bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of sulfur dioxide in white wines by flow injection with electrochemical detection
Authors: Cardwell Terence J. , Cattrall Robert W. , Nan Chen Guo , Iles Peter J. , Hamilton Ian C. , Scollary Geoffrey R.
Published: May 2005

The determination of sulfur dioxide in wines by flow injection analysis is described. The method is based on a dual electrochemical system, the upstream electrode being a coulometric electrode that eliminates interferences prior to the detection of the analyte at an amperometric electrode. At least 30 wine samples per hour can be determined by this procedure, and the results for free and total sulfur dioxide concentration in white wines compare favorably with those obtained by the standard aspiration‐oxidation, method.
Novel solvent systems for the preparation of phase‐inversion cellulose acetate size exclusion membranes: Voltammetric investigations
Authors: Kuhn Lance S. , Weber Stephen G.
Published: May 2005

Novel solvent systems have been developed for the casting of size exclusion electrode modifications by the phase‐inversion process. Solvent systems studied were (solvent/nonsolvent): pyridine/2‐octanol, pyridine/cyclohexanol, acetone/2‐octanol, tetrahydrofuran/aqueous Mg(ClO4)2, and tetrahydrofuran/toluene. These were compared to modifications made from the solvent system acetone/aqueous Mg(ClO4)2. The membranes were cast onto Pt microelectrodes embedded in glass. Cyclic voltammograms were recorded once per min after immersing the membrane‐modified electrode into a solution containing an electroactive species. Modified electrode response time to a concentration perturbation is correlated with the percent nonsolvent and percent polymer in the casting solution. The magnitude of the current from a solution of a 1500 dalton polyethylene glycol ferrocene carboxylate ester solute, and good casting reproducibility. This formulation is recommended for permselective coating applications; applications to biosensors are envisioned.
Electrocatalysis at hydrogenase or cytochrorme C3‐modified glassy carbon electrodes
Authors: Bianco Pierre , Haiadjian Jean
Published: May 2005

The immobilization of two redox proteins, hydrogenase and cytochrome c3 extracted from Desulfovibrio desulfurifcans sulfate‐reducing bacterium, on glassy carbon electrodes modified via carbodiimide procedure is reported. The catalytic activity at the hydrogenase‐modified glassy carbon electrode is detected in the presence of methylviologen, which acts as a shuttle between immobilized hydrogenase and the electrode surface. The effect of experimental parameters (e.g., methylviologen concentration or pH) on the catalytic activity is examined; maximum activity is observed at pH 9.5. Catalytic activity is also detected when methylviologen is replaced by cytochrome c3, which is the physiological partner of hydrogenase. The cytochrome C3‐modified glassy carbon does not yield a stable electrochemical response due to cytochrome c3 reconformation at the electrode surface.
Polarographic determination of some pesticides containing nitro group: Application to a study of adsorption on lignin
Authors: Rupp Elinore , Zhong Qiping , Zuman Petr
Published: May 2005

The polarographic method proved suitable for investigation of adsorption of acifluorfen (I) (5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2′‐nitrobenzoic acid) on lignin. Polarographic reduction of acifluorfen in aqueous buffers (pH < 7) is complicated by adsorption of the reduction product. In acidic media the reduction of the protonated hydroxylamino group occurs at such positive potentials that only a single six‐electron wave is observed. In buffers containing 33% (w/w) ethanol the effects of the adsorption are eliminated and the reduction of the hydroxylamino group occurs at more negative potentials, so that one four‐electron and one two‐electron wave are observed. Splitting of the four‐electron wave at pH > 7 is attributed to a decrease in protonation rate of the reduction intermediate. Unsubstituted p‐nitrophenyl phenyl ether (II) shows an analogous behavior. Reduction wave of the nitro group can be used for determination of aciflurofen (I), fluorodifen (III), oxyfluorfen (IV), and bifenox (V) in the 1 × 10−5 to 5 × 10−4 M range. Adsorption of acifluorfen depends on the nature of the lignin and pH.
Determination of tetramethrin by adsorptive stripping with square wave voltammetry
Authors: Hernández P. , Galán‐Estella F. , Hernández L.
Published: May 2005

The present work reports on an adsorptive stripping voltammetric procedure for the determination of tetramethrin. The best conditions found were pH 4 in 0.2 mol/L acetic acid/acetate buffer solution, and accumulation potential of −0.5 V (vs. Ag/AgCl electrode), an accumulation time of 60 s, frequency 120 Hz, step potential (Es) 2 mV. Under these conditions, determination limits of 1.7 ng/mL−1 (8.5 10−9 M) are achieved.
Phase‐selective alternating current adsorptive stripping voltammetry of folic acid on a mercury thin‐film electrode
Authors: del Pozo José Amez , García Agustín Costa , Miranda Ordieres Arturo J. , Blanco Paulino Tuñón
Published: May 2005

Optimum conditions for the mercury electrodeposition onto glassy carbon electrodes and the optimum alternating current (AC) adsorptive stripping signals of folic acid (vitamin B12) were found. The film was characterized by electron microscopy and the results obtained in the analysis of the vitamin were compared with those previously reported using conventional mercury electrodes (static or hanging). The mercury thin film electrode (MTFE) has shown more sensitive signals for folic acid with good performance and reproducibility. A detection limit down to 10−12 M could be reached by using 300 s accumulation time.
Voltammetric determination of the titrable acidity of milk using a platinum microelectrode
Authors: Daniele Salvatore , Baldo M. Antonietta , Ugo Paolo
Published: May 2005

