bluuebunny/crossref_metadata_2025 huggingface dataset:
XPS, SEM and electrochemical characterization of a platinum‐based glassy carbon modified electrode. Electrocatalytic oxidation of ethanol in acidic medium
Authors: Casella Innocenzo G. , Desimoni Elio
Published: May 2005

A platinum‐based chemically modified glassy carbon electrode (Pt‐CME) was characterized in acidic medium by X‐ray photoelectron spectroscopy, scanning electron microscopy and electrochemical techniques. A uniform distribution of platinum microparticles of different form and size (hexagonal, grain‐like and globular) was present on the surface of glassy carbon. The chemical species present on the electrode surface changed upon polarization. At higher potential values (1.5 V) species such Pt(OH)2, Pt(OH)ads and Pt(OH)4 formed at lower potential values were transformed into PtO, PtOads and PtO2 respectively. A few aspects of the electrooxidation of ethanol in acidic medium were investigated on the Pt‐CME described.
Voltammetry of MnII and CoII in the presence of polymethacrylate
Authors: Cancho Beatriz , Argudo Marco , Ariño Cristina , Esteban Miquel
Published: May 2005

Complex formation of MnII and CoII with polymethacrylic acid (PMA) is studied by differential pulse polarography, normal pulse polarography, reverse pulse polarography, cyclic voltammetry and differential pulse anodic stripping voltammetry. Because of the lack of a model for macromolecular metal systems including Mn+/M(Hg) couples with irreversible electrochemical behavior, the application of the theoretical model developed for reversible electrochemical systems is tested to the slow MnII/Mn(Hg) and CoII/Co(Hg) couples. The quality of the experimental results obtained allows us to calculate the formation constants of the predominating MnII/PMA and CoII/PMA complexes and also their dependence on complexation variables.
Electron‐transfer properties of pyrolytic graphite optically transparent electrodes
Authors: Kummer Matthias , Kirchhoff Jon R.
Published: May 2005

The electron‐transfer characteristics of metal mesh optically transparent electrodes, which were modified by chemical vapor deposition of pyrolytic graphite, are investigated. The pyrolytic graphite optically transparent electrodes are found to exhibit sluggish electron‐transfer toward several transition metal probes. Subsequent activation of the electrode surface is accomplished by RF plasma etching of the carbon layer to expose a higher density of edge plane carbon. A limiting current response is achieved after 2.5 min of RF exposure. As a result of the activation process, sharper voltammograms and reduced peak separations are observed in cyclic voltammetric measurements, while reduced equilibration times are found for thin‐layer spectroelectrochemical measurements. [Fe(CN)6],3‐, ferrocene monocarboxylic acid, cobalt(III)sepulchrate {[Co(sep)] 3+} and tris(1, l0‐phenanthroline)cobalt(III){[Co(phen)3]3+} are used to characterize the response of the pyrolytic graphite optically transparent electrodes for electrochemical and spectroelectrochemical measurements.
Pulsed amperometric detection of ethanol in breath by gold electrodes supported on ion exchange membranes (solid polymer electrolytes)
Authors: Schiavon Gilberto , Comisso Nicola , Toniolo Rosanna , Bontempelli Gino
Published: May 2005

A sensitive and fast‐responding amperometric sensor for the determination of ethanol in breath which eliminates oxygen interferences is described. It consists of a porous gold working electrode (facing the sample) supported on one face of an ion‐exchange membrane which serves as a solid polymer electrolyte (SPE). The other side of the membrane faces an internal electrolyte solution (1 M aqueous NaOH) containing the counter and reference electrodes. The fouling of the gold working electrode, due to the ethanol oxidation process, is overcome by continuously cleaning and reactivating its surface by applying a triple‐pulse potential waveform. The performance of this sensor has been tested in a closed‐loop flow apparatus fed with synthetic ethanol‐vapor samples obtained by evaporating aqueous solutions with known ethanol contents. The sensor displays a high current sensitivity and a low background noise, so that a low detection limit (2 μg L−1, 1ppm v./v.) is estimated for a signal‐to‐noise ratio of 3. The responses are characterized by both a good reproducibility and a linear dependence on the ethanol concentration over a fairly wide range (more than three orders of magnitude), as well as by a short response time (ca. 1 s). This fast response time arises from the lack of a gas‐permeable membrane and direct gas contact to the triple interphase among the gaseous analyte, the porous working electrode and the solid polymer electrolyte. The absence of significant interfering effects and the possibility of adopting such a device for the detection of ethanol in fermentation processes are also discussed.
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

