon paste electrodes for open‐circuit preconcentration and voltammetric determination of trace adenine
Authors: Cai Xiaohua , Ogorevc Božidar , Kalcher Kurt 
Published: May 2005

AbstractA new concept of electrode modification is presented, consisting of chemically assisted electrochemical oxidative pretreatment of the electrode surface. If carbon paste electrodes (CPEs) are polarized at +1.75 V (vs Ag/AgCl) in a dilute alkaline medium (1 × 10−3mol/L) containing 0.1 mol/L NaNO3 for 60s, they exhibit a unique ability to preconcentrate adenine, an important biological substance, that served as a model compound. In this work, a thorough study has been performed to explore the new pretreatment procedure, but also its analytical application for trace adenine determination was optimized. During the pretreatment of a CPE, a specific oxide layer is formed due to a synergistic effect of a combined anodic and chemical oxidation process, in which the presence of sodium nitrate plays a crucial role. In a subsequent step under open‐circuit conditions, adenine is oxidized by the oxide layer, and the resulting oxidation product is strongly adsorbed onto the electrode surface. After medium exchange, the adsorbed oxidation product of adenine is reduced at −0.5 V (vs. Ag/AgCl) and the voltammetric current response can be utilized for analytical purposes. Applying 10 min accumulation and square‐wave voltammetric operation, the detection limit of 20 μg/L (1.5 × 10−7 mol/L) of adenine in a sample solution was acquired. The voltammetric behavior of adenine at plain and pretreated CPEs is also presented and discussed.
Catalytic oxidation of methanol on a glassy carbon electrode electrochemically modified by a conductive NiII‐curcumin film
Authors: Ciszewski Aleksander 
Published: May 2005

AbstractThis work focuses on the electrochemical synthesis and characterization of a conductive polymeric nickel‐curcumin film and its application for electrocatalytic oxidation of methanol in alkaline solutions. It has been found that a glassy carbon electrode modified by this film acts as a very effective catalyst for oxidation of alcohols. Electropolymerization of the nickel‐curcumin complex and oxidation of methanol have been studied by cyclic voltammetry. The described modified electrode provides a durable catalytic surface which allows the voltammetric oxidation of methanol: in 0.1 M NaOH electrolyte the resulting anodic peak is at 0.59 V (vs. SCE). Electrooxidation was not possible at bare glassy carbon electrodes, at least before the onset of the electrolyte decomposition. The mechanism of modifying the film formation has been discussed.
Adsorptive stripping potentiometry of DNA at electrochemically pretreated carbon paste electrodes
Authors: Wang Joseph , Cai Xiaohua , Jonsson Colleen , Balakrishnan Mini 
Published: May 2005

AbstractPotentiometric stripping analysis is employed for highly sensitive measurements of single‐stranded DNA at carbon paste electrodes. Electrochemical (oxidative) pretreatment is used to condition the carbon paste surface prior to the accumulation process. The low background response of the potentiometric stripping mode offers convenient quantitation of low nanogram quantities of DNA. Experimental variables of the pretreatment and measurement procedures are explored and optimized. Results are also reported for the quantitation of nanogram levels of the long terminal repeat (LTR) from the human leukemia virus and for the stripping operation of microfabricated screen‐printed electrodes.
Electrochemical oxidation of 8‐hydroxyquinoline and selective determination of tin(II) at solid electrodes
Authors: Yang Z. P. , Alafandy M. , Boutakhrit K. , Kauffmann J.‐M. , Arcos J. 
Published: May 2005

AbstractThe electrochemical oxidation of 8‐hydroxyquinoline and several structurally related molecules has been investigated by cyclic voltammetry at solid electrodes (GCE, CPE, Pt) as a function of pH in aqueous acetate media. Oxine showed one irreversible oxidation peak whose magnitude decreased in the presence of cations readily complexed by oxine and with concomitent formation of a new oxidation peak at more positive potentials. Tin(II) was found to exhibit a distinct behavior as its oxidation was catalyzed by the presence of oxine in the analyzed solution. The tin(II)‐oxine oxidation peak was found to be linearly related to inorganic tin(II) concentration allowing its quantitative determination at micromolar levels.
Characterization of electrochemically prepared polyaminopyridines
Authors: Park Deog‐Soo , Shim Yoon‐Bo , Park Su Moon 
Published: May 2005