A platinum microelectrode with a radius of 12.5 μm was employed for determining the acidity of crude bovine milk samples by voltammetric titration. Solutions of sodium hydroxide and of several acids of different strengths were used as titrants. The relative standard deviation (RSD) was within 3%, regardless of the type of titrant agent employed. The data found with this approach were compared with those obtained by the classical methods commonly employed for the determination of the titrable acidity of milk.
An amperometric solid‐state sensor for Nitrogen dioxide based on a solid polymer electrolyte
Authors: Opekar František
Published: May 2005

A new sensor is described consisting of a Nafion membrane to which a very fine gold square grid indicator electrode is mechanically pressed. A platinum counter and a Pt/air reference electrode are prepared on the membrane using a chemical plating method. Nitrogen dioxide was determined in air by reduction at −0.3V vs. Pt/air electrode (0.75 V vs. SHE). The response dependence on the NO2 concentration was linear, with a sensitivity of 59 nA.ppm−1 (42% rel. humidity). The time constant and the time required to attain 95% of the steady ‐state response were 2.2 and 10 s, respectively. The response was independent of the air flow rate, but increased linearly with increasing relative humidity. The sensor sensitivity decreased with time–the longer the sensor was in contact with NO2. The decrease amounted to ca. 5% per 24 hours during constant exposure to NO2. The indicator electrode can be reactivated by cyclic polarization. On the basis of the sensitivity attained, the indicator electrode can be considered as an array of microband electrodes.
Voltammetric investigations of copper processes in the presence of oxygen
Authors: Krznarić Damir , Plavšić Marta , Ćosović Božena
Published: May 2005

The redox processes of copper ions were studied by alternating current (ac) voltammetry and cyclic voltammetry in 0.5 M NaCl and NaClO4 solutions. The studies were performed at different pH values in the presence of atmospheric oxygen or by the addition of H2O2 to the process. In the case of copper ions in NaCl solution both in the presence of atmospheric oxygen and added H2O2, a catalytic current was observed. With cyclic voltammetry the current was in the cathodic direction in spite of having an anodic sweep. The key factor is the presence of chloride ions as in the NaClO4 solution; the observed catalytic current peaks are much smaller. The mechanism for the observed redox processes of copper is proposed.
Characterization of uranyl‐monoperoxo species in 0.7 mol L−1 LiCIO4
Authors: Djogic Renata , Branica Marko
Published: May 2005

According to the calculations, in the presence of equimolar concentrations of uranyl‐ion and hydrogen peroxide at 5 < pH < 7, the predominant species is UO2O complex. Spectro‐photometrically, it has been confirmed in the bulk of the solution giving the apparent concentration stability constant K
= 2 × 105 mol−1 L. Electrochemically, normal, differential pulse polarography and cyclic voltammetry at DME and HMDE are used to elucidate the reduction scheme of the uranyl‐monoperoxo complex.
Homogeneous catalysis of electrochemical reactions. Channel electrode voltammetry and the EC′ mechanism
Authors: Compton Richard G. , Fisher Adrian C. , Spackman R. Anthony
Published: May 2005

The shape of the current–voltage curves at a channel electrode have been calculated for the various situations of the catalytic (EC′) mechanism. In particular the halfwave potential and limiting current are found to be highly sensitive to the solution‐flow rate and to the concentrations of the mediator and substrate employed. These observations provide a ready method of unambiguously characterizing the different pathways.
Electrochemical oxidation of L‐ascorbic acid at the graphite electrode and its monitoring by a thick‐film graphite sensor assembly
Authors: Xing Xuekun , Tan Thiam‐Chye , Shao Meijun , Liu Chung‐Chiun
Published: May 2005

The experimental results obtained in this study show that a thick‐film graphite sensor assembly (with a Pt counter and an Ag/AgCl reference electrode) can be conveniently fabricated by the photolithographic and screen‐print metallization techniques. This sensor has been successfully employed for quantitatively determining L‐ascorbic acid concentration in aqueous solutions with reasonably good reproducibility. This sensor provides the possibility of developing a miniature size practical device for detecting ascorbic acid in biochemical processing, such as in food and drug production. The mechanistic aspects of the oxidation of L‐ascorbic acid on optical pyrolytic graphite electrodes were further studied with a rotating OPG disk electrode in two different electrolyte solutions. It was found that the oxidation of L‐ascorbic acid is more favored in pH = 7 solutions than in pH = 1 solutions although a common 2‐electron transfer pathway is applied in both cases.
Polarographic studies and measurements of nitrite in cobalt(II)—thiocyanate—ascorbic acid solution
Authors: Li Peibiao , Zhao Zaofan , Gao Zhiqiang
Published: May 2005

In the cobalt(II)—thiocyanate—ascorbic acid solution (pH = 2.0), nitrite can form a ternary complex (CoSCNNO)+, which can be reduced at mercury electrode to −0.59 V (vs. SCE). The wave can be used for the polarographic determination of traces of nitrite in the concentration range of 1 × 10−8 −8 × 10−7 M (single sweep polarography), 1 × 10−7 −4 × 10−5 M (differential pulse polarography). or 1.5 × 10−6 −2 × 10−4 M (direct current polarography). The mechanism of the electrode process is studied by linear sweep voltammetry, DC polarography, cyclic voltammetry, double‐step chronocoulometry, and controlled potential coulometry. The polarographic wave is ascribed to the reduction of nitrogen monoxide in the complex to hydroxyamine. The procedure is used for the direct determination of nitrite in various real samples.
Determination of several catechols on bare and polymer coated glassy carbon electrode
Authors: Heiduschka Peter , Dittrich Jürgen
Published: May 2005