The 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

The 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

The 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

Cyclic 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

An 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

A 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

Cyclic 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

Biosensor 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

Glassy 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

A 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

Immobilization 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

This 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

Network 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

The 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

Square 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

The 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

Dipyridamole (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

A 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

Chemically 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

A 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

Mercury 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

An 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.
A thermodynamic test of the diffuse layer theory and its implications on electrode kinetics
Authors: González Ramon , Sanz Fausto
Published: May 2005

The thermodynamic compatibility of the diffuse layer theory with the chemical potential of ionic species in the solution bulk is introduced. From the electrocapillary equation, a compatibility equation, which relates the potential drop across the diffuse layer to the chemical potential of the ionic species in the solution bulk, is deduced for a binary electrolyte. When the Gouy–Chapman (GC) theory is introduced in the compatibility equation, the latter only becomes an identity if the ionic activity is taken as the ionic concentration, as expected. A compatible theory of the diffuse layer which has GC as the limit case at dilute solutions and fulfills the compatibility equation for whatever physical description of the ionic activity coefficients is stated. The significance of the compatible theory is that the electrode reaction rates calculated by means of the electrode kinetic equation with the Frumkin correction using this theory differ from those calculated using GC. In order to test both theories, we have studied the electroreduction of peroxodisulfate at an amalgamated copper rotating disk electrode. The experimental results fit our compatible theory better than GC does.
L‐Ascorbate sensor with polypyrrole‐coated carbon felt membrane electropolymerized in a cucumber juice solution
Authors: Uchiyama Shunichi , Hasebe Yasushi , Tanaka Masayasu
Published: May 2005

Polypyrrole membrane was coated on a carbon felt surface by electropolymerization of pyrrole in an undiluted cucumber juice solution which contains a large amount of ascorbate oxidase. It was found that the polymerized carbon felt exhibited a large ascorbate oxidase activity. An ascorbate sensor, combining an oxygen electrode and the treated carbon felt membrane, was prepared by placing this carbon felt on the oxygen gas permeable membrane of an oxygen electrode. The resulting sensor gave a large current response of L‐ascorbic acid, which is based on the consumption of oxygen catalyzed by ascorbate oxidase immobilized into the polypyrrole membrane. The optimum polymerization potential was found to be + 0.7 V (vs. SCE). The linear concentration range of L‐ascorbic acid ranged from 5 × 10−6 to 4 × 10−4 M. The enzyme immobilized into the polypyrrole membrane activity retained its activity for 5 days, and the half‐life of the immobilized enzyme was about 10 days at 4°C.
Amperometric biosensors based on NAD(P)‐dependent dehydrogenase enzymes
Authors: Lobo Maria Jesús , Miranda Arturo J. , Tuñón Paulino
Published: May 2005

This review deals with the use of pyridine‐nucleotide dependent dehydrogenase enzymes in amperometric biosensor design. The electrochemistry of the nicotinamide coenzymes, their mechanism and the challenges associated with their direct oxidation on solid electrodes are discussed. In addition, a survey of the different solutions proposed in the literature for addressing these problems and some of their applications are presented.
Applications of the channel flow cell for UV‐visible spectroelectrochemical studies: The kinetics of dimerization of the methyl viologen radical cation
Authors: Tam Kin Yip , Wang Rui Lin , Lee Chi Woo , Compton Richard G.
Published: May 2005

