bluuebunny/crossref_metadata_2025 huggingface dataset:
Bilayer lipid membranes as electrochemical detectors for flow injection immunoanalysis
Authors: Nikolelis Dimitrios P. , Siontorou Christina G. , Andreou Vangelis G. , Viras Kyriakos G. , Krull Ulrich J.
Published: May 2005

This work describes the use of filter‐supported stabilized bilayer lipid membranes (BLMs) for the rapid electrochemical monitoring of an immunological reaction in flowing solution streams. BLMs were prepared from egg phosphatidylcholine (egg PC) and dipalmitoyl phosphatidic acid (DPPA) and the ultrafiltration membranes used were composed of glass microfibers. Thyroxin (T4)/anti‐rabbit T4 was used as a representative immunological reaction for these studies. Antibody was incorporated into a floating lipid matrix at an air–electrolyte interface, and then a casting procedure was used to deliver the lipid onto the filter supports for BLM formation. Injections of antigen were made into flowing streams of a carrier electrolyte solution. Experiments were done in a stopped‐flow mode using lipid mixtures containing 15% (w/w) DPPA to provide only a single transient current signal with a magnitude related to the antigen concentration. Differential scanning calorimetric experiments provided evidence that the antibody‐lipid interactions at the BLMs occurred through electrostatic interactions. BLMs containing 35% DPPA were used to examine regeneration of the active sites of antibody after complex formation by washing with the carrier electrolyte solution. Repetitive cycles of injection of antigen followed by regeneration of antibody binding activity have shown that the maximum number of cycles is about 5, followed by a degradation of signal for a larger number of injections. However, the sensor can also be easily regenerated by recasting of the existing lipid/antibody film at the air–electrolyte interface to form fresh BLMs.
Synergistic electrochemical and chemical modification of carbon paste electrodes for open‐circuit preconcentration and voltammetric determination of trace adenine
Authors: Cai Xiaohua , Ogorevc Božidar , Kalcher Kurt
Published: May 2005

A new concept of electrode modification is presented, consisting of chemically assisted electrochemical oxidative pretreatment of the electrode surface. If carbon paste electrodes (CPEs) are polarized at +1.75 V (vs Ag/AgCl) in a dilute alkaline medium (1 × 10−3mol/L) containing 0.1 mol/L NaNO3 for 60s, they exhibit a unique ability to preconcentrate adenine, an important biological substance, that served as a model compound. In this work, a thorough study has been performed to explore the new pretreatment procedure, but also its analytical application for trace adenine determination was optimized. During the pretreatment of a CPE, a specific oxide layer is formed due to a synergistic effect of a combined anodic and chemical oxidation process, in which the presence of sodium nitrate plays a crucial role. In a subsequent step under open‐circuit conditions, adenine is oxidized by the oxide layer, and the resulting oxidation product is strongly adsorbed onto the electrode surface. After medium exchange, the adsorbed oxidation product of adenine is reduced at −0.5 V (vs. Ag/AgCl) and the voltammetric current response can be utilized for analytical purposes. Applying 10 min accumulation and square‐wave voltammetric operation, the detection limit of 20 μg/L (1.5 × 10−7 mol/L) of adenine in a sample solution was acquired. The voltammetric behavior of adenine at plain and pretreated CPEs is also presented and discussed.
Catalytic oxidation of methanol on a glassy carbon electrode electrochemically modified by a conductive NiII‐curcumin film
Authors: Ciszewski Aleksander
Published: May 2005

This work focuses on the electrochemical synthesis and characterization of a conductive polymeric nickel‐curcumin film and its application for electrocatalytic oxidation of methanol in alkaline solutions. It has been found that a glassy carbon electrode modified by this film acts as a very effective catalyst for oxidation of alcohols. Electropolymerization of the nickel‐curcumin complex and oxidation of methanol have been studied by cyclic voltammetry. The described modified electrode provides a durable catalytic surface which allows the voltammetric oxidation of methanol: in 0.1 M NaOH electrolyte the resulting anodic peak is at 0.59 V (vs. SCE). Electrooxidation was not possible at bare glassy carbon electrodes, at least before the onset of the electrolyte decomposition. The mechanism of modifying the film formation has been discussed.
Adsorptive stripping potentiometry of DNA at electrochemically pretreated carbon paste electrodes
Authors: Wang Joseph , Cai Xiaohua , Jonsson Colleen , Balakrishnan Mini
Published: May 2005

Potentiometric stripping analysis is employed for highly sensitive measurements of single‐stranded DNA at carbon paste electrodes. Electrochemical (oxidative) pretreatment is used to condition the carbon paste surface prior to the accumulation process. The low background response of the potentiometric stripping mode offers convenient quantitation of low nanogram quantities of DNA. Experimental variables of the pretreatment and measurement procedures are explored and optimized. Results are also reported for the quantitation of nanogram levels of the long terminal repeat (LTR) from the human leukemia virus and for the stripping operation of microfabricated screen‐printed electrodes.
Electrochemical oxidation of 8‐hydroxyquinoline and selective determination of tin(II) at solid electrodes
Authors: Yang Z. P. , Alafandy M. , Boutakhrit K. , Kauffmann J.‐M. , Arcos J.
Published: May 2005

