bluuebunny/crossref_metadata_2025 huggingface dataset:
Square wave voltammetry with arrays of liquid/liquid microinterfaces
Authors: Pereira C. Melo , Silva Fernando
Published: May 2005

Square wave voltammetry (SWV) has been successfully applied to arrays of liquid/liquid (L/L)microinterfaces formed across microholes perforated on a polyester film. The study of CIO4− ion transfer from water to 1.2‐dichloroethane (DCE) showed that the experimental parameters Esw, Es, and f are identical to those found for the reversible electron transfer on solid microelectrodes.
High‐Performance adsorptive cathodic stripping voltammetry of nickel and cobalt in seawater
Authors: Pérez‐Peña J. , Hernández‐Brito J. J. , Herrera‐Melián J. A. , Collado‐Sánchez C. , van den Berg C. M. G.
Published: May 2005

The voltammetric determination of trace metals in seawater suffers from the interference of dissolved oxygen and engine vibrations onboard ship. It is here attempted to overcome these interferences using a high‐frequency (1 to 20 kHz) staircase modulation during the voltammetric scan (high‐performance adsorptive cathodic stripping voltammetry, HPACSV). Comparative experiments using the square‐wave modulation showed that this modulation was not effective at such a high frequency. A comparison between various complexing agents (DMG and nioxime) and pH buffers (HEPES/NH4OH, borate/NaOH, and TEA/NH4OH) showed that the determination of nickel and cobalt was similarly improved by the high‐speed potential scan in all conditions. Fast potential scans cause a large increase of the peak area and peak heights using staircase modulation. The peaks are wider, and the peak potentials are shifted toward negative values due to the ohmic drop, but the analytical determination is not disturbed. Optimal sensitivity for the determination of cobalt and nickel in seawater was obtained using TEA buffer and DMG as the adsorptive ligand. The nioxime wave was found to interfere in the cobalt peak at high scan rates so that this ligand is not recommended for HPACSV. Comparative tests showed that the sensitivity for nickel and cobalt determinations was highly improved by the fast scan rates. Furthermore, the reduction current of dissolved oxygen was partially masked so that measurements could be taken without a previous purge of the sample. Finally, the scans were insensitive to the solution turbulence so measurements could be readily carried out onboard of an oceanographic vessel or without switching off the stirrer. Low levels of nickel (2 nM) could be determined in seawater by using a deposition time of 20 seconds and of 120 seconds for 0.05 nM cobalt from turbulent and unpurged solutions. A fast determination method for labile nickel and cobalt is proposed.
Development of a chronocoulometric method for the determination of uranium at trace levels by using the catalytic nitrate reduction
Authors: Cantagallo Maria Inês C. , Bertotti Mauro , G. R. Gutz Ivano
Published: May 2005

The electroanalytical determination of uranium at trace levels was studied with the purpose of improving the sensitivity of the uranium‐catalyzed reduction in the presence of nitrate on mercury electrode. Examination of the current dependence on time (chronoamperometry) revealed the advantage of measuring the current later and for a longer time interval than usual in pulse polarography. The uranium/nitrate system is particularly favorable in this sense because an intensification of the catalytic current with time is observed. The best signal‐to‐noise ratio was achieved using the technique of chronocoulometry. In this chronocoulometric catalytic determination (CCCD), analytical information was gathered, calculating the slope of the charge versus time curve during the period of 10 to 20 seconds after the application of the potential pulse and correcting it for the residual slope before the pulse. To establish the new analytical procedure, the effects of electrolyte composition, potential program, integration time, and blank correction were examined. A detection limit of 3 × 10−10 M was attained, a power of ten lower than the sensitivity reported for the same catalytic determination by differential pulse polarography. An exploratory study of the combination of this procedure with preconcentration of uranium on the electrode allowed reduction of the detection limit by an additional order of magnitude.
Electrochemical quantification of phenol using mushroom tyrosinase: Determination of the kinetic parameters of the enzyme
Authors: Rivas Gustavo A. , Solis Velia M.
Published: May 2005

This article presents a sensitive electroanalytical method for the determination of phenol in the presence of mushroom tyrosinase as well as a simple methodology to evaluate the kinetic parameters of this enzyme. The quantification is performed at low potential from the oxidation current of pyrocatechol that is formed by the action of mushroom tyrosinase in air‐saturated solutions. Any electrochemically activated glassy carbon electrode is used. The course of the reaction is followed by cyclic voltammetry. A linear relationship holds up to 9.0 × 10−5 M, a detection limit is 4.6 × 10−7 M with a precision of 3.2% and a correlation coefficient of 0.997. Kinetic parameters evaluated from the same experiments are Vmax = 0.005 μmol of pyrocatechol produced per minute and KM = 2.0 × 10–4 M.
Sensors based on carbon paste in electrochemical analysis: A review with particular emphasis on the period 1990–1993
Authors: Kalcher K. , Kauffmann J.‐M. , Wang J. , Švancara I. , Vytřas K. , Neuhold C. , Yang Z.
Published: May 2005

A review is presented dealing with the use of carbon paste as an electrode maaterial for electrochemical sensors (311 references). It covers mainly publications which appeared during the period 1990–1993; numerous applications demonstrate the widespread applicability of carbon paste in the field of electrochemical analysis, such as voltammetry, amperometry, and potentiometry, but also as an electrode for electrochemical detectors in flow systems.
Carbon paste electrodes modified with enzymes, tissues, and cells
Authors: Gorton L.
Published: May 2005