Glassy carbon electrodes were coated with a copolymer of styrene and maleic acid anhydride. The voltammetric behavior of catechol, ascorbic acid, dopamine, and DOPAC was examined at both bare and coated electrode using cyclic voltammetry and modified differential pulse voltammetry. Electrochemical pretreatment increased peak current of catechol and its derivatives; the polymer coating caused significant decrease of peak currents and shift of peak potentials. The signal of ascorbic acid is greatly suppressed, while that of DOPAC disappears even after polymer coating.
Catalytic polarographic detection of disulfides following liquid chromatography
Authors: Nagashima Kunio , Kamaya Minori , Ishii Eizen
Published: May 2005

Four kinds of disulfides in organic compounds were sensitively detected in NH4OH‐NH4Cl (0.2 M)‐Co2+ (5 × 10−4 M) solution by differential‐pulse polarography. This detection mechanism was based on the Brdicka reaction. A new flow‐through cell (on‐detector reactor) was used to combine the polarographic detection with high‐performance liquid chromatography. The detection limit for dithioglycolic acid was 1 × 10−4 M using 10 μl samples.
Evaluation of nafion as media for glucose oxidase immobilization for the development of an amperometric glucose biosensor
Authors: Fortier Guy , Vaillancourt Marc , Bélanger Daniel
Published: May 2005

A novel glucose biosensor has been prepared by deposition of a mixture containing glucose oxidase dissolved in water and Nafion dissolved in methanol at the surface of a platinum disk electrode. Glucose concentration is evaiuated by measuring the amperometric current corresponding to hydrogen peroxide electrooxidation at 0.7 V vs. SCE. The addition of glucose oxidase to Nafion resulted in a Nafion‐glucose oxidase film that was more permeable to anionic species than Nafion alone. The calibration curve for glucose is linear from 5 μM up to about 10 mM. In oxygen‐saturated solution, the linear range extended to 15 mM. The optimum pH for the assay was found to be 5.5. The enzyme is not stabilized against temperature deactivation when it is immobilized in Nafion. The Pt/Nafion‐glucose oxidase electrodes showed good stability when stored dry at room temperature with 80% of the initial response retained after 250 days.
An electrochemical assay for tissue plasminogen activator (t‐PA)
Authors: Cardosi Marco , Ho Wah On , Athey Dale , McNeil Calum
Published: May 2005

An electrochemical assay for tissue plasminogen activator (t‐PA) is described. The activity of t‐PA is measured in a coupled assay following the amidolytic cleavage of a synthetic tripeptide by the enzyme plasmin. The released electroactive label, p‐aminophenol, is detected anodically either at a glassy carbon indicator electrode or at a platinized activated carbon electrode in a specially constructed perspex cell. Calibration plot data for t‐PA are presented for buffered samples using the perspex block‐type cell. The limit of detection for t‐PA in this assay is 0.25 IU/ml. In addition, the assay format is adapted to yield kinetic information using repetitive square wave voltammetry as the mode of detection.
Removal of oxygen in flowing solutions using a photochemical process
Authors: Barisci Joseph N. , Wallace Gordon G.
Published: May 2005

A method for the on‐line removal of dissolved oxygen has been developed and applied to the determination of metals by anodic stripping voltammetry in flowing solutions. The removal of oxygen results from a photochemical reaction between the supporting electrolyte and oxygen, induced by ultraviolet light directed into the detector flow cell. Organic acids such as citric, formic, and oxalic acids have been used as supporting electrolytes. Citric acid was found to be the most efficient oxygen scavenger. The removal of oxygen with this acid was also more efficient than conventional removal with nitrogen gas. The determination of Cu, Cd, and Pb was used to demonstrate the method.
Adsorptive stripping square‐wave voltammetric behavior of the enzyme adenosine deaminase
Authors: Flores Juana Rodríguez , Alvarez José María Fernández
Published: May 2005

The adsorptive stripping voltammetric behavior of adenosine deaminase has been studied by both square‐wave and differential pulse modes, leading to analytical methodologies for its determination in aqueous samples. The application of a square‐wave mode for the stripping of adsorbed adenosine deaminase has proved to be much more sensitive, yielding signals 50 times larger than those obtained by applying a differential pulse scan. The precision obtained for both voltammetric methods, at a concentration level as low as 8 ppb of the enzyme, was shown to be 2.47% (r.s.d., n = 7) and 2.28% (r.s.d., n = 7), respectively.
Construction and application of an all‐solid‐state chlorphenigramine ion‐selective electrode
Authors: Qu Aiying , Xu Dafeng , Ren Lixin , Jin Xinglian , Cai Shengmin
Published: May 2005

Using chlorpheniramine‐silicotungstate or chlorpheniramine‐ phosphotungstate ion‐pair complexes as active materials and graphite rods as substrates, all‐solid‐state chlorpheniramine ion‐selective electrodes were prepared. The effects of various factors on the performance of these electrodes were studied in detail. The electrodes exhibited a Nernstian range from 10−2‐10−5 M, with a slope of 58 mv/decade, and were much better than the previously reported PVC membrane chlorpheniramine ion‐selective electrodes Satisfactory results were obtained by using the prepared electrode to analyze chlorpheniramine containing samples.
Identification of photochemical products of amino acids, peptides, and proteins in on‐line, postcolumn photolytic derivatization detection by HPLC‐electrochemistry
Authors: Dou Lin , Krull Ira S.
Published: May 2005