The electrochemical oxidation of 8‐hydroxyquinoline and several structurally related molecules has been investigated by cyclic voltammetry at solid electrodes (GCE, CPE, Pt) as a function of pH in aqueous acetate media. Oxine showed one irreversible oxidation peak whose magnitude decreased in the presence of cations readily complexed by oxine and with concomitent formation of a new oxidation peak at more positive potentials. Tin(II) was found to exhibit a distinct behavior as its oxidation was catalyzed by the presence of oxine in the analyzed solution. The tin(II)‐oxine oxidation peak was found to be linearly related to inorganic tin(II) concentration allowing its quantitative determination at micromolar levels.
Characterization of electrochemically prepared polyaminopyridines
Authors: Park Deog‐Soo , Shim Yoon‐Bo , Park Su Moon
Published: May 2005

Polymer‐modified electrodes have been prepared by electrochemical oxidation of 2‐aminopyridine and 4‐aminopyridine in acetonitrile and their chemical properties have been characterized. The polymer films thus prepared were insulators but can be doped with Ag+ or Fe(CN) to produce semiconducting films. The doping must have been accomplished by the complexation of Ag+ with functional groups or trapping of Fe(CN) in the polymer matrix. It has also been demonstrated that these films can be used for chemical analysis of Ag+ by first collecting Ag+ and running subsequent differential pulse voltammetric experiments. The dynamic linearity was excellent in the concentration range of 10−7–10−2 M and the detection limit was about 5 × 10−8M.
A microscopic study on carbon paste electrodes
Authors: Švancara Ivan , Hvízdalová Marie , Vytřas Karel , Kalcher Kurt , Novotný Radomír
Published: May 2005

Scanning electron microscopy has been used for observing the surface of several types of carbon paste electrodes in order to reveal the role of both pasting liquid and carbon powder on the formation of the carbon paste structure. The effect of pasting liquid was studied using carbon pastes prepared from RW‐B multicrystalline graphite powder and either liquid tricresyl phosphate or Nujol oil. The influence of carbon powders was investigated on carbon pastes made of two special carbon powders with globular particles (Sigradur K or Sigradur G, respectively) and of Nujol. Microscopic observations have shown marked alterations in the structure of the carbon pastes studied either due to different physico‐chemical properties of the pasting liquids or in consequence of specific characteristics of the powdered carbon materials, especially of the shape and size distribution of carbon particles. Information resulting from this microscopic study was then compared with conclusions of previous voltammetric investigations on the same types of carbon pastes, thus providing a way to characterizing better their overall electrochemical behavior.
Compression of the interfacial boundary electrode‐solution as the basis of new compression accumulation (stripping) techniques
Authors: Novotný Ladislav
Published: May 2005

A new approach is presented to the study, monitoring, control and utilization of electrode processes based on the compression of interfacial boundaries. The principle is demonstrated by the adsorption of 4,4′‐bipyridyl on mercury electrode from 0.1 M H2SO4 for which a compression diagram (isotherm) is provided and the phenomena accompanying the compression are analyzed. Prospects for the development of new compression techniques are discussed.
Electron transfer through an immunoglobulin layer via an immobilized redox mediator
Authors: Wittstock Gunther , Emons Hendrik , Heineman William R.
Published: May 2005

As a step towards a voltammetric immunoassay with antibodies directly attached onto the electrode surface, the mediated oxidation of a redox active label has been investigated with a model system. Butyl ferrocene served as a model for the mediator and was coimmobilized onto a glassy carbon electrode within a layer of bovine immunoglobulin G, which mimiked the antibody. An overlaid polyvinyl ferrocene layer was employed to simulate a ferrocene‐tagged high molecular weight antigen bound to the immobilized antibodies. A mediated electron transfer could only be demonstrated with butyl ferrocene as mediator, whereas other compounds failed to support an electron transfer between the polyvinyl ferrocene layer and the electrode through the layer of immunoglobulin.
Mushroom‐based cobalt phthalocyanine dispersed amperometric biosensor for the determination of phenolic compounds
Authors: Ozsoz Mehmet , Erdem Arzum , Kilinc Emrah , Gokgunnec Levent
Published: May 2005

The use of mushroom tissue as a source for polyphenol oxidase for the determination of phenolic compounds is described. The enzymatic reaction between mushroom polyphenol oxidase and phenolic compounds is coupled with the use of cobalt phthalocyanine dispersed in carbon paste. The effects of applied potential to the responses are investigated. Cobalt phthalocyanine dispersed electrodes give shorter response times and a lower applied potential compared to conventional tissue biosensors.
Needle‐type glucose biosensors based on a pyrolyzed cobalt‐tetramethoxy‐phenylporphyrin catalytic electrode
Authors: Atunasov Plamen , Gamburzev Sergej , Wiikins Ebtisam
Published: May 2005

Amperometric needle‐type glucose biosensors employing nonplatinum catalytic electrodes made from pyrolytic electrode of pyrolyzed cobalt‐tetramethoxy‐phenylporphyrin (CoTMPP) are described. A technique for preparation of the working electrode with catalyst and adsorbed enzyme (enzyme electrode) from a pressed matrix (tablet) is presented. This technique allows manufacturing numerous sensors from the same pressed tablet, all of which demonstrate a good reproducibility of their parameters (sensitivity, linear range, lifetime). Different glucose diffusion (external) membranes have been studied in order to extend the linear range of the biosensor response. Linearity of the sensor response to glucose concentrations up to 35 mM is reported when a cellulose paper membrane, impregnated with cellulose acetate. is used pressed into the needle sensor body. Sensors demonstrated a shelf lifetime of 30 days (with constant parameters of the signal output) and can be used for continuous glucose monitoring in vitro for at least 5 days.
Electrochemistry at the tetrathiafulvalene‐tetracyanoquinodimethane electrodes. Application to the study of c‐type cytochromes
Authors: Bianco Pierre , Haladjian Jean
Published: May 2005

