bluuebunny/crossref_metadata_2025_split huggingface dataset:
Redox polymers for electrocatalytic oxidation of NADH – Cationic styrene and ethylenimine polymers
Authors: Huan Zhengwei , Persson Bjórn , Gorton Lo , Sahni Suresh , Skotheim Terje , Bartlett Philip 
Published: May 2005

AbstractThe electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) by two redox polymers was evaluated from steady‐state measurements at drop‐coated solid graphite electrodes in 0.25 M phosphate buffer, pH 7.0, at 0 mV (vs. SCE). The redox polymers studied comprised a styrene polymer incorporating positive charges through quaternary amines and Toluidine Blue 0 (TBO) moieties (ST) and a branched polyethylenimine with part of its primary amine groups loaded with TBO (PE). The catalytic efficiencyjudged from the maximum NADH sensitivity for the PE polymer was estimated to be 230 μa cm.−2 mM−1 at a coverage of 40 μgcm−2 and for the ST polymer 300 μAcm−2 cmM−1 at about 100 μg cm−2. Reagentless biosensors sensing D‐glucose and L‐malate were constructed from bulk modified carbon paste containing the PE redox polymer, NAD+, polyethylenimine (PEI) and D‐glucose dehydrogenase or L‐malate dehydrogenase. The D‐glucose and L‐malate sensors were characterized in a flow injection system by apparent j′max− and K′M‐values of 230 μA cm−2 and 62mM and 3.3 μAcm−2 and 1.7mM, respectively. It was shown for glucose dehydrogenase that the presence of PEI in the paste in addition to the PE polymer, drastically improved the enzymatic conversion of glucose to gluconic acid.
Kinetics of o‐benzoquinone mediated oxidation of glucose by glucose oxidase at edge plane pyrolytic graphite electrode
Authors: Hui Tit‐Wah , Wong Kwok‐ Yin , Shiu Kwok‐Keung 
Published: May 2005

AbstractThe kinetic constants for the electrocatalytic oxidation of β‐D‐glucose by glucose oxidase in the presence of o− and p‐benzoquinone as electron mediators have been evaluated by cyclic voltammetry in pH 6–8. The rate constants for the reductive half‐reaction (reduction of glucose oxidase by β‐D‐glucose), kred, the oxidative half‐reaction (oxidation of glucose oxidase by the mediator), kox and the maximum turnover number for glucose oxidase, ko have been obtained. kox, was found to depend on the pH of the medium. At pH 7.0, kox for o‐benzoquinone and p‐benzoquinone are 6.0 × 106 and 4.7 × 105 mol−1 dm3 s−1 respectively. o‐Benzoquinone appears to be a more effective electron transfer mediator than p‐benzoquinone.
Development of a pyrroloquinoline quinone (PQQ) mediated glucose oxidase enzyme electrode for detection of glucose in fruit juice
Authors: Loughran Michael G. , Hall Jenny M. , Turner Anthony P. F. 
Published: May 2005

AbstractThe electrochemistry of pyrroloquinoline quinone (PQQ) was examined and the coupling of PQQ with glucose oxidase was studied at different pH values. Optimal interaction between PQQ and glucose oxidase was observed at pH 3.5. Results from these studies enabled construction of PQQ‐glucose oxidase‐modified enzyme electrodes for the detection of glucose in Ribena blackcurrant juice. The corresponding amperometric determination of glucose was in good agreement with results obtained using commercial enzymatic test kits supplied by Bochringer Mannheim and Sigma Diagnostics.
Electrochemical studies of lipophilic ion transport through BLM. The influence of sterols on its transport
Authors: Ding Lin , Wang Erkang 
Published: May 2005

AbstractCyclic voltammetry was employed to study the influence of sterols on the lipophilic ion transport through the BLM. The mole fraction of the sterols (cholesterol, oxidized cholesterol), as referred to total lipid, was varied in a range of 0–0.8. Data demonstrate that a thin‐layer model is suitable to this BLM system, By this model, the number of charges transported per lipophilic ion, the concentration of the ion in the membrane hulk phase and the aqueous/membrane phase partition coefficient could be calculated. These parameters proved that sterols had an obvious influence on the lipophilic ion transport. Cholesterol had a stronger influence on the ion transport than oxidized cholesterol. Its incorporation into egg lecithin membranes increased the partition coefficientβ of the ion up to more than 3‐fold. Yet, oxidized cholesterol incorporated into egg lecithin membranes only increased the β up to less than 2‐fold, and the β had no great variation at different oxidized cholesterol mole fractions. The higher β obtained was partly due to the trace amount of solvent existing in the core of the lipid bilayers. At the different sterol mole fractions, combining the change of β with the change of peak current, we also concluded that sterols had somewhat inhibiting effect on the ion transport at the higher sterols mole fraction (> 0.4). These results are explained in terms of the possible change of dipole potential of the membrane produced by sterols and the decrease of the membrane fluidity caused by the condensation effect of sterols and the thinning effect caused by sterols. The substituting group (in the oxidized cholesterol) had some inhibiting effects on the ion transport at higher mole fractions (oxidized cholesterol mole fraction > 0.4).
Flow‐injection analysis of ethanol with an alcohol dehydrogenase‐modified carbon past electrode
Authors: Lobo M. Jesus , Miranda Arturo J. , Tuñón Paulino 
Published: May 2005