A review is presented dealing with the use of carbon paste amperometric electrodes for electroanalytical purposes, with either the surface or the bulk being modified with biologically derived material such as enzymes, tissues, and cells. It covers virtually all the publications which have appeared from the very first enzyme‐modified carbon paste electrode up to early 1994 and includes 220 references.
Surface‐modified gold electrodes for electrocatalytic oxidation of NADH based on the immobilization of phenoxazine and phenothiazine derivatives on self‐assembled monolayers
Authors: Schlereth D. D. , Katz E. , Schmidt H.‐L.
Published: May 2005

Self‐assembled monolayers of cystamine and cysteine chemisorbed on gold electrode surfaces have been used as a support for covalent immobilization of some phenoxazine and phenothiazine derivatives. The covalent attachment was achieved after previous functionalization of the free amino groups on the electrode surface with bifunctional reagents (terephthaloyl chloride and 1,6‐hexamethylene diisocyanate) able to react with the imino form of the amino group in position 3 of the phenoxazine and phenothiazine derivatives.

In every case, a shift of the redox potentials between 130 and 180 mV towards more positive potentials, as well as an increase in the peak‐topeak separation between anodic and cathodic peaks was observed after covalent attachment. The surface coverages (10−11 < Γ < 10−10 mol/cm2) obtained from the cyclic voltammograms were those for a not densely packed monolayer and varied depending on the redox compound immobilized. The surface‐modified electrodes obtained were afterwards used for the electrocatalytic oxidation of NADH.

UV‐vis spectroscopy was used to monitor the successive steps of surface modification using gold semitransparent electrodes. The total surface coverage of redox mediator on the electrode surface could also be calculated from the optical difference spectra between the oxidized and the reduced state obtained ‘in situ’ in a spectroelectrochemical cell.
A flexible biosensor for glucose
Authors: Mitsubayashi K. , Dicks J. M. , Yokoyama K. , Takeuchi T. , Tamiya E. , Karube I.
Published: May 2005

A flexible glucose biosensor was constructed by immobilizing glucose oxidase within a gold‐coated, hydrophilic polytetrafluoroethylene membrane. All reagents and materials used were harmless and nontoxic. Enzyme immobilization was improved using a mesh mask during gold deposition, the grid pattern permitting better access into the membrane. The masked sensors had greatly improved output currents and linearity. The sensor was linear up to 662 mgL−1, the range covering the concentrations encountered in normal and diabetic human tear fluids. The current was proportional to the square of the electrode area, hence an electrode of known dimensions can be used without precalibration. Sterilization using 80% ethanol had a negligible effect on its response. The sensor is well suited to the detection of glucose or other analytes in body fluids, such as tears, airway mucus, sweat, and saliva.
Nitrate detection at Nafion‐modified electrodes incorporating ytterbium and uranyl electrocatalysts
Authors: Ugo P. , Moretto L. M. , Ballarin B.
Published: May 2005

The performances of Nafion‐coated thin mercury film electrodes and Nafion‐coated glassy carbon electrodes loaded in aqueous solutions of Yb3+ or UO, respectively, are examined in relation to their use for the electrocatalytic voltammetric detection of nitrate.

Electrocatalytic reaction between the incorporated, reduced species, namely Yb2+ and U3+, and the NO, substrate is observed in both cases; however, the rapid inactivation of the ytterbium‐based sensor prevents its use for practical purposes. More promising results were obtained for the uranyl‐based sensor, since a more stable, modified electrode is obtained which can be used for the detection of nitrate in the 2–400 μM concentration range; however, problems connected to the slow release of the catalyst from the coating remain to be solved. Finally, the limitations and possible development of such a voltammetric sensor are critically discussed.
Adsorptive stripping voltammetry of palladium(II) with thioridazine in situ modified carbon paste electrodes
Authors: Raber G. , Kalcher K. , Neuhold C. G. , Talaber C. , Kölbl G.
Published: May 2005

A method is described for the voltammetric determination of palladium(II) using a carbon paste electrode modified with thioridazine. The modifier was added to the analyte solution and adsorbed onto the electrode surface under closed circuit conditions. Palladium could be preconcentrated onto the electrode surface and determined by differential pulse voltammetry without medium exchange. The dependence between the current response and the concentration of palladium(II) was linear within a range of 1 to 450 μg L−1 with preconcentration times between 0 and 120 seconds. The influence of parameters such as modifier concentration and pH‐value on the determination of palladium were investigated. The applicability of this method for the voltammetric determination of palladium in fresh water and in catalysts used for synthetic organic reactions is demonstrated.
Electrochemical response of poly(vinylferrocenium)‐coated Pt electrods to some anions in aqueous media
Authors: Gülce H. , Özyörük H. , Yildiz A.
Published: May 2005

The electrooxidation behavior of iodide, thiocyanate, and cyanide on poly(vinylferrocenium)‐coated Pt electrodes was investigated using cyclic voltammetry and differential pulse anodic stripping voltammetry. IR and UV spectroscopic data, and differential scanning calorimetry (DSC) measurements indicated that these anions were incorporated in the polymeric structure as a result of anion exchange. Anodic stripping of these anions from the film was carried out after the initial preconcentration. Cyanide uptake was found to cause an irreversible change in the physical properties of the film, whereas thiocyanate and iodide are merely incorporated in the film structure as counter ions.
Enzyme‐modified microelectrodes for in vivo neurochemical measurements
Authors: Pantano Paul , Kuhr Werner G.
Published: May 2005

