bluuebunny/crossref_metadata_2025 huggingface dataset:
Benzo‐18‐crown‐6 and its lariat ether derivatives as ionophores for potassium, strontium, and lead ion‐selective electrodes
Authors: Attiyat Abdulrahman S. , Christian Gary D. , Cason C. Victor , Bartsch Richard A.
Published: May 2005

Ion‐selective microelectrodes were prepared by coating a matrix containing the crown ether benzo‐18‐crown‐6 or one of five polyether ring‐substituted benzo‐18‐crown‐6 derivatives on a preconditioned silver wire in a flow cell. Responses of the electrodes toward lithium, sodium, potassium, magnesium, calcium, strontium, and lead were measured. Selectivity coefficients were obtained by the matched potential, fixed interference, and separate solution methods. Compared with benzo‐18‐crown‐6, the nature of the side arm in the lariat ether derivatives was found to influence the selectivities in different ways. For specific ionophores, high selectivities of potassium over lithium, sodium, magnesium, calcium, and strontium, of strontium over magnesium and calcium, and of lead over magnesium, calcium, and strontium were demonstrated.
Bioaccumulation and quantitation of metals at peat moss‐modified electrodes
Authors: Wang Joseph , Naser Najih , Darnall Dennis , Gardea‐Torresdey Jorge
Published: May 2005

Plant materials of the genus Sphagnum have long been known to absorb cations preferentially from dilute solutions. Preconcentrating modified electrodes based on the incorporation of peat moss within carbon paste matrices, have been designed for bioaccumulating copper ions prior to their voltammetric quantitation. Operational conditions, such as paste composition, solution pH or ionic strength, accumulation time, and voltammetric waveform are characterized and optimized to allow quantitation of submicromolar concentrations. The surface is regenerated by placing the electrode in a hydrochloric acid solution, allowing the use of a single electrode in multiple determinations (RSD of 6% for 15 repetitions). The plant modifiers also strongly bind and retain multiple charged counterions. These surface‐bound ionic metal complexes are able to mediate electron transfer with solution species (such as hydrogen peroxide). The approach could be extended to other plant‐material modifier/analyte systems, as well as for preconcentration for other trace techniques. Preliminary data are given for the Spanish moss/silver system.
Liquid chromatography amperometric detection of catechol, resorcinol, and hydroquinone with a copper‐based chemically modified electrode
Authors: Zhou Jianxun , Wang Erkang
Published: May 2005

A copper‐based chemically modified electrode (CME) has been constructed and characterized for flow‐through amperometric detection of catechol, resorcinol, and hydroquinone. Novel potential dependence of the detector response was first obtained for these analytes at the Cu CME, where negative peaks together with positive ones were observed in one definite chromatogram using amperometric detection. Its advantages in chromatographic applications were demonstrated. From these observations it is proposed that the detector response was governed by formation of copper complexes with the solutes. A dynamic linear range over two orders of magnitude was obtained, when operating the detector at +0.10 V vs. SCE, from which ng detection limits were achieved.
Electrochemical investigations of 3‐(p‐sulfamoylphenylhydrazono)‐2,4‐pentanedione at pyrolytic graphite electrode
Authors: Goyal R. N. , Kumar Anoop , Bhargava Sandhya
Published: May 2005

The electrochemical behavior of 3‐(p‐sulfamoylphenylhydrazono)‐2, 4‐pentanedione has been studied in the pH range 2.2–10.2. It was observed that sulfamoylphenylhydrazone undergoes electrooxidation as well as electroreduction at the surface of a pyrolytic graphite electrode (PGE). The oxidation or reduction peaks observed can be used for the detection of this compound. The products corresponding to both processes have been separated and characterized using IR, NMR, and mass spectra. The reaction pathways have been proposed to account for the voltammetric, coulometric and spectral behavior.
The properties and applications of amperometric gas sensors
Authors: Cao Zhuang , Buttner William J. , Stetter Joseph R.
Published: May 2005

The properties and applications of amperometric gas sensors are reviewed. An introductory discussion of the general mechanism of electrochemical gas reactions and an outline of the construction of amperometric gas sensors is presented. The performance of sensors and the relationship of the sensor's performance to the materials of construction and sensor components are described. The analytical characteristics of a sensor such as sensitivity, selectivity, response time and noise are intimately related to the materials chosen for membranes, conductive electrolytes, and active electrocatalysts, as well as the choice of effective operating conditions. The applications of amperometric gas sensors to specific analytical problems are discussed in the context of required performance. Finally, this article points out technical gaps and the future direction of amperometric gas sensor research including some potential applications. References that are relevant to the field of amperometric gas sensors are summarized in a table which contains the author's name, the electrochemical reaction, and an exemplary application.
The EC′ mechanism: Split waves at the channel electrode
Authors: Fisher Adrian C. , Compton Richard G.
Published: May 2005