AbstractAn amperometric ethanol sensor based on carbon paste, chemically modified with alcohol dehydrogenase, nicotinamide adenine dinucleotide and Toluidine Blue O as a mediator, is described. The surface of the sensor is protected by covering with a dialysis membrane. Dialysis membranes with different molecular weight cut‐off were tested for preventing leaching of soluble species from the electrode. The influence of various experimental conditions was investigated for optimum analytical performance. Linear responses for ethanol in the range 2 × 10−5 M to 2.4 × 10−4M at 0.05 V (Ag/AgCl) and a response time of 60 s were obtained. The sensor was also used in flow‐injection analysis and tested on wine samples.
Properties and applications of carbon fiber dual‐cylinder microelectrodes
Authors: Zhang Chunguang , Zhang Xueji , Yang Cheng , Zhang Wuming , Yao Bin , Zhou Xingyao 
Published: May 2005

AbstractA series of dual‐cylinder microelectrodes with different interelectrode gap were constructed with 7 μm diameter carbon fibers. The collection‐efficiency, feedback and shielding properties were studied in dctail with cyclic voltammetry and chronoamperometry for the case of the ferrocyanide(III/II) couple. The effect of the collector potential on the collection‐efficiency and the currents at the anode and cathode electrode were discussed. The application of these dual‐cylinder microelectrodes to determine the electrochemical reaction mechanism was demonstrated.
Voltammetric and amperometric studies of selected thiols and dimethyldisulfide using a screen‐printed carbon electrode modified with cobalt phthalocyanine: Studies towards a gas sensor
Authors: Napier Anca , Hart John P. 
Published: May 2005

AbstractCyclic voltammetry was used to investigate the electrochemical behavior of hydrogen sulfide, methanethiol, ethanethiol and dimethyl‐disulfide at a cobalt phthalocyanine modified screen‐printed carbon electrode (SPE) in phosphate electrolytes of different pH values. The thiols and hydrogen sulfide were found to undergo electrocatalytic oxidation while dimethyldisulfide exhibited an electrocatalytic reduction reaction. These processes were considered to involve the central cobalt(II) ion in the phthalocyanine macrocycle. The possibility of monitoring the thiols by exploiting the electrocatalytic oxidation process and DMDS by the electrocatalytic reduction process was examined by amperometry. In one approach a bulk phosphate electrolyte, pH 12.0, was employed. The amperometric behavior of the low boiling liquids ethanethiol and DMDS were studied by making standard additions to a stirred solution; both species showed rapid response times at applied potentials of +0.15 V and −0.40 V, respectively. The gaseous thiols, hydrogen sulfide and methanethiol, were examined by bubbling these through the same bulk electrolyte and again rapid, reproducible and reversible signals were obtained. In another approach a gel was prepared by adding agarose to the same phosphate electrolyte and a thin layer was deposited over the working and counter/reference electrodes of a screen‐printed strip. This sensor showed favorable electrochemical characteristics for the gaseous species examined which suggested that the device had promise as an amperometric gas sensor.
Peroxidase‐modified carbon paste microelectrode as amperometric FI‐detector for peroxides in partial aqueous media
Authors: Popescu Ionel C. , Csöregi Elisabeth , Gorton Lo 
Published: May 2005

AbstractBiosensor characteristics of peroxidase‐lactitol‐modified carbon paste microclectrodes have been evaluated in aqueous and partial aqueous media (H2O–10% v./v. CH3OH and H2O–10% v./v. CH3CN), for hydrogen peroxide and 2‐butanone peroxide amperometric detection, using a flow injection system. The activity of the investigated peroxidases (horseradish and fungal peroxidase from Arthromyces ramosus) was higher for hydrogen peroxide than for 2‐butanone peroxide, irrespective of the solvent composition. For both peroxidases, the microelectrodes' sensitivity, estimated from the slopes of the linear domains as well as calculated from the Eddie‐Hofstee plots decreased in the sequence: H2O > H2O–10% v./v. CH3CN > H2O–10% v./v. CH3OH. It is suggested that this behavior was due to the difference between the polarity and other physical properties, such as kinematic viscosity and dielectric constant of the nonaqueous solvents.
Mercury film electrodes coated with negatively charged polymer films in speciation studies of trace amounts of lead
Authors: Dam Maria E. R. , Schrøder Knut H. 
Published: May 2005

