bluuebunny/crossref_metadata_2025 huggingface dataset:
Adsorptive‐catalytic stripping voltammetry‐enhanced reduction current of adsorbed CoII tetraaza[14]annulene complex in the presence of CO2
Authors: Muszalska Elżbieta , Bilewicz Renata
Published: May 2005

The macrocyclic cobalt(II) complex CoL (LH2 = 5,14dihydrodibenzo[b,i][1,4,8,11] tetraaza[l4]annulene) can be adsorptively preaccumulated on mercury electrodes from highly diluted aqueous solutions. The adsorbed CoII complex undergoes one‐electron reduction with subsequent protonation of [CoL]− to CoLH, also adsorbed on mercury. The electrode covered with adsorbed complex may be used to detect CO2, since upon substitution of argon by CO2 a large catalytic peak is observed at the potentials of CoLH complex reduction. At constant CO2 concentration, the peak first increases proportionally to the extent of coverage of the electrode with the adsorbed complex and then becomes constant when monolayer coverage is attained. At a monolayer covered electrode the catalytic reduction signal increases proportionally to the increase of CO2 concentration. The usefulness of the normal pulse voltammetry version of the adsorptive‐catalytic stripping procedure is also shown.
The reduction of m‐iodo‐nitrobenzene: A comparative study using microdisk and channel electrodes
Authors: Compton Richard G. , Dryfe Robert A. W. , Eklund John C. , Nei Lembit , Page Stephen D.
Published: May 2005

The reduction of m‐iodo‐nitrobenzene, m‐I‐ϕ‐NO2, in acetonitrile solution was studied using both microdisk and channel electrodes. A voltammetric wave with a halfwave potential of −1.09 V (vs. saturated calomel reference electrode) was observed and both techniques showed that more than one electron was passed per molecule of the substrate. The rates of mass transport were varied in both electrode systems by changing either the electrode radius in the case of microelectrodes, or the electrolyte flow rate in the case of channel electrodes so as to identify the kinetics and mechanism of the electrode process. Both approaches indicated an ECE mechanism operates: magnified image where HS denotes the solvent‐supporting electrolyte system. The rate constants for the decomposition of the radical anion, [m‐I‐ϕ‐NO2]˙, as determined by the two methods, were in excellent agreement and equal to 0.30(0.05) s−1. Comparisons between the use of microdisks and channel electrodes for such studies are reported and their relative sensitivity assessed.
Detection of cytochrome c using a conducting polymer mediator containing electrode
Authors: Lu Wen , Zhao Huijun , Wallace Gordon G.
Published: May 2005

In this work, we have demonstrated the feasibility of cytochrome c detection using a novel mediator‐incorporated conducting polypyrrole‐based electrode. The mediator used was Fe(CN). The effect of buffer solution pH and electrochemical conditions on the voltammetric responses of cytochrome c have been investigated. The analytical utility of this electrode has been demonstrated using flow injection analysis.
A potentiometric polypyrrole‐based glucose biosensor
Authors: Trojanowicz Marek , Hitchman Michael L.
Published: May 2005

A new concept is described for monitoring a biomolecule with a sensor having an enzyme entrapped in a conducting polymer. This is based on the sensitivity of the electroactive polymer itself to changes of pH in solution. The concept has been investigated for a glucose sensor with glucose oxidase (GOD) immobilized in a polypyrrole (PPy) layer on an inert platinum electrode. Measurements with a Pt/PPy/GOD electrode for glucose concentrations in the physiological range gave a linear correlation with logarithm of concentration over one decade with a satisfactory dynamic response. There was practically no change of slope or range of linear response to glucose after several days of use; this was in contrast to the amperometric response of the detector when there was about a 50% loss of sensitivity.
On the mechanism of electrooxidation of hydrazine on platinum electrodes in acidic solutions
Authors: García Maria D. , Marcos Maria L. , Velasco Jaime González
Published: May 2005

A systematic study of the electrooxidation mechanism of hydrazine on Pt electrodes in 0.5 M H2SO4 solutions has been made. The experimental rate equation found is magnified image This can be theoretically explained by a five step mechanism. The log I vs. log Chyd linear plot that results in the determination of the reaction order respect to hydrazine concentration can be used as a working curve for quantitative analytical determination of hydrazine concentrations. A mechanistic explanation has been found for the unusual dependence of the Tafel slope with the pH value.
Effect of membrane composition on the flow‐injection response of an ion‐selective electrode: A comparative study based on selectivity coefficients calculated using a data linearization technique
Authors: Davey David E. , Mulcahy Dennis E. , O'connell Gregory R.
Published: May 2005

Commercial iodide, sulfide and cadmium‐selective electrodes and four electrodes based on laboratory‐prepared pressed membranes, the latter composed of either silver iodide or a mixture of silver iodide and sulfide, were assessed for their flow‐injection response towards iodide in the absence and presence of bromide, thiocyanate and thiosulfate. With the exception of a pressed membrane based on a 3:1 mixture of AgI and Ag2S, which gave rise to erratic, irreproducible potentials, all the electrodes responded rapidly to iodide. While detection limits were generally similar, slope factors ranged from −44.6 mV/decade for a pressed AgI membrane to −61.2 mV/decade for a 1:3 AgI/Ag2S membrane. Selectivity coefficients were determined for each of the electrodes by intercalating mixed iodide‐interferent solutions into a 10−6 M iodide carrier stream, then processing the resultant data by both the accepted IUPAC graphical method and a proposed data linearization technique. Although the two methods returned comparable results for the electrodes and interferents examined, the linearization procedure would be the preferred option in cases where the selectivity coefficients determined are greater than unity. Using electrode membranes composed of either AgI or AgI/Ag2S, a trend in selectivity was observed which suggests a mechanism of response towards the interferents involving the oxidation of the sulfide in the membrane to either sulfate or elemental sulfur.
Electrochemical oxidation of the diuretic indapamide
Authors: Legorburu María J. , Alonso Rosa M. , Jiménez Rosa M.
Published: May 2005