A computational strategy is presented for the simulation of current‐voltage curves of electrode processes with very fast coupled homogeneous kinetics at the channel electrode. The approach is illustrated by consideration of the EC′ mechanism that relates to the homogeneous catalysis of electrochemical reactions. It is shown that for fast catalytic reactions “split” voltammetric waves are observed where the two components of the wave result first from the direct reduction (oxidation) of a mediator and, secondly, to a prewave in which mediated reduction of a substrate takes place.
A square‐wave voltammetry in a cathodic stripping mode
Authors: Lovrić Milivoj , Pižeta Ivančica , Komorsky‐Lovrić Šebojka
Published: May 2005

A model of cathodic stripping square‐wave voltammetry (SWV) of insoluble mercuric salt accumulated at the mercury drop electrode surface is developed. Theoretical relationships between the properties of responses and the parameters of both the redox reaction and the SWV signal are analyzed. Both reversible and quasireversible redox reactions are considered. The nature of quasireversible maximum is discussed. Numerical simulations are compared qualitatively with the SW stripping voltammograms of electrodeposited HgS.
The development of liquid chromatography/electrochemistry from a historical perspective
Authors: Kissinger Peter T.
Published: May 2005

A personal view of the development of liquid chromatography/electrochemistry from a laboratory curiosity to a practical tool for routine use. An introduction to a special issue of the journal devoted to recent developments in this field.
Column Liquid Chromatography in combination with immobilized enzymes and electrochemical detection and its applications in some industrial processes
Authors: Marko‐Varga György A.
Published: May 2005

The first part of the paper provides a review of the pre‐ and postcolumn derivatization systems used in Column Liquid Chromatography (CLC) in combination with immobilized enzyme reactors (IMERs) and electrochemical detection (EC). In the second part, an outline of important factors to consider in the optimization of CLC‐IMER‐EC systems are presented. Three industrial applications are described utilizing enzyme‐based detection or enzymes for sample handling purposes. In two of the cases, CLC‐IMER were used in combination with amperometric detection using chemically modified electrodes (CME). These applications were performed in our laboratory, and the high selectivity and sensitivity of these systems as well as the problems encountered in these complex samples will be discussed.
Capillary electrophoresis—electrochemistry of microdialysis samples for pharmacokinetic studies
Authors: O'Shea T. J. , Telting‐Diaz M. W. , Lunte S. M. , Lunte C. E. , Smyth M. R.
Published: May 2005

Electrochemical detection has been shown to be a sensitive method of detection in capillary electrophoresis (CE). The small sample volume required for CE makes it ideal for the analysis of microdialysis samples. In this paper, capillary electrophoresis with electrochemical detection is utilized in the analysis of samples obtained during continuous monitoring of the pharmacokinetics of L‐dopa in the rat. The detection limit for L‐dopa was 98 attomoles or 3.9 ng/mL. The elimination half‐life was calculated to be 10.3 ± 1.1 minutes. Voltammetric characterization was used to verify the identity of L‐dopa and its metabolites. The effects of electrochemical pretreatment on the detector performance was also investigated.
Analysis of salbutamol in human plasma by high‐performance liquid chromatography with electrochemical detection using a micro‐electrochemical flow cell
Authors: Sagar Kamal A. , Hua Chi , Kelly Mary T. , Smyth Malcolm R.
Published: May 2005

A high‐performance liquid chromatographic (HPLC) method for the determination of salbutamol in human plasma is described based on separation on a reversed‐phase C18 column followed by detection using a carbon fiber‐based electrochemical detector. The carbon fiber‐based flow electrode used in the analytical system showed some advantages over conventional electrochemical detectors using glassy carbon electrodes. It is easy to prepare, flexible to operate, and suffers less trouble from air bubbles and leaks. It was shown that this kind of microelectrode flow detector exhibits a better detection limit (1 ngml−1) to that obtained using a conventional glassy carbon electrode flow detector (3 ngml−1). The method was found to be reproducible, with a mean overall coefficient of variation (C.V.) of 5.4%, and drug recovery was in excess of 85% at the concentration levels studied.
A reticulated vitreous carbon spectroelectrochemical detector for flow injection analysis and liquid chromatography
Authors: Sorrels Janet Weiss , Dewald Howard D.
Published: May 2005

