bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron transfer from diaphorase in water/triton X‐100/butyl acetate microemulsion
Authors: Hall Geoffrey F. , Turner Anthony P. F.
Published: May 2005

The transfer of electrons from an enzyme in a microemulsion system to a glassy carbon electrode, via mediators of different solubilities, is demonstrated. A bienzymic reaction is carried out in a microemulsion formed by the nonionic detergent Triton X‐100 in butyl acetate. The enzymes used are alcohol dehydrogenase (ADH. EC 1.1.1.1) and diaphorase (EC 1.8.1.4). ADH catalyzes the conversion of primary alcohols to aldehydes with the concomitant reduction of its cofactor, nicotinamide adenine dinucleotide (NAD+) to NADH. Diaphorase reoxidizes NADH and can utilize a variety of molecules as an electron acceptor. It is demonstrated that these may be water soluble or solvent soluble.
NADH electrochemical sensor for the enzymatic determination of L‐ and D‐lactate and 3‐hydroxybutyrate using a flow injection analysis
Authors: Marrazza G. , Cagnini A. , Mascini M.
Published: May 2005

A NADH sensor in the submicromolar range, assembled in a wall‐jet cell using a flow injection analysis (FIA) procedure, was studied and coupled with enzyme reactors. Spectroscopic graphite was used as electrode material without any mediator. The measurements were performed at an applied potential of + 500 mV vs. Ag/AgCD. L‐, D‐lactate, and 3‐hydroxybutyrate dehydrogenase were immobilized on aminopropyl‐controlled pore glass beads using glutaraldehyde in a packed‐bed enzyme reactor, L‐, D‐lactate, and 3‐hydroxybutyrate were oxidized in the presence of NAD+, and an equivalent amount of NADH was produced and measured. By careful choice of pH, buffer, and NAD+ concentration, the analytes could be measured in the range of 1 × 10−6 to 1 × 10−4 M in a few seconds. Large blank effects were evidenced with this procedure if the carrier and the sample differed in ionic strength of about 1 × 10−3 M when the total ionic strength is 0.8 M. Therefore, the use of such a system for reach samples requires further investigation.
Voltammetric behavior of 1,4‐dihydropyridine calcium antagonists
Authors: Alvarez‐Lueje A , Nuñez‐Vergara L. J. , Squella J. A.
Published: May 2005

The anodic electrochemical behavior of the five members of the 1,4‐dihydropyridine calcium antagonists family was studied. In all of the studied compounds (nifedipine, nitrendipine, nimodipine, nicardipine, and furaldipine), the oxidation process reveals only one anodic peak due to the twoelectron oxidation of the dihydropyridine ring to form the pyridine derivative compound. The differential pulse voltammetric technique was used for the quantitation of the 1,4‐dihydropyridines in pharmaceutical forms. The voltammetric determination developed here represents a good analytical alternative, because sample preparation is easy (no excipient separation is necessary), is not time consuming, and is adequately accurate and precise. Furthermore, the developed method can be applied as an important tool in photodegradation studies.
Fast‐pulsed electrochemical detection at noble metal electrodes: The frequency‐dependent response at gold electrodes for chromatographically separated carbohydrates
Authors: Roberts Richard E. , Johnson Dennis C.
Published: May 2005

Waveforms used in pulsed electrochemical detection (PED) have frequencies of ca. 1 Hz when optimized to give a maximum signal‐to‐noise ratio (S/N) for carbohydrates. However, higher frequencies are desired for application of PED to capillary electrophoresis (CE) and microcolumn lipuid chromatography (MLC), which can produce narrow elution peaks. Minimization of the time periods for oxidative cleaning and reductive reactivation in PED waveforms generated by the Dionex pulsed Electrochemical Detector allows the increase in waveform frequency to ca. 3 Hz without change in the traditional time period of 200 ms, prescribed for integration of the anodic current. However, further increase in frequency requires a decrease in the integration period with a corresponding loss of signal strength.
Voltammetric studies with copper microelectrodes fabricated from borosilicate‐coated copper microwire
Authors: Bond A. M. , Brainian Kb. Z. , Loppenol M.
Published: May 2005

Copper microwire coated with a thin film of borosilicate glass can be used to provide a new and convenient method for fabricating high quality 7 μm diameter copper microdisk electrodes. The reversible reduction of the cobaltocenium cation to cobaltocene was studied in acetonitrile to assess the quality of electrode fabrication. If electrode polishing followed by potential, wave shape, and limiting current are all as theoretically expected for a reversible steady‐state voltammogram. However, if the nitric acid treatment is believed to remove a thin film of copper oxide which acts as an insulator with respect to the reduction of the cobaltocenium caton and, therefore, effectively decreases the electrode area. Studies on glycine which represents an example of a biologically important molecule previously determined by voltammetry at conventionally sized copper electrodes also were undertaken. An extremely well‐defined response is observed for glycine at a copper microelectrode, indicating the analytical usefulness of this new class of microelectrode. Additional aspects of the glycine mechanism which intimately involve the copper electrode surface are elucidated from the microelectrode studies.
Adsorption voltammetry of the titanium‐4‐[(4‐diethylamino‐2‐hydroxyphenyl)‐azo]‐5‐hydroxynaphthalene‐2,7‐disulfonic acid (beryllon III)system
Authors: Zhao Jingzhong , Sun Dezhi , Wei Xilian , Jin Wenrui
Published: May 2005

The behavior of Ti (IV) complex with Beryllon III, Ti (IV) A, at a mercury electrode has been investigated in acetate buffer (HOAc/NaOAc). The adsorption phenomena were observed by linear‐sweep voltammetry. The mechanism of the electrode reaction was found to be the irreversible reduction of Beryllon III in the complex adsorbed on the surface of the electrode. In 0.005 mol/LHOAc + 0.1 mol/L NaOAc and 5 × 10−10 to 1 × 10−7 mol/L, the detection limit of the method is 2.5 × 10−10 mol/L for a preconcentration time of 120 seconds. This method has been applied to samples of human hair.
Disposable electrodes for field screening of trace uranium
Authors: Wang Joseph , Baomin Tian , Setiadji Rossi
Published: May 2005