The electrochemical oxidation of the 3‐(Aminosulfonyl)‐4‐chloro‐N‐(2,3‐dihydro‐2‐methyl‐1H‐indol‐1‐y1)benzamide, Indapamide, was studied in aqueous alcoholic media (9:91 MeOH+H2O, pH range 1–13) and two different ionic media (KNO3 and KCl) at carbon electrodes. The oxidation processes attributed to indoline ring and benzamide moiety have been shown to be irreversible and diffusion‐controlled over the entire pH range in both media. A differential‐pulse voltammetric method was developed upon the basis of the voltammetric peak due to indoline ring, at pH around 2.3 (phosphate buffer) and using KNO3 as ionic medium. The peak current ip, showed a linear relationship with concentration in the range 5.92 × 10 −7 M–1.86 × 10 −5 M with a detection limit of 9.87 × 10−8 M (37 ppb) and a reproducibility (in terms of relative standard deviation) of 4.8% and 9.3% for 10 determinations of 2.67 × 10−6 M and 1.07 × 10−6M concentrations, respectively. The differential‐pulse voltammetric method for Indapamide was applied to assays of pharmaceuticals (Tertensif, 2.5mg) and urine samples.
Evaluation of diffusion coefficients of metallic ions in aqueous solutions
Authors: Kariuki Stephen , Dewald Howard D.
Published: May 2005

Many techniques are available for the determination of diffusion coefficients of ions in aqueous solutions. A review of classical and modern techniques is presented. Non‐electrochemical methods are discussed briefly. Electrochemical methods reviewed include chronoamperometry, chronopotentiometry, polarography, and hydrodnamics. Selected values of the diffusion coefficients determined by these electrochemical methods of the metallic ions AgI, BiIII, CdII, CuII InIII, PbII, TlI, and ZnII are presented.
Cyclic voltammetry with harmonic lock‐in detection: Applications to flow streams
Authors: Cullison John K. , Kuhr Werner G.
Published: May 2005

The second harmonic frequency is monitored using a conventional lock‐in amplifier in a continuous scan cyclic voltammetric experiment. The background charging current is predominantly composed of odd harmonic frequencies, while the analyte Faradaic signal is composed of both odd and even harmonic frequencies. By ‘locking‐in’ on the second harmonic frequency one can isolate the Faradaic current from the charging current in the frequency domain. Model compounds (hexaammineruthenium(III) chloride, ferrocene) at carbon and gold microelectrodes as well as carbohydrates at copper microelectrodes were examined in flow injection analysis experiments. Limits of detection an order of magnitude lower than DC amperometry were observed.
Ion‐selective electrodes – analogies and conclusions
Authors: Pungor Ernǒ
Published: May 2005

The author investigated the working mechanism of ion‐selective electrodes. The contradictions of theories deduced from so‐called analogous phenomena were discussed in detail. Based on experiments made by his research group he came to the conclusion that only the surface (the active groups located there) takes part in the potential‐determining reaction, and the bulk resistance of the membrane has a role only in the selection of the instrument used for potential measurement.
Cathodic stripping voltammetric determination of metallothioneins
Authors: Scarano Gioacchino , Morelli Elisabetta
Published: May 2005

A cathodic stripping voltammetric method for the determination of metallothioneins (MT) is proposed. The procedure is based on the controlled adsorption of the protein on the mercury electrode after addition of an excess of CuII to the solution. The effects of accumulation time, adsorption potential and copper concentration have been examined and the analytical procedure has been optimized. Using an accumulation time of 300 s, a MT concentration of 0.2 nM can be detected.
Detection of glucose at a rotating gold composite electrode by pulsed amperometric detection
Authors: Elliott Peter T. , Olsen Scott A. , Tallman Dennis E.
Published: May 2005

Segregated composite electrodes mimic microelectrode ensembles. In this preliminary report, the use of a rotating gold‐polychlorotri‐ fluoroethylene (or Kel‐F, a 3M Company polymer) composite electrode in combination with pulsed amperometric detection (PAD) is described for the detection of glucose. Comparisons are made with results obtained at a solid gold disk electrode. The composite electrode exhibits a higher signal and a lower background than does the solid gold electrode. In terms of current density, the enhancement of the signal above the background is over 3‐fold, similar to that observed with segregated graphite composite electrodes used in a constant potential mode. Little or no glucose signal is observed at either the solid gold or the gold composite electrode when employed in the constant potential mode. In the PAD mode, the signal is stable for periods in excess of an hour.
The electrochemical behavior of eastman AQ/meldola blue‐coated microelectrodes
Authors: Tian Min , Dong Shaojun
Published: May 2005

Eastman‐AQ 55D was coated onto a carbon fiber microelectrode surface, and the resulting modified electrodes exhibited high stability. Substantial improvement in the stability was observed as a result of good adhesion and the strong binding of large hydrophobic cations of Eastman AQ 55D. The electrode reaction of meldola blue bound in the polymer film showed a reversible, one‐electron transfer process. The effects of solution pH and influence of supporting electrolyte on the modified carbon fiber microelectrode are discussed. The diffusion coefficient of meldola blue in the AQ polymer film determined by chronoamperometry is 2.3 × 10−8 cm2 s−1, and the heterogeneous rate constant of meldola blue at the AQ polymer film/electrode determined by normal pulse voltammetry is 3.97 × 10−3 cm s−1.
Redox reaction of myoglobin at a benzimidazole‐modified silver electrode
Authors: Li Genxi , Fang Huiqun , Qian Yiqun , Chen Hongyuan
Published: May 2005