A channel flow cell specifically designed for ultraviolet‐visible spectroelectrochemical experiments is described. The performance of the cell was characterized using the oxidation of N,N, N′, N′‐tetramethyl‐p‐phenylenediamine in aqueous electrolytes and excellent agreement between theory and experiment was obtained. The technique was applied to study the dimerization rate of methyl viologen radical cations. The mechanistic results confirm that the electrogenerated methyl viologen radical cation dimerizes rapidly in aqueous solution and a previously unknown dimerization rate constant close to 104 M−1 s−1 is reported.
AC‐voltammetric determination of the total concentration of nonionic and anionic surfactants in aqueous systems
Authors: Sander Sylvia , Henze Günter
Published: May 2005

The tensammetric determination of the total concentration of mixtures of nonionic and anionic surfactants is desribed. By taking advantage of the different accumulation behavior of nonionic and anionic surfactants on the surface of the hanging mercury drop electrode (HMDE), it has been possible to determine the total concentration of nonionic surfactants without contribution from anionic surfactants. After subtraction of nonionic surfactant concentration from total, the concentration of anionic surfactants can be determined indirectly. Detection limits of 10 to 100 μg L−1for single compounds and 100 μg L−1for mixtures were calculated. Humic acids, relevant complexing reagents (like EDTA) and different cations do not interfere in the determination when they are present in typical concentrations found in surface waters. The method has been applied to several mixtures of surfactants. The possibility of solid‐phase‐extraction (SPE) for sample pretreatment has been investigated.
A bienzyme electrode for tyrosine‐containing peptides determination
Authors: Eremenko Arkadi V. , Makower Alexander , Bauer Christian G. , Kurochkin Ilya N. , Scheller Frieder W.
Published: May 2005

A bienzyme electrode for monitoring biologically important peptides containing tyrosine has been established on the basis of mushroom tyrosinase and quinoprotein glucose dehydrogenase (GDH). Tyrosine residues bound in the peptide chain are oxidized by tyrosinase resulting in consumption of oxygen. Subsequently, the dopaquinone residues are reduced in the GDH catalysed reaction which is driven by an excess of glucose. This reaction cycle leads to a considerable increase of sensitivity. Both enzymes were entraped in poly(vinyl)alcohol matrix and placed on the surface of a Clark‐type oxygen electrode (the working platinum electrode was potentiostated at −600 mV) (vs. Ag/AgCl reference electrode) between a polypropylene and cellulose membrane. The bienzyme‐modified Clark‐type oxygen electrode has a lower detection limit of 0.2 μM for the opioid peptides Tyr‐D‐Ser‐Gly‐Phe‐Leu‐Thr, Leu‐enkephalin, Tyr‐D‐Ala‐Gly‐Phe‐D‐Leu and morphiceptin. The dependence of response of the electrode on the length of peptide chain and position of tyrosine residue is discussed. The new electrode has been applied to the quality control of tyrosine containing peptides from pharmaceutical formulations and from peptide synthesis.
Determination of hydrogen peroxide by utilizing a cobalt(II)hexacyanoferrate‐modified glassy carbon electrode as a chemical sensor
Authors: Lin Meng Shan , Jan Bor Iuan
Published: May 2005

A mixed‐valence cluster of cobalt(II)hexacyanoferrate possesses an electron transfer property and is suitable for the development of an effective hydrogen peroxide detection scheme. The characteristics of cobalt(II)hexacyanoferrate have been studied using both elemental analysis and infrared spectra, confirming the structure is Co[FeII(CN)6]. The cobalt(II)hexacyanoferrate‐modified electrode exhibits a rapid response (t95% ‐ 6.5 s) to the injection of 5.0 × 10−5 M hydrogen peroxide. The linearity of the response is up to 1.1 × 10−3 M (correlation coefficients is 0.999). The sensitivity of this modified electrode is 11.8 μA/mM‐mm2. The detection limit of cobalt(II)hexacyanoferrate‐modified electrode to hydrogen peroxide is 6.25 × 10−8 M. The current chemical sensor modified with Co[FeII(CN)6] has better sensitivity than previous ones. The modified glassy carbon electrode shows no interference from ascorbic acid, uric acid, acetaminophen, 1,4‐dihydroxyquinone, dopamine at the 2.0 × 10−4 M level and polyamines at 5.0 × 10−5 M level.
Square‐wave voltammetry of 4,4′‐diisopropyl‐2,2′‐bithiazoline and its complex with copper(II)
Authors: Mlakar Marina , Čuljak Ivan
Published: May 2005