Electrodes made from pastes of the conducting organic salt, tetrathiafulvalene‐tetracyanoquinodimethane (TTF‐TCNQ), are prepared and characterized using electrochemical techniques. These electrodes behave as conventional solid electrodes within their stable potential range. An attractive property is their capability to achieve direct electrochemistry of c‐type cytochromes (horse heart cytochrome c, cytochrome c552 from Thiobacillus ferrooxidans). Resuits on pH‐dependence and kinetic data for these metalloproteins agree with previously published data. It is suggested that favorable interactions occur between the TTF‐TCNQ electrode surface and redox protein sites. Moreover, the analytical advantage of using permselective‐membrane TTF‐TCNQ electrode is demonstrated.
Sonovoltammetric behavior of ascorbic acid and dehydroascorbic acid at glassy carbon electrodes: Analysis using pulsed sonovoltammetry
Authors: Compton Richard G. , Matysik Frank‐Michael
Published: May 2005

The effect of power ultrasound on the voltammetric behavior of ascorbic acid and dehydroascorbic acid at a glassy carbon electrode is described. The voltammetric characteristics of both compounds were found to be modified by ultrasonically formed radicals. In the case of dehydroascorbic acid the single sweep voltammogram shows an anodic signal in the presence of ultrasound which probably results from the formation of an oxidizable radical known to be an intermediate of ascorbic acid oxidation. In the case of ascorbic acid pulsed sonovoltammetry is applied and characterized regarding the time dependence of the current decay and the reliability of its analytical performance. The utility of pulsed sonovoltammetry is demonstrated analyzing a pain killer tablet regarding the ascorbic acid content.
Application of an optimization procedure in adsorptive stripping voltammetry to the determination of nickel with DMG
Authors: Sanllorente Silvia , Ortiz M. Cruz , Arcos M. Julia , López‐Palacios Jesús
Published: May 2005

A procedure for the determination of nickel by adsorptive stripping voltammetry (AdSV), using dimethylglyoxime as complexing agent, has been optimized. The determination was carried out by two different techniques: differential pulse adsorptive stripping voltammetry (DPAdSV) and square wave adsorptive stripping voltammetry (SWAdSV). The selection of the experimental parameters was done using a factorial design which allows one to find the most significant variables, i.e., those which exert the greatest influence on the measured magnitude, with a reduced number of experiments. Posterior optimization of these variables provided the most adequate experimental conditions and it was under these conditions that the calibrations were made, using a robust regression method which allows the elimination of anomalous points.
The role of nickel as central metal in conductive polymeric porphyrin film for electrocatalytic oxidation of nitric oxide
Authors: Ciszewski Aleksander , Kubaszewski Eugeniusz , Łożyński Marek
Published: May 2005

This communication assesses the role of nickel in the electrocatalytic detection of nitric oxide at polymeric porphyrin coated glossy carbon electrodes.
Voltammetric determination of silver at ultratrace levels using a carbon paste electrode with improved surface characteristics
Authors: švancara Ivan , Kalcher Kurt , Diewald Wolfgang , Vytřas Karel
Published: May 2005

A differential pulse anodic stripping voltammetric method for the determination of silver is described. A new type of electrodeposition for preconcentrating the analyte, Ag+, was investigated, enhancing the electrolytic accumulation efficiency onto a carbon paste electrode by ion pair formation. A carbon paste electrode containing tricresyl phosphate as a pasting liquid was modified in situ with heptylsulfonic acid (sodium salt). The modifier gave rise to an additional accumulative effect towards the target ions based on ion pairing which resulted in an enhanced sensitivity of the electrode. Additional activation of the electrode surface at −1.0 V (vs. SCE) for 60 s improved the detection limit significantly. The detection limit was found to be 2.5 × 10−12 M Ag+ (accumulation time 15 min), and could be even lowered by increasing the period of preelectrolysis. The current response was linearly dependent on the concentration up to 2 × 10−5 M Ag under optimized conditions. The effects of paste composition, voltammetric parameters, composition of the supporting electrolyte as well as the influence of alkylsulfonic acids and of cathodic activation upon the determination of Ag were studied. Interferences from about 20 elements were investigated with particular attention to Cu, Hg, and Au. By masking with ethylenediaminetetraacetate (EDTA), Cu and Hg did not affect the response of Ag up to a 10000‐fold and 500‐fold molar excess in concentration, respectively. Au did not interfere with the determination of Ag up to a 100‐fold molar excess if its absolute concentration was lower than 5 × 10−7 M. For higher concentration levels, [AuCl4]− could be separated by passing the analyte solution through an anion‐exchanger column (Dowex‐1) prior to stripping analysis. Due to the extremely low detection limit and high selectivity, the method could be applied to determine Ag at its ubiquitous level in tap water. With this method, the corrosion of silver cutlery in tap water could be monitored. The results agreed well with those obtained by using inductively coupled plasma mass spectrometry (ICP‐MS).
Microdialysis sampling and high performance liquid chromatography with amperometric detection for sugar analysis in milk products
Authors: Mannino Saverio , Cosio Maria S. , Zimei Paola
Published: May 2005

A rapid and highly efficient method for the direct quantification of the major carbohydrates, glucose, fructose, sucrose and lactose in milk‐based products is described. Rapid and selective monitoring of each sugar is accomplished by microdialysis sampling coupled with HPLC separation and amperometric detection with a chemically modified electrode. This new scheme offers simultaneous monitoring of sugars with little or no sample pretreatment. The results obtained from the application of the proposed procedure to milk and milk‐based products are discussed.
A serial array of ISEs for use in a portable battery‐powered flow injection analyzer
Authors: Dimitrakopoulos Telis , Alexander Peter W. , Hibbert D. Brynn
Published: May 2005