Various approaches to the production of miniaturized chemical sensors for in vivo applications are reviewed with special regard to the measurement of chemical transients in the mammalian brain. The basic tenants of biosensor principles are discussed in terms of the temporal response of enzyme‐modified electrodes and selection of redox enzymes. The effects of electron transfer mediators and differential measurements to gain selectivity are also examined. A broad range of immobilization methods including membrane entrapment, physical and chemical adsorption, cross‐linking agents, polymeric entrainment, electropolymerized films and covalent derivatization are examined. The use of polymer layers and redox polymers to gain selectivity are discussed. The discussion is limited to microelectrode surfaces (< 100 μm diameter) and various electrode types are examined, including bare and platinized carbon fibers, platinum microelectrodes, conducting organic salts and carbon paste electrodes.
The application of various immobilized crown ether platinum‐modified electrodes as potentiometric and amperometric detectors for flow injection analyses of catechol and catecholamines
Authors: Lunstord Suzanne K. , Ma Yi‐Long , Galal Ahmed , Striley Cynthia , Zimmer Hans , Mark Harry B.
Published: May 2005

Different crown ethers were electrochemically polymerized or adsorbed onto a platinum electrode for the analysis of catechols by either static potentiometric, potentiometric FIA or amperometric FIA. The static potentiometric responses of all the crown ether modified electrodes were linear over about three decades of catechol concentration (10−5−10−8 M). The potentiometric FIA response of all the crown ether modified electrodes exhibited linear responses over four decades of catechol concentration (10−2−10−6 M). The amperometric FIA responses were linear over a 10−2−10−5 M range. Comparing the different techniques; static potentiometric, potentiometric FIA, and amperometric FIA, all had markedly different response slopes for the different crown ethers. Overall, the crown ether modified electrodes, except for an open‐crown ether, displayed excellent response stability for successive injections in both FIA modes. The lowest detection limits were about 0.5 × 10−6 M for the potentiometric FIA with minimal interference from ascorbic acid, uric acid and acetaminophen. For amperometric FIA the detection limits were about 0.5 × 10−5 M, but for ascorbic acid, uric acid, and acetaminophen the interference was significant. Experimental parameters which influence the mechanism of the potentiometric response are discussed.
Electroreduction mechanism of some sugars on mercury
Authors: Pezzatini Giovanni , Wei He , Innocenti Massimo , Guidelli Rolando
Published: May 2005

The electroreduction mechanism on mercury of the aldoses glucose and galactose, the ketoses fructose and tagatose, and the disaccharides lactose and lactulose was investigated in neutral and weakly alkaline solutions. Measurements at different temperatures ranging from 0 to 45°C indicate that the chemical reaction of the hemiacetal ring opening, which controls the polarographic limiting current, proceeds mainly in the adsorbed state below room temperature and in the nonadsorbed state above room temperature. Along the rising portion of the polarographic wave the electrode process is under the mixed control of the chemical reaction of ring opening and of a subsequent electrochemical step involving the uptake of the first transferring electron, with no protonation step in between.
A flow‐injection/XPS investigation of the effect of redox equilibria on the selectivity of an iodide‐selective electrode
Authors: Davey David E. , Mulcahy Dennis E. , O'Connell Gregory R. , Smart Roger StC.
Published: May 2005

Flow‐injection selectivity coefficients for a solid‐state iodide‐selective electrode were determined for three moderately interfering species—bromide, thiocyanate and thiosulfate–by injecting mixed iodide–interferent solutions into selected reagent streams. The use of neutral and acidified iodate and bromate oxidant streams was found to increase the selectivity of the iodide electrode towards the three interferents. The acidified streams also visibly modified the surface of the electrode membrane, although the resultant coating, ascribed to the formation of elemental sulfur and iodine, was easily removed by manual polishing with slurried alumina and a lint‐free cloth. X‐ray photoelectron spectroscopy (XPS) performed on pressed AgI/Ag2S pellets following immersion in the acidified iodate and bromate solutions revealed substantial surface modification, with the formation of AgIO3 and AgBr, respectively. Use of ascorbic acid or metabisulfite reducing streams resulted in higher selectivity towards iodide than that obtained using either of the neutral oxidant streams, but less than that obtained in the presence of a simple nitrate reagent stream. In contrast, the use of a thiosulfate stream irreparably damaged the surface of the electrode to the point where subsequent flow‐injection experiments showed excessive peak broadening and very poor baseline recovery. XPS studies performed on the damaged membrane revealed a surface dominated by hydroxides and almost totally devoid of either AgI or Ag2S.
A new indicator electrode for oxygen sensors
Authors: Nei Lembit
Published: May 2005

The electrochemical reduction of O2 was studied at Ni‐Cu alloy electrodes in aqueous alkaline solution (0.1–6.0 M KOH) and in unbuffered neutral solution (0.1–2.0 M KCl) using the rotating disk electrode technique. Voltammetric measurements showed that the overall O2 reduction process at the electrodes containing 70–90% Cu is transport‐limited at cathodic potentials, and that they can be used as indicator electrodes for galvanic‐type oxygen sensors. An industrially produced Ni‐Cu alloy “melhior”, which contains ∼ 30% Ni, was also studied, and this alloy proved to be an excellent O2 reduction catalyst. Melhior electrodes were utilized as indicator electrodes for oxygen sensors, and showed high output current stability and a long lifetime (exceeding one year).
Amperometric flow‐injection determination of citric acid in food using free citrate lyase and co‐immobilized oxalacetate decarboxylase and pyruvate oxidase
Authors: Matsumoto Kiyoshi , Tsukatani Tadayuki , Okajima Yuko
Published: May 2005

