bluuebunny/crossref_metadata_2025 huggingface dataset:
Potentiometric pH sensor with anthraquinonesulfonate adsorbed on glassy carbon electrodes
Authors: Shiu Kwok‐Keung , Song Fayi , Dai Hong‐Ping
Published: May 2005

Electrochemically activated glassy carbon electrodes adsorbed with anthraquinonesulfonate species showed potentiometric responses toward pH changes for pH range between 1 and 11, with a near Nernstian slope of about 56.4 mV/pH and a lifetime of more than one month. The effects of electrode pretreatment and preparation conditions, as well as the effects of interfering ions on the electrode response were studied.
Sol‐gel‐derived metal‐dispersed carbon composite amperometric biosensors
Authors: Wang Joseph , Pamidi Prasad V. A. , Park Deog Su
Published: May 2005

The advantages which accrue from the coupling of sol‐gel enzyme electrode preparation processes with the dispersion of electrocatalytic metal centers are described. In particular, ruthenium‐dispersed sol‐gel carbon thick‐film bioelectrodes couple the low‐temperature curing process with the elimination of contributions from easily oxidizable interfering species. The remarkable selectivity towards the glucose substrate is combined with a greatly enhanced sensitivity. Factors influencing the performance of these sol‐gel‐derived metal‐doped enzyme strips are discussed.
Redox reactions in the presence of an ion‐exchange/hydrogel composite film
Authors: Somasundrum Mithran , Bannister Joe V.
Published: May 2005

The formation of a composite ion‐exchange/hydrogel membrane using a mixture of Nafion and poly(vinyl alcohol), is described. The structure of the composite is investigated by following the cyclic voltammetry of anionic redox couples present in bulk solution, and by following the diffusional characteristics of cationic redox couples entrapped within the films. Hydrophobic redox species exhibit greater rates of diffusion within the composite films than within films of homogeneous Nafion. The films show greater resistance to protein adsorption than cellulose acetate or poly(carbonate). Electrical communication between co‐immobilized enzyme (glucose oxidase) and hydrophobic mediator is demonstrated.
Voltammetric study of chiral active compound 4,4′‐diisopropyl‐2,2′‐thiazoline and its interaction with copper(II)
Authors: Mlakar Marina , Čuljak Ivan , Daković Senka , Branica Marko
Published: May 2005

The electrochemical investigation of the chiral active compound, (4S)‐4‐diisopropyl‐2‐2′‐bithiazoline (DPT), commonly used in asymmetric syntheses as well as in diastereoselective reactions, and its interaction with copper(II) ion by cathodic stripping voltammetry at a HMDE electrode, was performed. DPT reduction occurs in two steps, at potentials about −0.2 and −0.45V (vs. Ag/AgCl), through the formation of an electrodeposited layer of DPT‐Hg at the electrode surface. DPT complex with copper(II) is reduced at about −0.36 V, through the formation of DPT‐Cu deposit at the electrode surface. The reduction process of DPT‐Hg and DPT‐Cu complex, as well as DPT, depend upon pH, on the electrolyte solution, as well as on the concentration and ratio of the ligand and metal ion. The mechanisms of those electrode processes were investigated. Due to their strong adsorption, low concentration levels of DPT, through DPT‐Hg complex reduction, and copper, through DPT‐Cu complex reduction, about 10−9 M, can be determined, with the accumulation time of 10 minutes at 0.0 V (vs. Ag/AgCl), at pH 2.8 in 0.55 M NaCl.
Detection of hydrogen peroxide and other molecules of biologicl importance at an electrocataltic surface on a carbon fiber microelectrode
Authors: Nowall Wilbur B. , Kuhr Werner G.
Published: May 2005

The electrocatalytic oxidation of hydrogen peroxide in solution at a modified carbon fiber electrode has been investigated. A simple electrochemical procedure has been developed to dramatically improve the voltammetry for the peroxide, NADH, and several other species under steady state and fast scan voltammetry. The surface is generated by the electrochemical oxidation of NASH followed by exposure to peroxide. This procedure yields a surface which is sensitive to peroxide and stable in air for more than 90 days. This oxidation occurs at a potential such that it is easily discriminated from the analytes tested in this study.
Diffusion coefficients of gallium(III) in potassium nitrate and potassium chloride supporting electrolytes
Authors: Kariuki Stephen , Dewald Howard D.
Published: May 2005

The diffusion coefficient values of GaIII in potassium nitrate and potassium chloride supporting electrolytes have been obtained polarographically. The half‐wave potential, E1/2, and E3/4‐E1/4 values have also been determined. The E3/4 ‐ E1/4 values confirm the irreversibility of GaIII reduction in KNO3 and KCl electrolytes.
Use of neural networks in solving interferences caused by formation of intermetallic compounds in anodic stripping voltammetry
Authors: Lastres Ernesto , de Armas Graciela , Catasüs Miguel , Alpízar Jesüs , García Luciano , Cerdà Víctor
Published: May 2005

Neural networks (NNs) were used to overcome interferences by formation of intermetallic compounds in anodic stripping voltammetry (ASV). The software developed for this purpose allows one to construct NNs of virtually any type of architecture and train it automatically using the back‐propagation method. The ability of NNs for addressing interferences arising from interactions with the hanging mercury drop electrode is demonstrated for the Cu–Zn binary system.
Calix[4]Arenes in the partial cone conformation as ionophores in silver ion‐selective electrodes
Authors: O'Connor Katherine M. , Henderson William , O'Neill Eva , Arrigan Damien W. M. , Harris Stephen J. , McKervey M. Anthony , Svehla Gyula
Published: May 2005