Portable flow injection potentiometry (FIP) is described with a flow‐through multi‐ion sensor array system based on a planar design. Potassium, sodium and nitrate sensors are used as examples for simultaneous multi‐ion determinations based on the availability of a planar sensor design for these ions. The miniaturized flow cell developed with the three sensors in series in the FIP system is used to demonstrate the reliability of this portable design when using manual injection of the sample solution. The system is characterized by its small size, light weight and low power requirements, and makes use of a notebook computer for real‐time display of data and data acquisition. Rapid FIP response characteristics are shown after optimization of flow carrier conditions, and are successfully applied to the analysis of mineral water samples.
Immobilized ferrocene and glucose oxidase on titanium(IV) oxide grafted onto a silica gel surface and its application as an amperometric glucose biosensor
Authors: Milagres Benjamin G. , Kubota Lauro T. , Neto Graciliano De Oliveira
Published: May 2005

The voltammograms obtained with an electrode containing carbon paste with ferrocene immobilized on a titanium‐oxide/silica gel material showed good response and stability in aqueous media. From pH 4 to 8 the electrode response remained almost constant, but a small shift in the midpoint potential towards more positive values was observed when the pH was decreased. The nature of the cation does not affect the voltammetric response. However, the nature of the anion affects the midpoint potential significantly. Cyclic voltammetry investigation showed that the electrode with immobilized glucose oxidase is an excellent biosensor. The mechanism of the electron transfer was proposed as being electron tunneling by the flavin of the enzyme to mediator, and the high current level is assigned to the high surface area of the silica matrix. The amperometric measurements showed a linear response in the range from 1.0 × 10−4 to 8.0 × 10−4 M. Above this range, saturation of the enzyme was observed. The response time was about 15 s. Determination of glucose in blood serum showed an excellent correlation when compared with Merck's Kit method. The immobilized material presented an excellent stability mantaining the same activity for at least six months.
The mechanism of the electro‐reduction of some azo dyes
Authors: Gooding Justin J. , Compton Richard G. , Brennan Colin M. , Atherton John H.
Published: May 2005

The pH dependence of the reduction mechanism of the azo dyes Orange G and Sunset Yellow FCF was investigated using a mercury plated rotating disk electrode, The reduction was shown to proceed via a CE mechanism except at very high pH, where direct reduction was observed. It is proposed that the chemical step of the CE reaction, namely protonation of the azo bond, could occur either intramolecularly, via azo/hydrazone tautomerism, or intermolecularly from bulk solution. At low pH the protonation from free H+ predominated while above neutral pH, until deprotonation of the ortho hydroxyl group involved in the tautomerism, the intramolecular mechanism was more prevalent. The kinetic parameters for the chemical steps in each of the two protonation mechanisms were determined.
Development of an amperometric enzyme biosensor for the determination of the antioxidant tert‐butylhydroxyanisole in a medium of reversed micelles
Authors: Ruiz M. Asuncion , Reviejo A. Julio , Parrado Concepcion , Pingarrón Jose M.
Published: May 2005

A biocdtalytic scheme, based on the enzyme tyrosinase, has been developed for the determination of the antioxidant tert‐butylhydroxyanisole (BHA) in food samples. Reversed micelles formed with ethyl acetate as organic solvent, dioctyl sulfosuccinate (AOT) as emulsifying agent, and phosphate buffer of pH 7.4 as aqueous phase, has been employed as the working medium. The potential applied to the tyrosinase electrode, as well as the temperature of the working reversed micelle, the percentage of aqueous phase, and the pH of the phosphate buffer solution have been optimized. The stability of the enzyme electrode with time has been also evaluated. A very good selectivity has been found with respect to potential interference from other substances commonly present in commercial antioxidant mixtures in food. An Eastman‐AQ/enzyme immobilization approach has been employed to improve the stability of the tyrosinase biosensor in reversed micelles flowing streams. A flow injection method with amperometric detection for the determination of BHA has been developed and applied to the analysis of this antioxidant in commercial biscuits.
Evaluation of a new disposable screen‐printed sensor strip for the measurement of NADH and its modification to produce a lactate biosensor employing microliter volumes
Authors: Sprules Steven D. , Hart John P. , Pittson Robin , Wring Stephen A.
Published: May 2005

A combined sensor strip was fabricated by screen‐printing a Meldola Blue modified carbon working electrode and a Ag/AgCl combined reference/counter electrode alongside each other on a PVC substrate. This was investigated as an amperometric sensor for NADH, at an applied potential of 0 V, both in bulk solutions under hydrodynamic conditions and using 20 μL volumes without agitation. The former technique gave linear responses in the range 3–60 × 10−6mol dm−3 and the latter in the range 10−5 × 10−4 mol dm−3 of NADH. Further modification of the electrodes with NAD+ and lactate dehydrogenase converted the device to a biosensor for lactate both in spiked phosphate buffer and bovine serum. The sensors demonstrated good linear responses in the range 0–20 × 10−3 mol dm−3.
Meta1 displacement at the zinc‐diethyldithiocarbamate‐modified carbon paste electrode for the selective preconcentration and stripping analysis of mercury(II)
Authors: Khoo Soo Beng , Cai Qiantao
Published: May 2005