A novel electrochemical sensor for trace (μg/L) Uranium, based on adsorptive stripping potentiometry, is described. The sensor operation relies on the adsorptive accumulation of the uranium‐cupferron complex onto a mercury‐coated screen‐printed carbon electrode. The disposable nature of these electrodes makes them very attractive for on‐site characterization of nuclear energy sites. Various variables affecting the potentiometric stripping response were characterized and optimized to yield low‐detection limit (e.g., 0.5 μg/L following a 5 minute adsorption) and good precision (relative standard deviation (RSD) = 1.4% for n = 15, 25 μg/L uranium). Convenient measurements can be carried out in nondeaerated and quiescent solutions. Applicability to the quantitation of uranium in groundwater samples is demonstrated.
Ultratrace determination of molybdenum in the presence of 2‐(2′‐thiazolylazo)‐p‐cresol by catalytic‐adsorptive stripping voltammetry
Authors: Farias Pércio A. M. , Obara Aniy K. , Nóbrega Armi W. , Gold Jon S.
Published: May 2005

The adsorptive collection of the molybdenum (VI) complex of 2‐(2′‐thiazolylazo)‐p‐cresok (TAC), coupled with the catalytic current of the adsorbed complex, yield an ultrasensitive voltammetric procedure for the determination of molybdenum. Optimal experimental conditions were found with the use of a stirred acetate buffer (pH 2.9) supporting electrolyte, a TAC concetration of 1.0 × 10−5 M, and a concentration of 0.1 M potassium nitrate. In addition, a preconcentration potential of −0.13 V (vs. Ag/AgCl), equilibrium time of 30 seconds, and an anodic scan rate of 200 mV/s from −0. 93 to −0. 20 was used. A catalytic effect was observed when nitrate was present. The response was found to be linear over a concentration range of 0.0 to12.0 μg L−1 Mo (VI). For a preconcentration time of 3 minutes, the detection limit was found to be 11 pM. Possible interferences by anions and other trace metals were investigated. The interference by copper may be masked by CDTA, and sequential determination with molybdenum is possible. The merits of the procedure are demonstrated in the analysis of sea and mineral water.
Bioelectrocatalysis and diffusion kinetics glucose oxidase: Glucose reaction using a water‐soluble 1,1′‐dimethylferrocene‐2‐hydroxypropyl‐β‐cyclodextrin complex
Authors: Brown R. Stephen , Luong John H. T.
Published: May 2005

The mediation of the glucose oxidase (GOx): glucose reaction by 1,1′‐dimethylferrocene (DMF) solubilized in 2‐hydroxypropyl‐β‐cyclodextrin (hpβCD) was studied. Cyclic voltammetry (CV) was used to examine the effects of complexation with hpβCD on the oxidation potential of DMF through the analysis of half‐wave potentials. This indicated a one‐to‐one complex between DMF and hpβCD, with a formation constant of (1.2 ± 0.3) × 103 M−1 The working potential for electrodes using the mediator complex could be reduced by minimizing the hpβCD concentration, though a lower limit of 2.5 mM was observed for the 0.5 mM DMF solutions used in this work, below which the DMF became insoluble, and its electrochemistry was not well behaved.

Cyclic voltammetry measurements at different scan rates were used to determine kinetic‐parameters, resulting in a second‐order rate constant for the reaction of oxidized DMF with reduced GOx of 3.4 × 104 M−1 s−1 to 1.9 × 104 M−1 s−1 for solutions containing 4 mM to 10 mM hpβCD. These values are on the order of one‐quarter the literature value for free DMF and are in the range reported for ferrocene, indicating that the complexed DMF is able to function as an efficient mediator. The rate constant determined for 2.5 mM hpβCD was anomalously high and probably indicated insolubility of the DMF at this hpβCD concentration. A rate constant versus the hpβCD concentration plot was used as an indication of the lower limit of hpβCD concentration at which reproducible results could be obtained.
Adsorptive stripping voltammetric determination of trace tellurium in the presence of oxine
Authors: Wang Joseph , Lu Jianmin
Published: May 2005

Ultratrace levels of rellurium can be determined after adsorptive collection of the tellurium‐oxine complex on a hanging mercury drop electrode. The adsorptive‐catalytic stripping voltammetric procedure is optimized to give an extremely low detection limit of 8 ng/L (6.4 × 10−11 M) tellurium following 10 minutes accumulation. The improved sensitivity (over conventional stripping methods for tellurium) is coupled with high selectivity and precision. For example, the response is not affected by a large excess of selenium, which commonly interferes in analogous anodic stripping measurements. The relative standard deviation (at the 500 ng/L level) is 1.9%.
Electrochemical behavior of redox proteins entrapped in nafion films
Authors: Bianco Pierre , Haladjian Jean
Published: May 2005

Several redox proteins are studied at Nafion‐coated pyrolytic graphite (PG) electrodes. The electrochemical behavior of polyheme c‐type cytochromes and spinach ferredoxin is described using cyclic and square‐wave voltammetry (SWV). No signals are detected when Nafion‐coated electrodes are exposed to the protein solutions. In contrast, electrochemical responses are observed when droplets of protein solutions, deposited on the PG surface are dried then entrapped in Nafion layer. These Nafion‐modified electrodes permit one to detect very small amounts (1 μg) of cytochrome c3. The stability of entrapped molecules upon repetitive cycling has been investigated. Such modified electrodes offer new perspectives for studying proteins confined at electrode surfaces.
Investigation on mechanisms for the electrooxidation of some bile pigments by spectroelectrochemistry
Authors: Niu Jianjun , Dong Shaojun
Published: May 2005