In previous studies we have developed a method for the electrochemical detection of aromatic amino acids, sulfur‐containing amino acids, peptides, and proteins in HPLC by using photolytic derivatization approaches. Upon irradiation, nonelectroactive (or even inherently electroactive) amino acids and peptides can be converted to electroactive (or more electroactive) compounds, in an on‐line, postcolumn manner, which can be detected electrochemically in HPLC. In the case of proteins, the same method can be used to change the electroactivity of proteins photochemically. It is important to identify these photochemically converted compounds, especially those which are electroactive, in order to understand the detection mechanisms of the method. In this paper the results of identification of electroactive photoproducts for aromatic amino acids, peptides, and proteins are presented. Mainly, these studies were carried out by HPLC and direct electrochemical detection of off‐line photolyzed analytes.
Voltammetry in static and flowing solutions with a large‐amplitude sine wave potential
Authors: Long John T. , Weber Stephen G.
Published: May 2005

Voltammetric detection is a potentially powerful method of detection for high performance liquid chromatography and flow injection analysis. A problem that needs a solution is its inferior detection limit compared to that obtained with amperometric detection. The shape of the potential waveform has been investigated in the search for methods of improving the detection limit of voltammetric detection. As a result, large amplitude sine wave potential perturbations have been found to give improved signal‐to‐noise ratios when compared to the values found for a corresponding triangle waveform (by a factor of from 1.1 to 5). This is principally due to the fact that the background current from a large amplitude triangle perturbation is spread over a wider frequency region. Signal processing techniques such as digital filtering have also been investigated. Digital bandpass filtering can be used to improve the signal to noise ratio by a factor of 2–13. Qualitative information (e.g., half‐wave potential) is obtained through observing the phase angle at harmonics of the fundamental frequency.
Photoelectrochemical detection of alcohols
Authors: Barisci Joseph N. , Wallace Gordon G.
Published: May 2005

A method for photoelectrochemical detection of alcohols in liquid chromatography and flow injection analysis based on the reaction of the analyte with a photosensitized quinone (benzoquinone) has been developed. Irradiation of the flowing solution and electrochemical detection of the generated photoproduct is carried out within the detector flow cell. Pulsed amperometric detection produced higher sensitivities than conventional potentiostatic amperometry. Samples of vodka and beer were successfully analyzed using the proposed method.
Micro‐volume extraction for differential‐pulse voltammetric determination of iron in biological materials
Authors: Nagaosa Yukio , Bond A. M.
Published: May 2005

A method based on separation by gas‐stirred extraction and differential‐pulse voltammetric detection of Fe(III) (0.50–8.0 μg) as the N‐phenylbenzohydroxamic acid complex in an ethyl acetate/acetonitrile phase (approximately 300 μ1) with a newly designed microcell provides sufficient sensitivity for its determination in biological materials. In the extraction and oxygen removal steps, nitrogen gas is passed through the aqueous and organic phases with a glass capillary. The proposed technique has been successfully applied to bovine liver and control serum.
Unsegmented flow systems as interfaces between samples and electrochemical detectors
Authors: de Castro M. D. Luque
Published: May 2005

The state‐of‐the‐art in the use of electrochemical detectors in unsegmented flow systems in general, and flow injection analysis (FIA) in particular, is presented. The different ways in which unsegmented flow systems can help to improve the performance and scope of electrochemical detectors (e.g., facilitating automation and miniaturization, allowing the on‐line implementation of continous separation techniques and multidetermination methods) are discussed. Current trends in this context are also covered.
Complexes of hydroxamates VIII. The affinity of methioninehydroxamic acid for mixed metal complexation potentiometric and polarographic studies
Authors: Marafie Hayat M. , Makhyoun Mohamed , Al‐Salem Najeeb , El‐Ezaby Mohamed S.
Published: May 2005

Binary metal complexations of Ni(II), Cu(II), and Zn(II) with methionine‐hydroxamic acid (MX) were studied potentiometrically at 37°C and μ = 0.15 M NaCl. The mixed metal complexes with MX, (MXCu(II)Zn(II), and MXNi(II)Zn(II)) were also studied under the same conditions. The ternary enhancement was discussed in terms of the binary complex formation. In addition, the binary and ternary systems were studied by differential pulse polarography and the behavior of the reduction properties of the different ternary species were correlated with those of the simple metal ions and the binary species.
Channel electrode voltammetry: Thin‐layer effects and the shape of quasi‐reversible current‐voltage curves
Authors: Compton Richard G. , Wellington R. Geoffrey
Published: May 2005

A computational approach to the calculation of irreversible and quasi‐reversible current voltage curves at channel electrodes is presented. The method has generality since, in particular, no assumptions are made as to the electrode geometry or electrolyte flow rates so that both Lévěque and, with novelty, thin‐layer conditions may be explored. An approximate analytical theory for the shape of current‐voltage curves which predicts the flow rate dependence of the half‐wave potential is presented for the latter case and found to be in good agreement with rigorous computational theory.
The anodic oxidation of hydrazine on glassy carbon electrode
Authors: Wang Baochen , Cao Xueqiang
Published: May 2005

The anodic oxidation kinetics of hydrazine (N2H4) on glassy carbon (GC) electrode was examined by cyclic voltammetry, rotating disk and ring‐disc electrode techniques. The possible mechanisms of N2H4 oxidation in both aqueous and nonaqueous solutions are proposed.
Determination of alkaloids by differential pulse polarography. III Corydalis alkaloids
Authors: Temizer H. , Sener B. , Temizer A. , Kir S.
Published: May 2005