A carbon paste electrode modified with zinc diethyldithiocarbamate was used for the selective accumulation of mercury(II) based on the metal displacement principle. Selectivity was achieved by exploiting differences in conditional extraction constants. After accumulation, medium exchange was performed. The accumulated HgII was then reduced to metallic mercury in 0.10 M KSCN − 0.010 M HC104 followed by differential pulse anodic stripping voltammetry in the same medium. Factors affecting the accumulation, reduction and stripping steps were systematically investigated. An optimized procedure was then developed for the determination of HgII. Under optimum conditions, a detection limit of 8.0 × 10−10 M Hg(II) was obtained for a 15 min accumulation. For 6 determinations each of 1.00 times l0−7 M and 5.00 times 10−8 M HgII, relative standard deviations were 1.5% and 3.3%, respectively. The presence of selected metal ions and other organic and inorganic substances gave no observable interferences. However, interferences were observed when 1.00 times 10−3 M NH4SCN, Na2EDTA and NH4Br were present. These interferences can be readily overcome by digesting the samples with oxidizing agents. The developed method was applied to the analysis of mercury in a U.S. Environmental Protection Agency water quality control sample and also in a human urine sample.
Catalytic‐adsorptive stripping voltammetric determination of chromium in environmental materials
Authors: Gao Zhiqiang , Siow Kok Siong
Published: May 2005

Trace levels of chromium in natural water, soil and plants can be determined directly after accumulation of the chromium(III)‐2,2‐bipyridine complex on a hanging mercury drop electrode, coupled with the catalytic effect of the adsorbed complex on the reduction of nitrite. The adsorptive‐catalytic characteristic of the complex provides the needed sensitivity and selectivity for direct determination of ultratrace concentrations of chromium in environmental samples. The effect of various experimental parameters on the catalytic current was investigated. Under optimal conditions, the adsorptive‐catalytic stripping voltammetric procedure produces a detection limit of 20 pM (1.0 ppt) chromium and a linear catalytic current‐chromium concentration relationship up to 50 nM, following 5 s of accumulation. Most of the coexisting metals do not interfere with the measurements.
Characterization of tyrosinase‐teflon/graphite composite electrodes for the determination of catechol in environmental analysis
Authors: Puig David , Ruzgas Tautgirdas , Emnéus Jenny , Gorton Lo , Marko‐Varga György , Barceló Damia
Published: May 2005

Amperometric biosensors incorporating tyrosinase into Teflon/graphite composite were developed for the detection of catechol. The homogeneity of Teflon/graphite was elucidated by means of chronoamperometry (using ferricyanide) and the calculation of the electrochemically active and total surface area of the electrodes. The homogeneity of composite is increased when working with the frozen Teflon. The mechanical strength, sensitivity, apparent Michaelis‐Menten constant, maximum currents, and the compatibility with methanol and acetonitrile of the bioelectrodes were investigated. It was found that 10–30% of graphite in Teflon were suitable for the preparation of electrodes of high mechanical strength and low electrical resistivity. The sensitivity was found to be dependent on the ratio of Teflon/graphite where higher percentage of graphite gave the highest sensitivity. Electrode responses for catechol decreased 5% during one hour of its operation in buffer solution containing 10% methanol.
Regression by least median squares in the calculation of transition times for calibration in chronopotentiometry
Authors: Ortiz María C. , Palacios Jesús López , Sarabia Luis A. , Piangerelli Maria G. , Cingolani Deborah
Published: May 2005

The ability of the least median squares (LMS) method in detection of several straight segments in experimental continuous curves is tested using chronopotentiometric data. As a common experimental system, the chronopotentiometric reduction of Fe(CN)on a Pt electrode is used for this purpose. LMS allows for the correct estimation of transition times and then, for the calibration of the system. LS calibration without outliers detected by LMS assures a better prediction and therefore better calibration quality, because the standard error of estimation is 32.43% less than one obtained with the whole data.
A PVC‐based benzo‐15‐crown‐5 membrane sensor for cadmium
Authors: Srivastava Suresh K. , Gupta Vinod K. , Jain Suresh
Published: May 2005

A plasticized poly (vinyl chloride) (PVC)‐based membrane of benzo‐l5‐crown‐5 exhibits a good response for Cd2+ in a wide concentration range (3.16 × 105−1.00 × 10−1M) with a slope of 20mV per decade of [Cd2−]. The response time of the membrane sensor is < 30 s and the same can be used in a pH range 3.8 to 7.0. The electrode has been used, at one stretch, for a period of two months and displays good selectivity for Cd2+ over alkali, alkaline earth and transition metal ions. The membrane sensor has also been used as an indicator electrode in potentiometric titration involving cadmium(II) ions.
Rapid calibration‐free determination of lead in microliter amounts of whole blood
Authors: Jagner Daniel , Ma Feng , Wang Yudong
Published: May 2005

A calibration‐free method using portable instrumentation and thus suitable for field screening of lead in whole blood is described. Whole blood (2.5 μL) is diluted first with distilled water (5.0 μL) and then with a matrix‐modifying solution (17.5 μL) containing 0.50M HCl, 600 mg/L HgII, 5% v./v. Triton X‐100 and l00 μg/L of cadmium(II), the latter being used for performance check. A 12 μL subsample is then electrolyzed for 2 min. on a vibrating glassy carbon electrode whereby 90% of the lead(II) ions are reduced to amalgamated lead. Stripping oxidation is then performed with a constant current of 40μA. In two consecutive stripping oxidations the chemical contribution (chemical current) to the oxidation is determined facilitating calculation of the total amount of lead(II) in the sample using Coulombs law subsequent to correction for nonquantitative electrolysis. Results obtained on analysis of certified blood standards deviated less than 14 μg/L on the 3 sigma level in the concentration range 22–118 μg/L and by less than 13% on the 3 sigma level in the range 220–616 μg/L.
Controlled incorporation of heavy metals from aqueous solutions and their electrorelease using composite polypyrrole films
Authors: Hepel Maria , Dentrone Laura
Published: May 2005