A flow‐injection analytical system for the determination of citrate in food has been developed. Citrate lyase, oxalacetate decarboxylase, and pyruvate oxidase were used, and the latter two enzymes were co‐immobilized. Hydrogen peroxide, which was produced by three enzyme reactions, was monitored amperometrically with a platinum electrode. The carrier solution used was 0.1 M phosphate buffer (pH 7.0) containing 10 mM MgCl2, 80μM thiamine pyrophosphate (TPP), and 10μM flavine adenine dinucleotide (FAD). The detection limit was 0.02mM, and the range of determination was 0.1‐1.0 mM. The relative standard deviation was 1.23% for 10 successive determinations at the 0.5 mM level. The determination frequency was about 15 tests per hour. The present system was applied to the determination of citrate in several fruits. The results showed good agreement with those obtained using a conventional method (F‐kit method).
Stabilized bilayer lipid membranes for flow‐through experiments
Authors: Nikolelis Dimitrios P. , Siontorou Christina G. , Andreou Vangelis G. , Krull Ulrich J.
Published: May 2005

This work reports a technique for the stabilization of solventless bilayer lipid membranes (BLMs), and the use of stabilized BLMS as flow detectors. Microporous filters composed of glass fibers, polytetrafluoroethylene (PTFE) and polycarbonate (nominal pore sizes from 1 to 5 μM) can serve as interfaces that separate two solution compartments. The micropores in the filter media can act as supports for formation and stabilization of BLMs. One of the solution compartments is used to cast lipid films on the filters, while a carrier electrolyte solution concurrently flows through the opposing compartment. Optimization of the flow cell design, and the chemical composition and methods for preparation of stabilized BLMs, are described. Lipid membranes composed of mixtures of phosphatidyl choline and phosphatidic acid could respond rapidly to pH alterations of the carrier electrolyte solution. Signals would reproducibly appear within a few seconds following the injection of an electrolyte of different pH than the carrier. Signals took the form of a single ion current transient with magnitude of tens of picoamperes (pA) and a duration of seconds. The mechanism of signal generation is explored by differential scanning calorimetry. The results show that a phase transition within a lipid membrane can be triggered by pH alterations of the electrolyte solution. Stabilized BLMs which provide artificial ion gating events hold prospects for chemical sensing of process streams.
Amperometric gas‐diffusion/enzyme electrode
Authors: Iliev Ilia , Kaisheva Anastassia , Scheller Frieder , Pfeiffer Dorothea
Published: May 2005

An amperometric enzyme gas‐diffusion electrode has been developed which combines a porous, air breathing gas‐diffusion electrode with an enzyme [glucose oxidase (GOD)] immobilized with Nation into its porous catalytic layer. The catalytic layer contains pyrolyzed Co‐ tetramethoxyphenylporphyrine (CoTMPP), which is very active towards the electrochemical oxidation of H2O2. The behavior of this electrode was investigated when the oxygen needed for the enzymatic reaction was supplied from the air (in the gas phase) through the porous structure of the gas‐diffusion electrode. It was shown that in the presence of the substrate (glucose), the amperometric signal obtained in this mode of operation was much higher than that obtained when only the oxygen dissolved in the electrolyte was involved in the enzymatic reaction. The developed enzyme gas‐diffusion electrode allows a versatile and rapid change in the O2 concentration in the zone where the enzymatic reaction is taking place. This electrode can be used as a model system for the investigation of the influence of O2 on the performance of both the peroxide or the mediated enzyme electrodes in an effort to develop oxygen independent biosensors.
Tubular band microelectrode. I. Design and electrochemical behavior
Authors: Corti Horacio R. , Goldfurb Darío L. , Ortiz Martin Scalabrini , Magallanes Jorge F.
Published: May 2005

The effect of supporting electrolyte concentration and sample flow rate on the electrochemical behavior of a tubular band microelectrode was studied and compared to the results obtained by simulation. The conditions for the current to be independent of the hydrodynamic flow rate are established. The experimental results are compared to those obtained by digital simulation based on the explicit hopscotch method. These calculated results are also compared to those obtained for microband and infinite planar geometries. It was concluded that this microelectrode very rapidly reaches a stationary state, providing a stable and fast response to concentration changes in the solution, as is required for analytical purposes.
The behavior of polypyrrole doped with different anions as an ion‐selective electrode
Authors: Jovanović Vladislava M. , Markičević Ljiljana , Stanković Slavka , Stanković Rade , Jovanović Momir S.
Published: May 2005

Polypyrrole (PPy) films were electrochemically deposited on glassy carbon from aqueous solutions of different sodium salts (F−, Cl−, NO, HSO). Methods applied were potentiostatic polymerization or cyclic voltammetry. The electrochemical behavior of such electrodes was studied by cyclic voltammetry. The results obtained show that the reaction is localized at the electrode surface for polypyrrole doped with CI− and NO, anions and diffusion‐controlled for F− anions. The polypyrrole films, examined as ion‐selective electrodes in solutions of anions corresponding to the dopant ones, exhibit lower or higher deviation from the Nernstian response depending on the dopant. When polypyrrole doped with HSO was tested, a cationic response was obtained. The chemical exchange process of dopant anion was studied. The results show that this process depends on the nature of the dopant anion and the anion from the solution.
Ion exchanged polypyrrole‐based glucose biosensor: Enhanced loading and response
Authors: Ramanathan Kumaran , Sundaresan N. S. , Malhotra Bansi D.
Published: May 2005