Benzimidazole could be attached to a silver electrode by a covalent bonding method to give a high stable chemically modified electrode. Not only was the modified electrode electroactive, myoglobin could also undergo redox reactions at the surface of the electrode. In 0.20 mol/L NaAc‐HAc buffer (pH 5.5), the benzimidazole modified electrode gave a pair of redox waves with a cathodic peak potential Epc of 0.10V and an anodic peak potential Epa of 0.25 V. On addition of myoglobin to the buffer, the peaks all increased due to the redox processes of the protein. In addition, comparison studies of the purified protein with the commercial sample revealed that myoglobin could still give electrode response even though it had not been previously purified. Therefore, benzimidazole modified silver electrode might be very attractive for the electrochemical studies of myoglobin.
Amperometric flow injection analysis of organic thiols and proteins
Authors: Hidayat Achmad , Hibbert D. Brynn , Alexander Peter W.
Published: May 2005

The amperometric determination of thiols by injection into a mercury carrier stream is shown to be a sensitive method when using a tungsten wire as the working electrode in a three‐electrode flow cell. Hg2+ gives sharp peaks when injected into phosphate buffer at pH 3.1 at an operating voltage of −0.24V (against a Ag/AgCl reference electrode). Hg2+ was determined in the range 0.43 to 25.0 μM with linear response. Injection of cysteine into the mercury carrier causes a decrease in the cathodic current, and sharp flow injection peaks are observed with a peak width of approximately 60 s. Optimization of various parameters was performed, including buffer effects, mercury concentration, injection volume, and the effects of various cations and anions on the response were determined. Linear calibrations in the range 0.25 μM to 100 μM for cysteine and 1.3 to 1000 ng for the other thiols glutathione, thiourea, albumin, and DNA were found. The responses to cysteine and thiourea were most sensitive, and interference from silver and iodate was observed at concentrations in excess of the thiols. The method may be used as a rapid means of detecting thiols in various samples and as an HPLC detection method.
Characterization of blend membranes of regenerated silk fibroin and PVA for immobilizing glucose oxidase and its application to a first generation of glucose sensors
Authors: Qian Jianghong , Liu Haiying , Liu Yongcheng , Yu Tongyin , Deng Jiaqi
Published: May 2005

The structure, water absorbability and mechanical properties of the blend membranes of regenerated silk fibroin and poly(vinyl alcohol) were investigated. IR spectra showed regenerated silk fibroin in the blend membranes exists chiefly in the silk I structure after ethanol treatment. An amperometric biosensor for glucose was constructed by coupling glucose oxidase in the blend membrane of regenerated silk fibroin and PVA with platinum electrode. Its experimental parameters such as pH, temperature and applied potential were optimized. It determined glucose in less than 25 s with good reproducibility and exhibited high storage and operational stability.
Variability of the slopes of standard addition plots in the analysis of copper in seawater by anodic stripping voltammetry
Authors: Sánchez‐Misiego Antonio , Carra Rosa García‐Moncó , Zirino Alberto
Published: May 2005

Copper in seawater was analyzed with a ‘hybrid’ mercury film‐glassy carbon electrode using linear sweep, square wave and differential pulse anodic stripping voltammetry. The analyses were made in HCl (pH 2) and ethylenediamine (EN)‐spiked seawater (9 < pH < 10), with and without purging the sample of dissolved oxygen. The relative slopes of the standard addition plots were used to determine the effect of mode and media alteration on the results. Square‐wave voltammetry in EN‐altered seawater, without oxygen purging, was found to be not only the most practical technique, but also highly sensitive. The ‘chemistry’ of the oxidation reaction during the stripping step was found to affect the experimental results markedly. For this reason, the peak current is an experimentally dependent measure of the ion flux, both, into and out of the electrode.
Application of a chelite P modified carbon paste electrode to copper analysis and speciation
Authors: Agraz Raquel , De Miguel Javier , Sevilla Maria‐Teresa , Hernandez Lucas
Published: May 2005

A carbon paste electrode modified with the commercial resin Chelite P, containing amino‐phosphonic groups, was used in the determination and speciation of copper. Copper analysis was performed with cyclic voltammetry and differential pulse voltammetry, allowing copper determination in the μg/L level. A detection limit of 1.9 μg/L (3α) was found for a 10 min preconcentration. Interferences from other ions and organic substances were examined. For speciation purposes, a ligand competition methodology was used and different model ligands in solution were tested. Copper complexes were characterized as a function of their thermodynamic and kinetics properties. Results were compared with those obtained employing a strong chelating resin (containing iminodiacetic acid) as electrode modifier. The method was applied to a water sample from the Jarama river in Madrid, where copper was mainly present as strong low‐dissociating complexes.
Programmed‐potential voltammetric determination of nitrate at a static mercury drop electrode in natural waters and soil extracts
Authors: Markušová Kveta , Kohútová Lýdia , Dzurov Ján
Published: May 2005

Linear‐scan or differential pulse voltammetry with electrode surface modified at a mercury drop presweep potential of −1.8 V is used for the determination of nitrate in the presence of trivalent cations. The method has been applied to the determination of nitrate in drinking and riverwaters, and in soil extracts with determination limit of 0.3 μ M (20 μg L−1).
Local anesthetics measured by lipophilic β‐cyclodextrin‐based ion‐selective electrodes
Authors: Kataky Ritu , Palmer Simon
Published: May 2005