AbstractGlassy carbon electrodes modified with Nafion or poly(3‐thiopheneacetate) and subsequently plated with mercury where used for lead speciation studies in buffered (0.1 M Tris, pH 8) sodium chloride (0.6 M) solutions. The complexing agents studied were nitrilotriacetic acid, ethylenediamine, oxalic acid and the well known electrode ‘foulant’ huinic acid. Most measurements were performed with square wave anodic stripping voltammetry. Films of Nafion were spin‐coated and heat‐cured, and poly(3‐thiopheneacetate) films were produced by base hydrolysis of electropolymerized poly(ethyl 3‐thiopheneacetate). The results are, to a certain extent, supporting the permselective model which has been suggested for Nafion modified electrodes. However, they d o not allow the conclusions that negative species in general are not sensed by these ionomer coated electrodes, because the negatively charged groups of the ionomers may compete successfully for metal cations with chelating agents forming labile species. The nonlabile, negatively charged lead‐NTA, where hardly measurable at the polymer‐coated electrodes, and the lead‐oxalate complexes were also to a certain extent excluded by the ionomers. The response of the Nafion‐coated electrode to the positively charged lead‐ethylenediamine complexes was in accordance with the earlier reported permselective properties of the polymer when the literature values of the stability constant were used to calculate the lead species distribution. At the poly(3‐thiopheneacetate) film, the response to lead‐ethylenediamine complexes were higher than to the lead‐oxalate complexes, but not as high as one could have expected if charge dependent permselectivity prevailed. As a means to understand the partition of ligands between bulk solution and polymer film, stability constants for the lead complexes of these were determined at the polymer‐coated electrodes as well as at the bare mercury film electrode.
Potentiometric determination of alkaline phosphatase in blood serum using a hordenine‐sensitive membrane electrode
Authors: Katsu Takashi , Yamanaka Koji , Hiramaki Shima , Tanaka Takao , Nagamatsu Tomohisa 
Published: May 2005

AbstractA hordenine‐sensitive membrane electrode was constructed and applied for the determination of alkaline phosphatase (ALP) in blood serum. The method is based on the detection of hordenine formed by the enzymatic reaction of 4‐O‐phosphonohordenine (hordenine phosphate) with ALP. The hordenine electrode was constructed by incorporating sodium tetrakis[3,5‐bis(2‐methoxyhexafluoro‐2‐propyl)phenyl]borate as an ion‐exchanger and 2‐fluoro‐2′‐nitrodiphenyl ether as a solvent mediator in a poly(vinyl chloride) membrane matrix. This is the first attempt to apply an ion‐selective electrode for the assay of serum ALP. The results were compared with those obtained by colorimetry using phenyl phosphate as a substrate.
Entrapment of enzymes in electropolymers for biosensors and graphite felt based flow‐through enzyme reactors
Authors: Rüdel Ulrich , Geschke Oliver , Cammann Karl 
Published: May 2005

AbstractImmobilization of glucose oxidase in conducting polymers electrochemically generated from pyrrole, N‐methylpyrrole, aniline and ortho‐phenylene diamine on platinum surfaces was used to construct amperometric glucose biosensors. High sensitivity was obtained with a sensor utilizing polymerized o‐phenylene diamine as entrapment matrix. This polymer, as well as polypyrrole, was used to prepare a new type of enzyme reactors with immobilized glucose or lactate oxidase by depositing enzyme‐polymer layers on pieces of graphite felt. Mounted into a column, the felt can then be applied as an enzyme reactor in a flow system. It can either be used as working electrode itself in an electrochemical detection system or be combined with a separate detector. A microelectrode array was chosen as an example of the latter. With this system, detection limits lower than 500 μM and a linear range up to 10 mM were obtained for glucose and a detection limit lower than 50 μM and a linear range up to I mM for lactate, respectively.
Flow electroanalysis of metal alloy films: Application to the compositional assay of Copper‐Nickel alloys
Authors: Zhou Mai , Myung Noseung , Rajeshwar Krishnan 
Published: May 2005