The electrooxidation behavior of bilirubin (BR), biliverdin (BV), purpurin (Pu), and choletelin (Ch) in dimethylformamide (DMF) have been investigated by voltammetry, in situ electron spin resonance (ESR) thin‐layer spectroelectrochemistry and especially in situ rapid scan spectrometer. Radical cations and multiple chemical reactions were found to occur during the electrooxidation processes of these bile pigments The proposed oxidation mechanism of BR corresponds to mixed processes of ECECC and ECECEC, while that of BV and Pu are all ECECC.
Surfactant modified carbon paste electrode: Part 2: Analytical performances
Authors: Digua K. , Kauffmann J.‐M. , Khodari M.
Published: May 2005

The hexadecylsulfonic acid (sodium salt) modified carbon paste electrode (HDSNa‐CPE) has been studied in batch and flowing systems, and its analytical performance has been established in comparison with a conventional carbon paste electrode (CPE). Amperometry, linear scan, and preconcentration voltammetry have been used for the investigation of several analytes of pharmacological interest. Because of the presence of surface functionalities, markedly different electrode responses have been observed at the HDSNa‐CPE depending on the nature (hydrophobicity and charge) of the investigated molecule. The HDSNa‐CPE showed, in linear scan voltammetry and for all the species investigated, higher responses compared to the CPE. The HDSNa‐CPE showed important current enhancements in voltammetric analysis of hydrophobic organic cations in acidic media and at low ionic strength.
Voltammetric determination of the antioxidant tert‐butylhydroxytoluene (BHT) at a carbon paste electrode modified with nickel phthalocyanine
Authors: Ruiz M. Asunción , áńez‐Sedeń Paloma , Pingarrón José M.
Published: May 2005

The voltammetric behaviar of the antioxidant tert–butyltydroxytoluene (BHT) at a carbon paste electrode modified with nickel phthalocyanine is described, and method for the determination of this antioxidant based on its oxidations at the modified electrode it proposed. Cyclic voltammograms showed a well defined oxidations peak for BHT at potentials approximately. 200 mV lower than the poorly defined peck obtained in the absence of the electocatalyst. A 35%, methanol :water medium, a modifier concentrations of 2%, and pH 2 were chosen as working conditions. Results obtained suggest that the oxidation signal arisen as a result of BHT chemically reducing Ni(II)to Ni(I) in the phthalocyanine, and the subsequent electrochemical oxidations of the latter. Using differential pulse voltammetry at ΔE =50 mV, a linear calibration range was obtained between 1 and 50 mg L−1 BHT with a detection limit of 0.17 mg L−1 BHT interferences from other substances commonly present in commercial antioxidant mixtures were tested. The developed method was applied to the determinations of BHT in stabilized diethyl ether.
Four potential step differential amperometry in a single pulse sequence mode
Authors: Fang Yuzhi , Tong Wei , He Pingang , Wang Rener , Jin Litong
Published: May 2005

A new type of four potential step differential amperometry in a single pulse sequence mode is proposed on the basis of four potential step differential normal voltammetry. The charging current tends to be eliminated, and the background current is set at zero after the differentiation and addition of the sampling currents on these four potential steps. The signal‐to‐noise ratio is enhanced by utilizing a series of pulses. In addition, since the potential returns to its initial point, it is advantageous for electrode cleaning and the study of solid electrode and adsorption systems. This provides an alternative approach for electrical current‐type electrochemical sensors, electrochemical detection in liquid chromatography, and electrode kinetics studies.
Determination of kinetic parameters from the steady‐state voltammograms at microring electrodes
Authors: Zhnang Qian‐Kun , Cben Hong‐Yuan
Published: May 2005

Under steady‐state conditions, the i‐E equations at thin microring electrodes for reversible, quasi‐reversible, and irreversible systems are derived by using uniform surface concentration boundary condition. Using these results, the heteroger eous rate constants of several fast electron transfer reactions under steady‐state diffusion conditions are measured. The measured rates are in good agreement with existing data. As a result, all these efforts are successful in a simplified way compared to those required for relaxation techniques.
Adsorptive stripping voltammetric determination of folic acid in pharmaceutical preparations
Authors: Szczepaniak W. , Ren M.
Published: May 2005

An adsorptive stripping voltammetric (AdSV) procedure is proposed for determination of folic acid (FA) in cores and coated pellets of Hemofer (FA/iron tablet). The adsorptive stripping response was evaluated with respect to the electrolyte solution, the accumulation time and potential, and the concentration dependence. The relationship between ip and FA concentration was linear over the range 1 × 10−8 to 5 × 10−7 M FA. The conditions of cores and pellets preparation for analysis were established. The relative standard deviation is 2.4% for a content of FA of 0.35 mg per core (n = 5).
Nitro radical anion formation from nitro‐substituted amphetamine derivatives
Authors: Nuñez‐Vergara Luis J. , Matus C. , Alvarez‐Lueje A. F. , Cassels B. K. , Squella J. A.
Published: May 2005

The cyclic voltammetric characteristics of two nitroamphetamine derivatives (2‐nitro‐4,5‐dimethoxyamphetamine and 2‐nitro‐4,5‐methylenedioxyamphetamine) have been investigated in different media. In mixed media (aqueous buffer and DMF, dioxane, or acetonitrile) a reversible one‐electron reduction takes place to form a stable nitro radical anion. At more negative potential values, a further three‐electron reduction occurs irreversibly to give the hydroxylamine derivative. Cyclic voltammetry (CV) has been employed to study the tendency of the nitro radical anions to undergo further chemical reactions. The subsequent chemical reaction corresponds to a second‐order process, a dismutation reaction electrochemically initiated. Data about rate constants and half‐life times in mixed media are reported.
Electroreduction of benzoylacetanilides in nonaqueous medium
Authors: Abou‐Elenien G. M. , El‐Anadouli B. E. , Baraka R. M.
Published: May 2005