Two calix[4]arene derivatives, in the partial cone conformation, with sulfur‐containing functionalities, were tested as neutral carrier ionophores in potentiometric silver‐selective electrodes of conventional membrane and membrane‐coated glassy carbon electrode types. Comparison with a calix[4]arene in the cone conformation was made. The membranes were prepared using either 2‐nitrophenyl octyl ether or bis(ethylhexyl)sebacate as plasticizers and potassium tetrakis(p‐chlorophenyl)borate as the lipophilic salt in a poly(vinyl chloride) matrix. Both calix[4]arenes yielded electrodes of good sensitivity (approx. 47 mV dec−1) in the range 10−4–10−1 M and excellent selectivity [log KAg,MH+ < −1.5] of transition, alkali and heavy metal cations, including sodium, mercury(II) and lead(II) cations. Temperature effects and reproducibility of response were determined and the interfering effects of mercury(II) and lead (II) ions on the membranes were noted. The partial cone conformation allows improved selectivity over certain cations relative to calix[4]arenes in the cone conformation.
The determination of copper at thin film electrodes by constant current stripping potentiometry
Authors: Bradshaw Mark P. , Scollary Geoffrey R.
Published: May 2005

A comparison of the determination of copper by constant current stripping potentiometry (CCSP) at mercury and gold films has been carried out. The preferred solution conditions for the mercury film study were determined to be 0.1M ammonium acetate at pH 4.5 and 0.1M HCl for the gold film study. The influence of chloride on the stripping signal was investigated and it was found that for the mercury film conditions, well‐formed stripping signals could be obtained up to a chloride concentration of 0.5 M which permitted the ready determination of copper in seawater. With the gold film, high chloride concentrations affected both the film stability and the glassy carbon surface and repeatable results were difficult to obtain. The optimized CCSP methods were applied to various aqueous samples including tap water, seawater, TCLP (acetic acid) extracts as well as TCLP extracts using groundwater and ocean water. Based on the results obtained for these various matrices, it was concluded that there are several advantages favoring the mercury film. The interference from organic components in the sample matrix on the general applicability of CCSP for the determination of copper at either a mercury or gold film is discussed.
Electroreduction of some pyridine carboxamides on carbon electrodes in aqueous solutions
Authors: Angulo Matiide , Montoya Mercedes Ruiz , Galvin Rafael Marin , Mellado José Miguel Rodriguez
Published: May 2005

The electroreductions of the NAD+ model compounds nicotinamide (I), N1‐methyl nicotinamide (II), N′‐methyl nicotinamide (III) and isonicotinamide (IV) on carbon electrodes have been studied in aqueous media in the pH range 0–12 by linear‐sweep cyclic voltammetry (Scheme 1, I‐IV). Logarithmic analyses of the reduction peaks were performed by computing the convolution of the current with time as a function of the potential. On the basis of the experimental results it was concluded that the irreversibility of the electron transfers increased when a glassy carbon electrode was used, and this irreversibility being more marked when a plastic formed carbon electrode was employed. The reduction processes occurred with more difficulty on carbon electrodes than on mercury electrodes. Both the reduction and the reoxidation (when occurred) processes changed with respect to those observed on mercury electrodes, being irreversible electron transfers the rate‐determining steps in most cases. Thus, for compounds I, II and III at pH < 2 the reductions occurred by the uptake of two electrons and two H+ ions, and the rate determining step was found to be the first one‐electron transfer, for I and III, and the irreversible second electron transfer, preceded by the uptake of an H+ ion, for II. At pH>3 the processes consisted of electrodimerization reactions, preceded by the protonation of the heterocyclic nitrogen in cases I and III. The second electron transfer of the electroreduction of IV always appeared irreversible, in contrast with that found for mercury electrodes.
Electroanalysis in flowing systems – the propagation of depletion effects downstream of a channel micro‐band electrode
Authors: Bidwell Matthew J. , Alden John A. , Compton Richard G.
Published: May 2005

Analytical and numerical methods are used to establish concentration distributions around channel microband electrodes both in isolation and as part of multi‐electrode arrays. The importance of axial diffusion in addition to convection and diffusion normal to the electrode surface is stressed. In particular, downstream depletion effects are shown to occur over many electrode lengths, so that the diffusion fields of electrodes within arrays overlap and interfere. A simple analytical expression is derived to describe this depletion and permits the design of practical arrays in which electrodes operate essentially independently of each other.
Electrochemical sensing of gases based on liquid collection interfaces
Authors: Huang Huiliang , Dasgupta Purnendu K.
Published: May 2005

Although many electrochemical gas sensors have been reported, electrochemical gas sensors based on liquid collection constitute a smaller subset. Minimally, a liquid interface based electrochemical gas sensor is composed of two electrodes and an ion conducting electrolyte. There is a large number of possible arrangements of these parts, and many choices exist for their composition and preparation methods. This results in a diverse and rich technology now available for gas sensing. The measurement of some analyte gases of interest, notably ozone, nitrogen oxides, hydrogen peroxide, formaldehyde, ammonia, sulfur dioxide and hydrogen sulfide are specifically discussed. Finally, the recent reviews that are likely to be the most relevant to the further development of electrochemical detection approaches for gases with a liquid collection interface are cited and discussed.
Dimethylglyoxime doped sol‐gel carbon composite voltammetric sensor for trace nickel
Authors: Wang Joseph , Pamidi Prasad V. A. , Nascimento Valberes B. , Angnes Lucio
Published: May 2005