(4S)‐4′‐diisopropyl‐2,2′‐bithiazoline (DPT) is an electroactive organic chiral compound giving two reduction responses in square‐wave voltammograms at potentials about −0.2 and −0.4 V by forming a complex with mercury which deposits at the electrode surface. By the addition of copper(II) ion to the solution of DPT a third peak appears between them at about −0.3 V, which corresponds to the reduction of adsorbed Cu‐DPT complex. Optimal pH for the investigation of those redox processes was found to be 2.8. By square‐wave voltammetric measurements it was interpreted that these redox reactions were quasireversible with immobilized reactants. By plotting ip/f vs. frequency a quasireversible maximum was obtained, and the apparent standard reaction rate constants were calculated: log (ks)DPT=(0.91 ± 0.9) and 1 < ks < 65S−1, log (ks)CuDPT= (0.35 ± 0.9) and 0.3 < ks < 18 S−1 in 0.55 M NaCl.
Screen‐printed electrochemical hybridization biosensor for the detection of DNA sequences from the Escherichia coli pathogen
Authors: Wang Joseph , Rivas Gustavo , Cai Xiaohua
Published: May 2005

An electrochemical biosensor for the specific detection of short DNA sequences from the E. coli pathogen is described. This hybridization device relies on the immobilization of a 25‐mer oligonucleotide probe, from the E. coli lacZ gene, onto a screen‐printed carbon electrode. Chronopotentiometric detection of the Co(bpy)3+3 indicator is used for monitoring the hybridization event. Numerous variables of the assay protocol, including those of the probe immobilization step, the hybridization event, and the indicator association/detection, are characterized and optimized. Hybridization times of 2‐ and 30‐min are sufficient for detecting 300‐ and 50 ng/mL, respectively, of the E. coli DNA target. Applicability to analysis of untreated environmental water samples is illustrated. Such single‐use electrochemical sensors hold great promise for decentralized environmental and food testing for the E. coli pathogen.
The electrochemical polymerization of redox dye‐nile blue for the amperometric determination of hemoglobin
Authors: Zhou Dong‐Mei , Chen Hong‐Yuan
Published: May 2005

A semi conducting polymer‐modified glassy carbon electrode was fabricated by cyclically sweeping in the potential range of −0.4–1.2 V(vs. SCE) or by electrolyzation at constant potential of 1.4 V in 0.5 M sulfuric acid solution containing 1.0 mM Nile Blue. This redox active polymer could successfully be used for the amperometric determination of hemoglobin. The effect of pH was studied for the polymerization of Nile Blue. It was found that the polymerization did not occur in neutral or basic solutions. The formal potential of this film is −410 mV (pH 7.0) which is more negative than that obtained at the bare electrode in the Nile Blue bulk solution. The electrochemical characteristics of this polymer are discussed. The modified electrode could electrocatalyze the reduction of hemoglobin, and a good linear amperometric response could be obtained over the range of 0.05–7.0 mg/mL (correlation coefficient: 0.985). This modified electrode exhibited good stability and reproducibility for long‐term use.
Electrochemical determination of prolintane in pharmaceutical formulations and in human urine
Authors: Espartero Amparo G. , Pérez‐López José A. , Zapardiel Antonio , Bermejo Esperanza , Hernández Lucas
Published: May 2005