The electroreduction of three series of benzoylacetanilides has been investigated in benzonitrile at a platinum electrode. One series (I) contains substituents on the benzoyl moiety, the second (II) has the substituents on the anilide moiety, and the third (III) has substituents on both the anilide and benzoyl moieties. All of these compounds are reduced in a single irreversible two‐electron process forming the corresponding dianion which abstracts protons from the media to saturate the anilide CO. A good linearity is obtained when the E1/2 value is plotted against the substituent constant of the substituents in the different series (I–III).
Electrochemical reduction behavior and analysis of some organophosphorous pesticides
Authors: Subbalakshmamma M. , Reddy S. Jayarama
Published: May 2005

The electrochemical reduction behavior of organophosphorous pesticides such as monocrotophos, phosphamidon, and dichlorvos have been studied by employing dc polarography, cyclic voltammetry, ac polarography, differential pulse polarography miilicoulometry, and controlled potential electrolysis. The general reduction mechanism of these compounds has been suggested based on the results obtained. A differential pulse polarographic method is developed for the determination of title compounds in agricultural formulations. Both standard addition and calibration methods are used for the analysis experiments. The lower detection limits are found to be 1.0 × 10−8, 1.25 × 10−8 and 1.2 × 10−8 respectively.
Formation of an intermetallic compound between selenium and copper
Authors: Somer Güler , Karacan Mehmet S.
Published: May 2005

When selenite solutions are determined in the presence of copper using anodic stripping voltammetry (ASV), a new peak appears, which is not associated with copper or selenium. It is attributed to the formation of an intermetallic compound between copper and selenium. To verify the existence of such a compound, cyclic voltammograms have been recorded. It has been shown that there is formation of such a compound, and its composition depends on the copper‐to‐selenite ratio.
Stabilization of the redox polymer [Os(bipy)2(PVP)10Cl]Cl by in situ chemical cross‐linking
Authors: Doherty Andrew P. , Buckley Tim , Kelly David M. , Vos Johannes G.
Published: May 2005

The redox polymer [Os(bipy)2(PVP)10Cl]Cl, where bipy is 2,2′‐bipyridy and has been physically stabilized by chemical cross‐linking at various levels via the solid‐state reaction with the cross‐linking agents p‐dibromobencane, 1,5‐dibromopentane, and 1,10‐ dibromobencane. The stability of the resulting polymer films under the severe hydrodynamic conditions of thin‐layer flow cells and at rotating disk electrodes (RDEs) was greatly increased compared to the uncross‐linked polymer. The charge transport properties of the redox polymer were maintained or improved by cross‐linking. The surface and Nernstian behavior of the cross‐linked redox materials are not found to be substantially affected by cross‐linking.
Electrochemical immunoassay: Simple kinetic detection of alkaline phosphatase enzyme labels in limited and excess reagent systems
Authors: Treloar Paul H. , Nkohkwo Asa'ah T. , Kane John W. , Barber Don , Vadgama Pankaj M.
Published: May 2005

Kinetic measurement of an alkaline phosphatase enzyme label was performed with amperometric detection using conversion of substrate 4‐aminophenyl phosphate to the electroactive phenolic, measured at +125 to +200 mV tvs. Ag/AgCl. Calibration plots for thyroxine‐binding globulin (TBG) and cortisol were obtained by excess reagent and limited reagent immunoassays, respectively, which were comparable with those obtained using colorimetric detection. These provided a measurement range of 31–1000 μg/L for TBG and 100–2000 nM for cortisol. An antibody‐bound label was monitored in this system, and covering the electrode with a simple dialysis or polycarbonate membrane avoided electrode fouling. The kinetic mode of detection reduced assay time and helped to simplify the assay protocol.
Electrochemical study of isopolymolybdate(VI) anion transfer across the water/nitrobenzene interface
Authors: Wang Erkang , Wang Hanming
Published: May 2005

Isopolymolybdate (VI) anion transfer across the water/nitrobenzene (w/n) interface was studied by cyclic voltammetry. The effect of pH and responsed kinetics of isoplymoybdate anion's formation in the water phase on the transfer behavior have been studied. At 1.0 < pH < 3.0 and 7.0 > pH > 5.8, transfer species are [HMo8O26]3− and [H2Mo–O24]4−, respectively. At 5.8 > pH > 3.0, the two anions can transfer across the w/n interface simultaneously. Transfer process was contrilled by difusion of isopolymolybdate anions toward the interface. The standard transfer potentials Δφ0 and the standard Gibbs energy ΔG, of the two isopolymolybdate anions were determined, and the transfar mechanism has been discussed.
Utilization of Canavalia maritima as biocatalyst for urea biosensors
Authors: de Oliveira Neto Gracliano , Godinho Oswaldo E. S. , Aleixo Luiz M. , da Silva Valdinete L.
Published: May 2005

Seeds of Canavalia maritima are ground after removal of the external coat and are used for the construction of a new enzymatic electrode for urea. Aliquots (10 mg of the powder) are immobilized at the surface of an ammonia gas‐sensing electrode, via glutaraldehyde or, alternatively, on PVC membranes. The analytical performance of the biosensors for serum urea determination is comparable to the spectrophotometric method.
Investigations of platinized and rhodinized carbon electrodes for use in glucose sensors
Authors: White Stephen F. , Turner Anthony P. F. , Schmid Rolf D. , Bilitewski Ursula , Bradley Joanne
Published: May 2005