A spectroelectrochemical detector for flow injection and liquid chromatography is described. The detector design has dimensions of a standard 1 cm sample cuvette with a replaceable reticulated vitreous carbon working electrode. No special cell holder or modifications to the spectrophotometer are required to use the detector. Chronocoulometry is used to indicate a trend from thin‐layer behavior toward semi‐infinite diffusion behavior as the electrode pore size increases. Ferro‐/ferricyanide solutions were used to evaluate the flow injection characteristics of the detector. A sampling rate of 180 injections per hour was used. Linear calibration curves in the micromolar range were achieved with a reproducibility of 2–7%. A mixture of phenol, chlorophenols, and nitrophenols was used to investigated the simultaneous electrochemical and optical response for liquid chromatography.
Determination of 2‐thiothiazolidine‐4‐carboxylic acid in urine by liquid chromatography with electrochemical detection
Authors: Ciucu Anton , Baldwin Richard P.
Published: May 2005

An assay procedure utilizing liquid chromatography and amperometric detection at a chemically modified electrode (CME) has been developed for the determination of 2‐thiothiazolidine‐4‐carboxylic acid (TTCA) in urine samples. The electrocatalytic activity of the CME, which consisted of a glassy carbon surface coated with an electropolymerized cobalt phthalocyanine film, permitted optimum response at a potential of +0.75 V vs. Ag/AgCl with a detection limit of 7 pmol for TTCA and with no sample preparation required. In case of fouling of the electrode surface by sample constituents, the polymeric cobalt phthalocyanine electrode surface could be renewed with a variability of less than 10% and an equilibration time of less than 15 minutes.
Multienzyme containing tissue‐based and ferrocene‐mediated bioelectrode for the determination of polyamines
Authors: Lin Meng Shan , Hare Minoru , Rechnitz Garry A.
Published: May 2005

Oat seedling tissue and ferrocene/ferricinium were coimmobilized in a carbon paste matrix to construct a biosensor for polyamines. The oat tissue is rich in the enzymes polyamine oxidase and peroxidase while the mediator facilitates electron transfer between the electrode and hydrogen peroxide. The determination of the polyamines spermine and spermidine, in both batch and flow injection modes, was evaluated. The concentration of polyamine was monitored through hydrogen peroxide in the presence of oxygen as cosubstrate of polyamine oxidase. A reductive potential of 0.0 V was chosen for monitoring ferricinium which is generated by peroxidase. The detection limit (S/N = 3) for spermidine and spermine in the batch system was 0.19 and 1.15 μM, respectively. The relative standard deviation for twelve replicate analyses of 10 μM spermidine was 4.5%. The activity of the tissue modified carbon paste electrode decreased to 45% of the original value after a storage for 8 days in buffer solution at 4°C.
Crown ether derivatives of anthraquinone as ionophores in ion‐selective electrodes
Authors: Allen John R. , Cynkowski Tadeusz , Desai Jayant , Bachas Leonidas G.
Published: May 2005

1,8‐anthraquinono‐18‐crown‐6 and 10‐[(2,4‐dinitrophenyl)azo]‐9‐hydroxy‐1,8‐anthraceno‐18‐crown‐6 were prepared from 1, 8‐dichloroanthraquinone and used in the development of ion‐selective electrodes. The electrodes based on 10‐[(2,4‐dinitrophenyl)azo]‐9‐hydroxy‐1,8‐anthraceno‐18‐crown‐6 displayed better selectivity for potassium over sodium and had fewer interferences. The differences and similarities between the ionophores, as well as the optimum conditions for the preparation of the electrodes are discussed.
Influence of methyl group on the differential pulse polarographic activity of guanosine
Authors: Kamal M. M.
Published: May 2005

The polarographic activity of guanosine, 1‐methylguanosine, 2‐methylguanosine, and 7‐methylguanosine was investigated over a wide pH range by using differential pulse polarography. It was found that only 7‐methylguanosine exhibits a well‐developed reduction peak, whereas the other compounds are apparently polarographically inactive. The polarographic response of 7‐methylguanosine results from the attachment of the methyl group at N7 of the imidazole ring, which facilitates the reduction process at the N7C8 center. The dependence of the reduction peak on the various experimental conditions is considered. 7‐Methylguanosine can be determined over the concentration range of 2–10 μM.
Indirect determination of cesium in brine by single‐sweep oscillopolarography
Authors: Dan Dezhong , Du Gu , Wan Yuping
Published: May 2005