Composite polypyrrole/catechol films with cation‐exchange properties have been prepared by electropolymerization on AT‐cut 10 MHz gold piezoelectrodes at constant potential. The use of the electrochemical quartz crystal microbalance allowed us to diagnose the type of ion dynamics in these films. Incorporation of a variety of heavy metals was feasible by applying potentials more negative than −200mV (vs. SCE). Regeneration of these films was performed by releasing these metals into the solution during the reverse potential step. Incorporation of the following metal ions PbII, CdII, CoII, and NiII into polymer matrix was found even in the presence of large excess of sodium ions.
Electrochemical and electroreflectance spectroscopic study of copper tetrakis(n‐butoxy carbonyl)phthalocyanine
Authors: Shim Yoon‐Bo , Jin Chang‐Soo , Feng Zhi‐Qiang , Niki Katsumi
Published: May 2005

Electrochemical and in‐situ spectroelectrochemical behavior of copper tetrakis(n‐butoxy carbonyl) phthalocyanine (tbcCuPc) was studied using a pyrolytic graphite electrode (PGE). Cyclic voltammogram (CV) shows two consecutive one‐electron redox peaks appearing at ‐670 mV / −640 mV and −770 mV / −710 mV (vs. Ag/AgCl). The reduction processes of tbcCuPc on PGE involved only the ligand. The formal potentials of the adsorbed species determined by UV‐vis electroreflectance (ER) voltammetry were −650 mV and −760 mV (vs. Ag / AgCl electrode). The major peak in the ER spectrum of tbcCuPc appearing near 600 nm was obtained at −760 mV. The peak potential of tbcCuPc‐adsorbed electrode, as observed by ER voltammogram at 600 nm, changed linearly with pH values between 1 and 13. The heterogeneous rate constant, ks, of the electrode reaction of tbcCuPc adsorbed on the PGE surface was determined to be 8.78 × 102 s −1 by analyzing the frequency dependance of the ER signals.
Low temperature spectroelectrochemistry for the characterization of highly reduced σ‐alkyl iron halogenated porphyrins
Authors: Gueutin Claire , Lexa Doris
Published: May 2005

Low temperature spectroelectrochemistry was performed to generate highly reduced σ‐alkyl iron porphyrins, which were unstable at room temperature and oxygen sensitive. Suitable conditions for obtaining a stable compound were provided by keeping the thin‐layer cell under strictly anaerobic conditions. To calibrate the cell and check the deoxygenation the electrochemically produced radical anion of ZnTPP was used as an oxygen probe. By satisfying the anaerobic conditions, mainly due to the fact that no Teflon or Kel F spacers were used, it was possible for the first time to generate and characterize highly reduced σ‐alkyl iron porphyrins at low temperatures. The ligation reactions of these species were also stabilized.
Linear and cyclic sweep voltammetry at a rotating disk electrode. A digital simulation
Authors: Strutwolf Jörg , Schoeller Wolfgang W.
Published: May 2005

The transport equation for the rotating disk electrode is solved numerically with appropriate boundary conditions for reversible and nonreversible redox reactions. A comparison of the computational mode with experimentel data is presented. The adaption of a steady state under variations of experimental parameters ν (scan rate) and ω (angular frequency of rotation) is investigated. It is shown that a triangular voltage scan can be used to indicate the attainment of a steady state in every zone of the current‐voltage curve.
Simultaneous determination of chloride and fluoride ions in waters by sequential injection analysis
Authors: Alpízar Jesús , Crespí Antonio , Cladera Andreu , Forteza Rafael , Cerdà Víctor
Published: May 2005

A sequential flow injection method for simultaneous chloride and fluoride determination in waters with potentiometric detection is described. The method is based on the simultaneous chloride and fluoride potentiometric detection using two ion selective electrodes in two serial flow‐through cells. The necessary ionic strength adjustment is obtained by mixing the TISAB solution with the sample by diffusion during the propelling process to the detection cells. The new method was applied successfully to drinking water samples.
Electrochemical determination of nitrites in natural waters with ultramicroelectrodes
Authors: Silva S. M. , Alves C. R. , Muchado S. A. S. , Mazo L. H. , Avaca L. A.
Published: May 2005

This work reports the application of carbon‐fiber and gold ultramicroelectrodes for the determination of nitrites in different media. The linear‐sweep voltammetric response for nitrite oxidation on carbon fiber and gold was investigated in the anodic potential range up to 1.6 V (vs. the saturated calomel electrode). The experiments were performed in sulfate solutions, pure and natural waters. Natural water samples were obtained from a commercially available mineral water and from a heavily polluted urban creek. Very well‐defined waves were always obtained showing a half‐wave potential near to the value previously reported for NO oxidation. It was demonstrated that neither O2, or NO exert any influence in the nitrite oxidation response. The detection limits calculated were within the range of 2.6 to 9.7 μM, the highest being associated to the polluted water sample on carbon fiber and the lowest to mineral water on gold ultramicroelectrodes.
Potentiometric determination of L‐dopa, carbidopa, methyldopa and aspartame using a new trinitrobenzenesulfonate selective electrode
Authors: Badawy S. S. , Issa Y. M. , Tag‐Eldin A. S.
Published: May 2005