Graphite electrodes were modified by the electrodeposition of either platinum or rhodium, using cyclic voltammetry. Following only brief periods of treatment, platinized carbon electrodes were able to directly oxidize glucose at a potential of +350 mV (vs. Ag/AgCl). By narrowing both the potential range of deposition (–450 to –500 mV) and cycling period (50 seconds at a scan rate of 10 mV s−1), the effects of direct glucose oxidation could be significantly reduced. Detection of H2O2 at +400 mV was possible; glucose enzyme electrodes were constructed, with glucose oxidase immobilized in hydroxyethylcellulose, and operated at this potential. These sensors had a linear range of 0.1 to 25 mM glucose and a slope of 8 nA/mM. Other electrodes were prepared by the electrodeposition of rhodium. These base electrodes proved to be insensitive to glucose and produced‐higher currents (compared to low platinum electrodes) to H2O2. Glucose sensors were constructed using rhodinked electrodes. Again operating at + 400 mV, these sensors had a linear range from 0.1 to 20 mM and a slope of 21 nA/mM glucose.
Indirect determination of surfactants by adsorptive voltammetry: Part 1: Determination of Trace and Ultratrace Concentrations of Sodium Dodecylbenzene Sulfonate
Authors: Adeloju S. B. , Shaw S. J.
Published: May 2005

The determination of sodium dodecylbenzene sulfonate based on the suppression of the adsorptive voltammetric response of nickel in the presence of dimethylglyoxime is described. Sensitive and accurate determination of the anionic surfactant is accomplished at trace and ultratrace concentrations by the use of a combination of electrodes, such as the hanging mercury drop electrode (HMDE), glassy carbon mercury film electrode (GCMFE), and a dropping mercury electrode (DME), The first two electrodes enabled the determination of sodium dodecylbenzene sulfonate down to ultratrace concentrations, while the latter was useful for rapid determination of trace concentrations of the surfactant. Despite the higher sensitivity obtained for the anionic surfactant on the GCMFE, the best limit of detection of 100 μg/L and the optimum recovery efficiency of 104 ± 8% were accomplished with the HMDE. Compared with the widely accepted spectrophotometric method, the adsorptive voltammetric approach is more rapid, has a much wider linear concentration range (based on the combined use of an HMDE or GCMFE and the DME), and is applicable at the ultratrace level.
Indirect determination of surfactants by adsorptive voltammetry: Part 2: Determination of hexadecyl trimethyl ammonium bromide and cetyl pyridinium chloride in industrial and consumer products
Authors: Adeloju S. B. , Shaw S. J.
Published: May 2005

A method is described for the indirect determination of trace and ultratrace concentrations of hexadecyltrimethylammonium bromide (HTMAB) and cetyl pyridinium chloride (CPC) in industrial and consumer products by adsorptive voltammetry The determination of HTMAB at the trace concentration was accomplished by an indirect adsorptive polarography on a dropping mercury electrode (DME), while the determination of ultratrace amounts of CPC was performed by an indirect adsorptive stripping voltammetry on a hanging mercury drop electrode (HMDE). The detection limits accomplished for these surfactants were 5 mg/L and 10 μg/L, respectively. These were up to 100 times lower than those obtained by the spectrophotometric method. The linear concentration ranges accomplished for the surfactants under the specified conditions were 0–65 mg/L and 0–300 μg/L, respectively. The development and the incorporation of a simple and rapid separation scheme based on the use of a C18 sep‐pak cartridge with the adsorptive polarographic and voltammetric techniques were effective in overcoming the matrix interference problem from commercial domestic products. The application of the method to industrial and consumer products, such as disinfectant, lozenges, and mouth wash solutions was successful, resulting in an average recovery efficiency of 93 ± 9% for both surfactants.
Inner reference electrodes and filling solutions conferring linear temperature characteristics on glass pH electrodes
Authors: Midgley Derek
Published: May 2005

Glass electrodes with linear temperature characteristics are described. By use of a Ag‐AgBr inner reference element and an inner reference solution containing a zwitterionic buffer (MOPS), an electrode is obtained that almost has the ideal characteristics of isopotential pH (pHiso = 7) and zeropoint pH (pH0 = 7) necessary for use with the temperature compensation circuits on most pH meters. A conventional Ag‐AgCl (3 M KCl) external reference electrode is used. Excellent linearity of changes in standard potential has been observed in the range tested (5 to 65°C), and the slope factor, thermal hysteresis, and speed of response to temperature change are as good as for commercially available electrodes. The application of electrodes with these characteristics should improve the accuracy of temperature compensation in industrial and environmental measurements. Other inner‐reference electrodes and buffers are considered.
Fabrication and characterization of tips for electrochemical scanning tunneling microscopy
Authors: Chen Zhen Fang , Wang Erkang
Published: May 2005

We report a new technique for preparing tips for electrochemical scanning1 tunneling microscopy (ECSTM) with particular consideration of its simplicity and reproducibility. In preparing scanning tunneling microscopy (STM) tips by electrochemical etching, we chose an etching process with the formation of a neck‐shaped part of an etched wire by applying a suitable etching voltage, and then we adopted a two‐step etching process to prevent over etching. The prepared tip possessed a curvature of 100 to 300 nm, much smaller than that of the tip prepared by the conventional method. The etched tip was insulated with silicon rubber or epoxy resin under an optical microscope. This controllable technique allows that a reproducible tip with an exposed area of 0.44 to 7.76 μm2, which has proved to be available for in situ experiment, could be made.
Amperometric flow‐injection analysis of purine nucleotides: Comparison of selectivity for hydrolytic cleavage of purine nucleotides
Authors: Yao Toshio , Tsureyama Kiminori , Nakahava Taketoshi
Published: May 2005