A new method for indirect determination of cesium by single‐sweep oscillopolarography is presented. The method is based on the quantitative precipitation of cesium with tetraiodobismuthate(III) ion (BiI); the BiI ion can yield a well‐defined polarographic derivative wave at −0.24 V (vs. SCE) in acetic acid solution. The linear range for cesium was dependent on Bil concentration. The detection limit was 10 μg. The procedure is simple, rapid, and convenient, and has been used to determine cesium in brine after extraction with large granular ammonium phosphomolybdate and BAMBP. The polarographic behavior and mechanism of reduction are investigated. The redox process appears to be irreversible and controlled by diffusion with adsorptive characteristics.
Some observations on the accumulation potential in adsorptive stripping voltammetry
Authors: Li Chiang , James Bruce D. , Magee Robert J.
Published: May 2005

A newly named parameter, “initial scan potential”, the potential from which the voltammetric scan starts rather than the widely accepted accumulation potential, has been found to be responsible for some of the important features of voltammograms obtained in the adsorptive stripping voltammetry (AdSV) of some organochlorine compounds (DDT, Dieldrin, 2,4‐ dichlorophenoxyacetic acid, 2,4,5‐trichlorophenoxyacetic acid). The experimental evidence reported strongly confirms the nonfaradaic nature of the preconcentration step in adsorptive stripping voltammetry.
Monte Carlo simulation of diffusional noise at microelectrodes
Authors: Borkowski Marcin , Stojek Zbigniew
Published: May 2005

The Fick's diffusion laws, which employ continuous concentration functions, may be at their limit when a combination of a microelectrode and a very short experimental time is used. This situation became a reality when the applied scan rates reached the level of MV/s. So, a model based on random motions of particles, and thus belonging to Monte Carlo methods, was developed to enable constructing theoretical electroanalytical curves loaded with expected diffusional noise. The obtained theoretical curves indicate that the diffusional noise may increase dramatically when a very small electrode size and a very short pulse time or a very high sweep rate are employed. For high concentrations, the model becomes equivalent to the Finite Difference scheme. Partial verification of the theory is possible, as smoothing of the theoretical “noisy” curves should produce the signals predicted by the known analytical solutions.
Conductance studies with use of an oscillometric detector
Authors: Pungor Ernö , Pál Ference , Slezsák István , Hrabéczy Andrea
Published: May 2005

By comparing calculated and experimental data, the accuracy of the assumed equivalent circuit of the oscillometric microcell was proved. The cell parameters were defined and can be used to characterize the cell and to establish the range of its applicability. The correlation between the output voltage of the oscillator and the sample concentration was studied in the case of the measuring principle applied (measurement of quality factor Q). A relationship was derived for describing the dependence of the analytical signal on the concentration, which enabled the factors influencing the sensitivity to be determined. All these studies served to optimize the cell geometry and oscillator circuit.
Automatic mercury drop electrode with double solenoid activated valve
Authors: Pedrotti Jairo , Angnes Lucio , Gutz Ivano G. R.
Published: May 2005

The construction and evaluation of a simple, low cost, and versatile automatic mercury electrode, working as dropping (DME), hanging (HMDE), or static drop electrode (SMDE), is described. Fast action of the needle valve is obtained with two solenoids, one for opening the valve and the other for closing it. The electrode can be controlled from a microcomputer or with a digital circuit. The performance of this electrode compares favorably with that of commercial ones in terms of area reproducibility (std. dev. < 0.05%), response time of the valve, current profile during potentiostatic extrusion of the drop, and flexibility of use.
Use of ion exchangers for the voltammetric determination of NTA and EDTA in natural waters
Authors: Voulgaropoulos Anastasios , Tzivanakis Nicolaos
Published: May 2005

The indirect trace determination of NTA and EDTA in natural waters is carried out by differential pulse anodic stripping voltammetry (DPASV), after their complexation with bismuth(III). Chloride ions in relatively high concentrations as well as iron(III) and copper(II) interfere with the determination of EDTA and NTA in natural waters. These interferences can be removed by using ion exchangers in the pretreatment of the sample before the voltammetric determination. The interferences of phosphonic acids and humic acids can also be negated. The determination was performed in sea, lake, river, rain, and waste waters.
Binding capacity of casein to lead and voltammetric speciation of lead in milk with a nafion coated electrode
Authors: Vidal Juan C. , Viñao Rosa B. , Castillo Juan R.
Published: May 2005