Enhanced loading of glucose oxidase in polypyrrole films via manipulation of the polymer morphology is reported. The exchange of bulky anions such asp‐toluene sulfonate and ferricyanide present as dopant ions in polypyrrole, with chloride ion in solution leads to greater porosity and resultant maximization of glucose oxidase (GOx) immobilization in polypyrrole. The polypyrrole–Gox electrode thus prepared exhibits improved performance as an amperometric glucose sensor. The fractal dimension estimated from chronoamperometric data demonstrate the increased dimensionality of the polypyrrole network after ion exchange.
Electroanalysis with interdigitated array microelectrodes
Authors: Niwa Osamu
Published: May 2005

This review discusses electroanalysis with interdigitated array (IDA) microelectrodes. The basic electrochemical properties of IDAs are presented along with a calculation of diffusion‐controlled current and an example of generation collection voltammetry to clarify the advantages of IDA for electroanalysis. The fabrication procedures of metal and novel carbon based IDAs are also summarized because the fabrication of very small IDAs is advantageous for electroanalysis. Previously reported electroanalytical applications of IDAs are overviewed. Among them are the measurement of redox electron conduction and molecular diffusion in various films, various types of enzyme sensors and electrochemical switches, an example of highly sensitive and selective generation collection voltammetry, a new stripping analysis using self‐induced redox cycling and the detectors for flow cells and liquid chromatography.
Amperometric glucose biosensors based on an osmium (2+/3+) redox polymer‐mediated electron transfer at carbon paste electrodes
Authors: Pravda Miloslav , Adeyoju Olubunmi , Iwuoha Emmanuel I. , Vos Johannes G. , Smyth Malcolm R. , Vytras Karel
Published: May 2005

Four glucose sensors have been developed by modifying carbon paste electrodes with glucose oxidase as a biocomponent and a conducting redox osmium‐polymer as the mediating compound. The enzyme was immobilized by crosslinking with glutaraldehyde and bovine serum albumin in three modifications of electrodes and physical adsorption in one electrode. The optimal concentrations of the modifying compounds were determined and the response of the sensors to 2–20 mM glucose were characterized. The influence of pH, temperature, interferences, and storage on the responses of the sensors were investigated.
Biosensing of tyrosinase inhibitors in nonaqueous solvents
Authors: Stancik Lubor , Macholán Lumír , Scheller Frieder
Published: May 2005

An amperometric biosensor based on a Clark oxygen electrode coupled with a biocatalytic layer containing tyrosinase has been developed for measurement in nonaqueous solvents. Glass filter paper was soaked with the enzyme and fixed on top of the electrode by a dialysis membrane. Thiourea derivatives were detected in hexane by evaluating the decrease in the response towards phenol. This method was fast and highly sensitive with detection limits in the range of 13–181 nM depending on the structure of the inhibitor compounds. The response time was up to 10min and depended on the inhibitor's structure. The mechanism of inhibition is discussed using kinetic parameters.
Electrocatalysis with an acetylcholinesterase immobilized graphite electrode
Authors: Stoytcheva Margarita
Published: May 2005

On the basis of the acetylthiocholine iodide hydrolysis, catalyzed by the enzyme acetylcholinesterase and leading to an electroactive product, an amperometric sensor is developed. An electrochemically modified graphite electrode is used, with acetylcholinesterase covalently linked directly on its surface. The kinetic parameters of the enzymatic reaction, in the presence and in the absence of inhibitors, are determined using an electrochemical approach.
Study of cation transfer across the water/nitrobenzene interface facilitated by a synthetic neutral dicarboxamide
Authors: Hu Zhongmin , Zhang Weiqing , Zhao Pingsan , Qi Deyao
Published: May 2005

The transfer of proton, alkali, and alkaline earth metal ions across the water/nitrobenzene interface, facilitated by a synthetic neutral dicarboxamide ionophore in the nitrobenzene phase was investigated using cyclic voltammetry. The ionophore‐facilitated transfer of Li+, Ca2+, and Ba2+ ions showed cathodic current peaks, and the transfer of H+ ions apparently resulted in peaks of both anodic and cathodic currents within the potential window. The transfer process of these ions was found to be controlled by the diffusion of the ionophore in the nitrobenzene. The formation of a 1 : 1 complex for H+ and of 1 : 2 (cation to ionophore) complexes for Li+, Ca2+, and Ba2+ ions was inferred, through peak separation or the dependence of the cathodic peak potential on the logarithm of the ionophore concentration, to be involved in the transfer process. The equilibrium constants KLI,M for the exchange reaction of the ion MZ+ with the Li‐+ ionophore complex at the water/nitrobenzene interface were evaluated and correlated with the potentiometric selectivity coefficients K.
All‐solid‐state chloride‐selective electrode with poly(pyrrole) solid contact
Authors: Hulanicki Adam , Michalska Agata
Published: May 2005