AbstractPolymer‐modified electrodes have been prepared by electrochemical oxidation of 2‐aminopyridine and 4‐aminopyridine in acetonitrile and their chemical properties have been characterized. The polymer films thus prepared were insulators but can be doped with Ag+ or Fe(CN) to produce semiconducting films. The doping must have been accomplished by the complexation of Ag+ with functional groups or trapping of Fe(CN) in the polymer matrix. It has also been demonstrated that these films can be used for chemical analysis of Ag+ by first collecting Ag+ and running subsequent differential pulse voltammetric experiments. The dynamic linearity was excellent in the concentration range of 10−7–10−2 M and the detection limit was about 5 × 10−8M.
A microscopic study on carbon paste electrodes
Authors: Švancara Ivan , Hvízdalová Marie , Vytřas Karel , Kalcher Kurt , Novotný Radomír 
Published: May 2005

AbstractScanning electron microscopy has been used for observing the surface of several types of carbon paste electrodes in order to reveal the role of both pasting liquid and carbon powder on the formation of the carbon paste structure. The effect of pasting liquid was studied using carbon pastes prepared from RW‐B multicrystalline graphite powder and either liquid tricresyl phosphate or Nujol oil. The influence of carbon powders was investigated on carbon pastes made of two special carbon powders with globular particles (Sigradur K or Sigradur G, respectively) and of Nujol. Microscopic observations have shown marked alterations in the structure of the carbon pastes studied either due to different physico‐chemical properties of the pasting liquids or in consequence of specific characteristics of the powdered carbon materials, especially of the shape and size distribution of carbon particles. Information resulting from this microscopic study was then compared with conclusions of previous voltammetric investigations on the same types of carbon pastes, thus providing a way to characterizing better their overall electrochemical behavior.
Compression of the interfacial boundary electrode‐solution as the basis of new compression accumulation (stripping) techniques
Authors: Novotný Ladislav 
Published: May 2005

AbstractA new approach is presented to the study, monitoring, control and utilization of electrode processes based on the compression of interfacial boundaries. The principle is demonstrated by the adsorption of 4,4′‐bipyridyl on mercury electrode from 0.1 M H2SO4 for which a compression diagram (isotherm) is provided and the phenomena accompanying the compression are analyzed. Prospects for the development of new compression techniques are discussed.
Electron transfer through an immunoglobulin layer via an immobilized redox mediator
Authors: Wittstock Gunther , Emons Hendrik , Heineman William R. 
Published: May 2005

AbstractAs a step towards a voltammetric immunoassay with antibodies directly attached onto the electrode surface, the mediated oxidation of a redox active label has been investigated with a model system. Butyl ferrocene served as a model for the mediator and was coimmobilized onto a glassy carbon electrode within a layer of bovine immunoglobulin G, which mimiked the antibody. An overlaid polyvinyl ferrocene layer was employed to simulate a ferrocene‐tagged high molecular weight antigen bound to the immobilized antibodies. A mediated electron transfer could only be demonstrated with butyl ferrocene as mediator, whereas other compounds failed to support an electron transfer between the polyvinyl ferrocene layer and the electrode through the layer of immunoglobulin.
Mushroom‐based cobalt phthalocyanine dispersed amperometric biosensor for the determination of phenolic compounds
Authors: Ozsoz Mehmet , Erdem Arzum , Kilinc Emrah , Gokgunnec Levent 
Published: May 2005

AbstractThe use of mushroom tissue as a source for polyphenol oxidase for the determination of phenolic compounds is described. The enzymatic reaction between mushroom polyphenol oxidase and phenolic compounds is coupled with the use of cobalt phthalocyanine dispersed in carbon paste. The effects of applied potential to the responses are investigated. Cobalt phthalocyanine dispersed electrodes give shorter response times and a lower applied potential compared to conventional tissue biosensors.
Needle‐type glucose biosensors based on a pyrolyzed cobalt‐tetramethoxy‐phenylporphyrin catalytic electrode
Authors: Atunasov Plamen , Gamburzev Sergej , Wiikins Ebtisam 
Published: May 2005