The complexation of lead with casein (CS) was studied by several voltammetric methods, as was the selective determination and speciation of lead in milk. First, cyclic voltammetry (CV) was used to examine the influence of adsorbed casein and complexation on the electrochemical response of lead at neutral and alkaline pHs. Second, by titrating solutions of CS with lead, two mathematical methods based on differential‐pulse anodic stripping voltammetry (DPASV) for evaluating the binding properties of CS to lead were compared with a hanging mercury drop electrode (HMDE) and a Nafion‐covered mercury film electrode (Nf‐MFE). In all cases, the conditional stability constants for the Pb‐CS complex agreed well and were close to log β′ = 5.5 at pH 7.0. Finally, lead was directly determined with the chemically modified electrode in acidified samples (≈︁pH 0.3) of whole and skim milk at the ng/ml level, with no need for preliminary acid digestion.
The mathematical modelling of ionic diffusion through stagnant layers: A modification of the Morf and Simon equation
Authors: Lucas Sam , Desai Mohamed , Vadgama Pankaj
Published: May 2005

An improved mathematical model of dynamic responses of a glass pH electrode and its correlation with that of a membrane‐mounted glass pH electrode on the basis of HCl diffusion through the stagnant layer is reported here. The application of such a model and its validity to aqueous and gel films, such as porcine gastric mucus, is evaluated across the pH spectrum. Dynamic responses of the membrane‐mounted glass pH electrode, modelled on this basis gave an excellent fit to the experimental data across the pH range for both films. The modified model described here takes into account the presence of any effect at the membrane/mucus interface for the experimental set‐up. The technique and model thus enables determination of ion flux in mucus or any coated ion selective electrode.
Synergic effect of fulvic acids on the differential pulse adsorptive voltammetry of the Mo(VI)‐phenanthroline complex
Authors: Quentel François , Elleouet Catherine , Madec Christian
Published: May 2005

In acidic chloride media (pH 2), a chelate of Mo(VI) with 1, 10‐phenanthroline is adsorbed on a hanging mercury drop electrode and reduced at −0.575 V. In presence of fulvic acids, the signal is strongly enhanced owing to the formation of a mixed complex which is more readily adsorbed. The effect of various operational parameters (pH, ligand, and molybdenum concentrations, potential and time collection) on the response is discussed, and a sensitive adsorptive voltammetric procedure is developed.
Simultaneous polarographic chemometric trace analysis of pyrazine and its methyl derivatives
Authors: Yongnian Ni , Kokot Serge , Selby Mark , Hodgkinson Mark
Published: May 2005

The polarograms of mixtures of the cocoa flavor compounds, pyrazines, consist of overlapping peaks. This generally precludes the direct analysis of these compunds without prior separation. In this paper, polarographic conditions for the analysis of up to four component mixtures of pyrazines present at trace levels (150 ppb‐1 ppm) were investigated using differential pulse polarography (DPP) at a static mercury drop electrode (SMDE). A series of pyrazine mixtures were analyzed at pH 4.8 (phosphate/citric acid buffer) and the results were interpreted using partial least squares (PLS), principal component regression (PCR), and multiple linear regression (MLR) chemometric routines. In each case an orthogonally designed training set was used to facilitate predictions. The PLS and the PCR models produced acceptable results with recoveries, in general, being in the 97–104% range and RSD in the 4–10% range depending on the nature and complexity of the mixture analyzed.
Electrochemical reduction behavior and determination of nicoumalone
Authors: Reddy C. Suresh , Reddy S. Jayarama
Published: May 2005

The electrochemical reduction behavior of nicoumalone has been studied by using dc polarography, cyclic voltammetry, ac polarography, differential pulse polarography, millicoulometry, and controlled potential electrolysis in universal buffers ranging from pH 2.0 to 12.0 in DMF—water mixtures. Kinetic parameters such as diffusion coefficient (D) and forward rate constant (k) values are evaluated and a reduction mechanism is proposed. A simple and rapid differential pulse polarographic method has been developed for the determination of nicoumalone in pharmaceutical formulations using the standard addition method. The detection limit is 2.7 ng mL−1.
Direct electron transfer reaction of a blue protein from Alcaligenes faecalis strain 6
Authors: Iwasaki Yuzuru , Suzuki Masayasu , Takeuchi Toshifumi , Tamiya Eiichi , Karube Isao , Nishiyama Makoto , Horinouchi Sueharu , Beppu Teruhiko , Kadoi Hideo , Uchiyama Shunichi , Suzuki Schuichi
Published: May 2005