The oxidative behavior of 1‐[1‐(phenylmethyl)butyl]pyrrolidine, prolintane, was studied at a glassy carbon electrode using linear‐sweep and differential‐pulse voltammetry. The oxidation process was shown to be irreversible using 0.04 M Britton–Robinson buffer and was diffusion‐adsorption controlled. Two voltammetric methods were developed for the determination of prolintane using different techniques: linear‐sweep and differential‐pulse voltammetry. The peak current varied linearly with prolintane concentrations in the range of 1.0 × 10−5 −2.5 × 10−4 M, with a detection limit of 8.5 × 10−6 and 4.0 × 10−6 M, and with relative standard deviations of 2.1 % and 3.1 %, respectively. The methods were applied to commercial preparations, giving relative errors less than 3.1 % and relative standard deviations lower than 4.8 % (n = 10).

Determination of prolintane (down to the 8.5 × 10−8 M level) can be performed by using a preconcentration step prior to the determination by differential‐pulse voltammetry in 0.04 M Britton–Robinson buffer (pH 8.0) with preconcentration potential of 0.0 V. The detection limit was found to be 6.2 × 10−8 M (4 min preconcentration) and the relative standard deviation for 2.5 × 10−7 M prolintane (n = 5) was 4.6 %. Applicability to human urine analysis is illustrated (recovery 98 ± 2 %). Standard additions method can be used to determine prolintane in real samples of urine.
Biodegradation of soluble redox polymers. Part 2: (0.017ferrocene)amylose at a rotating disk electrode
Authors: Gnedenko Boris B. , Galkin Alexander M. , Ryabov Alexander D.
Published: May 2005

The behavior of (ferrocene)amylose (FA), in the presence of amylolytic depolymerases (α‐amylase from Aspergillus oryzae and human saliva), has been investigated by cyclic voltammetry at a rotating disk electrode (CVA/RDE). Growth of the limiting current with time in the presence of the enzymes is proportional to the amount of enzyme introduced. The quantitative data treatment to assay the endoamylolytic activity of enzymes at CVA/RDE involves plotting (idt/id0)4.5 against time; the slope of the linear plot being equal to (rate) Mn0C−1, where idt and id0 are the limiting currents at time t and 0, respectively, (rate) is the enzymatic activity, Mn0 is the number averaged molecular weight of FA at t = 0, and c is its concentration. The comparison of CVA/RDE with the 3,5‐dinitrosalicylic acid and the Somogyi–Nelson reducing saccharides procedures shows advantages of the former, especially in assaying small quantities of enzymes. Also the CVA/RDE approach is simpler and takes place under much milder conditions. The main disadvantage of CVA/RDE is the inhibiting effect of Triton X‐100 in the reaction between FA and the amylases which is not observed in the case of native, ferrocene‐free amylose. In general, CVA/RDE appears to be an attractive analytical method for monitoring diverse enzymatic depolymerization reactions.
Voltammetric behavior and ion chromatographic detection of nitrite at a dispersed platinum glassy carbon electrode
Authors: Casella Innocenzo G. , Salvi Anna M.
Published: May 2005

Cyclic voltammetry was used to investigate the electrochemical behavior of nitrite at a platinum‐modified glassy carbon electrode (Pt‐CME) in phosphate buffer (pH 4.5). Experiments in flow injection analysis and ion‐chromatography (IC) were performed to characterize the electrode as an amperometric sensor for the determination of nitrite ions. The effects of several common interferences on the amperometric signal were estimated. The electrode stability, precision, limit of detection, and linear range were evaluated at a constant applied potential of 1.1 V. Calibration plots were linear from 0.03 μM to 0.5 mM with a slope of about 21 μA/mM and a correlation coefficient of 0.9987. The limit of detection (LOD) was 15 nM (0.7 ppb) in a 100 μL injection. The electrode response was sufficiently stable: over 6 h of operating time a 2.8% signal loss was observed. The determination of nitrite in milk and pear juices was achieved by IC and the relevant results were compared with those obtained with a standard spectrophotometric method.
Cyclic voltammetry study of the peptide Lys‐Cys‐Thr‐Cys‐Cys‐Ala [56‐61] MT i in the presence of cadmium
Authors: Harlyk Charlotte , Bordin Guy , Nieto Oscar , Rodriguez Adela Rosa
Published: May 2005