Four hydrolases (alkaline phosphatase, apyrase, 5′‐nucleotidase, and adenosine‐5′‐triphosphatase) are immobilized onto the controlled‐pore glass, respectively. They are used as the reactor for the enzyme‐catalyzed hydrolytic cleavage of purine nucleotides, in a flow‐injection system based on the combined use of the following coimmobilized purine nucleoside phosphorylase–xanthine oxidase reactor and amperometric detector downstream. Four hydrolase‐immobilized reactors possess interesting differences in the selectivity for the hydrolytic cleavages of purine nucleotides. The alkaline phosphatase reactor catalyzes enzymatically the complete conversion of all the purine nucleotides to the corresponding nucleosides. The apyrase reactor converts completely both nucleoside triphosphate and diphosphate to nucleoside monophosphate. The 5′‐nucleotidase reactor is selective for the hydrolytic cleavage of nucleoside monophosphate to nucleoside. The analytical importance of these hydrolase‐immobilized reactors is discussed for the selective detection of purine nucleotides.
Micromachined electrochemical flow cell for biosensing
Authors: Murakami Yuji , Uchida Takashi , Takeuchi Toshifumi , Tamiya Eiichi , Karube Isao , Suda Masayuki
Published: May 2005

A miniaturized electrochemical flow cell was fabricated on a silicon substrate using micromachining techniques, including photolithography, vacuum deposition, anisotropic etching, and fusion bonding. The flow cell consisted of a glass plate with gold elearodes, a silicon chip with a V‐shaped groove, and immobilized glucose oxidase. Hydrogen peroxide and glucose were measured by direct‐batch injection and by using the device in flow‐injection analysis (FIA) system.
Electrocatalytical oxidation of glucose on graphite using covalently immobilized glucose oxidase and 1,6‐dithia‐ and 1,6‐dioxapyrenes as mediators
Authors: Kulys J. , Razumas V. , Kazlauskaite J. , Marcinkeviciene J. , Buch‐Rasmussen T. , Hansen H. E. , Bechgaard K. , Christensen J. B. , Frederiksen P.
Published: May 2005

Electrocatalytical oxidation of glucose on graphite using new mediators (1,6‐dithiapyrenes (DTPs) and 1,6‐dioxapyrenes) was performed. The electrocatalysis of glucose oxidase (GO) was based on the dithia(dioxa)pyrene cation‐radicals reaction with reduced GO. The rate of reduced GO oxidation by the cation‐radical of dithiapyrene was 4.8 × 104 M−1 s−1 at 25°C (pH 7.0). For enzyme electrode preparation, the GO was covalently immobilized by carbodiimide, and the mediator was adsorbed on a graphite electrode. The dithia(dioxa)pyrenes mediated glucose oxidation proceeds at potentials higher than 0.1 V (versus standard calomel electrode (SCE)). Of the investigated substituted dithia(dioxa)pyrenes, the largest electrocatalytical current was observed with electrodes comprising of DTP. Linear calibration graphs of these electrodes were obtained up to 12 mM of glucose, the maximal electrode activity was in the range of pH 6.5 to 8.0, and the temperature coefficient was 5.6%/°C. The investigated electrocatalytical systems can be used for construction of disposable senses for glucose determination in physiological solutions.
Individual and simultaneous determination of zinc and cadmium in biological tissues by flow injections / stripping voltammetric analysis
Authors: Izquierdo A. , De Castro M. D. Luque , Valcárcel M.
Published: May 2005

A flow‐injection (FI) voltammetric‐stripping method for the simultaneous determination of Cd and Zn is proposed after a systematic study of the variables affecting the method. The low determination limits, 1 × 10−9 and 5 × 10−9 M (detection limits 8 × 1010– and 2 × 10−9 M for Cd and Zn, respectively), and rsd. values, 1.57 and 5.16% for Cd and Zn, respectively, allow one to apply the method to real samples (biological tissues and reference materials) with good results. No formation of intermetallic compounds was detected.
Electrochemical behavior and determination of β‐carboxyethylgermanium sesquioxide
Authors: Hasebe Kiyoshi , Hikima Satoshi , Motonari Masayuki , Yamagishi Akihiko , Kakizaki Teiji
Published: May 2005

This article describes the electrochemical behavior of β‐carboxyethylgermanium sesquioxide (Ge‐132) on mercury electrodes in weakly acidic solution. The Ge‐132 exhibits two Well‐defined cathodic waves in linear‐sweep voltammetry and polarography. The first wave in a voltammiogram of Ge‐132 is a simple two‐electron reduction and exhibits the property of adsorption. From chronoamperometry, the reaction in die second wave, however, proves to be an ECE mechanism and ultimately yields metallic germanium and propionic acid. The determination of small amounts of Ge‐132 is investigated by differential pulse polarography in an acetate buffer. The detection limits of Ge‐132 are below 0.2 μmol dm−3.
Electroanalytical study of chelating extractants: LIX 34
Authors: Huebra Marta M. , Elizalde Maŕia P. , Castresana José M.
Published: May 2005

The voltammetric behavior of 4‐methyl‐N‐8‐quinolinybenzenesulfonamide, closely related to the active component of the commercial extractant LIX 34, has been studied in 0.1 M KCl/25% methanol medium as a function of pH, using polarography and cyclic voltammetry techniques. The elearochemical behavior of the extractant in the presence of Cu (II) ions has also been described. The commercial LIX 34 product exhibits a similar behavior both in differential pulse polarography and cyclic voltammetry, and polarogrnahic determination methods have been developed for both reagents. The relationship between reduction peak current and concentration is linear up to 1.96 × 10−6 M for 4‐methyl‐N‐8‐quinolinylbenzenesulfonamide, and the corresponding function for LIX 34 indicates a low percentage of the active component in the commercial extractant.
New amperometric dehydrogenase electrodes based on electrocatalytic NADH‐oxidation at poly (methylene blue)‐modified electrodes
Authors: Karyakin Arkady A. , Karyakina Elena E. , Schuhmann Wolfgang , Schmidt Hanns‐Ludwig , Varfolomeyev Sergei D.
Published: May 2005