The direct election tranfer reaction of a copper‐containing blue protein from Alcaligenes faecalis strain 6 (AfBP) was investigated. AfBP showed quasi‐reversible electron transfer kinetics at an edge‐plane—oriented pyrolytic graphite electrode (PGE) without any electrode modifier. Investigation of the effect of solution conditions on the reaction suggested that a weak electrostatic interaction between the electrode and the protein facilitates the electron transfer.
Electrocatalysis of nitrite reductase fromAlcaligenes faecalisstrain 6 mediated by native redox partner
Authors: Iwasaki Yuzuru , Takeuchi Toshifumi , Tamiya Eiichi , Karube Isao , Nishiyama Makoto , Horinouchi Sueharu , Beppu Teruhiko , Kadoi Hideo , Uchiyama Shunichi , Suzuki Shuichi , Suzuki Masayasu
Published: May 2005

A protein‐mediated electrocatalytic reaction is described. A blue protein fromAlcaligenes faecalisstrain 6 (AfBP) was used as a redox mediator for a nitrite reductase (NIR) from the same organism. Two steps of a homogeneous chemical reaction (AfBP‐NIR and NIR‐substrate), following the direct electron transfer reaction of AfBP (E C′C′), were analyzed, and the bimolecular rate constant of 1.8 × 106M−1·S−1for the AfBP‐NIR reaction was calculated from electrocatalytic current in cyclic voltammetry. The kinetic relation of the first and the second homogeneous reaction was discussed.
New amperometric biosensor for citrate with mercury film electrode
Authors: Hikima Satoshi , Hasebe Kiyoshi , Taga Mitsuhiko
Published: May 2005

We describe a new amperometric biosensor which is constructed from a mercury film electrode and an enzyme‐immobilized membrane. This biosensor is based on detecting the reduction current of an organic acid produced by enzyme reactions. The detection range of this biosensor was 5.0 × 10−4 – 3.0 × 10−3 M and relative standard deviation, R.S.D. at 1.0 × 10−3 M was 4.8%.
Electroanalytical determination of lormetazepam in pharmaceutical preparations and human urine
Authors: Zapardiel A. , Bermejo E. , Pérez López J. A. , Mateo P. , Hernández L.
Published: May 2005

The electrochemical properties of the drug lormetazepam have been studied at the mercury electrode. A method for determination of the drug in commercial preparations by differential pulse polarography has been devised, with mean relative errors lower than 1.4% and relative standard deviations lower than 3.3%. Controlled adsorptive accumulation of lormetazepam at a hanging mercury drop electrode (HMDE) provided the basis for its determination by stripping voltammetry at nanomolar concentration levels. The adsorptive stripping response was evaluated with respect to experimental conditions and parameters such as electrolyte, pH, accumulation potential, accumulation, time and concentration. A drug determination method for use in urine with previous extraction (98% recovery) has been developed, with a detection limit of 23 ngm·1−1 (40 second accumulation time) and a relative standard deviation around 6.8%.
Lettuce seed meal tissue‐based membrane electrode with high biocatalytic activity for hydrogen peroxide
Authors: Fang Yao , Cai Ronghui , Deng Jiaqi , Deng Zifeng
Published: May 2005

A newly developed hydrogen peroxide selective membrane electrode using lettuce seed meal as source biocatalyst is described. This amperometric‐based probe exhibits high biocatalytic activity, long lifetime and favorable selectivity for the measurement of hydrogen peroxide.
Flow monitoring of glutamate and aspartate in foods and pharmaceutical products with immobilized bienzyme electrochemical cells
Authors: Palleschi G. , Lavagnini M. G. , Compagnone D. , Bertocchi P. , Moscone D.
Published: May 2005

Electrochemical enzyme cells for glutamate and aspartate analysis have been assembled and used in continous‐flow and in flow‐injection analysis. The enzymes, glutamate oxidase (GOD) and aspartate amino‐transferase (AST), were co‐immobilized on an Immobilon Immuno‐affinity membrane, which was placed into a three‐electrode, flow‐through cell. Additional protective membranes were used to reduce the electrochemical interferences and to protect the immobilized enzymes. Thin‐layer and walljet cells were used and compared. Calibration curves for glutamate and aspartate showed a linearity range of 1–500 μmol/L and 10–500 μmol/L respectively. The sensitivity was higher using the flow‐through system with a response time of 2 min. Better reproducibility was achieved using the FIA procedure with a response time of less than 1 min. Glutamate in foodstuffs and asparatate in some pharmaceutical products were analyzed. Results were compared and correlated well with an HPLC procedure.
Anaesthetic lidocaine and dicaine transfer across liquid/liquid interfaces
Authors: Wang Erkang , Yu Zemu , Li Nan
Published: May 2005