A selective PVC membrane electrode based on the ion‐pair of cetylpyridinium (CP+) and 2,4,6‐trinitrobenzenesulfonate (TNBS−) as the electroactive species was developed. The electrode exhibits a rapid and Nernstian response to TNBS− from 5.0 × 10−5 to 1.0 × 10−2M at 25 ± 0.1°C. The response is unaffected by the change of pH over the range 2–12. Selectivity coefficients for a larger number of organic and inorganic anions and sugars are given. The electrode has been successfully applied to the determination of L‐dopa, carbidopa, methyldopa and aspartame in pure solutions and in their pharmaceutical formulations with a precision and accuracy of 0.9–1.3% without interference from excipients.
The standard potentials of the electrode “dissolved atomic mercury/dissolved mercury ions”
Authors: Scholz Fritz , Lovrić Milivoj
Published: May 2005

The standard potentials of the redox electrodes “dissolved atomic mercury/dissolved mercury ions” are calculated to be E0(Hg0/Hg2+) = 0.661 V (vs. SHE and E0/Hg0 Hg) = 0.410V (vs. SHE). The standard potential of the electrode “metallic mercury/dissolved mercury ions” E0(Hg/Hg2+) = 0.8535V (vs. SHE) is the formal potential of the electrode “dissolved atomic mercury/dissolved mercury ions” at saturation activity of atomic mercury. In all calculations involving dissolved atomic mercury below saturation activity, the standard potentials E0(Hg0/Hg2+) and E0(Hg0/Hg22+) have to be used or the relation between them and E0(Hg/Hg2+) and E0(Hg/Hg) has to be taken into account.
A novel approach to the solid‐state electrochemistry of fullerenes: Cyclic voltammetry at a C‐modified graphite‐PTFE composite electrode
Authors: Kutner Włodzimierz
Published: May 2005

A Buckminsterfullerene (C60)‐modified graphite‐PTFE composite electrode was prepared by pelletizing a powder mixture of 10% C60, 30% graphite, and 60 % PTFE (by weight). Multicyclic voltammetry of the electrode in acetonitrile solution of tetra‐n‐butylammonium perchlorate shows reproducible, two‐step, C60 charging and discharging, in the potential range for which only the first two, i.e., C and C electroreductions occur. This behavior favorably compares to that reported earlier for the C60 solid films, in the same solution. The composite electrode is recommended as a convenient tool for investigation of the solid‐state electrochemistry of fullerenes.
Immobilization of pyrroloquinoline quinone on gold by carbodiimide coupling to adsorbed polyamines: Stability comparison to attachment via a chemisorbed thiol monolayer
Authors: Moore Andrew N. J. , Katz Eugenii , Willner Itamar
Published: May 2005

Pyrroloquinoline quinone (PQQ) was immobilized on gold electrodes by prior adsorption of the polyamines polyethylenimine, and triethylene tetraamine, followed by carbodiimide coupling of PQQ to the surface‐adsorbed amine groups. The stability and electrochemical behavior of the electrodes, in which the amino‐containing linker molecule is adsorbed on the electrode surface, were compared with those of electrodes prepared by carbodiimide coupling of PQQ to a cystamine monolayer, in which the sulfur‐containing linker molecule is associated with the gold surface. The electrodes prepared using adsorbed polyethylenimine showed comparable stability to those based on a cystamine monolayer, but reveal enhanced stability to application of negative potentials (< −1.1 V). The method provides an alternative to the conventional functionalization of Au electrodes by thiols.
Renewable, reagentless glucose sensor based on a redox modified enzyme and carbon‐silica composite
Authors: Sampath Srinivasan , Lev Ovadia
Published: May 2005

A new type of sol‐gel derived, ferrocene derivatized glucose oxidase based amperometric biosensor is introduced. The electrode consists of graphite powder impregnated with a ferrocene modified enzyme imbedded in an organically modified silicate network. In this assembly, graphite powder provides percolation conductivity, the organic modification of the silicate ensures that the whole bulk of the material is not wetted by the analyte, thus providing a thin reactive layer. The ferrocene which is covalently attached to the enzyme acts as a mediator for the enzymatic reaction, thereby communicating with the conducting graphite in the matrix. The electrode can be reproducibly renewed by mechanical polishing. Thick film biosensors, where a drop of the analyte is sufficient for the sensing process is also demonstrated with this material.
Enhanced selectivity and sensitivity of first‐generation enzyme electrodes based on the coupling of rhodinized carbon paste transducers and permselective poly(o‐phenylenediamine) coatings
Authors: Wang Joseph , Chen Liang , Liu Jie , Lu Fang
Published: May 2005

Highly specific oxidase‐based amperometric biosensors, based on the coupling of anti‐interference layers with selective metal‐dispersed carbon transducers are described. In particular, the efficient and preferential electrocatalytic action of rhodinized carbon pastes towards the peroxide product is combined with the discriminative properties of poly(o‐phenylenediamine) (PPD) films. Such focus on both the transducer and recognition layer offers freedom from interferences, while resulting in higher sensitivity towards the substrate. The influence of preparation parameters is explored, and the surface microstructures are discussed. Similar improvements are reported for the electrodeposition of rhodium, PPD and glucose oxidase onto glassy carbon transducers.
Fast amperometric immunoassay for hantavirus infection
Authors: Krishnan Rajesh , Ghindilis Andrey L. , Atanasov Plamen , Wilkins Ebtisam , Montoya Jim , Koster Frederick T.
Published: May 2005