AbstractAmperometric needle‐type glucose biosensors employing nonplatinum catalytic electrodes made from pyrolytic electrode of pyrolyzed cobalt‐tetramethoxy‐phenylporphyrin (CoTMPP) are described. A technique for preparation of the working electrode with catalyst and adsorbed enzyme (enzyme electrode) from a pressed matrix (tablet) is presented. This technique allows manufacturing numerous sensors from the same pressed tablet, all of which demonstrate a good reproducibility of their parameters (sensitivity, linear range, lifetime). Different glucose diffusion (external) membranes have been studied in order to extend the linear range of the biosensor response. Linearity of the sensor response to glucose concentrations up to 35 mM is reported when a cellulose paper membrane, impregnated with cellulose acetate. is used pressed into the needle sensor body. Sensors demonstrated a shelf lifetime of 30 days (with constant parameters of the signal output) and can be used for continuous glucose monitoring in vitro for at least 5 days.
Electrochemistry at the tetrathiafulvalene‐tetracyanoquinodimethane electrodes. Application to the study of c‐type cytochromes
Authors: Bianco Pierre , Haladjian Jean 
Published: May 2005

AbstractElectrodes made from pastes of the conducting organic salt, tetrathiafulvalene‐tetracyanoquinodimethane (TTF‐TCNQ), are prepared and characterized using electrochemical techniques. These electrodes behave as conventional solid electrodes within their stable potential range. An attractive property is their capability to achieve direct electrochemistry of c‐type cytochromes (horse heart cytochrome c, cytochrome c552 from Thiobacillus ferrooxidans). Resuits on pH‐dependence and kinetic data for these metalloproteins agree with previously published data. It is suggested that favorable interactions occur between the TTF‐TCNQ electrode surface and redox protein sites. Moreover, the analytical advantage of using permselective‐membrane TTF‐TCNQ electrode is demonstrated.
Sonovoltammetric behavior of ascorbic acid and dehydroascorbic acid at glassy carbon electrodes: Analysis using pulsed sonovoltammetry
Authors: Compton Richard G. , Matysik Frank‐Michael 
Published: May 2005

AbstractThe effect of power ultrasound on the voltammetric behavior of ascorbic acid and dehydroascorbic acid at a glassy carbon electrode is described. The voltammetric characteristics of both compounds were found to be modified by ultrasonically formed radicals. In the case of dehydroascorbic acid the single sweep voltammogram shows an anodic signal in the presence of ultrasound which probably results from the formation of an oxidizable radical known to be an intermediate of ascorbic acid oxidation. In the case of ascorbic acid pulsed sonovoltammetry is applied and characterized regarding the time dependence of the current decay and the reliability of its analytical performance. The utility of pulsed sonovoltammetry is demonstrated analyzing a pain killer tablet regarding the ascorbic acid content.
Application of an optimization procedure in adsorptive stripping voltammetry to the determination of nickel with DMG
Authors: Sanllorente Silvia , Ortiz M. Cruz , Arcos M. Julia , López‐Palacios Jesús 
Published: May 2005

AbstractA procedure for the determination of nickel by adsorptive stripping voltammetry (AdSV), using dimethylglyoxime as complexing agent, has been optimized. The determination was carried out by two different techniques: differential pulse adsorptive stripping voltammetry (DPAdSV) and square wave adsorptive stripping voltammetry (SWAdSV). The selection of the experimental parameters was done using a factorial design which allows one to find the most significant variables, i.e., those which exert the greatest influence on the measured magnitude, with a reduced number of experiments. Posterior optimization of these variables provided the most adequate experimental conditions and it was under these conditions that the calibrations were made, using a robust regression method which allows the elimination of anomalous points.
The role of nickel as central metal in conductive polymeric porphyrin film for electrocatalytic oxidation of nitric oxide
Authors: Ciszewski Aleksander , Kubaszewski Eugeniusz , Łożyński Marek 
Published: May 2005

AbstractThis communication assesses the role of nickel in the electrocatalytic detection of nitric oxide at polymeric porphyrin coated glossy carbon electrodes.
Voltammetric determination of silver at ultratrace levels using a carbon paste electrode with improved surface characteristics
Authors: švancara Ivan , Kalcher Kurt , Diewald Wolfgang , Vytřas Karel 
Published: May 2005