2,3,6‐Trioctyl and 2,6‐didodecyl‐β‐cyclodextrins have been incorporated in ion‐selective electrodes as neutral ionophores for the detection of the local anesthetics procaine, prilocaine, lidocaine and bupivacaine hydrochlorides. Nernstian response and excellent limits of detection were observed (−log [C]≥5.0). Interference from ‘serum’ levels of sodium, potassium and calcium (150.0 mmol dm−3 Na+, 1.26 mmol dm−3 Ca2+ 4.30 mmol dm−3 K+ ), was negligible (−log K,) (overall)≥4.0). The major organic interferents were molecules of similar size and structure which caused reduced slope and drift in baseline potentials at 10 mmol dm−3 levels of concentrations. However, the interferences were substantially reduced when the interferent concentration was reduced by a factor of 10. Nernstian response was maintained in the presence of bovine serum albumin (BSA), serum (HS) and aI acid glycoprotein (AAG). A polyurethane, (Tecoflex SG80) membrane matrix was more biocompatible when compared to PVC as evidenced by lower E0 (internal) shifts with the former.
A comparative study of some phenoxazine and phenothiazine modified carbon paste electrodes for ethanol determination
Authors: Lobo M. Jesús , Miranda Arturo J. , Tuñón Paulino
Published: May 2005

An amperometric ethanol electrode is described based on carbon paste modified with alcohol dehydrogenase (ADH) and a mediator. The possibility of coupling this enzymatic system with some commercially available phenoxazines [Meldola Blue (MB), Nile Blue (NB) and Brilliant Cresyl Blue (BCB)] and phenothiazines [Toluidine Blue 0 (TBO)], that allows the electrocatalytic oxidation of NADH, was investigated. Different strategies of mediator immobilization in the carbon paste were compared. The most suitable immobilization technique was the coverage of the modified carbon paste surface with a dialysis membrane and the best electrocatalytic structure was the phenothiazine TBO. The TBO(10%)‐ADH(5%)‐modified carbon paste electrode shows steady state signals for ethanol within 30 s. The influence of various experimental conditions was explored for optimum analytical performance. Amperometric detection of ethanol at an applied potential of 50mV (Ag/AgCl) gives linear responses over the concentration range of 10–l0μM, with a detection limit of 5 × 10−6M. The modified electrode was applied to the determination of ethanol in wine.
Flow‐type cyanide sensor using an immobilized microorganism
Authors: Ikebukuro Kazunori , Honda Masahiro , Nakanishi Keijiro , Nomura Yoko , Masuda Yuzo , Yokoyama Kenji , Yamauchi Yoshihiro , Karube Isao
Published: May 2005

A flow system for cyanide detection using Saccharomyces cerevisiae is described. This sensor system consists of two oxygen electrodes and immobilized S. cerevisiae whose respiration activity is measured by the oxygen electrodes. Since cyanide inhibits S. cerevisiae's respiration, it can be detected by measuring this inhibition. Two types of systems were constructed, characterized and compared. One is a membrane‐type flow system in which S. cerevisiae was immobilized onto a cellulose membrane. The other is a reactor‐type flow system in which S. cerevisiae was immobilized onto the glass beads. The sensor response was examined in the range from 0 to 15μM. The reactor‐type sensor system displayed lower detection limit (0.15 μM) and better stability (16 days).
Alkaline phosphatase assay using a redox procationic labeled substrate and a renewable Nafion‐loaded carbon paste electrode
Authors: Rapicault Stéphane , Limoges Benoît , Degrand Chantal
Published: May 2005

The indirect electrochemical determination of alkaline phosphatase was achieved with a detection limit of 2 Ul−1 at a fresh surface of a renewable Nafion‐loaded carbon paste electrode, without preconditioning. [N‐ferrocenoyl]‐4‐aminophenyl phosphate was used as substrate and the enzyme reaction proceeded for 15 min in Tris buffer at pH 9.0. [N‐ferrocenoyl]‐4‐aminophenol was thus generated, which was further preconcentrated at the modified carbon paste electrode during a 5 min accumulation step in neutral medium. A potential of 0.35 V was applied during this step, and so the substituted phenol was irreversibly entrapped as a ferrocenium salt within Nafion before being detected by square wave voltammetry.
Trace measurements of insulin by potentiometric stripping analysis at carbon paste electrodes
Authors: Wang Joseph , Rivas Gustavo , Cai Xiaohua , Chicharro Manuel , Farias Percio A. M. , Palecek Emil
Published: May 2005

A potentiometric stripping method for trace measurements of insulin at carbon paste electrodes is described. The method is based on the controlled adsorptive accumulation of this polypeptide hormone at the anodically pretreated carbon surface followed by constant‐current chronopotentiometric measurements of the surface species. A well‐defined peak, associated with the oxidation of the tyrosine residues, is observed over the flat baseline of the potentiometric stripping operation. Variables of the pretreatment and measurement steps are optimized to offer a detection limit of 2 × 10−9M after 5 min preconcentration. Excess of nunierous potential interferences does not influence the response observed after transferring the electrode (with the accumulated insulin) to a blank electrolyte solution. A similar protocol is described for trace measurements of the protein myoglobin.
Ohmic distortion of mass transport and of current–voltage curves at a channel electrode
Authors: Cales Barry A. , Compton Richard G. , Larsen Jane P. , Anthony Spackman R.
Published: May 2005