The determination of specific antibodies against Hantavirus in blood plasma has been developed. The assay technique is based on a flow through amperometric immunoelectrode. Highly dispersed carbon material serves as an immunosorbent and at the same time as an electrode material. The analysis employed the ‘sandwich’ assay scheme. Recombinant protein of Hantavirus was immobilized on the surface of the immunosorbent. Target analyte captured by the immunosorbent at the first stage of incubation interacts with the peroxidase labeled antihuman antibodies at the second stage of incubation. The detection of peroxidase label was conducted amperometrically by electroreduction of iodine formed as a product of peroxidase catalyzed reaction. The technique permits determination of specific antibodies against Hantavirus in blood plasma using a 22 min assay time.
The effect of organic solvent properties on a catalase enzyme sensor for monitoring hydrogen peroxide in nonaqueous solutions
Authors: Campanella Luigi , Martini Umberto , Sammartino Maria P. , Tomassetti Mauro
Published: May 2005

A catalase based biosensor for determining hydrogen peroxide in organic solvents, operating directly in nonaqueous solutions, was prepared, characterized (using water saturated chloroform as solvent) and applied in comparative tests using four different anhydrous organic solvents in order to determine their effect on biosensor sensitivity and thus on enzymatic activity in different organic solvents. Results are discussed in terms of log P and dielectric constant (DEC) values of the solvents considered.
Amperometric sulfur dioxide sensors using the gold deposited gas‐diffusion electrode
Authors: Chiou Chiou‐Yen , Chou Tse‐Chuan
Published: May 2005

A dispersed catalyst gas‐diffusion electrode for SO2 sensors has been developed. The particle size of the catalyst electrode was obtained. A three‐electrode potentiostat was used to test the sensing electrode at an optimal constant potential. When the SO2 diffuses through the porous electrode, the electrochemical oxidation of SO2 takes place at the active gold sites. The results indicated that the SO2 sensor was stable and the response time was fast. The sensitivity of the developed SO2 sensor was l.002μAcm−2ppm−1, and its performance was good.
D‐Fructose sensing electrode based on electron transfer of D‐fructose dehydrogenase at colloidal gold‐enzyme modified electrode
Authors: Yabuki Soichi , Mizutani Fumio
Published: May 2005

A complex of colloidal gold (Au) particles and D‐fructose dehydrogenase was prepared. A glassy carbon (GC) electrode was modified with the complex. The anodic current response to D‐fructose was measured by using the GC electrode modified with the complex at +0.5 V (vs. Ag/AgCl). Response time was within 15 s. No current response was observed in the absence of enzyme, so that the increased oxidation current was confirmed to be caused by the electron transfer from enzyme to electrode. Linear response range of the electrode was up to 0.5 mM fructose concentration. Fructose concentrations of soft drinks which were determined using the electrode agreed well with the results of the F‐kit.
A polarographic and voltammetric study of the copper‐phenazopyridine monohydrochloride system in phosphate buffer medium
Authors: Çakir Osman , Biçer Ender
Published: May 2005

The electrochemical behavior of copper complexed with phenazopyridine monohydrochloride (2.6‐diamino 3‐phenylazo‐pyridine monohydrochloride, pyridium) has been studied in 0.1 M phosphate buffer (pH 6.0). It was observed that CuII ions in the presence of pyridium are reduced at the mercury electrode in two distinct stages; this is a consequence of the interaction of pyridium with CuI ions. Tests showed that pyridium forms stable complexes with CuI and CuII ions. However, it was found that pyridium formed a 1 : 1 complex with CuII and a 1 : 2 complex with CuII ions.
Adsorption and detection of peptide nucleic acids at carbon paste eletrodes
Authors: Wang Jpseph , Rivas Gustavo , Cai Xiaohua , Chicharro Manuel , Dontha Narasaiah , Luo Denbai , Palecek Emil , Nielsen Pater E.
Published: May 2005

Peptide nucleic acids (PNA) are new DNA analogs which offer great promise for highly specific DNA biosensors, for use as antisense drugs, or for various molecuilar biology applications. This article evaluates the interfacial behavior of PNA at carbon paste electrodes, in comparison to DNA. While both PNA oligomers display a strong adsorption onto the carbon surface, they differ intheir interfacial properties due to differences in change and structure. Factors influencing the adsorption behavior, including the adsorption potential or time, PNA concentration, coexisting anions and cations, or buffer concentration, are explored. The strong adsorption is exploited for an effective preconcentration step prior to the chronopotentiometric measurement. The resulting adsorptive stripping potentiometric protocol offers convenient quantitation of ng/mL levels of PNA, as desired for future diagnostic, pharmaceutical and biological applications of these DNA analogs.
Highly sensitive heavy metal analysis on platinum‐ and gold‐ultramicroelectrode arrays
Authors: Uhlig Albrecht , Schnakemberg Uwe , Hintsche Rainer
Published: May 2005

The use of platinum‐and gold‐ultramicroelectrode arrays for heavy metal analysis is described. The noble metal microelectrodes are structured with standard silicon technologies. The geometry of the electrode array is varied and optimized in regard to the microelectrode characteristic. Mercury film formation and–dissolution on platinum microelectrode arrays is characterized and compared with iridium electrodes of the same geometry. Gold microelectrode arrays are shown to be useful for mercury detection. The repeated use of the sensors has been studied. Optimizing the electrode gemoetry and the stripping procedure results in detection limits down to the ng/L range.