Poly(methylene blue) (PMB)‐modified electrodes show excellent properties for the electrocatalytic oxidation of NADH concerning the optimal working potential of 0 to 100 mV (vs. SCE)and their operation stability. By means of dehydrogenases entrapped within a Nafion film on top of the PMB layer, new amperometric biosensors for glucose, lactate, malate, and ethanol could be obtained with improved integration of the enzyme and the electrocatalyst directly on the electrode surface. Coentrapment of the negatively charged NAD+within the negatively charged Nafion Polyelectrolyte leads to reagentless dehydrogenase electrodes for one‐shot or short‐term applications.
Lactate biosensor based on a lactate dehydrogenase/nicotinamide adenine dinucleotide biocomposite
Authors: Wang Joseph , Chen Qiang
Published: May 2005

A new biocomposite, fabricated by incorporating lactate dehydrogenase (LDH) and nicotinamide adenine dinucleotide (NAD+) within a graphite‐epoxy matrix, is used as a polishable (renewable) and robust biosensor for lactate. Highly sensitive and rapid amperometric biosensing is accomplished at relatively low potentials. The regeneration capability of the biocomposite probe circumvents problems of surface fouling inherent to the detection of NADH. Flow injection detection of lactate, with a sample throughput of 60/h, detection limit of 5 × 10−4 M, precision of 2.5% (RSD for n = 40), and linearity up to 2 × 10−2 M, is illustrated.
Polypyrrole‐based amperometric biosensor for sulfite determination
Authors: Adeloju S. B. , Shaw S. J. , Wallace G. G.
Published: May 2005

An amperometric biosensor for sulfite determination, based on the incorporation of sulfite oxidasen (SOD) into a polypyrrole film by galvanostatic formation, has been successfully developed. The use of the biosensor involves the application of a constant potential of –700 mV, which promotes oxgen reduction as the predominant reaction. The optimum analytical conditions for the biosensor were 0.1 M phosphate buffer with 0.5 M KC1. pH 7.0, and a platinum disk electrode. The response of the biosensor to sulfite was linear from 0 to 80 mg/L, and the minimum detectable amount was found to be 5 mg/L. Usual interferants in sulfite determination such as ascorbic acid, sodium nitrite, and sodium sulfate did not interfere with the biosensor. The excellent resproducibility of the sulfite response with 4 hours of repeated use provides the basis for the construction of a disposable or renewable biosensor for sulfite determination.
Simultaneous determination of copper, lead, cadmium, and zinc in previously lyophilized biological tissues using flow‐injection analysis/anodic stripping voltammetry
Authors: Izquierdo A , de Castro M. D. Luque , Valcárcel M.
Published: May 2005

Improvements in three main aspects of the analysis of metal traces in biological tissues are proposed, namely: (a) lyophilization of the samples both to preserve them and to favor the digestion process; (b) digestion of the lyophilized tissues using an effective and fast procedure; and (c) automatic determination of the target analytes by flow‐injection analysis/anodic stripping voltammetry (FIA/ASV). After optimization of these steps, the overall procedure was successfully applied to the simultaneous determination of copper, lead, cadmium, and zinc in certified reference materials (CRMs) and fresh bovine liver samples with good results. Finally, the performance of the method was validated by a statistical study using parameters of the certification campaign of the CRMs; the results obtained being within, or close to, the confidence levels of the certification campaign.
A biosensor for L‐amino acids using polytyramine for enzyme immobilization
Authors: Cooper Julia C. , Schuber Florian
Published: May 2005

Electrodeposition of polytyramine is demonstrated to be a simple and convenient procedure for electrode modification, generating amine groups to which L‐amino acid oxides can be covalently bound. An L‐amind acid oxidase (L‐AAOD)‐polytyramine electrode can be used for detection of L amino acids, via the current due to oxidation of enzymatically produced hydrogen peroxide. The calibration graph of the sensor for phenylalanine is linear up to 1.4 mM with a lower limit of detection of 0.07 mM. The useful measuring range for leucine is between 0.07 and 3 mM. The enzyme‐polytyramine electrodes are stable for more than 1 month. The polymer coating affords some protection of the elearode from direct (nonenzymic) oxidation of electroctive amino acids, which may otherwise cause elecatrode fouling, although at present, the polymer selectivity is insufficient to prevent errors in estimation of analyte concentration.
Electrochemical characterization of a novel organic electrolyte gel
Authors: Nahir Tal M. , Qiu Yong‐Jian , Williams Joel L.
Published: May 2005

The fabrication and electrochemical characterization of a variety of self‐supported thermorevrsible organic electrolyte gels prepared using l,3:2,4‐dibenzylidene sorbitol (DBS) as a gelling agent are reported. Impedance analysis and cyclic voltammetry were used to examine these gel systems, which exhibit ionic conductivities similar to corresponding liquid electrolyte solutions.
Amperometric glucose sensor containing nondiffusional osmium redox centers: Analysis of organic‐phase responses
Authors: Iwuoha Emmanuel I. , Smyth Malcolm R. , Vos Johannes G.
Published: May 2005