Lidocaine transfer across the water/1,2‐dichloroethane and the water/nitrobenzene interfaces has been investigated by chronopotentiometry with linear current scanning and cyclic voltammetry. The irreversible hydrolysis occurring in the phase transfer of dicaine at the water/nitrobenzene interface is discussed.
Covalent immobilization of DNA onto glassy carbon electrodes
Authors: Millan Kelly M. , Spurmanis Aleksandrs J. , Mikkelsen Susan R.
Published: May 2005

Denatured calf thymus deoxyribonucleic acid (DNA) and synthetic poly(dG)poly(dC) have been covalently immobilized onto oxidized glassy carbon electrode surfaces using the water‐soluble carbodiimide, 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide. Immobilized DNA has been detected using the complex Co(bpy) (bpy = 2,2′ ‐bipyridine). This complex has a reversible one‐electron oxidation (Eo′ = 0.33 V versus SHE), binds electrostatically in the minor groove of the DNA double helix, and preconcentrates at the surface of the DNA‐modified electrode prior to a voltammetric scan. Our cyclic voltammetric data indicate that larger Co(bpy) signals are observed at low ionic strength; this is consistent with the larger association constants obtained for the binding of Co(bpy) with calf thymus DNA at low ionic strength. While immobilizations were attempted for four species, poly(dA)poly(dT), native calf thymus DNA, denatured calf thymus DNA, and poly(dG)poly(dC), only the last two species could be successfully immobilized with the carbodiimide procedure; these results show that guanosine and/or cytosine bases will bind covalently to the o‐acylisourea on the glassy carbon surface.
The application of ferrocene‐modified n‐type silicon in glucose biosensors
Authors: Dicks J. M. , Cardosi M. F. , Turner A. P. F. , Karube I.
Published: May 2005

This article describes the application of ferrocene‐modified n‐type silicon electrodes to the anaerobic redox catalysis of glucose oxidase. The electrodes are modified with ferrocene either directly, by using (1,1′‐ferrocenediyl)dichlorosilane, or via an underlying polypyrrole film. Light‐activated catalytic waves are detected in both cases in the presence of glucose oxidase and glucose, thereby demonstrating rapid heterogeneous kinetics between the covalently immobilized mediator and glucose oxidase. A glucose‐sensitive electrode is made by simple adsorption of glucose oxidase from an aqueous buffered solution into the surface film.
Organic‐phase biosensors based on the entrapment of enzymes within poly(ester‐sulfonic acid) coatings
Authors: Wang Joseph , Lin Yuehe , Chen Qiang
Published: May 2005

The utility and advantages of the poly(ester‐sulfonic acid) ionomer (Eastman AQ‐55D, Eastman Chemical Products) for entrapping enzymes onto electrodes for organic‐phase biosensing are described. This type of immobilization scheme relies on the stability of Eastman AQ films in various organic solvents. The resulting organic‐phase enzyme elecrodes couple the entrapment of high enzyme loadings with discrimination against anionic interferences, short response times, and a rapid stabilization of the baseline current. The immobilization of the enzymes tyrosinase and horseradish peroxidase (HRP) is evaluated in connection with the biosensing of phenolic and peroxide compounds in acetonitrile solutions. Various conditions of this simple preparation route are explored.
Polarographic and electrochemical studies of some aromatic and heterocyclic nitro compounds: Part V. Polarographic reduction of cyano‐and carboxamido‐nitropyrazoles
Authors: Dumanović D. , Jovanović J. , Marjanović B. , Zuman P.
Published: May 2005