The responses of all‐solid‐state potentiometric chloride sensors with an internal poly(pyrrole) contact and a plastic membrane with methyltridodecylammonium chloride were investigated. The influence of the poly(pyrrole) doping anion was studied. Chloride‐selective electrodes with a poly(pyrrole) solid contact were characterized by good stability. The selectivity coefficients for this electrode are slightly better than for the internal solution electrode.
The liquid–liquid micro‐interface for the amperometric detection of urea
Authors: Osborne Murray D. , Girault Hubert H.
Published: May 2005

The detection of the ammonium ion produced by the enzymatic action of urease on urea is investigated electrochemically by means of Facilitated ion transfer reactions at liquid–liquid micro–interfaces. The urease was used either in a dissolved form (free in aqueous solution) or immobilized onto the surface of an ammonia gas permeable membrane. The sensing structure utilizing the ammonia gas permeable membrane allowed the detection of urea from 200μM to 4mM. Thick film technology was utilized in conjunction with UV excimer laser photoablation techniques to fabricate a inicroelectrode strip sensor for the ammonium ion.
Biosensing of rapeseed glucosinolates using amperometric enzyme electrodes based on membrane‐bound glucose oxidase or tyrosinase
Authors: Stančík Lubor , Macholán Lumír , Pluháček Ivo , Scheller Frieder
Published: May 2005

Sinigrin, the β‐D‐thioglucoside of the cruciferous plant species was hydrolyzed for 15 min at pH 7 and 30°C by the enzyme myrosinase to liberate glucose and mustard oil allylisothiocyanate as aglucone. A Clark‐type pO2 sensor overlaid with a glucose oxidase + catalase membrane served for the glucose measurements, whereas the isothiocyanate component was measured (after conversion to allylthiourea) from the inhibition degree of a tyrosinase membrane/pO2 sensor. The total amounts of glucosinolates found with the glucose probe in six assorted samples of rapeseed meal and evaluated in sinigrin equivalents (13.6 −147 μmol/g) agreed with those obtained using gas chromatography as the reference. Poor agreement (results: 111.4–112.3%) was achieved when a different method of fat removal was used prior to electroanalysis. The amounts of progoitrin (not convertible to thiourea) estimated indirectly from the difference of both the glucose and the aglucone biosensor analyses were found to be in the range 6.2–103 μmol/g (44.3–83.8% of the total glucosinolates).
Simultaneous determination of lead and tin in biological and environmental materials by differential pulse cathodic voltammetry on a glassy carbon mercury film electrode
Authors: Adeloju Samuel B. O. , Pablo Fleurdelis
Published: May 2005

A method involving a nonelectrolytic accumulation of a tin(IV)–catechol complex, followed by differential pulse cathodic voltammetric reduction of the tin‐catechol complex and the direct reduction of lead(II) ions, is described for the simultaneous determination of trace amounts of tin and lead on a glassy carbon mercury film electrode. The selective reaction of tin with catechol enables adequate resolution of its peak from the lead response. The resulting peaks which appeared at −0.39V, −0.50V and −0.66V (vs. Ag/AgCl), correspond to the reduction of SnIV, PbII and SnII, respectively. The lowest detectable concentrations in 0.10 M acetate buffer electrolyte (pH between 4.2 and 4.7) containing 5 × 10−4M catechol with an accumulation period of 300s are l.0μg L−1 and 0.5 μg L−1 for lead and tin, respectively. The linear concentration range for lead and tin in the presence of 20 μ L−1 of either element are 0–4 mg L−1 and 0‐34 μg L−1, respectively. The simultaneous determination of both elements was accomplished in solutions containing up to 4000‐fold more lead than tin. The method is successfully demonstrated for the reliable simultaneous determination of lead and tin in some biological and environmental materials.
Electrocatalysis of adsorbed Co‐cyclam at Au electrodes for nitrate reduction in concentrated alkaline solution
Authors: Ma Ling , Li Hulin
Published: May 2005

Cobalt‐cyclam, trans‐CoIII‐([14]aneN4)Cl2, was directly adsorbed on Au electrodes to form adsorbed Co‐cyclam modified electrodes. The presence of Co‐cyclam on the surface of the electrodes was determined by XPS (X‐ray photoelectron spectroscopy), differential capacity, and the voltammetric behavior of the Co‐cyclam modified electrode in 3 M NaOH solution. The electrocatalytic activity of this modified electrode towards nitrate reduction was examined in 3M NaOH solution, and a comparison of the electrocatalytic activities of the Co‐cyclam modified electrode and the Co‐cyclam incorporated Nafion film modified Au electrode is discussed. The results showed that the new modified electrode exhibited a more efficient catalytic effect.
A simple method for catalyst immobilization on electrode surfaces
Authors: De Smet Steven , Cassidy John , McCormac Tim , Maes Noel A.
Published: May 2005

Catalytic layers of a cobalt tetraphenylporphyrin/polystyrene composite coated on a glassy carbon electrode are shown to allow the reduction of oxygen at less negative potentials than at the bare electrode. When this layer was overcoated with a glucose oxidase (GOD) layer, the glucose could be determined under aerobic conditions. A similar ferrocene/polystyrene composite overcoated with a glucose oxidase layer allowed the determination of glucose under anaerobic conditions.
Novel application of potentiometric microelectrodes: Scanning potentiometric microscopy
Authors: Tóth Klára , Nagy Géza , Wei Chang , Bard Allen J.
Published: May 2005