The Corydalis alkaloids have been investigated by differential pulse polarography as part of our continuing study of alkaloids. In this study, the alkaloidal content of Corydalis solida (L.) subsp. solida was determined. The results were compared by their structure and reduction mechanism. Quantitative analysis illustrates that Corydalis alkaloids can be determined down to sub‐ppm level using differential pulse polarography in Britton‐Robinson buffer pH 10. The amount of the various alkaloids in Corydalis solida (L.) subsp. solida have been shown. It was concluded that the reduction process at the dropping mercury electrode was catalytic in nature.
Voltammetric study of zinc(II) and lead(II) ions in the presence of alginate and pectin
Authors: Ariño Cristina , Nadal Anna Maria , Esteban Miquel , Casassas Enric
Published: May 2005

Complex formation of Zn(II) and Pb(II) with alginates and pectins was studied by normal‐pulse (NPP), reverse‐pulse (RPP), and differential‐pulse polarography (DPP), cyclic voltammetry (CV), and differential pulse anodic stripping voltammetry (DPASV). The systems appear to be labile on the different time scales of the various techniques. Adsorption of both polysaccharides, and the further induced adsorption of Zn(II) and Pb(II), are evidenced clearly by NPP. On the other hand, induced adsorption of metal ions is minimized under the RPP conditions. The reversibility of the redox couples Zn2+/Zn(Hg) and Pb2+/Pb(Hg) is not strongly affected by the presence of polysaccharides. Titrations of Zn(II) and Pb(II) with alginates or pectins were carried out by DPP and DPASV in order to determine formation constants, which was only found for the Zn(II)‐ion systems.
Polarographic and electrochemical studies of some aromatic and heterocyclic nitro compounds, part II: Polarographic and voltammetric reduction of some nitramines, pyrazolium, and imidazolium nitro derivatives
Authors: Dumanović D. , Jovanović J. , Sužnjević D. , Erceg M. , Zuman P.
Published: May 2005

Reduction of 1‐nitropyrazole (I) results in acidic media in a cleavage of the NN bond and formation of nitrous acid which is further reduced at more negative potentials. At pH > 4 a competitive reduction of the nitramine to nitrosamine occurs. Four‐electron reduction of nitro derivatives of pyrazolium (II) and (III) and imidazolium (IV) and (V) salts results in a formation of a hydroxylamine derivative. The reduction follows the scheme: H+, e, e, H+, 2e, 2H+. In the reduction product the azolium ring is reduced at more negative potentials. Whereas the effect of pyrazolium and imidazolium rings on the reducibility of the nitro group is comparable, the interaction between the nitro group and the azolium ring markedly depends on the position of the nitro group on the ring.
Potentiometric detectors for the determination of acidity by discontinuous flow analysis
Authors: Cardwell Terence J. , Cattrall Robert W. , O'Connell Gregory R. , Petty John D. , Scollary Geoffrey R.
Published: May 2005

Three potentiometric detectors, each incorporating a vibrating reed mixer, were investigated for use in the determination of acidity by discontinuous flow analysis (DFA). Two of these used PVC and glass membrane pH‐sensors, and the third employed a novel differential titration technique based on two quinhydrone electrodes. These detectors were applied to the determination of the total acidity of vinegars and the titratable acidity of wines, the results agreeing well with standard procedures. The analysis of wine proved to be difficult because of the gradual change in pH at the end‐point and so a method was developed which determined the titratable acidity at pH 8.3.
Cathodic stripping voltammetry of vanadium based on adsorptive accumulation of its solochrome violet RS complex at the static mercury drop electrode
Authors: Farias Pércio A. M. , Takase Iracema
Published: May 2005

A very sensitive electrochemical stripping procedure for vanadium is reported. Accumulation is achieved by controlled adsorption of the vanadium/solochrome violet RS complex on the static mercury drop electrode. Optimal experimental parameters found include an accumulation potential of −0.22 V, solochrome violet RS concentration of 2.0 × 10−6M, and a differential pulse stripping mode. After 5 minutes preconcentration, a detection limit near 1.7 × 10−10 M vanadium is obtained. The response is linear over the 0–21 μg1−1 concentration range, and the relative standard deviation (at the 11.2 μg1−1 level) is 3.8%. The possible interference by other trace ions are investigated. Simultaneous determination of vanadium with molybdenum and cadmium is illustrated. The merits of this procedure are demonstrated in the analysis of sea and river waters.
Electrochemical methods for food and drink analysis
Authors: Mannino Saverio , Wang Joseph
Published: May 2005

This review article assesses the status of electroanalysis in the food industry. Modern trends in electroanalysis, which offer unique possibilities for assays of foods and drinks, and for monitoring food production processes, are discussed. Particular attention is given to the utility of new biocatalytic sensors, stripping techniques, and electrochemical flow detectors in the food industry. More than 90 references are given and future prospects are discussed.
Double‐layer capacitance measurements of self‐assembled layers on gold electrodes
Authors: Świetlow Aleksander , Skoog Mikael , Johansson Gillis
Published: May 2005