A new class of modified sol‐gel carbon composite electrodes, based on the encapsulation of complexing ligands, is described. Such modified electrodes couple the versatility and tunability of sol‐gel processes with the advantages of the preconcentration/voltammetric strategy. The incorporation of the ligand dimethylglyoxime (DMG) within the carbon‐silicate ceramic network is used to illustrate the new concept in connection with the voltammetric sensing of trace nickel. The sol‐gel carbon composite serves as a favorable host matrix for DMG, which retains its nickel binding characteristics. Factors influencing the sensor response, including the sol‐gel hydrolysis time, DMG loading or preconcentration time are explored. The electrode displays good linearity up to 800 μg/L nickel, a detection limit of 15 μg/L (following a 5 min accumulation), and a relative standard deviation of 7.7%. Applicability to assays of river water is illustrated. Doping of other ligands into sol‐gel carbon composites should result in similar voltammetric sensors for other important metals.
Experimental and calculated complex formation curves as an optimization tool in speciation studies of polarographically labile metal‐ligand systems
Authors: Cukrowski Ignacy
Published: May 2005

The PbII‐N,N′‐di‐2‐picolylethylenediamine (DPA‐2) system was studied by differential pulse polarography (DPP) and glass electrode potentiometry (GEP) at fixed total‐ligand to total‐metal concentration ratio and varied pH. The polarographic experimental complex formation curve (ECFC) and calculated complex formation curve (CCFC) are used for modeling of a metal‐ligand system and the refinement of stability constants. The ECFC is used instead of a shift in the peak potential plotted vs. pH and it appears to be a characteristic function for a particular metalligand system. The CCFC is a theoretical curve calculated for the assumed metal‐ligand model from mass‐balance equations. The final model of metal species formed is the one which is accepted by these two experimental techniques and for which stability constants of metal complexes obtained from DPP and GEP differ the least. Four lead complexes Pb(HL), PbL, PbL2(OH) and PbL(OH)2 and their stability constants as log β found from DPP 12.67 ± 0.08, 9.68 ± 0.07, 16.12 ± 0.08 and 14.88 ± 0.06, respectively, are reported. Results obtained from GEP and DPP differ only within experimental errors typical for these techniques.
Anodic stripping voltammetry at hydrodynamic mercury thin film electrodes. Numerical simulation of stripping peaks for reversible processes at uniformly accessible electrodes
Authors: Ball Jon C. , Compton Richard G.
Published: May 2005

The time dependent backwards implicit method is used to simulate the shape and position of the stripping peaks in DC (linear scan) anodic stripping voltammetry at mercury thin film hydrodynamic electrodes for electrochemically reversible systems. The effect of variable diffusion layer thickness, assumed uniform and experimentally controllable in the case of rotating disk systems, in influencing both the peak potential and peak shape, is quantified and the implications for anodic stripping voltammetry under convective conditions noted.
Determination of adenine and guanine by capillary zone electrophoresis with end‐column amperometric detection at a carbon fiber microdisk array electrode
Authors: Jin Wenrui , Wei Huiying , Zhao Xin
Published: May 2005

Capillary zone electrophoresis was employed to the analysis of adenine and guanine by using end‐column amperometric detector with a carbon fiber microdisk array electrode. Optimum conditions of separation and detection are 0.01 mol/L H3PO4–0.01 mol/L H3BO3–0.01 mol/L HAc‐NaOH (pH 9.2) for the buffer solution, 20 kV for the separation voltage, 3.0 kV and 5 s for injection voltage and time, respectively, and 1.00 V (vs.SCE) for the detection potential. The limit of detection is 8.2 fmol for adenine and 2.9 fmol for guanine (S/N = 2). The method was applied to determination of adenine and guanine in hydrolytic product of yeast‐RNA and calf thymus‐DNA.
Determination of trace vanadium in various waters by differential pulse adsorptive stripping voltammetry
Authors: Rao K. Sreenivasa , Palrecha M. M. , Dhaneshwar R. G.
Published: May 2005

A sensitive voltammetric method is developed for the determination of trace amounts of vanadium in various water samples. The method is based on the preconcentration of the VV‐2‐(5‐bromo‐2‐pyridylazo)‐5‐diethylaminophenol (5‐Br‐PADAP) complex at a potential of −0.5 V (vs. Ag/AgCl). The adsorbed complex is then reduced, producing a response with a peak potential of −0.8 V. The catalytic action of bromate ions on the reduction of the VV‐5‐Br‐PADAP complex has also been investigated. The high catalytic currents obtained in presence of bromate ions are taken advantage of enhancing the sensitivity of the method. From the preliminary studies the optimal conditions for the determination of vanadium by differential pulse adsorptive stripping voltammetry have been established. The interference of various elements in this method has also been studied. The method of standard addition is employed in evaluating the concentration of vanadium in water samples. The determination limit is 20 ng/L and the RSD is 12% for vanadium concentrations of 500 ng/L.
Potentiometric detection of metal ions separated by liquid chromatography using a tungsten oxide electrode
Authors: Chen Zuliang , Alexander Peter W.
Published: May 2005