The distortion caused by the ohmic resistance of the solution in a channel electrode experiment has been calculated by combining a three‐dimensional finite element approach based on a resistor network, solved by the SPICE program, in an iterative procedure with the backward‐implicit finite difference method, for the case of a reversible 1‐electron reduction. By this means, the current distribution over the electrode may be calculated taking into account not only the nonuniform potential distribution imposed by the electrolyte resistance but also the alteration to mass transport induced by the potential distribution. The potential‐dependent variation in Tafel slope introduced by the ohmic distortion is calculated and is shown to be in close agreement with experimental data obtained from the reversible one‐electron reduction of p‐chloranil, allowing the practical current range for experimental measurements to be assessed and if necessary extended. The three‐dimensional SPICE simulation has also been applied to study the effect of reducing the electrode width to a small fraction of the channel width, when significant current flow to the sides of the electrode will occur.
Rotating disk ion selective electrodes
Authors: Cassidy John , Mullen David , Casey Karen , Cullen Patrick
Published: May 2005

A simulation was undertaken to predict the transient potential response following a concentration step at a rotating disk electrode comprised of an ion selective layer. A basis for this simulation was that the potential response would be independent of rotation rate since the diffusion layer is larger than the double layer at the electrode. In practice it was found that the potential response does vary with rotation rate. The response was such that the apparent concentration of the analyte in solution decreased with increased rotation rate. The reason for this behavior is due to the disruption of the double layer at the electrode surface by convection.
Determination of carbendazim with a graphite electrode modified with silicone OV‐17
Authors: Hernandez Pedro , Ballesteros Yolanda , Galan Fernando , Hernandez Lucas
Published: May 2005

The cyclic voltammetric characterization of a graphite electrode modified with silicone OV‐17 was carried out on a solution of ferroine. Afterwards, the electrochemical behavior of carbendazim following its accumulation on the electrode surface, was studied. Best conditions for its determination in the preconcentration and measurement steps were established. The method, with a relative error of 3.7% and a determination limit of 9.1 ng/mL, was applied for wine, apple and cultivated soil samples.
Electrochemical determination of carboplatin in serum using a DNA‐modified glassy carbon electrode
Authors: Brett Ana Maria Oliveira , Serrano Sílvia H. P. , Macedo Tice A. , Raimundo Dulce , Helena Marques M. , La‐Scalea Mauro A.
Published: May 2005

An electrochemical method for the determination of the anticancer platinum drug carboplatin using a DNA‐modified electrode was developed. This electrode was successfully used for the electrochemical determination of carboplatin in serum samples of patients with ovarian cancer undergoing treatment. The electrochemical results clearly demonstrated that, for low concentrations, carboplatin interacts preferentially with adenine rather than guanine groups in the DNA and they can contribute to clarifying the mechanisms of interaction of platinum anticancer drugs with DNA. The pharmacokinetics corresponding to the administration of the drug was followed electrochemically and the detection limit in serum samples was 5.7 × 10 −6M. Due to a similar mechanism of reaction with DNA other platinum anticancer drugs can be determined by this method.
Fast adsorptive stripping voltammetry of iron in oxygenated seawater
Authors: Gelado‐Caballero María D. , Hernández‐Brito José J. , Herrera‐Melián José A. , Collado‐Sanchez Cayetano , Pérez‐Peña Jesús
Published: May 2005

A fast adsorptive stripping voltammetric procedure for the determination of ultratrace amounts of iron in unpurged oceanic waters is reported. The method is based on that developed by van den Berg et al. [l]. It was modified to increase the sensitivity, to measure in the presence of oxygen and to reduce drastically the analysis time at the ultratrace level (pM). The scan rate, pH and concentrations of reagents were optimized to avoid interferences using background correction. The catalytic effect of the hydrogen peroxide was not found using high scan rate. The instability of the peak was related to colloidal iron. Acidified or heated samples showed stable peaks. The method is insensitive to the turbulence of the solution during the scan. The reproducibility (±40 pM) and detection limits (120 pM) of the method were calculated using 60s deposition time and oceanic waters (600pM). The detection limit can be lowered to 70 pM using 3 min accumulation.
Voltammetric detection of phosphate ion binding to β‐amino‐cyclodextrin
Authors: Godínez Luis A. , Lin James , Muñoz Marc , Coleman Anthony W. , Kaifer Angel E.
Published: May 2005

The complexation of phosphate ion by β‐amino‐cyclodextrin (host 1) was detected by voltammetric methods through the competitive displacement of water‐soluble ferrocene derivatives from their complexes with host 1 in neutral aqueous media. The half‐wave potential and the anodic peak current for oxidation of the ferrocene derivative were found to be sensitive to the phosphate concentration throughout a range which is determined, among other factors, by the concentration of host 1 and the binding constant between the selected ferrocene derivative and the β‐amino‐cyclodextrin host.
The reduction of bromate at molybdenum oxide film cathodes
Authors: Bertotti Mauro , Pletcher Derek
Published: May 2005

The catalytic reduction of bromate at vitreous carbon electrodes modified with a molybdenum oxide film at pH 3 has been investigated further. In addition, the reduction has been investigated at lower pH using molybdenum oxide films formed in situ from solutions containing both MoVI and BrO. It is shown that in both systems, the variation of the current for bromate reduction with potential passes through a maximum and, hence, at more negative potentials, the surface is markedly less active for bromate reduction. With MoVI in solution, a recovery in the catalytic activity slowly occurs and this effect has also been investigated.
Reactor type sensor for cyanide using an immobilized microorganism
Authors: Lee Jeong Im , Karube Isao
Published: May 2005