The double‐layer capacitance of self‐assembled unsubstituted and ω‐substituted n‐alkanethiol layers on gold electrodes was studied using a potential step technique. A four‐element equivalent circuit model was used for the evaluation of the current response. The double‐layer capacitance and the conductivity were both found to decrease with increasing chain length for alkanethiol homologues. Substitution with COOH, OH, and NH2 in the ω‐position caused the double‐layer capacitance to rise dramatically, whereas the general pattern of decreasing capacitance with increasing chain length was confirmed for a series of homologue ω‐mercaptoalcohols. The effect of polar substituents is explained by the introduction of permanent dipoles into the self‐assembled layers. The capacitance was independent of the applied potential for dodecanethiol but increased with voltage for butanethiol when tested in the range of −200 to 500 mV versus Ag/AgCl. Buffer strength had little influence on the double‐layer capacitance above 5 mM (phosphate buffer, pH 7.0). The self‐assembly of mercaptoethanol was completed within 3 minutes from an aqueous solution and that of alkanethiols within 10 minutes using acetone solutions. The electrodes were stable for at least several hours.
Potentiometric monitoring of proteins: Part 5. A voltammetric study of copper electrodes
Authors: Hitchman Michael L. , Trojanowicz Marek
Published: May 2005

A voltammetric study has been made of copper electrodes in the presence and absence of amino acids and proteins. The results are discussed in terms of oxide formation on the copper surface and the complexation of the biomolecules with the copper. It is shown that in the presence of strongly complexing ligands, the copper surface is effectively self‐cleaning, and reproducible potentiometric results can be obtained without any rigorous electrode precleaning procedures. In the presence of weakly complexing ligands, on the other hand, it is shown why it is necessary to reduce the electrode surface beforehand in order to carry out reproducible potentiometry.
A finite‐element method for determining ohmic distortion of current‐voltage curves at hydrodynamic electrodes
Authors: Coles Barry A. , Compton Richard G. , Spackman R. Anthony
Published: May 2005

A finite‐element method is described that predicts the effects of ohmic distortion of current‐voltage curves for arbitrary cell and hydrodynamic electrode geometries using the widely available circuit analysis program SPICE. Simulated and experimental data are presented for a channel electrode flow cell showing the displacement of the half‐wave potential and the potential‐dependent error in the Tafel slope for the case of an electrochemically reversible electrode reaction. Error curves are provided that may be scaled for different electrolyte conductivities as a guide to the maximum current levels that may be used in practice. For analytical flow detection work, the displacement of the half‐wave potential under certain conditions implies that high detection potentials must be used to obtain the correct concentration‐related current intensity. The implications for quantitative measurements using practical electrodes are assessed.
Polarographic and electrochemical studies of some aromatic nitro compounds: Part VII. Polarographic, voltammetric, and controlled potential electrolytic reduction of meta‐ and para‐nitrobenzaldehyde
Authors: Fijalek Zbigniew , Pugia Michael , Zuman Petr
Published: May 2005

In acidic media, at pH < 7, the nitro groups in both meta‐ and para‐nitrobenzaldehyde are reduced in a four‐electron process and form corresponding formylhydroxylamines. These species are reduced in protonated forms to corresponding formylanilines, which are further reduced in two‐electron steps to alcohols. At pH > 7, the formylhydroxylamine condenses rapidly to form a nitrone, which is further reduced to two two‐electron steps, for the derivative of meta‐nitrobenzaldehyde overlap. The addition of ortho‐ to para‐nitrobenzaldehyde results in cross‐condensation.
Highly sensitive electrochemical sensor for ozone in water using porous carbon felt electrode
Authors: Uchiyama Shunichi , Ikarugi Takao , Mori Masayuki , Kasama Kaname , Ishikawa Yoichi , Kaneko Mitsunori , Umezawa Akira
Published: May 2005

A novel electrochemical sensor with a [polytetrafluoroethylene] (PTFE) membrane (10% voids) and a porous carbon felt electrode has been fabricated for the determination of residual ozone in water. The carbon felt has a large specific surface area which can capture all of the ozone transferred from the sample solution through a PTFE membrane, and an extremely low concentration of ozone (about 0.5 ppb) can be detected. The relationship between the current response and the ozone concentration obtained by the Indigo method was linear over the range 5–800 ppb. The sensitivity was calculated to be approximately 10 μA/(ppm cm2) at 12°C. The relative standard deviations (RSDs) of the response currents were below 5% when the ozone concentration was higher than 50 ppb. The response to 1 ppm residual chlorine is about 1.3% of that of the same concentration of ozone in solution at pH 5. The measured current was reproducible over three months and was found to be suitable for use as an on‐line sensor.
The effect of complexation equilibria on the response of chemically modified electrodes for the determination of silver
Authors: Labuda Ján , Vaníčková Mária
Published: May 2005

The determination of silver using anodic stripping voltammetry at graphite electrodes modified with various macrocyclic thia ligands and a Nafion film was examined in different media. The electrode response is proportional to the stability constant of the silver complex with the immobilized thia ligand. In the presence of cyanide or thiosulfate ions in the silver solution, the signal is diminished according to the concentration of the foreign ligand and the value of the corresponding conditional stability constant. The effect of the accumulation time on the detected fraction of silver is reported, and the consequences for speciation studies are indicated.
Catalytic reduction of benzoquinone at polyaniline and polyaniline/enzyme films
Authors: Cooper Julia C. , Hall Elizabeth A. H.
Published: May 2005