The use of a tungsten oxide sensor for the potentiometric detection of metal ions separated by liquid chromatography is described. Separation of metal ions such as Fe3+, Fe2+, Cu2+ and Pb2+ was performed by ion chromatography using a mobile phase containing 25 mM sodium tartrate/2 mM ethylenediamine at pH 3.8. Calibration plots were linear in the range 0.5 to 3.5 mM. Potentiometric detection was also applied to ion‐interaction chromatography. The results showed that separation of metal ions was improved and the detection limits for the test metals in the range of 0.5–5 nmol were obtained in the presence of sodium citrate/1‐octanesulfonic acid at pH 3.0. The potentiometric detection described in this article is shown to have advantages in terms of low cost, simplicity and sensitivity.
Electrocatalytic activity of a C60‐γ‐cyclodextrin (1:1) and nafion chemically modified electrode to hemoglobin
Authors: Li Mei‐Xian , Li Nan‐Qiang , Gu Zhen‐Nan , Zhou Xi‐Huang , Sun Yi‐Liang , Wu Yong‐Qing
Published: May 2005

The electrochemical behavior of films of C60‐γ‐cyclodextrin (1:1) and Nafion has been studied in an aqueous solution. A reversible surface‐confined one‐electron‐transfer electroreduction wave was detected by cyclic voltammetry. The CME displayed electrocatalytic activity to hemoglobin in a 0.10 M KCl solution.
Electropolymerization of amphiphilic monomers for designing amperometric biosensors
Authors: Cosnier Serge
Published: May 2005

The principle and potentialities of an original electrochemical procedure of biosensor construction based on amphiphilic pyrrole derivatives are reviewed. The two‐step procedure consists of the adsorption of an aqueous amphiphilic pyrrole monomers–biomolecule mixture on an electrode surface followed by the electrochemical polymerization of the adsorbed amphiphilic monomers. This method is compared with the more conventionally used electrochemical procedures of biosensor construction. Examples of multienzyme and additive entrapments, organic phase enzyme electrode, microelectrode functionalization and the electrical wiring of immobilized enzymes are presented.
Potentiometric response behavior of parallel arrays of cation‐ and anion‐selective membrane electrodes as reference devices
Authors: Morf Werner E. , de Rooij Nicolaas F.
Published: May 2005

The potential response of reference devices consisting of parallel arrays of cation‐ and anion‐selective membrane electrodes is studied on a theoretical basis. A general treatment of the overall electric potential difference is offered that accounts for contributions by diffusion potentials, boundary potentials, ohmic potential drops, and streaming potentials. Explicit solutions are given for special cases. The treatment makes it possible to recognize the capabilities and the limitations of membrane‐based reference devices, and to compare their performance with the behavior of conventional reference electrodes using liquid‐junction contacts. The applicability of membrane‐based reference systems is found to be restricted to relatively specific samples.
Diphenhydramine‐selective plastic membrane sensor and its pharmaceutical applications
Authors: Erdem Arzum , Ozsoz Mehmet , Kirilmaz Levent , Kilinc Emrah , Dalbasti Tayfun
Published: May 2005

Different types of PVC‐matrix ion‐selective electrodes (ISEs) that respond to the cationic form of diphenhydramine (Dph) are described. Three ion‐pairing agents, namely tetraphenylborate (TPB), phosphotungstate (PT), reineckate (RN) are investigated. The best PVC polymeric membrane contains Dph‐TPB as active material. The electrode, based on the ion‐pair complex with TPB anion shows near‐Nernstian response in the concentration range 10−2 to 3.5 × 10−5 M (Dph.HCl). Changing pH within the range 2.0–7.5 did not affect the electrode performance. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coeffcient of the electrode (0.00156 V/°C) The electrode showed a good selectivity for Dph with respect to a large number of inorganic and organic cations. The standard addition method and potentiometric titration were applied to determine Dph amounts in pharmaceutical preparations. The Dph selective membrane electrode was also applied to the determination of the dissolution profile of Dph tablets. The dissolution results were compared with spectrophotometrically determined ones.
Microdialysis fiber enzyme electrode involving amplification by substrate recycling
Authors: Yao Toshio , Suzuki Seita , Nishino Hirohito , Nakahara Taketoshi
Published: May 2005

A microdialysis fiber electrode involving amplification for the NAD+/NADH couple is described. The electrode contains glucose‐6‐phosphate dehydrogenase, lactate dehydrogenase and lactate oxidase held stationary within its cavity, with a platinum fiber coated with poly(1,2‐diaminobenzene) film as a working electrode and a silver/silver chloride fiber as a reference electrode. Both NAD+ and NADH are recycled enzymatically in the presence of an excess of glucose‐6‐phosphate and pyruvate in the measuring buffer solution. As a result, a large amount of L‐lactate produced in the electrode cavity is converted to pyruvate to produce hydrogen peroxide, which can be detected ampero metrically at the platinum fiber with a size‐exclusion film. Both NAD+ and NADH were detected with a 25‐fold increase in sensitivity compared with the unamplified responses. The detection limit was 1 × 10−7 M.
Acetylcholine minisensor based on metal‐supported lipid bilayers for determination of environmental pollutants
Authors: Rehák M. , Šnejdárková M. , Hianik T.
Published: May 2005

Immobilization of avidin‐modified acetylcholinesterase and choline oxidase (A‐COxACE) on a metal supported biotinylated membrane allowed us to developed a minisensor based on changes in anticholinesterase activity by several environmental pollutants. The concentrations of acetylcholine and choline have been determined amperometrically on the basis of anodic oxidation of hydrogen peroxide, a product of choline oxidase. The immobilization of the complex A COxACE was controlled by the electrostriction method which allowus to determine changes of membrane capacitance C and elasticity modulus E⟂ in a direction perpendicular to the s‐BLM surface. The binding of the A‐COxACE complex to s‐BLM resulted in a decrease of C and in an increase of E⟂ suggesting increase in the membrane ordering. Using the simple amperometric method we were able to use this minisensor for detection of acetylcholine and choline. Detection limits were 0.79 mM and 1.25 mM for acetylcholine and choline, respectively. The biosensor was tested for acetylcholinesterase inhibition in the presence of organophosphorus Trichlorphon and eserine.
Electrochemical behavior of H2O2 on gold
Authors: Gerlache Marc , Senturk ZÜHre , Quarin Guy , Kauffmann Jean‐Michel
Published: May 2005