AbstractThis article describes a flow electroanalysis (FEA) alternative to the atomic absorption spectrometry (AAS) procedure commonly employed for the compositional assay of Cu‐Ni alloy thin films. Nine alloy film samples were plated on polycrystalline Au foil by varying the deposition potential and the concentration of Cu2+ ions in the plating bath to afford alloys varying in copper content from ca. 10 % to ca. 70 % (by mass). The FEA technique is based on first chemically stripping the alloy components from the support into the flow stream. The Cu2+ ions are then analyzed by differential pulse anodic stripping voltammetry (DPASV) at a thin film mercury electrode. Since these Cu2+ ions interfere with nickel analyses by DPASV, they are removed from the flow stream at a “filter” cell containing a Hg‐coated reticulated vitreous carbon electrode. The nickel content of the alloy can then be assayed at the downstream detector cell. The data from this twin‐cell FEA procedure are compared with those obtained on the same alloy samples by the standard AAS technique.
Network simulation of the first‐ and second‐order catalytic mechanism for chronoamperometry
Authors: Horno José , García‐Hernández María T. , Castilla Juan , González‐Fernández Carlos F. 
Published: May 2005

AbstractNetwork approach is a simulation method whereby physico‐chemical systems are replaced by electrical networks and solved by applying the software package PSPICE. In order to show the explicit use of this method, the modeling and simulation of the catalytic mechanism have been carried out. The results are compared with analytical and numerical solutions of the differential equations.
Study of the reduction of palladium(II) on a mercury electrode in the presence of dimethylglyoxime
Authors: Georgieva Marija , Pihlar Boris 
Published: May 2005

AbstractThe adsorptive behavior of PdII ions in the presence of dimethylglyoxime (DMG) was investigated using voltammetric techniques. It was found that the bis‐dimethylglyoximato palladium(II) complex is adsorbed strongly between pH 3 and 5 and between the potentials 0 and −0.3 V (vs. Ag/AgCl). The peak current is proportional to the Pd‐DMG surface concentration, and increases linearly with scan rate (∂log ip/∂ν = 0.97). The adsorptive stripping response was evaluated with respect to pH, the concentration of the electrolyte, the addition of surfactants and the preconcentration potential. From the results a general scheme for the reduction process is given.
Square wave adsorptive stripping voltammetry of nickel and cobalt at wall‐jet electrodes in continuous flow
Authors: Brett Christopher M. A. , Garcia M. Beatriz Quinaz , Lima José L. F. C. 
Published: May 2005

AbstractSquare wave adsorptive stripping voltammetry (SWAdSV) of nickel and cobalt at wall‐jet electrodes in a continuous flow system has been evaluated. Characteristics and advantages relative to differential pulse adsorptive stripping voltammetry (DPAdSV) in continuous flow systems are explored. Under optimized experimental conditions, sensitivity is approximately a factor of ten higher than DPAdSV, and one‐nanomolar detection limits are achieved. Solution deoxygenation is unnecessary and sample throughput is increased.
Potentiometric determination of total and ionized calcium in osteoblast‐like cell culture medium
Authors: Morais Simone , Carvalho Graça S. , Sousa João P. 
Published: May 2005

AbstractThe effect of the ionic strength and composition of solutions in the direct potentiometric determination of total and ionized calcium content using a calcium selective electrode was investigated. In the presence of a constant complexation buffer (CCB), the addition of sodium chloride and sodium bicarbonate causes a decrease in the limit of detection of the potentiometric response. When the procedure was tested in osteoblast‐like cell culture medium no electrode interferences or method interferences were observed by the presence of proteins, i.e., the total and ionized calcium in this medium can be measured by potentiometric means.
Dipyridamole plastic membrane electrodes based on individual and mixed ion‐exchangers of dipyridamolium phosphotungstate and tetraphenylborate
Authors: Issa Yousry M. , Rizk Mahmound S. , Shoukry Adel F. , El‐Nashar Rasha M. 
Published: May 2005

AbstractDipyridamole (Dp) selective PVC membrane based on dipyridamolium phosphotungstate (Dp‐PTA), dipyridamolium tetraphenylborate (Dp‐TPB) and a mixture of both (Dp‐PTA/TPB) were prepared. The electrodes displayed a linear response over the concentration range 6.3 × 10−6–1.0 × 10−1 mol dm−3 dipyridamole hydrochloride (DpCI). The working pH ranges of the above electrodes were 2.0–7.5, 2.0–7.5 and 2.0–7.0 and their isothermal coefficients were 0.00096, 0.00010 and 0.00144 V/°C, respectively. The electrodes showed good selectivity to DpCI with respect to many inorganic cations, sugars and amino acids. Potentiometric titration and standard additions methods were used to determine DpCI in pure solutions and in pharmaceutical preparations with high accuracy and precision.
Solid‐state amperometric sensors for gas phase analytes: A review of recent advances
Authors: Alber Kathryn S. , Cox James A. , Kulesza Pawel J. 
Published: May 2005