The enzyme‐mediator‐conducting polymer model provides a convenient charge transporting immobilization matrix for redox enzymes in potential biosensor constructions. This study considers the charge transport mechanism in the benzoquinone (Q)‐polyaniline (Pani) system. An enhanced current can be obtained on Pani, compared with Pt, using Q as enzyme mediator. Two‐electron redox pathways are available for the Q/H2Q (hydroquinone) system, but the kinetics limit this conversion. On Pt, one‐electron equivalent is estimated. On Pani‐modified electrodes, reduction of Q on Pani is a nearly reversible two‐electron process at stationary electrodes at low pH. At rotating electrodes, the initial reaction occurs at the surface of the polymer at pH 1.1, but the second electron transfer is prevented by loss of the intermediate from the surface before it can migrate into the film. At stationary electrodes, the H2Q product is stabilized, possibly by the formation of a charge‐compensating complex between the H2Q anion/radical and the polymer. At higher pH, charge transfer through the polymer is slow and no reduction of Q occurs on the outside of the film, instead occurring in a layer at the electrode limited by the exchange kinetics there. Promotion of the two‐electron pathways on Pani is proposed as the source of current enhancement when Q is employed as an enzyme mediator.
Amperometric biosensing of alcohols at electrochemically pretreated glassy‐carbon enzyme electrodes
Authors: Wang Joseph , Gonzalez‐Romero Elisa
Published: May 2005

Substantial improvements in the performance of amperometric biosensors for alcohols are achieved by subjecting the glassy carbon transducer to an electrochemical pretreatment prior to the immobilization of alcohol dehydrogenase. The enzymatically generated dihydronicotinamide adenine dinucleotide (NADH) can thus be detected at a substantially (∼340 mV) lower potential compared to the untreated surface. Hence, highly sensitive low‐potential amperometric sensing of alcohols is accomplished without the assistance of a surface‐bound electron mediator. Applicability to alcoholic beverages is illustrated.
Comparison of detector cell configurations in flow‐injection potentiometry
Authors: Davey David E. , Mulcahy Dennis E. , O'Connell Gregory R.
Published: May 2005

A comparative assessment has been made of three detector cell configurations, flow‐through, wall jet, and edge jet, based upon the flow‐injection performance of a solid‐state iodide‐selective electrode. Several aspects of the observed behavior have been explained with reference to flow patterns visualized by intercalation of Eriochrome T indicator into the flow stream and filmed under high magnification. The edge jet, a thin‐layer design incorporating an inlet channel at 45° to the sensing surface of the electrode, performed well over a considerable range of cell volumes, while the wall‐jet and flow‐through arrangements were prone to flow instability at higher volumes, resulting in irregular peak profiles and irreproducible baseline recovery times. Best response and recovery were recorded for all three cells when the distance between the inlet nozzle and the electrode membrane did not exceed 1.0 mm.
Investigation of the polarographic behavior of biliverdin in the presence of hydrogen peroxide
Authors: Zeng Baizhao , Zhou Xingyao
Published: May 2005

In hydrogen peroxide‐EDTA‐sodium phosphate solution (pH 11.0), biliverdin (BV) shows a very sensitive cathodic polarographic wave at about −0.82 V (vs. Saturated Calomel Electrode, SCE). By using derivative single‐sweep polarography, the wave height varies linearly with BV concentration over a range of 6 × 10−8 M to 2 × 10−6 M, so it can be used for the determination of BV. Various electrochemical techniques have been used to investigate the characterìstics of the wave and the electrode reaction mechanism. As a result, the polarographic wave is identified to be an adsorptive‐catalytic wave, and the electrode mechanism is considered to be a catalytic reaction coupled to an irreversible charge transfer process. In the electrochemical process, BV acts as catalyst and hydrogen peroxide as oxidizer. In this article, the rate constant of the catalytic reaction is also determined.
Electrocatalytic flow detection of amino acids at ruthenium dioxide‐modified carbon electrodes
Authors: Wang Joseph , Lin Yuebe
Published: May 2005

Fixed‐potential anodic detection of ammo acids and peptides can be carried out at ruthenium dioxide (RuO2) ‐modified carbon paste and graphite epoxy electrodes. The effect of various experimental variables on the electrocatlytic response is explored. Optimal detection is obtained under strongly alkaline conditions and a low ( + 0.45 v vs. Ag/AgCl) operating potential. With flow injection, the response is fast, linear, and reproducible )relative standard deviations of 1.5 to 1.7%, n = 32). Similar advantages are reported for the incorporation of cobalt oxide (CO3O4) into carbon paste detectors.
Amperometric detection of purine nucleotides utilizing immobilized enzyme reactors and on‐line amplification by substrate recycling
Authors: Yao Toshio , Tsureyama Kiminori
Published: May 2005

Flow‐injection systems with an immobilized enzyme reactor are proposed for the amperometric detection of purine nucleotides. One system studied is based on the combined use of an alkaline phosphatase (AlP) immobilized reactor and a purine nucleoside phosphorylase (PNP)‐xanthine oxidase (XO) coimmobilized reactor, which responds to purine nucleotides With high selectivity. Another system with a coimmobilized AlP‐PNP‐XO reactor gives responses amplified by substrate recycling. When carrier solution was pumped at a flow rate of 0.5 mL min−1, purine nucleotides could be detected with 9 to 26 times the sensitivity in the latter system compared with the former, with the detection limit of 4 × 10−8 M for a 20 μL injection.
Voltammetric determination of nitrate with a modified carbon paste electrode
Authors: Neuhold Christian , Kalcher Kurt , Diewald Wolfgang , Cai Xiaohua , Raber Georg
Published: May 2005

