bluuebunny/crossref_metadata_2025_split huggingface dataset:
A thermodynamic test of the diffuse layer theory and its implications on electrode kinetics
Authors: González Ramon , Sanz Fausto 
Published: May 2005

AbstractThe 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

AbstractPolypyrrole 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

AbstractThis 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

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractA 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

Abstract(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

AbstractAn 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractCyclic 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractPolarograms 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.
Enzyme‐catalyzed direct electron transfer: Fundamentals and analytical applications
Authors: Ghindilis Andrey L. , Atanasov Plamen , Wilkins Ebtisam 
Published: May 2005

AbstractThis article overviews the fundamentals of the phenomenon of direct electron transfer in enzyme‐catalyzed electrode reactions and the development of electroanalytical applications of the bioelectrocatalytic systems. A brief description of the enzymes capable of catalyzing electrochemical reactions by means of direct electron transfer is given. The physico‐chemical background of bioelectrocatalysis is discussed in terms of the different concepts underlying the mechanism of electron transfer. The concept of a “molecular transducer” is introduced to designate a complex, formed by the electrocatalytically active enzyme on the electrode‐electrolyte interface, which is directly responsible for the transduction of the chemical signal to an electric one. The role of this “molecular transducer” in enzyme electrodes and immunoelectrodes is discussed. The analytical applications of bioelectrocatalysis are categorized as systems employing either amperometric or potentiometric detection. Discussion focuses on the advantages of systems based on enzyme‐catalyzed direct electron transfer as opposed to other enzyme‐catalyzed electroanalytical devices. In conclusion, the trends towards upcoming practical applications are suggested as well as some directions in fundamental studies of bioelectrocatalysis as a phenomenon.
Determination of antimony(III) and antimony(V) in copper plant electrolyte by anodic stripping voltammetry
Authors: Bond Alan M. , Kratsis Steven , Newman O. Michael G. 
Published: May 2005

AbstractThe concentration of antimony in copper plant electrolyte needs to be known at the ppm level. Spectroscopic techniques for trace metal determination in this electrolyte, such as atomic absorption and inductively coupled plasma (ICP) spectrometry only enable total antimony to be determined, whereas ideally the concentration of both the antimony(III) and antimony(V) oxidation states needs to be known. For the determination of antimony(III) and antimony(V) by differential pulse anodic stripping voltammetry (DPASV), the similar stripping peak potentials of −0.37 V(vs. Ag/AgCl) for copper and −0.27 V(vs. Ag/AgCl) for antimony in 5 M HCl mean that concentrations of copper greater than 6 times that of antimony cause difficulties in resolving the antimony and copper stripping peaks. In this article, a simple procedure is reported for the determination of antimony(III) and (V) in copper plant electrolyte after separation of antimony from copper by passing an ammoniacal solution of plant electrolyte through a column of Chelex‐100 ion‐exchange resin. Most of the copper is retained on the column so that the determination of antimony(III) and (V) by DPASV is possible after addition of hydrochloric acid to the eluent. Total antimony is determined in 5 M HCl and antimony(III) in 0.1 M HCl. Total antimony concentrations correlate well with data obtained by ICP and recoveries of antimony in both oxidation states are > 96%.
Investigation of the performance of microelectrodes with micrometer size structural diameters
Authors: Tian Min , Jing Xinli 
Published: May 2005

AbstractA microelectrode was fabricated by coating a silicon dioxide film on the Pt wire surface. The fabricated electrode was then characterized by scanning electron micrographs, energy spectrum, cyclic voltammetry, differential pulse voltammetry and AC impedance spectroscopy. A welldefined sigmoidal response for reduction of potassium ferricyanide showed that the electrode has a high mass transport rate, which is the feature of the microelectrode. The micrometer scale size permits it to be used in vivo, and the absence of epoxy resin (as insulator material) also makes the presented microdisk electrode suitable for electroanalysis in nonaqueous media.