The techniques for the fabrication of a new type of potentiometric scanning electrochemical microscopic tip are described. Ion‐concentration profiles generated in electrochemical model experiments, by enzyme catalyzed reaction and corrosion processes, as well as by the electrochemical reduction of zinc ions, have been studied and followed with micropipet ion‐selective electrode based probe microscopy. Efforts devoted to developing methods to measure scanning tip‐to‐target distances are surveyed.
Applicability of the phase boundary potential model to the mechanistic understanding of solvent polymeric membrane‐based ion‐selective electrodes
Authors: Bakker Eric , Nägele Matthias , Schaller Ulrich , Pretsch Ernö
Published: May 2005

Recent experimental evidence suggests that the equilibrium partitioning of sample ions at the sample/membrane interface is the main parameter governing the potentiometric response of polymeric membrane‐based ion‐selective electrodes (ISEs). It is shown that the response of a neutral‐carrier‐based H+‐selective electrode can be fully predicted on the basis of equilibrium concentrations measured optically within a thin organic film having the same composition as the ISE membrane. Consequently, using this simple and powerful phase boundary potential model together with mass balances and observed complex formation constants, the response and selectivity of various ISE membranes may be described. In this contribution, the most recent applications of the model are reviewed including: (1) a novel and general selectivity description, which is related to the so‐called matched potential method and clearly shows the limitations of the extended Nicolsky–Eisenman equation if ions of different charge are considered; (2) the measuring range of neutral‐carrier‐based H+‐selective ISEs, showing that previous experimental findings can now be explained by theory; (3) prediction of the influence of anionic and cationic sites on the selectivity of charged‐carrier‐based ISEs demonstrating that such ISE membranes need the incorporation of sites of the same charge type as the analyte ion to induce optimum potentiometric selectivity; and (4) the determination of the concentration of anionic impurities in poly(viny1 chloride) by measuring the influence of the anionic site concentration on the divalent/monovalent ion selectivity of a neutral‐carrier‐based ISE.
Lifetime of glass membrane electrodes: Theoretical model for the corrosion of silicate glasses
Authors: Morf Werner E.
Published: May 2005

While misfunctions of pH‐sensitive glass electrodes, as found in routine work at room temperature, are usually due to coatings on the glass membrane or to clogging of the reference electrode junction, the practical lifetime of glass electrodes at elevated temperatures is often limited by a critical increase of the electrical membrane resistance, by a gradual appearance of sluggish response phenomena, by deteriorations with respect to selectivity and linear response range, and/or by the generation of asymmetry potentials. Such aging behavior has been attributed to decomposition processes that occur on the glass surfaces in contact with aqueous solutions, such as selective ion exchange of alkali and alkaline earth metal ions for hydrogen ions from the solution (leaching), congruent matrix corrosion of the entire silicate network (etching), and enrichment of nearly insoluble components at the interface. This article reports on the corrosion dynamics of different electrode glasses. The theory of ion exchange and the effects of leached layers on glass surfaces are summarized. A thermodynamic approach to corrosion kinetics, originally devised for simulating the corrosion of minerals and glasses under hydrogeochemical conditions, was adopted for modeling the matrix corrosion of silicate glasses of various compositions.
Electroanalytical and biocompatibility studies on microfabricated array sensors
Authors: Lindner Ernô , Cosofret Vasile V. , Buck Richard P. , Johnson Timothy A. , Ash R. Bruce , Neuman Michael R. , Kao Weiyuan J. , Anderson James M.
Published: May 2005

pH, potassium and calcium ion‐selective membranes based on neutral ionophores TDDA, valinomycin and ETH‐1001, respectively and immobilized in high molecular weight (HMW) and carboxylated poly(viny1 chloride) (PVC‐COOH) as well as in aliphatic polyurethane (Tecoflex) matrices with normal and reduced amounts of plasticizers were investigated with respect of their general analytical properties, biocompatibility and cellular responses. The analytical performance of the PVC‐COOH based potassium electrodes was not effected by reducing the plasticizer content from 66% (w/w) to 33% (w/w) while that of pH electrodes was significantly deteriorated at the lower plasticizer level. High molecular weight PVC and Tecoflex membranes with low plasticizer content induce less inflammatory response compared to membranes cast with high plasticizer concentrations or PVC‐COOH as matrix. o‐NPOE plasticized membranes are correlated with an increased acute, but a decireased chronic inflammatory response, when compared to membranes cast with DOS as plasticizer.
Ionophores containing ethoxylate units for ion sensing
Authors: Thomas J. D. R.
Published: May 2005

The role of ethoxylate‐containing molecules as ion‐selective electrode (ISE) type potentiometric sensors is illustrated by studies carried out in the author's laboratories [1]. The molecules discussed include long chain acyclic polyethoxylates, crown and bis‐crown ethers, diphenylethers of tetraethyleneglycol and tripodal type receptors. Attention is given to performance of the ISEs for alkali and alkaline earth metal ions, uranyl and organic cations. Additionally, there is some discussion of fundamentals and of the role of electrodes with membranes based on appropriate tetraphenylborates of barium complexed with polyethoxylate in the analysis and critical micelle concentration determination of nonionic polyethoxylate detergents.
Kinetic characterization of the effects of organic solvents on the performance of a peroxidase‐modified electrode in detecting peroxides, thiourea and ethylenethiourea
Authors: Adeyoju Olubunmi , Iwuoha Emmanuel I. , Smyth Malcolm R.
Published: May 2005