A method for the voltammetric determination of nitrate in drinking water is presented. Nitrate exerts a catalytic effect on the reduction and reoxidation of thallium (1 ↔ 0) in cyclic and differential pulse voltammetry, leading to a peak enhancement. Nitrate can be preconcentrated together with tetrachlorothallate(III) from hydrochloric acid solutions onto a carbon paste electrode modified with a liquid anion exchanger. (Amberlite LA2) under open circuit conditions. After reduction of the Tl(III) to Tl(0) at the electrode surface at a potential of −1.2 V (vs. SCE), the increase of the reoxidation current of Tl(III) to TI(I) by nitrate is exploited for analytical purposes. Linearity between current and concentration exists for 0.5 to 60 μg · mL−1 nitrate when applying anodic differential pulse vokammetry. Mechanical regeneration of the electrode surface is necessary after each measurement. The interference of other anions and the influence of methodical parameters are invistigated. The applicability of this method for the determination of nitrate in drinking wat concise overview on the the electroanalytical techniques for the Quantitative determination of nitrate is also presented.
Highly selective electrochemical detection of dopamine using interdigitated array electrodes modified with nafion/polyester lonomer layered film
Authors: Niwa Osamu , Morita Masao , Tabei Hisao
Published: May 2005

The highly selective electrochemical detection of dopamine has been developed using an interdigitated microarray (IDA) electrode coated with Nafion and polyester ionomer (Kodak AQ29D) layered films. Because high redox cycling of dopamine can be maintained in the AQ29D bottom layer, a low detection limit of 50 nmol/dm3 is obtained. Since the upper Nafion laybr prevents L‐ascorbic acid from diffusing into the AQ29D layer, the acid concentration in this layer rapidly decreases when potentiostating one IDA electrode (anode) above and the other (cathode) below the redox potential of dopamine. This is because L‐ascorbic acid molecules in the AQ29D layer are removed quickly by the electrochemical or electrocatalytic oxidation at the anode. On the other hand, almost all of the oxidized dopamine molecules are reduced at the cathode, which maintains a constant dopamine concentration in the film during measurement. After the potential step, the influence of L‐ascorbic acid is almost completely eliminated within a few seconds due to the reduction in acid concentration in the modified layer. As a result, dopamine can be detected quantitatively at the cathode in the presence of 100‐fold excess of L‐ascorbic acid.
pH measurements based on a palladium electrode
Authors: Shao Meijun , Xing Xuekun , Liu Chung‐Chiun
Published: May 2005

The feasibility of a metal palladium electrode as the pH sensor in air‐saturated aqueous solutions was evaluated. The measurement was based on an “on‐site” precleaning step and a potential decay process. The experimental results showed a linear pH response with a sensitivity of around 60 mV/pH and good reproducibiliry. The temperature effect on the measurement was also evaluated.
Integrated amino acid sensors for detection of L‐glutamate, L‐lysine, L‐arginine, and L‐histidine
Authors: Suzuki Hiroaki , Tamiya Eiichi , Karube Isao
Published: May 2005

Using microfabricated Clark oxygen electrodes, we integrated amperometric amino acid sensors to detect L‐glutamate, L‐lysine, L‐arginine, and L‐histidine. The oxygen electrodes consists of an anisotropically etched rectangular groove with a silver cathode and a Ag/AgCl anode, a Fluorinated Ethylene‐Propylene (FEP) gas‐permeable membrane, and a 0.1 M KCl electrolyte gel inserted after fabrication. Enzymes were immobilized on the gas‐permeable membrane. L‐glutamate was measured using L‐glutamate oxidase. To detect L‐lysine, L‐arginine, and L‐histidine, decarboxylases and autotrophic bacteria were used. The response times of the sensors ranged from 30 seconds to 10 minutes and a fairly linear relationship was observed between the output current of each sensor and the substrate concentration. We operated the sensors in the same buffer solution.
Reduction of electrooxidizable interferent effects: Optimization of the applied potential for amperometric glucose sensors
Authors: Jobnson Kirk W. , Bryan‐Poole Nancy , Mastrototaro John J.
Published: May 2005

The selectivity originally anticipated for enzyme‐based amperometric electrochemical sensors, specifically glucose sensors based on the oxidation of hydrogen peroxide, has not achieved due to the oxidation of interfering compounds. These interfering compounds are analytes normally present in physiological fluids or tissues that oxidize at the electrode surface and give “false” current readings. The effect of lowering the potential applied to a plantium black working electrode was studied. In vitro studies showed that lowering the applied potential from +0.60 V to +0.35 V greatly decreased the current due to oxidation of acetaminophen, a common interferent, while leaving the current output due to glucose virtually unchanged. In vivo studies revealed that the positive, constant offset observed when comparing the plasma glucose concentration to the glucose concentration indicated by an implanted glucose sensor was greatly minimized by reducing the applied potential from +0.60 V to +0.35 V. The offset was thought to be due to the oxidation of interferents. The linearity, magnitude, and stability of the sensor's in vitro and in vivo response to glucose was unchanged by the reduction in the applied potential.
Selectivity of liquid membrane electrode based on mercurated polystyrene as ion‐exchanger to anionic surfactants and soaps
Authors: Szczepaniak Walenty , Ren Maria
Published: May 2005

An electrode that employs a solution of mercurated polystyrene in 1,1′,2,2′ tetrachloroethane as the sensor in a liquid‐state membrane has been developed. The electrode was tested toward some common anions, anionic surfactants, and soaps. This electrode displays an unusually high level of selectivity for anionic surfactants, in particular to bis(2‐etylhexyl)sodium sulfosuccinate, sodium dodecylbenzenesulfonate, and sodium dodecylsulfate, over many common anions, such as NO, ClOF−, Cl−, and Br−. The electrode may find application in the analysis of surfactants, as an indicator electrode in the potentiometric titration and in the physicochemical studies of surfactant solutions.