A reactor type biosensor using an immobilized bacteria (Pseudomonas fluorescens NCIMB 11764) columm and an oxygen electrode was developed for cyanide. The optimum conditions for the sensor in a flow system (pH 9, 25°C, flow rate 2.5 mg/min) resulted in a response time of less than 5min. A linear relationship was observed between the current decrease and the cyanide concentration over the range of 0.05−1 mg/L. Operating at 25 °C, the sensor was stable up to 30 days. Alginate gel as the immobilized matrix was more suitable than other matrices (agars, polyurethane, porous glass beads, zeolite, chitopearl). Satisfactory results were obtained when the sensor was applied to determine the concentration of cyanide in the river water.
Effect of HY‐zeolites on the performance of tyrosinase‐modified carbon paste electrodes
Authors: Marko‐Varga György , Burestedt Elisabeth , Svensson Carl Johan , Emnéus Jenny , Gorton Lo , Ruzgas Tautgirdas , Lutz Mareike , Unger Klaus K.
Published: May 2005

The dependence of electrode response on additive properties in enzyme‐modified carbon paste was studied. Four different HY‐zeolite powders, dealuminated to different extents and characterized by both Si/Al ratio and hydrophilicity, were used as the carbon paste modifiers. The enzyme tyrosinase used in biosensors for the detection of catechol and other phenolic compounds was chosen as the model system for the construction of a composite carbon paste biosensor incorporating different HY‐zeolites as additives. Tyrosinase was trapped on the HY‐zeolite particles from a buffer solution, dried and mixed with graphite powder and a pasting oil. It was found that by incorporating HY‐zeolites into the carbon paste the heterogeneous reaction rate of catechol redox conversion and the signal response for catechol were increased. In the latter case a higher response was observed for increased hydrophilicity, i.e., decreased Si/Al ratio of the HY‐zeolite. The carbon paste/solution interface is considered to be an aqueous/organic phase and the characteristics of the enzyme‐ modified carbon paste electrode are related to theories, explaining enzymatic catalysis in organic solvents.
Off‐line and on‐line differential pulse anodic stripping voltammetric techniques for the determination of antimony(III) and antimony(V) in zinc plant electrolyte
Authors: Bond Alan M. , Kratsis Steven , Newman O. Michael G. , Pfund B. Valentin
Published: May 2005

Antimony, in both its trivalent and pentavalent states may be detrimental to the electrochemical deposition of zinc. Ideally, therefore antimony should be monitored in both oxidation states throughout an electrolytic zinc plant. At hydrochloric acid concentrations ( > 4 M) both antimony(III) and (V) present in zinc plant electrolyte can be reduced at a hanging mercury drop electrode (HMDE) to form an antimony amalgam, Sb(Hg). Consequently a very sensitive analytical signal is obtained for the determination of total antimony by differential pulse anodic stripping voltammetry (DPASV) using a 1:1 mixture of plant electrolyte and concentrated hydrochloric acid. In contrast, at low acid concentrations (0.1 M) predominantly only antimony(III) can be reduced and therefore determined in zinc plant electrolyte by DPASV at a HMDE by use of a 1:1 mixture of plant electrolyte and 0.2 M hydrochloric acid. The antimony(V) concentration is calculated by the method of subtraction of antimony(III) from total antimony. Consequently, simple addition of high and low concentrations of hydrochloric acid to zinc plant electrolyte can be used to provide a suitable electrolyte for both off‐line and on‐line methods for determining the concentration of total antimony, antimony(III) and antimony(V). The method described in this article has been applied to a wide range of zinc electrolyte samples and an on‐stream analyzer technique has been successfully used for several years at the Pasminco Metals‐BHAS electrolytic zinc plant in Port Pirrie, Australia.
Flow characteristics of a versatile wall‐jet or radial‐flow thin‐layer large‐volume cell for electrochemical detection in flow‐through analytical systems
Authors: Soucaze‐Guillous Benoît , Kutner Włodzimierz
Published: May 2005

Flow characteristics of a versatile large‐volume flow‐through electrochemical cell, which features exchangeable disk, ring‐disk or microdisk working electrodes, are presented. The cell operates in a radial‐flow thin‐layer, wall‐jet or wall‐tube mode, under amperometric or voltammetric conditions, being therefore suitable for flow analytical techniques, such as high performance liquid chromatography (HPLC) and flow injection analysis (FIA). The operation mode is selected by using the inlet capillary either of a flat or conical nozzle and by suitably adjusting the nozzle‐to‐electrode distance. The cell is equipped with a micrometer screw which allows for adjusting of this distance to be as small as 10 ± 5 μm. The inlet solution stream is centered axially against the working electrode surface. Under radial‐flow thin‐layer conditions, flow‐through detection at a ring‐disk electrode benefits from shielding and collecting properties which are enhanced as compared to those for the rotating ring‐disk electrode conditions. The HPLC extracolumn effects due to detection were determined by the peak variance analysis of a mixture of regio isomers of nitrobenzene derivatives. Despite the large (35mL) geometric cell volume, the effective detection volume of the cell is of the microliter order. Therefore, the cell is suitable for detection both in the analytical and microbore‐column HPLC. Due to the large geometric cell volume, solution composition can be different, under wall‐jet conditions, for detection than that for HPLC separation. Hence, in situ postcolumn modification of the mobile phase or analyte is feasible.
Differential pulse cathodic stripping voltammetric determination of manganese(II) and manganese(VII) at the 1‐(2‐pyridylazo)‐2‐naphthol‐modified carbon paste electrode
Authors: Khoo Soo Beng , Soh Ming Koon , Cai Qiantao , Khan Miriam R. , Guo Si Xuan
Published: May 2005