Cyclic voltammetric studies of hydrogen peroxide on a polycrystalline gold electrode have permitted to point out that the oxidation of the molecule may occur at two distinct potentials depending on the sample composition and cleanliness and on the redox state of the electrode. At a clean gold surface, the oxidation of hydrogen peroxide gives only one wave at +490 mV (vs. Ag/AgCl) at pH 7.4, besides the gold oxidation wave at +820 mV. Species in solution which adsorb readily on gold (trace impurities originating because of sonication or solution stirring), gold oxide and acidic pH values, inhibit this wave and oxidation of hydrogen peroxide is occurring at a higher potential, i.e., +870 mV in phosphate buffer pH 7.4. Cyclic voltammograms show these two waves, depending on the degree of inhibition of hydrogen peroxide. At oxidized gold electrodes or contaminated by surface active species, oxidation of hydrogen peroxide gives only one wave at +870 mV. From these data it may be inferred that hydroxy species adsorbed on clean gold favor the formation of the first wave. Both waves may be advantageously exploited for quantitative purpose. The latter is not affected by surface active species and permits quantification of hydrogen peroxide down to 20 μM with a detection limit of 4 μM.
β‐cyclodextrin and carboxymethylated β‐cyclodextrin polymer film modified electrodes, hosting cobalt porphyrins, as sensors for electrocatalytic determination of oxygen dissolved in solution
Authors: D'Souza Francis , Hsieh Yi‐Ying , Wickman Heang , Kutner Wlodzimierz
Published: May 2005

New oxygen sensors, based on polymer film modified electrodes, were prepared and applied for electrocatalytic determination of dioxygen dissolved both in aqueous and aqueous‐organic, mixed solvent solutions. The sensors were made of gold electrodes coated with thin polymer film matrices of either neutral β‐cyclodextrin polymer, β‐CDP, or cation‐exchange carboxymethylated β‐cyclodextrin polymer, β‐CDPA, hosting electrocatalytically active centes of cobalt tetraphenylporphyrin, (TPP)Co, cobalt tetrakis‐(N‐methylpyridyl)porphyrin, (TMPyP)Co, or cobalt tetrakis‐(4‐sulfonatophenyl)porphyrin, (TPPS)Co. Films were cast from aqueous solutions of the respective β‐cyclodextrin prepolymer, cobalt porphyrin and glutaric dialdehyde used as the polycondensation crosslinking reagent. Catalytic dioxygen electroreduction at the electrode coated with polymer film hosting the cobalt porphyrin catalyst involves two electrons and two protons resulting in the formation of hydrogen peroxide. The sensitivity of dioxygen determination largely increases in the order (TPPS)Co <(TPP)Co<(TMPyP) Co for the β‐CDPA film electrodes, being governed by ion‐exchange equilibria with respect to the cobalt porphyrin catalyst, while it depends only slightly on the nature of the cobalt porphyrin catalyst for the β‐CDP film. The catalytic rate constant of the dioxygen reaction with the cobalt porphyrin catalyst in the film was estimated as k ≈︁ 2 × 104 M−1 s−1 being larger than those for either adsorbed or electropolymerized catalyst at the electrode and close to that for the catalyst present in solution. The performance of the sensors is presented with respect to the detection signal linearity, reproducibility, long‐term stability, reversibility regarding dioxygen binding and response time.
Hydrocarbon pasting liquids for improved tyrosinase‐based carbon‐paste phenol biosensors
Authors: Wang Joseph , Lu Fang , Kane Stephen A. , Choi Yong‐Kook , Smyth Malcolm R. , Rogers Kim
Published: May 2005

Short‐chain hydrocarbons are used as pasting liquids in carbon‐paste tyrosinase amperometric biosensors. The response of the phenolic substrates decreases rapidly upon increasing the chain length of the hydrocarbon binder from C10 to C14, and then it levels off to a size similar to that of the mineral oil biosensor. For example, the dodecane‐based enzyme electrode offers a 17.8‐fold signal enhancement compared to the mineral‐oil one. Such sensitivity enhancements are attributed to the extractive accumulation of the phenolic substrates. The change in the carbon‐paste binder influences also the selectivity of the tyrosinase electrode and the Km, app values. Flow‐injection analysis yields a detection limit of 6 nM catechol and a relative standard deviation of 2.5% (n = 30). A dual enzyme electrode chromatographic detection, based on the use of different pasting liquids, provides unique characterization of the phenolic substrates. The merits of this strategy are illustrated in connection with a river water sample.
Graphite‐teflon‐peroxidase composite electrodes. Application to the direct determination of glucose in musts and wines
Authors: del Cerro Maria Antonia , Cayuela Gabriela , Reviejo A. Julio , Pingarrón Jose M. , Wang Joseph
Published: May 2005