Horseradish peroxidase (HRP) modified electrodes were constructed by entrapping the enzyme in an Eastman AQ 55D polymer. The biosensor detects butanone peroxide (BTP) as a substrate, and thiourea (THU) and ethylenethiourea (ETU) as HRP inhibitors. The kinetic parameters for this sensor in organic media such as Imax and K′m for BTP detection and K′i for ETU and THU detection were evaluated. The differences in the values of these parameters were explained in terms of the physico‐chemical properties of the organic reaction media. A possible solvent‐induced deviation of the biosensor behavior from Michaelis–Menten kinetics in the detection of ETU and THU was evaluated using the Hill analysis. The least deviation was observed in acetonitrile. Spectroelectrochemistry was also used to qualitatively assess solvent–HRP, BTP–HRP and inhibitor–HRP interactions.
Handling low frequency drifting background noise in data from a swept‐potential electrochemical detector
Authors: Msimanga Huggins Z. , Sturrock Peter E.
Published: May 2005

The quality of measurements obtained from high‐performance liquid chromatography using electrochemical detection is often obscured by both the low‐frequency drifting background noise and the high‐frequency background noise. While the quality of measurements can be greatly improved by digital filtering techniques which are capable of minimizing high‐frequency noise, these techniques are very limited in handling low‐frequency drifting background noise. A method for effectively performing background correction (the moving band method) has been developed and applied to a few chemical systems which were studied in our laboratory. The method examines each sweep (chromatograms or voltammogram) for the presence of the analyte peak. Once the peak has been detected, the base of the peak is then generated by interpolation and then refined visually by adjusting the base peak width. The generated base, along with the data points which do not contain the peaks, constitutes the background of that sweep. This background is then subtracted from the original sweep, leaving the analyte signal on a flat baseline. Before the method is applied to a sweep, high‐frequency noise is removed by fast Fourier transforms digital filtering. The moving band method is tested and evaluated using data matrices of nitrophenols and catecholamines at concentrations of about 5.0 ng/10 μL where the drifting background noise is significant. The quality of the data matrices is greatly improved due to the improved signal‐to‐noise ratios.
Sensitive adsorptive stripping voltammetric determination of xanthine and its derivatives
Authors: Shubietah Raqi M. , Zuhri Ali Z. Abu , Fogg Arnold G.
Published: May 2005

Sensitive cathodic stripping voltammetric procedures for trace determination of xanthine (I), 7‐methylxanthine (II) and 1,7‐dimethylxanthine (III) are reported. The methods are based on the accumulation of the copper(I) complexes of the compounds on the hanging mercury drop electrode. The adsorptive stripping response was evaluated with respect to accumulation time, potential, concentration, pH and other variables. Linear calibration graphs were obtained over the range from 2.0 × 10−8 to 2.0 × 10−9 M; the limits of detection, with accumulation times of 4 min for I and III, and of 6 min for II, were calculated to be 5.0 × l0−10 1.0 × 10−9 and 5 × 10−10 M, respectively. Possible interferences by other purine derivatives were examined. The simultaneous determination of 1.7‐dimethylxanthine (paraxanthine) and theophylline is possible by the proposed method.
The derivatization of molecular iodine to iodoform and its determination by adsorptive stripping voltammetry
Authors: Möller Ada , Scholz Fritz , Lovrić Milivoj
Published: May 2005

The determination of elementary iodine in aqueous solutions is possible by a preliminary liquid–liquid extraction into benzene, followed by a derivatization to iodoform with alcoholic KOH solution. The iodoform is measured by adsorptive stripping voltammetry at a signal which corresponds to the reaction

The calibration plot is linear up to 1 × 10−5 mol/L. The detection limit is at least 2 × 10−8 mol/L and the standard deviation of the entire analytical procedure is 10%. The procedure is applicable to seawater.
A new simple long‐path‐length thin‐layer spectroelectrochemical cell in various uses
Authors: Niu Jianjun , Dong Shaojun
Published: May 2005

This article describes the design of a new type of long‐path‐length thin‐layer cell (LPTLC), which is constructed by inserting two Teflon cell bodies into a standard cuvette. This cuvette holder enables the LPTLC to combine with photometric instrumentation conveniently. Gold, platinum, glassy carbon, and other materials can be used for the working electrode. Since no soluble adhesive material is used, the cell can meet various needs (in situ conventional and derivative UV‐vis, in situ circular dichroism, etc.) in both aqueous and nonaqueous systems.
Determination of hesperidin by catholic stripping voltammetry in orange juice and helopyrin, a phytopharmaceutical preparation
Authors: Obendorf Dagmar , Reichart Edgar
Published: May 2005

The electrochemical behavior of hesperidin at the mercury electrode (HMDE, DME) has been studied by differential pulse polarography. Determination of hesperidin can be achieved either by direct reduction of the carbonyl group in the γ‐pyrone ring at −1.1 V (versus Ag/AgC1) or indirectly by cathodic stripping voltammetry via the formation of two different hesperidin‐mercury complexes at the electrode surface that can be reduced at −0.20 V and −0.40 V, respectively. The advantage of cathodic stripping voltammetry is higher sensitivity and due to the possibility of higher sample dilution less influence of matrix effects. The new method is suitable for the determination of lower hesperidin concentrations between 0.1 ppm (1.64 × 10−7 M) and 25 ppm (4.1 × 10−5 M). The application to the determination of hesperidin in orange juice and in Helopyrin tablets, a phytopharmaceutical preparation, is demonstrated.