A carbon paste electrode modified with 1‐(2‐pyridylazo)‐2‐naphthol was fabricated and used to preferentially accumulate Mn(II) at open circuit. After medium exchange, the accumulated Mn(II) at the electrode surface was electrochemically oxidized. The hydrated MnO2 thus formed was then cathodically stripped using differential pulse voltammetry. Various factors influencing the accumulation and stripping were studied. An optimized procedure was then developed for the determination of Mn(II). Mn(VII) could also be determined by chemical conversion to Mn(II) using acidified H2O2. Following this, the Mn(VII) concentration could be obtained by subtraction. Under optimum conditions, a detection limit of 6.9 × 10−9 M Mn(II) (0.38 ppb) was found for 200s accumulation. For 8 determinations, each of Mn(II) concentrations of 1.00 × 10−6 M, 1.00 × 10−7 M and 1.00 × 10−8 M, relative standard deviations of 2.90%, 4.46% and 7.20% were obtained, respectively. Selected metal ions were tested for interferences and it was found that, when determining 1.00 × 10−6 M Mn(II) (150s accumulation), Co(II), Hg(II) and Fe(II) at 1.00 × 10−5M interfered. These interferences were readily eliminated by masking with complexing agents such as sodium citrate and sodium diethyldithiocarbamate. The developed method was tested using a certified sample and then applied to the determination of manganese in seawater.
Organized self‐assembled lipoyl‐β‐cyclodextrin derivative monolayer on a gold electrode
Authors: He Pingang , Ye Jiannong , Fang Yuzhi , Suzuki Iwao , Osa Tetsuo
Published: May 2005

An organized self‐assembled monolayer of β‐cyclodextrin (β‐CD) derivatives on a gold surface has been prepared using two lipoyl‐β‐cyclodextrin derivatives with different chain lengths, which are more flexible than heptakis (dodecyl sulfide) β‐cyclodextrin. The surface coverage of the monolayers were found to be in agreement with the surface coverage of a highly organized monolayer of β‐CD. It has been revealed by cyclic voltammetry that the β‐CD derivative monolayers have the characteristics of: (a) selective barriers blocking the permeability for those molecules, such as ferricyanide, and p‐aminophenol, which are incapable of complexing with β‐CD; and (b) have selective transport for electroactive organic species, such as ferrocene carboxylic acid and hydroxyquinone, which can form host‐guest inclusion complexes with β‐CD receptors. The selective transport can be controlled by blocking the β‐CD cavities with some guest molecules such as cyclohexanol borneol and ursodeoxycholic acid, and the controlling mode can be expected for detection of organic compounds.
Electrochemical behavior of mutagenic nitro and amino derivatives of carbazole
Authors: Carlier Roger , Raoult Eugène , Tallec André , Andre Vèronique , Gauduchon Pascal , Lancelot Jean‐Charles
Published: May 2005

The electrochemical behavior of nitro and amino carbazole derivatives has been investigated. In aprotic medium, both in reduction and oxidation, the electrochemical process is complicated by “father‐son” protonation reactions. In protic medium, the hydroxylamines resulting from 4‐electron reduction of nitrocarazoles are unstable in very acidic medium, but relatively stable in acetic or ammoniacal buffer, except for 3‐hydroxyl‐aminocarbazole; reduction of amino‐nitrocarbazoles leads to unstable hydroxylamines. Oxidation of aminocarbazoles is a 2‐electron process, the 2‐amino compounds being more difficult to oxidize than the 3‐amino derivatives. The relationships between these electrochemical behaviors and mutagenic properties of the studied compounds are also discussed.
A study in the use of an extrapolation method to find the equilibrium potential for certain ion‐selective electrodes
Authors: Watkins Peter J.
Published: May 2005

The equivalent potentials for certain ion‐selective electrodes (lead, cadmium, iodide, chloride, nitrate) are found by an extrapolation method, rather than wait for the steady‐state potential to be reached.
In situ electrochemistry of Ru(NH3) in a perfused rat heart
Authors: Schoenfisch Mark H. , Pemberton Jeanne E. , Ovadia Marc , Levy Margaret
Published: May 2005

Simple two‐electrode potential sweep and potential step electrochemical measurements are reported in a perfused living rat heart prepared using a modified in situ Langendorff preparation. Cyclic voltammetry of Ru (NH3) at Pt electrodes is performed in vivo after retrograde aortic perfusion of Ca2+‐and albumin‐free, oxygenated Krebs buffer containing Ru(NH3) to assess uniformity of perfusion. Four types of voltammetric response are observed depending on the placement of the working electrode. These types are distinguished on the basis of the relative contributions of diffusive and hydrodynamic mass transport as mnifest in the shapes of the current‐potential curves. Chronoamperometric measurement of double layer charging was used to estimate extracellular tissue resistance. These chronoamperometric experiments are performed in buffer solutions by small potential steps around a set potential of non‐Faradaic activity. Tissue. resistance was estimated to be ca. 598 ± 138 Ω from the chronoamperometric data. The electrochemical responses observed from both measurements exhibit good reproducibility between individual heart preparations.
Flow‐injection potentiometric detection of metal ions based on tungsten oxide electrode
Authors: Chen Zuliang , Alexander Peter W.
Published: May 2005

The use of a tungsten oxide electrode for potentiometric flow‐injection analysis of transition metal ions is described. The effect of a variety of experimental conditions, including the carrier pH, the types of ligands and their concentrations, was studied. It was found that the best sensitivity for the ions tested was obtained using EDTA as a ligand. The electrode exhibited a linear response for Fe3+, Cu2+, Pb2+ and Ca2+ in the range of 2.5 × 10−4 M to 2 × 10−3 M using with 1 × 10−3 M EDTA at pH 5.0 as carrier. The detection limits were found to be between 1 × 10−5 to 5 × 10−5 M. Reproducibility for Fe3+ was about 1.7% with a stable baseline potential.
Electrochemical oxidation of isoniazid catalyzed by the 2,2,6,6,‐tetramethyl‐4‐acetylpiperidine‐1‐oxy radical and its analytical application
Authors: Tong Jian , Dang Xiao‐Jun , Li Hu‐Lin
Published: May 2005