AbstractA differential pulse anodic stripping voltammetric method for the determination of silver is described. A new type of electrodeposition for preconcentrating the analyte, Ag+, was investigated, enhancing the electrolytic accumulation efficiency onto a carbon paste electrode by ion pair formation. A carbon paste electrode containing tricresyl phosphate as a pasting liquid was modified in situ with heptylsulfonic acid (sodium salt). The modifier gave rise to an additional accumulative effect towards the target ions based on ion pairing which resulted in an enhanced sensitivity of the electrode. Additional activation of the electrode surface at −1.0 V (vs. SCE) for 60 s improved the detection limit significantly. The detection limit was found to be 2.5 × 10−12 M Ag+ (accumulation time 15 min), and could be even lowered by increasing the period of preelectrolysis. The current response was linearly dependent on the concentration up to 2 × 10−5 M Ag under optimized conditions. The effects of paste composition, voltammetric parameters, composition of the supporting electrolyte as well as the influence of alkylsulfonic acids and of cathodic activation upon the determination of Ag were studied. Interferences from about 20 elements were investigated with particular attention to Cu, Hg, and Au. By masking with ethylenediaminetetraacetate (EDTA), Cu and Hg did not affect the response of Ag up to a 10000‐fold and 500‐fold molar excess in concentration, respectively. Au did not interfere with the determination of Ag up to a 100‐fold molar excess if its absolute concentration was lower than 5 × 10−7 M. For higher concentration levels, [AuCl4]− could be separated by passing the analyte solution through an anion‐exchanger column (Dowex‐1) prior to stripping analysis. Due to the extremely low detection limit and high selectivity, the method could be applied to determine Ag at its ubiquitous level in tap water. With this method, the corrosion of silver cutlery in tap water could be monitored. The results agreed well with those obtained by using inductively coupled plasma mass spectrometry (ICP‐MS).
Microdialysis sampling and high performance liquid chromatography with amperometric detection for sugar analysis in milk products
Authors: Mannino Saverio , Cosio Maria S. , Zimei Paola 
Published: May 2005

AbstractA rapid and highly efficient method for the direct quantification of the major carbohydrates, glucose, fructose, sucrose and lactose in milk‐based products is described. Rapid and selective monitoring of each sugar is accomplished by microdialysis sampling coupled with HPLC separation and amperometric detection with a chemically modified electrode. This new scheme offers simultaneous monitoring of sugars with little or no sample pretreatment. The results obtained from the application of the proposed procedure to milk and milk‐based products are discussed.
A serial array of ISEs for use in a portable battery‐powered flow injection analyzer
Authors: Dimitrakopoulos Telis , Alexander Peter W. , Hibbert D. Brynn 
Published: May 2005

AbstractPortable flow injection potentiometry (FIP) is described with a flow‐through multi‐ion sensor array system based on a planar design. Potassium, sodium and nitrate sensors are used as examples for simultaneous multi‐ion determinations based on the availability of a planar sensor design for these ions. The miniaturized flow cell developed with the three sensors in series in the FIP system is used to demonstrate the reliability of this portable design when using manual injection of the sample solution. The system is characterized by its small size, light weight and low power requirements, and makes use of a notebook computer for real‐time display of data and data acquisition. Rapid FIP response characteristics are shown after optimization of flow carrier conditions, and are successfully applied to the analysis of mineral water samples.
Immobilized ferrocene and glucose oxidase on titanium(IV) oxide grafted onto a silica gel surface and its application as an amperometric glucose biosensor
Authors: Milagres Benjamin G. , Kubota Lauro T. , Neto Graciliano De Oliveira 
Published: May 2005

AbstractThe voltammograms obtained with an electrode containing carbon paste with ferrocene immobilized on a titanium‐oxide/silica gel material showed good response and stability in aqueous media. From pH 4 to 8 the electrode response remained almost constant, but a small shift in the midpoint potential towards more positive values was observed when the pH was decreased. The nature of the cation does not affect the voltammetric response. However, the nature of the anion affects the midpoint potential significantly. Cyclic voltammetry investigation showed that the electrode with immobilized glucose oxidase is an excellent biosensor. The mechanism of the electron transfer was proposed as being electron tunneling by the flavin of the enzyme to mediator, and the high current level is assigned to the high surface area of the silica matrix. The amperometric measurements showed a linear response in the range from 1.0 × 10−4 to 8.0 × 10−4 M. Above this range, saturation of the enzyme was observed. The response time was about 15 s. Determination of glucose in blood serum showed an excellent correlation when compared with Merck's Kit method. The immobilized material presented an excellent stability mantaining the same activity for at least six months.
The mechanism of the electro‐reduction of some azo dyes
Authors: Gooding Justin J. , Compton Richard G. , Brennan Colin M. , Atherton John H. 
Published: May 2005