The performance of graphite‐70%Teflon‐peroxidase‐ferrocene composite electrodes, fabricated by simple physical inclusion of the enzyme and the mediator into the bulk of a graphite‐Teflon matrix, by using both batch and flow‐injection modes, is reported. The electrode responds very rapidly to changes in H2O2concentration due to the absence of a membrane barrier on the electrode surface and of a covalent attachment of the enzyme to graphite. The composite enzyme electrode showed a long‐term operation due to the renewability of its surface by polishing. Reproducible amperometric responses were achieved with different electrodes fabricated from different composite matrices, and no significant loss of the enzyme activity was observed after seven months of dry‐storage at 4°C. A bienzymatic graphite‐70%Teflon‐peroxidase‐glucose oxidase‐ferrocene electrode has been developed, too, showing a rapid response to the changes in the glucose concentration. The stability of the bienzymatic composite electrode was similar to that of the peroxidase biosensor. This biosensor was applied to the determination of glucose in must and wine samples by batch amperometry and flow injection with amperometric detection modes.
Development of a sol‐gel enzyme inhibition‐based amperometric biosensor for cyanide
Authors: Park Tae‐Myung , Iwuoha Emmanuel I. , Smyth Malcolm R.
Published: May 2005

An amperometric sol‐gel‐based enzyme inhibition electrode for the detection of low levels of cyanice was constructed by immobilizing horseradish peroxidase (HRP) and an osmium redox polymer ([Os(bpy)2(PVP)10Cl]Cl; abbreviated Os‐polymer) as mediator. Upon addition of hydrogen peroxide to the solution, a bioelectrocatalytic reduction wave was observed, which was diffusion controlled. This reduction current is subsequently inhibited by cyanide. The steady‐state hydrogen peroxide catalytic reduction current reached a plateau at 150 mV (vs. Ag/AgCl) and cyanide could be determined amperometrically with good sensitivity at 0mV (vs. Ag/AgCl). The concentration range of linear response, apparent inhibition constant (K), and detection limit were 0.004–0.04 mM, 0.0637 mM, and 0.5 μM, respectively. Sodium azide, potassium thiocyanide and thiourea were all found not to interfere at this potential. The biosensor was found to be stable for over 1 week on storage at room temperature.
The application of cholinesterase potentiometric biosensor for preliminary screening of the toxicity of waste waters
Authors: Evtugyn G. A. , Rizaeva E. P. , Stoikova E. E. , Latipova V. Z. , Budnikov H. C.
Published: May 2005

The application of cholinesterase biosensor for preliminary testing of total pollution of domestic and industrial discharges has been investigated. The results indicate that biosensor‐based testing is more sensitive than paramecia bioassay. For numerous samples tested, the inhibition degree of biosensor response exceeds the appropriate value of acute toxicity on Paramecium caudatum. Electrochemical oxidation of the samples, before the biosensor testing readily removes oxidizable compounds which do not effect a real risk of environmental pollution. Simultaneous determination of inhibitory effect, acute toxicity and biochemical (chemical) oxygen demand makes it possible to infer a possible source of contamination of waters.
Ascorbate sensor based on ‘self‐doped’ polyaniline
Authors: Zhou Dong‐Mei , Xu Jing‐Juan , Chen Hong‐Yuan , Fang Hui‐Qun
Published: May 2005

Self‐doped polyaniline modified electrodes were successfully fabricated by copolymerization of aniline and m‐aminobenzoic acid in 0.5 mol L−1 sulfuric acid. The electrochemical characteristics of this resulting polymer were investigated. The polymer displayed electrochemical activity with the formal potential of 50 mV in pH 7.0 buffer solution. Also, such ‘self‐doped’ polyaniline was rather stable for a long‐term use. Ascorbate was electrocatalytically oxidized at these ‘self‐doped’ polymer‐modified electrodes. The effect of pH on the catalysis of ascorbate was explored. By constant potential method, such polymer was also deposited on a dual platinum disk electrode with a gap of 10 μm. The dependence of the film conductivity on the potential, which showed a peak‐shaped curve, was obtained. The device also showed a fast off‐on response sensitive to ascorbate with a linearity up to 6.0 × 10−3mol L−1 (correlation coefficient 0.996).
Correlation between the redox potentials of 9‐substituted anthracenes and the results of PM3 calculation
Authors: Okazaki Satoshi , Oyarna Munetaka , Nomura Satoshi
Published: May 2005

The formal redox potentials of 9‐substituted anthracenes (9XA) were measured by means of a fast scan cyclic voltammetry (FSCV) with a microelectrode. Because the FSCV depresses the influence of subsequent fast reactions, the redox potentials could be measured for a series of substituents in both the oxidation and the reduction processes. The correlation of the redox potentials with the results of molecular orbital calculations were demonstrated, in particular with the PM3 method. The plots of the redox potential versus the energy difference between the redox states gave better correlat on than those versus the energy levels of the HOMO and LUMO.
Photo‐cured ammonium and hydrogen ion selective coated‐wire electrodes used simultaneously in a portable battery‐powered flow injection analyzer
Authors: Alexander Peter W. , Dimitrakopoulos Telis , Hibbert D. Brynn
Published: May 2005

Nonactin and N,N‐dioctadecylmethylamine ionophores, each in an epoxydiacrylate polymer, were photo‐cured on silver wires (0.8 mm i.d.) and evaluated as ammonium and hydrogen (pH) coated wire electrodes. The photo‐cured membranes prepared in this study exhibited excellent adhesion to the metal substrate and improved mechanical strength compared to PVC based membranes. The ammonium electrode exhibited a Nernstian response over a concentration range between 0.01 mM and 100 mM with a detection limit of 0.0005 mM. The ammonium electrode exhibited improved selectivity against most common interfering ions, including potassium compared to previous studies. The hydrogen selective electrode exhibited a near‐Nernstian slope of 55.9 ± 0.8 mV change/log a between pH 4.0 and pH 11.0 in the steady‐state mode. The ammonium and pH sensors each responded quickly reaching 90% of steady‐state value in < 5 s, making these coated wire sensors ideal for flow injection potentiometry measurements. In the FIP mode, both the photo‐cured ammonium and pH electrodes exhibited near‐Nernstian responses of 49.2 ± 1.0 mV change/activity decade and 50.2 ± 0.4 mV change/log a, respectively, over a similar concentration range as in the steady‐state mode. The photo‐cured ammonium and pH electrodes were used simultaneously in the analysis of hydroponic nutrient solutions and waste water samples obtained from a local greenhouse grower in the flow injection potentiometric mode.
Screen‐printed voltammetric sensors for 2‐furaldehyde based on nickel‐modified and amalgam‐stabilized mercury‐coated carbon inks
Authors: Slater Jonathan M. , Dilleen John W.
Published: May 2005