Glucose oxidase (GOx) electrodes were constructed by complexing GOx with the redox osmium macromolecule, [Os(bpy)2(PVP)20Cl]Cl (abbreviated Os‐Polymer). The biosensor produced high catalytic current densities in response to β‐D‐glucose in solvent media that were up to 100% in acetonitrile. The sensor, which functions by relaying electrons between GOx flavin adenine dinucleotide redox sites {GOx(FAD/FADH2)} and the electrode, showed great improvement in its organic‐phase responses in the presence of certain amounts of water. Cyclic voltammograms were analyzed for the elucidation of reaction mechanism and determination of the formal electrode potential (E°′). The electrode potential E°′ decreased as water content of the medium increased. Steady‐state responses of the sensor in CH3CN/H2O mixtures, 1 to 35% v/v in H2O, were observed at 450 mV. The kinetic analysis of the steady‐state amperometric response of the biosensor was based on a rapid charge propagation within the polymer compared to the enzyme kinetics. Maximum steady‐state current density jmax and apparent Michaelis‐Menten constant KM were evaluated from electrochemical Eadie‐Hofstee plots. Our results show that jmax reached an optimal value of 282 μA cm−2 in CH3CN/H2O (80 + 20% v/v). There was no drastic change in KM for the different CH3CN/H2O media. This indicates that CH3CN does not bind to, or act as a cosubstrate for, the immobilized GOx. Effect of water on sensor response in the polar organic solvent has been explained on the basis of its role in increasing the flexibility of the immobilized GOx active site environment.
A study of the differential pulse polarographic and stripping voltammetric behavior of the H+/K+ ATPase inhibitor SK&F 95601 and its degradation products
Authors: McClean S. , Maxwell T. , Ramachandran V. N. , O'Kane E. , Smyth W. F.
Published: May 2005

The differential pulse polarographic (DPP) behavior of SK&F 95601 (I) has been studied I the pH range 0 to 14. At pH ≤ 2, (I) rapidly degrades into the sulfenamide (D) and (D), which are both reduced by 2e− processes, the former being subject to strong reactant adsorption. SK&F 95601 itself is reduced in a 4e process up to pH10, and either pK2 or pK3 values, determined spectrophotometrically, are manifested polarographically at neutral pH. A pK5 value of 9.0 corresponding to the benzimidazole N‐H group deprotonation is manifested polarographically with a pK′5 value of ca. 11. SK&F 95601 and its degradation produce D, degraded D, and D can all be determined by adsorptive stripping voltammetry (AdSV) with limit of detections (LODs) of 10−8 mol dm−3, except for the latter molecule with an LOD of 10−7 mol dm−3. These LODs are superior to those determined by DPP. Mixtures of these molecules can also be resotved with similar LODs. Cd2+ can be determined by ASV with a superior LOD in the presence of (I), i.e 0.08 ppb as compared to 0.57 ppb in its absence, due to chelation phenomena.
The adsorption of 1,4‐dibromobenzene on gold electrodes: A combined in situ infrared and surface‐enhanced raman spectroscopic investigation
Authors: Schomaker Silke , Holze Rudolf
Published: May 2005

1,4‐dibromobenzene (DBB) was adsorbed on a polycrystalline gold electrode from aqueous solutions. In situ vibrational infrared (IR) and Raman spectroscopy yielded results implying an edge‐on coordination of the adsorbed molecule. Adsorption does not only involve the ring an system of the molecule, but also its bromide substituents. In comparison to the potential‐modulated in situ IR method, the Raman spectroscopy shows higher sensitivity for adsorbate detection.
Wall‐Jet electrode system for anodic stripping voltammetry
Authors: Omanović D. , Peharec Ž , Magjer T. , Lovrić M. , Branica M.
Published: May 2005

A construction of an electroanalytical cell with a wall‐jet electrode (WJE) system consisting of a built‐in centrifugal pump and a thin mercury film‐covered glassy carbon stationary disk working electrode and its application to the differential pulse anodic stripping voltammetric measurements of traces of cadmium and lead are described. Characteristics of the new hydrodynamic electrode system are compared with the properties of the rotating disk electrode (RDE). The new described system yields rather high flow rates (2 to 12 mL/s) exhibiting about a twofold higher accumulation rate than the RDE. It allows shorter deposition time, faster analysis, and lower determination limits of trace metals in water samples. Experimental determination limit for lead ions of 8 × 10−12 M, after accumulation of 7.5 minutes with turbine rotating of 2500 rpm, was obtained.
Ligand‐catalyzed metal ion reduction: Kinetics and analytical applications of nickel reduction catalyzed by nicotinamide
Authors: Bǎnicǎ Florinel‐Gabriel , Doicin Luminiţa‐Irinel , Fodor Alexandrina , Ion Ana
Published: May 2005

The catalytic reduction of Ni (II) in the presence of nicotihamide (NA) at pH < 7 was studied by direct‐current and differential‐pulse polarography (DPP). The prewave (with E1/2 around –0.78 V (versus saturated calomel electrode (SCE)) shows the typical behavior of an electrode process with regeneration of the reactant by a second‐order, rate‐determining chemical reaction. This reaction consists in the formation of the reducible nickel complex. The kinetics of the electrode process was studied by means of an adapted form of the equation derived by Koutecký for electrochemical reactions with a parallel chemical step. The rate constant for the formation of nickel‐nicotinamide complex is slightly dependent en pH and buffer composition and ranges between 4.5 and 6.7 × 103 mole−1 L s−1. This electrode process enables the selective determination of Ni (II) in presence of a large excess of cobalt. For example, nickel impurity in cobalt salts can be determined by DPP, in acetate buffer (pH 4.6) containing 0.01 M nicotinamide and about 0.1 M cobalt salt sample.
An ion‐gate response of a glutathione monolayer assembly highly sensitive to lanthanide ions
Authors: Takehara Kô , Aihara Makoto , Ueda Nami
Published: May 2005

The self‐assembled glutathione (γ‐L‐glutamyl‐L‐cysteinyl‐glycine, GSH) monolayer was formed on a gold electrode via a sulfur attachment of the cysteinyl residue. The effect of lanthanide ions (La3+, Eu3+ and Lu3+) on the ion‐gate behavior of this electrode was studied by using cyclic voltammetry (CV) and Fe(CN)63– as a probe ion. These ions were found to open the ion gate with a few micromoles, and the effect was in the order of La3+ > Eu3+ Lu3+.