AbstractA review is geven on solid‐state amperometric sensors designed for the detection of gaseous analytes. Attention is geven primarily to sensors used in the absence of a bulk liquid phase that have been reported in the literature since 1992, although a historical perspective is presented. The review is limited to sensors employing solid polymer electrolytes, transition metal powders, and inorganic materials prepared by sol‐gel processes as the solid‐state electrylyte. The wide applicability of solid atate sensors to gas phase species is demonstrated through numerous examples. Analytes determined include O2, H2, CO, NO2, NH3, and SO2.
Electrocatalytic reduction of hemoglobin at a chemically modified electrode containing riboflavin
Authors: Sun Wenliang , Kong Jilie , Deng And Jiaqi 
Published: May 2005

AbstractChemically modified electrode (CME) exhibting electrocatalytic response toward hemoglobin (Hb) is constructed by constructed by absorbing the riboflavin mediator onto spectroscopic graphite surface. The electron transfer between the riboflavin functionality and the graphie is fast. The surface coverage is at most 9.6 × 10−10 mol cm−10. The modified electrode permits the electroreduction of hemoglobin to take place at a low potential corresponding to the reduction potential of the mediator molecule. For neutral and slightly acidic solutions, this corresponds to very modest negative potentials (vs.Ag/AgCi). Characterization of the performance of the CME is carried out. After 30 min of continuous potential scanning of pH6.8, 60% of the original coverage remains for the CME. The linear range of the calibration plot is 30–480 μmol/L. The effect of the solution pH on the electrocatalytic activity of the CME for hemoglobin reduction is investigated. Due to its high sensitivity and durability, this CME coulde be used as an analytical sensor for detecting hemoglobin in real samples.
Square wave adsorptive stripping voltammetry of nickel(II) in flowing systems at a wall‐jet mercury film electrode plated in situ
Authors: Rocha Maria M. G. S. , Neto Maria M. P. M. , Torres Maria Odete , de Varennes Amarilis 
Published: May 2005

AbstractA rapid and highly sensitive adsorptive stripping voltammetry method for the measurement of traces of nickel(II) in flowing systems is described. The method involves a mass‐transport controlled preconcentration step, during which the NiII‐dimethylglyoxime complex is adsorbed onto an in situ plated mercury film wall‐jet electrode, followed by a reductive square wave stripping scan. The optimization of the experimental conditions and square wave parameters was carried out in order to achieve high sensitivity, reproducibility and fast response. The detection limit, restricted by the amount of nickel in the blank solution, was found to be 1.3 × 10−10 M, with a relative standard deviation of ±12.2% (n = 15), for a 1‐min accumulation time. Linear calibration plots were obtained up to 8 × 10−10 M. This method can be applied to continuous on‐line monitoring of trace levels of nickel in flowing systems, enabling easy automation.
Nickel quantification in mice organs by adsorptive cathodic stripping voltammetry using mercury microelectrodes
Authors: Pereira Maria C. , Faria Joaquim L. , Reis Maria L. , Sousa João P. 
Published: May 2005

AbstractMercury film microelectrodes (MFMs) were used to quantify trace levels of nickel accumulated in mice organs samples after dosing the mice with a physiological solution containing 150 ppm of Ni ions over a period of time, by performing adsorptive cathodic stripping square wave voltammetry (AdSWV). The residues obtained after digestion of the biological organs with nitric acid which affects the electrochemical response of Ni were investigated by XRD and IR spectrometry and found to be mainly composed by p‐nitrobenzoic acid. Electrochemical conditions for the quantification of Niwith MFMs in the biological solutions were optimized. The electrochemical data compared favorably with that obtained by atomic absorption spectrometry.
An amperometric glucose sensor with modified Langmuir–Blodgett films
Authors: Tsuji Hidehiko , Mitsubayashi Kohji 
Published: May 2005

AbstractAn output current of an amperometric glucose sensor was controlled by modifying the electric charge at a head group and the number of deposited layers of Langmuir–Blodgett films. The output current was enhanced by using a positively charged LB film, because the zeta‐potential of glucose oxidase was negative in preparing condition. The response increased proportionally to the number of deposited layers from 4 to 8. The current signal of a 16‐layer sensor, however, was lower than that of the 8‐layer one. Glucose diffusion was suppressed by the densely packed LB films. The glucose concentration was measured up to 50 mM.