This article describes a general method for stabilizing microdroplets of mercury on thick‐film screen printed electrodes (SPEs). Electrodes modified with nickel metal powder are compared with amalgam stabilized mercury SPEs. Application of the electrodes to the measurement of organic materials is demonstrated by the electrochemical determination of 2‐furaldehyde, a marker for power transformer condition monitoring. The electrodes were characterized by cyclic voltammetry and subsequently a square‐wave voltammetric method was used to extend the detection limit of the measurement. The resulting cathodic currents for the reduction of 2‐furaldehyde was proportional to the concentration of 2‐furaldehyde. Plots of 2‐furaldehyde concentration against response at a nickel‐modified carbon SPE gave linear regions for concentrations in the range 3.7–14.3 ppm (regression equation; Y = 0.99 + 0.15x,r = 0.999, n = 3), and linear regions at mercury‐coated silver‐modified carbon SPEs in the range 8.9–36.4 ppm (regression equation; Y = 1.71 + 0.14x,r = 0.999, n = 3) and in the range 0.9–8.9 ppm (regression equation; Y = 1.34 + 0.17x,r = 0.980, n = 3), respectively. A particular advantage of using the mercury‐modified SPE rather than the nickel‐modified base card is that the well‐defined electrochemistry of furan derivatives allow them to be individually distinguished. The half‐wave potentials at the mercury SPE for 2‐furaldehyde (E1/2 = −1.15 V vs. Ag/AgCl) and two possible interferents 2‐acetyl‐furan and 5‐methyl‐2‐furaldehyde (E1/2 = −1.2 and −1.31 V vs. Ag/AgCl) are sufficiently well separated to allow the individual components to be resolved whereas at a nickel‐modified SPE a combined signal is observed.
Electrochemistry of hemoglobin at modified silver electrodes is not a redox‐process of iron protoporphyrin IX
Authors: Katterle Martin , Wollenberger Ulla , Scheller Frieder W.
Published: May 2005

The direct heterogenous electron transfer between hemoglobin and modified silver and gold electrodes has been investigated using cyclic voltammetry. Cathodic and anodic peak currents have been obtained for hemoglobin, methemoglobin, carbonylhemoglobin, cyanohemoglobin and oxyhemoglobin, as well as for apohemoglobin and bovine serum albumin, exclusively at modified silver electrodes at potentials around 70 and 270 mV (vs. Ag/AgCl). The results demonstrate that the observed redox chemistry was not a result of direct electron transfer to the redox centre protoporphyrin IX. Spectrometrical measurements were made to substantiate this conclusion. A possible reaction mechanism which takes place at the modified silver electrode is suggested.
Digital simulation of potential step experiments using the extrapolation method
Authors: Strutwolf JÖRg , Schoeller Wolfgang W.
Published: May 2005

For large values of the model diffusion coefficient the Crank‐Nicolson scheme produces poor numerical results, if it is used for the simulation of a potential step experiment. On the other hand the Backward Euler or fully implicit scheme, not suffering from this drawback, is of lower accuracy. We apply the extrapolation method introduced by Morris et al. to the simulation of Cottrellian diffusion and to a simple catalytic mechanism. The extrapolation method, does not show the oscillating behavior of numerical solutions and is of higher accuracy than the fully implicit scheme. Comparison to other implicit difference schemes are presented. The extrapolation schemes show superior results for the diffusional problem and for the short time behavior of the catalytic mechanism.
The problem of complex curves in normal pulse polarography
Authors: Sanecki Przemysław , Lechowicz Jaromir
Published: May 2005

Two types of complex curves are discussed: (I) those obtained for binary mixtures of substances redcing at similar potentials and (II) those corresponding to the two‐electron consecutive processes: O → Z → R and O ⇌ Z → R. A convenient procedure of curve fitting for the above two cases of complex normal pulse polarographic (NPP) curves is presented and applied for some two‐electron consecutive electroreductions.
Temporal profiles of neuronal degeneration, glial proliferation, and cell death in hNFL(+/+) and NFL(−/−)mice
Authors: McLean Jesse R. , Sanelli Teresa R. , Leystra‐Lantz Cheryl , He Bei Ping , Strong Michael J.
Published: May 2005