The electrochemical oxidation of isoniazid catalyzed by the 2,2,6,6‐tetramethyl‐4‐acetylpiperidine‐1‐oxy(TMAPO) radical at a glassy carbon electrode in phosphate buffer solution has been studied. The rate constant of the reaction for isoniazid and the oxoammonium salt evaluated by rotating disk voltammetry is (2.36 ± 0.12)×104 dm3 mol−1 s−1. The electrochemical behavior of the TMAPO radical and the stability of the oxoammonium salt have also been investigated by cyclic voltammetry. The linear relationship between the catalytic peak current and the isoniazid concentration over the range of 4 × 10−4‐2 × 10−3M was used for the determination of isoniazid in isoniazid tablets. A method for analysis of isoniazid was established.
Thin‐film gold electrodes produced by magnetron sputtering. Voltammetric characteristics and application in batch injection analysis with amperometric detection
Authors: Brett Ana Maria Oliveira , Matysik Frank‐Michael , Vieira M. Teresa
Published: May 2005

Thin‐film gold electrodes were produced by radio‐frequency sputtering using a polyvinyl chloride foil as substrate. The voltammetric behavior was characterized in various electrolyte solutions. In alkaline and neutral aqueous solutions reliable voltammetric measurements can be performed while in acidic media some nondefined phenomena occur. A novel type of electrode for batch injection analysis (BIA) is presented which is produced from circular pieces of the thin‐film material. This electrode can be used for BIA in conventional voltammetric cells. Pulsed amperometric detection is demonstrated to be viable with thin‐film gold electrodes and shows analytical advantages over constant‐potential detection in the BIA of hydrogen peroxide.
Anodic stripping voltammetric determination of vanadium(V) using a carbon paste electrode modified in situ with cetyltrimethylammonium bromide
Authors: Stadlober Monika , Kalcher Kurt , Raber Georg
Published: May 2005

A method for the voltammetric determination of vanadium(v) using a carbon paste electrode in situ modified with cetyltrimethylammonium bromide (CTAB) is described. Vanadium is preconcentrated at the electrode surface via its anionic oxalate complex from acidic solution (0.01 M oxalic acid, 0.25 mM CTAB, pH 2.2) at a potential of −0.9 V [vs. the saturated calomel electrode (SCE)]. Simultaneously during accumulation, vanadium(v) in the complex is reduced to its tetravalent state. Differential pulse anodic stripping voltammetry exploiting the reoxidation can be used for the determination of trace levels of vanadium(v). Linearity between current and concentration exists for a range of 5 to 200 μg.L−1 Vv with a preconcentration time of 1 min. The limit of detection (calculated as 3 σ) is 0.07 μg.L−1 with a preconcentration time of 10 min.
A simple digital coulometer
Authors: Holze Rudolf
Published: May 2005

A simple design for a digital coulometer based on standard commercial circuits with features particularly suited for electrochemical applications is described.
The coulometric determination of chemical oxygen demand
Authors: Pamplin Kim L. , Johnson Dennis C.
Published: May 2005

The chemical oxygen demand (COD) of solutions containing various organic compounds is calculated from the net faradaic charge (Qnet) estimated for the total electrolytic oxidation of CrIII generated during oxidative degradation of the organic compounds in acidic media containing excess CrVI. Values of Qnet for conversion of CrIII to CrVI are estimated from the linearized chronoamperometric data plotted as In {itat, t} vs. t. This procedure is preferred over determinations of Qnet from the total integrals of itot over the entire electrolysis period because of large errors that can result from uncertainty in the background current (ibkg) for t → ∞. The proposed coulometric procedure offers the benefit that reagent solutions can be reused, thereby minimizing the need for disposal of wastes containing toxic CrVI. This procedure was applied in a single digest solution for consecutive determinations of COD. Average COD values for potassium acid phthalate and glucose were 103.8% (s ‐ 6.0, N ‐ 10) and 100.2% (s ‐ 4.2, N ‐ 11), respectively, based on the theoretical degradation to CO2. In comparison for these same samples, an EPA approved method, based on colorimetric determination of CrIII, gave COD values of 101.4% (S ‐ 1.4, N ‐ 5) and 100.1% (s ‐ 1.4, N ‐ 5) of the theoretical. Statistical tests indicate no significant difference in the COD values determined for these compounds using the coulometric and EPA methods.
Applications of the channel flow cell for UV‐visible spectroelectrochemical studies. Part 2: Transient signals
Authors: Wang Rui Lin , Tam Kin Yip , Marken Frank , Compton Richard G.
Published: May 2005

The use of the channel flow cell for ultraviolet‐visible (UV‐vis) spectroelectrochemical experiments has been developed to determine the diffusion coefficients of electrogenerated species by means of monitoring the transient absorbance response resulting from a potential step at a working electrode immediately upstream of the incident spectrophotometric beam. The technique is applied to measure the diffusion coefficient of tris(4‐bromophenyl)amine (TBPA) radical cation in acetonitrile at 25°C. It is shown that the diffusion coefficient of electrogenerated TBPA radical cation (1.64 ± 0.02 × 10−5 cm2 s−1) is very close to that of the parent molecule (1.57 ± 0.03 × 10−5 cm2 s−1).