AbstractThe pH dependence of the reduction mechanism of the azo dyes Orange G and Sunset Yellow FCF was investigated using a mercury plated rotating disk electrode, The reduction was shown to proceed via a CE mechanism except at very high pH, where direct reduction was observed. It is proposed that the chemical step of the CE reaction, namely protonation of the azo bond, could occur either intramolecularly, via azo/hydrazone tautomerism, or intermolecularly from bulk solution. At low pH the protonation from free H+ predominated while above neutral pH, until deprotonation of the ortho hydroxyl group involved in the tautomerism, the intramolecular mechanism was more prevalent. The kinetic parameters for the chemical steps in each of the two protonation mechanisms were determined.
Development of an amperometric enzyme biosensor for the determination of the antioxidant tert‐butylhydroxyanisole in a medium of reversed micelles
Authors: Ruiz M. Asuncion , Reviejo A. Julio , Parrado Concepcion , Pingarrón Jose M. 
Published: May 2005

AbstractA biocdtalytic scheme, based on the enzyme tyrosinase, has been developed for the determination of the antioxidant tert‐butylhydroxyanisole (BHA) in food samples. Reversed micelles formed with ethyl acetate as organic solvent, dioctyl sulfosuccinate (AOT) as emulsifying agent, and phosphate buffer of pH 7.4 as aqueous phase, has been employed as the working medium. The potential applied to the tyrosinase electrode, as well as the temperature of the working reversed micelle, the percentage of aqueous phase, and the pH of the phosphate buffer solution have been optimized. The stability of the enzyme electrode with time has been also evaluated. A very good selectivity has been found with respect to potential interference from other substances commonly present in commercial antioxidant mixtures in food. An Eastman‐AQ/enzyme immobilization approach has been employed to improve the stability of the tyrosinase biosensor in reversed micelles flowing streams. A flow injection method with amperometric detection for the determination of BHA has been developed and applied to the analysis of this antioxidant in commercial biscuits.
Evaluation of a new disposable screen‐printed sensor strip for the measurement of NADH and its modification to produce a lactate biosensor employing microliter volumes
Authors: Sprules Steven D. , Hart John P. , Pittson Robin , Wring Stephen A. 
Published: May 2005

AbstractA combined sensor strip was fabricated by screen‐printing a Meldola Blue modified carbon working electrode and a Ag/AgCl combined reference/counter electrode alongside each other on a PVC substrate. This was investigated as an amperometric sensor for NADH, at an applied potential of 0 V, both in bulk solutions under hydrodynamic conditions and using 20 μL volumes without agitation. The former technique gave linear responses in the range 3–60 × 10−6mol dm−3 and the latter in the range 10−5 × 10−4 mol dm−3 of NADH. Further modification of the electrodes with NAD+ and lactate dehydrogenase converted the device to a biosensor for lactate both in spiked phosphate buffer and bovine serum. The sensors demonstrated good linear responses in the range 0–20 × 10−3 mol dm−3.
Meta1 displacement at the zinc‐diethyldithiocarbamate‐modified carbon paste electrode for the selective preconcentration and stripping analysis of mercury(II)
Authors: Khoo Soo Beng , Cai Qiantao 
Published: May 2005

AbstractA carbon paste electrode modified with zinc diethyldithiocarbamate was used for the selective accumulation of mercury(II) based on the metal displacement principle. Selectivity was achieved by exploiting differences in conditional extraction constants. After accumulation, medium exchange was performed. The accumulated HgII was then reduced to metallic mercury in 0.10 M KSCN − 0.010 M HC104 followed by differential pulse anodic stripping voltammetry in the same medium. Factors affecting the accumulation, reduction and stripping steps were systematically investigated. An optimized procedure was then developed for the determination of HgII. Under optimum conditions, a detection limit of 8.0 × 10−10 M Hg(II) was obtained for a 15 min accumulation. For 6 determinations each of 1.00 times l0−7 M and 5.00 times 10−8 M HgII, relative standard deviations were 1.5% and 3.3%, respectively. The presence of selected metal ions and other organic and inorganic substances gave no observable interferences. However, interferences were observed when 1.00 times 10−3 M NH4SCN, Na2EDTA and NH4Br were present. These interferences can be readily overcome by digesting the samples with oxidizing agents. The developed method was applied to the analysis of mercury in a U.S. Environmental Protection Agency water quality control sample and also in a human urine sample.