Neurofilament (NF) aggregate formation within motor neurons is a pathological hallmark of both the sporadic and familial forms of amyotrophic lateral sclerosis (ALS). The relationship between aggregate formation and both microglial and astrocytic proliferation, as well as additional neuropathological features of ALS, is unknown. To examine this, we have used transgenic mice that develop NF aggregates, through either a lack of the low‐molecular‐weight NF subunit [NFL (−/−)] or the overexpression of human NFL [hNFL (+/+)]. Transgenic and wild‐type C57bl/6 mice were examined from 1 month to 18 months of age, and the temporal pattern of motor neuron degeneration, microglial and astrocytic proliferation, and heat shock protein‐70 (HSP‐70) expression characterized. We observed three overlapping phases in both transgenic mice, including transient aggregate formation, reactive microgliosis, and progressive motor neuron loss. However, only NFL (−/−) mice demonstrated significant astrogliosis and HSP‐70 upregulation in both motor neurons and astrocytes. These in vivo models suggest that the development of NF aggregates in motor neurons leads to motor neuron death, but that the interaction between the degenerating motor neurons and the adjacent non‐neuronal cells may differ significantly depending on the etiology of the NF aggregate itself. © 2005 Wiley‐Liss, Inc.
CD46 on glial cells can function as a receptor for viral glycoprotein‐mediated cell–cell fusion
Authors: Cassiani‐Ingoni Riccardo , Greenstone Heather L. , Donati Donatella , Fogdell‐Hahn Anna , Martinelli Elena , Refai Daniel , Martin Roland , Berger Edward A. , Jacobson Steven
Published: May 2005

Membrane cofactor protein (CD46) is a regulator of complement activation that also serves as the entry receptor for human herpes virus 6 (HHV‐6) and measles virus (MV) into human cells. While it is clear that oligodendrocytes and astrocytes are cell types commonly infected by these viruses, it is unclear whether oligodendrocytes express CD46, or which are the cellular mechanisms underlying the infection. We show that adult oligodendrocytes, as well as astrocytes and microglial cells, express CD46 on the cellular surface. Moreover, we employed a quantitative fusion assay to demonstrate that HHV‐6A infection of T lymphocytes enables cell–cell fusion of these cells to astrocytes or to oligodendroglial cells. This fusion is mediated by the interaction between viral glycoproteins expressed on the membrane of the infected cells and CD46 on the glial targets, and is also observed using cells expressing recombinant MV glycoproteins. These data suggest a mechanism that involves cell–cell fusion by which certain viruses could spread the infection from the periphery to the cells in the nervous system. Published 2005 Wiley‐Liss, Inc.
Effects of cytokines on microglial phenotypes and astroglial coupling in an inflammatory coculture model
Authors: Hinkerohe Daniel , Smikalla Dirk , Haghikia Aiden , Heupel Katharina , Haase Claus G. , Dermietzel Rolf , Faustmann Pedro M.
Published: May 2005

Cytokines play an important role in the onset, regulation, and propagation of immune and inflammatory responses within the central nervous system (CNS). The main source of cytokines in the CNS are microglial cells. Under inflammatory conditions, microglial cells are capable of producing pro‐ and antiinflammatory cytokines, which convey essential impact on the glial and neuronal environment. One paramount functional feature of astrocytes is their ability to form a functionally coupled syncytium. The structural link, which is responsible for the syncytial behavior of astrocytes, is provided by gap junctions. The present study was performed to evaluate the influence of inflammation related cytokines on an astroglial/microglial inflammatory model. Primary astrocytic cultures of newborn rats were cocultured with either 5% (M5) or 30% (M30) microglial cells and were incubated with the following proinflammatory cytokines: tumor necrosis factor‐α (TNF‐α), interleukin‐1β (IL‐1β), interleukin‐6 (IL‐6), interferon‐γ (IFN‐γ), and the antiinflammatory cytokines transforming growth factor‐β1 (TGF‐β1) and IFN‐β. Under these conditions, i.e., incubation with the inflammatory cytokines and the high fraction of microglia (M30), microglial cells revealed a significant increase of activated round phagocytotic cells accompanied by a reduction of astroglial connexin 43 (Cx43) expression, a reduced functional coupling together with depolarization of the membrane resting potential (MRP). When the antiinflammatory mediator TGF‐β1 was added to proinflammatory altered M30 cocultures, a reversion of microglial activation and reconstitution of functional coupling together with recovery of the astroglial MRP was achieved. Finally IFN‐β, added to M5 cocultures was able to prevent the effects of the proinflammatory cytokines TNF‐α, IL‐1β, and IFN‐γ. © 2005 Wiley‐Liss, Inc.
Involvement of neuropsin in the pathogenesis of experimental autoimmune encephalomyelitis
Authors: Terayama Ryuji , Bando Yoshio , Yamada Masahiro , Yoshida Shigetaka
Published: May 2005

Inflammation, demyelination, and axonal damage of the central nervous system (CNS) are major pathological features of multiple sclerosis (MS). Proteolytic digestion of the blood‐brain barrier and myelin protein by serine proteases is known to contribute to the development and progression of MS. Neuropsin, a serine protease, has a role in neuronal plasticity, and its expression has been shown to be upregulated in response to injury to the CNS. To determine the possible involvement of neuropsin in demyelinating diseases of the CNS, we examined its expression in myelin oligodendrocyte glycoprotein (MOG)‐induced experimental autoimmune encephalomyelitis (EAE), a recognized animal model for MS. Neuropsin mRNA expression was induced in the spinal cord white matter of mice with EAE. Combined in situ hybridization and immunohistochemistry demonstrated that most of the cells expressing neuropsin mRNA showed immunoreactivity for CNPase, a cell‐specific marker for oligodendrocytes. Mice lacking neuropsin (neuropsin−/−) exhibited an altered EAE progression characterized by delayed onset and progression of clinical symptoms as compared to wild‐type mice. Neuropsin−/− mice also showed attenuated demyelination and delayed oligodendroglial death early during the course of EAE. These observations suggest that neuropsin is involved in the pathogenesis of EAE mediated by demyelination and oligodendroglial death. © 2005 Wiley‐Liss, Inc.