The electrochemical study of the peptidic fragment Lys‐Cys‐Thr‐Cys‐Cys‐Ala [56–61] MT I (FT) alone and in the presence of cadmium was performed, by cyclic voltammetry using a hanging mercury drop electrode, in order to enable comparisons between the behavior of Cd, Zn metallothioneins and that of this less complex molecule, intrinsic to the metallothionein structure. The influence of the equilibration time, of the scan rate, and of the solution pH was investigated. The influence of the addition of cadmium with different Cd–FT ratios was also studied. Samples containing both Cd and FT give complex voltammograms showing different peaks. Several electrochemical systems were distinguished: the mercury electrode itself is involved in the charge transfer step in the presence of thiol groups coming from the FT structure; another system can be attributed to the oxido‐reduction of cadmium either as free ion or complexed by the peptide. The adsorption phenomena play an important role in the electrochemical process. Both dissolved and adsorbed species are electroactive.
Preparation of polymer‐coated electrodes containing metal ions complexing sites by electropolymerization of 2‐mercaptobenzimidazole and 2‐mercaptobenzothiazole on glassy carbon
Authors: de Fátima Brito Sousa Maria , Dallan Émerson José , Yamaki Saulo Barbosa , Bertazzoli Rodnei
Published: May 2005

The possibility of producing polymer‐coated electrodes containing complexing agents capable of collecting metal ions was investigated. The organic ligands 2‐mercaptobenzimidazole and 2‐mercaptobenzothiazole were used as monomers for electropolymerization on glassy carbon electrodes. The electroanalytical applicability of the modified electrodes was evaluated for Hg2+ ions, by applying a chemical preconcentration step with subsequent measurement by differential pulse voltammetry. The influence of some electropolymerization parameters, such as scan rate, monomer concentration and the number of cyclic scans, on the voltammetric response of mercury(II) was studied. A 5 min preconcentration period allowed the detection of 0.08 mg/L (4.0 × 10−7 mol L−1) mercury.
Characteristic behavior of macro‐, semimicro‐ and microelectrodes in voltammetric and chronoamperometric measurements
Authors: Nirmaier Hans‐Peter , Henze Günter
Published: May 2005

The advantages of microelectrodes such as the improvement of signal‐to‐noise ratio, the ability to perform electrochemical measurements in high resistive solutions and small RC‐time constants give the possibility of an extended use for voltammetric and chronoamperometric techniques in analytical chemistry. In this comparative study, the microelectrode properties of three selected electrodes were examined. The characterization of a RAM‐microarray electrode, an epoxy‐impregnated carbon electrode and a conventional glassy carbon macroelectrode was performed by cyclic voltammetry at different scan rates, by DP‐voltammetric measurements using different concentrations of supporting electrolyte and by transient measurements. It could be shown, that in comparison to the microarray electrode and to the glassy carbon macroelectrode, respectively, the results obtained by using the epoxy‐impregnated carbon electrode are caused by its semimicroelectrode character.
Calculation of the formation constant of the 1:1 complex between manganese(II) and the anion of 2‐mercaptopyridine N‐oxide (pyrithione) by polarographic measurements
Authors: Galvín R. Marín , Angulo M. , Mellado J. M. Rodríguez
Published: May 2005

Polarograms of mixtures of MnII and the anion of 2‐mercaptopyridine N‐oxide (pyrithione) in neutral media do not show separate waves for the metal ion, either complexed or not, nor for the ligand, free or in the complex. The two‐electron reduction of MnII is shown to be an ErEi process in the absence of ligand and CrErEi process in the presence of ligand, with a fast previous reaction. From measurements made at constant MnII concentration and variable ligand concentration it is shown that the 1:1 complex is formed. The logarithm of the formation constant of this complex is obtained from these and other measurements, this value being log Kf = 3.76 ± 0.03.