Reduction of the nitro group in 1‐alkyl‐4‐cyano‐5‐nitropyrazoles follows a pattern similar to that of 1‐alkyl‐5‐nitropyrazoles, involving the sequence H+, e, H+, e, 2e, 2H+. On the other hand, the sequence of proton and electron transfers in the reduction of the nitro group in 1‐alkyl‐3‐nitro‐4‐cyanopyrazoles differs from that in 1‐alkyl‐3‐nitropyrazoles. Similarly, the reductions of 4‐cyano‐3(5) ‐nitropyrazole differs from that of 3(5)‐nitropyrazole, even when both of these reductions are affected by the dissociation of the NH group with pKB = 6.26 and 9.81, respectively. Similarly, the behavior of 1‐alkyl‐4‐carboxamido‐5‐nitropyrazoles resembles that of 1‐alkyl‐5‐nitropyrazoles, but that of 1‐alkyl‐3‐nitro‐4‐carboxamidopyrazoles is different from that of 1‐alkyl‐3‐nitropyrazoles. In 1‐alkyl‐4‐carboxamido‐5‐hydroxylaminopyrazoles, the carboxamido group is reduced in a two‐ and four‐electron process, but the low absolute value of the limiting current of wave i2 indicates the presence of competitive side reactions.
Elucidation of electrochemical reactions using three‐dimensional voltammetry
Authors: Papadopoulos Nikos , Hasiotis Costas , Kokkinidis Giorgos , Papanastasiou Giorgos
Published: May 2005

In this article, we demonstrate that three‐dimensional voltammetry can be used very efficiently as a reversal technique in complicated reactions. Three‐dimensional voltammetry, based on double potential step chronoamperometric data, has been used to obtain information on the reaction products of the electrochemical reduction of 4‐nitroquinoline‐N‐oxide. The study was carried out in aqueous 0.5 M HClO4 solutions on Pt/Bi (upd) electrode.
Alkali and alkaline earth metal ion transfer across the liquid/liquid interface facilitated by ionophore ETH157
Authors: Wang Erkang , Yu Zemu , Qi Deyao , Xu Chengmin
Published: May 2005

The H+, Li+, Na+, K+, Mg2+, Ca2+ and Ba2+ ion transfer across the water/nitrobenzene (NB) and water/1,2‐dichloroethane (DCE) interfaces, facilitated by the ionophore ETH157, has been investigated by cyclic voltammetry (CV). The mechanism of the transfer process has been discussed, and the diffusion coefficients and the stability constants of the complexes formed in the nitrobenzene phase have been determined.
Differential pulse polarographic determination of the artificial sweeteners acesulfame‐K and saccharin in beverages
Authors: Hannisdal Atle , Schrøder Knut H.
Published: May 2005

A fast differential pulse polarographic method for the determination of the artificial sweeteners acesulfame‐K and saccharin in beverages has been developed. Polarograms of the sweeteners are recorded directly in a supporting electrolyte containing 0.1 M NaCl (5.8 g/L) and 0.004 M tetrabutyl ammonium iodide (1.5 g/L). The pH of the supporting electrolyte is adjusted to 1.9 with concentrated HCl. The results are found to be in good agreement with high performance liquid chromatography (HPLC) results.
Biocatalysis and electrocatalysis at carbon paste electrodes doped by diaphorase‐methylene green and diaphorase‐meldola blue
Authors: Kulys Juozas , Gleixner Gerd , Schuhmann Wolfgang , Schmidt Hanns‐Ludwig
Published: May 2005

The electrocatalytical oxidation of dihydronicotinamide adenine dinucleotide (NADH) and ascorbic acid was investigated on carbon paste (CP) electrodes doped by diaphorase and the mediators methylene green (MG) and meldola blue (MaB). Bioelectrocatalytical oxidation of NADH proceeds at the potential 0–0.25 V versus saturated calomel electrode (SCE). Km(app), Imax, and sensitivity were 0.9 and 3.6 mM, 1.4 and 6.7 μA, and 0.20 and 0.24 mA mM−1 cm−2 for MaB‐ and MG‐doped CP electrodes, respectively. The biocatalytical process of NADH oxidation is not sensitive to oxygen, and optimum activity is at pH 7.3. The nonenzymatic electrocatalytical oxidation of NADH and ascorbic acid on CP electrodes doped by mediators proceeds at the same potential, and the efficiency of NADH oxidation was 50% in comparison to the biocatalytical process. Ascorbate oxidase immobilized on graphite powder was used to increase the selectivity of the electrocatalytical system of NADH oxidation over the electrochemical oxidation of ascorbic acid.
Voltammetric assay of thrombin adsorbed on the carbon paste electrode
Authors: Randriamanazaka H. N. , Nigretto J. M.
Published: May 2005

An electrochemical procedure to assay a protease adsorbed on a carbon paste electrode (CPE) is described. In the conformation described, the catalysis is induced by thrombin, an enzyme of the blood coagulation system. The kinetics are followed for increasing intervals of time, by monitoring with the modified enzyme electrode an electrogenic redox probe (either p‐nitroaniline or p‐aminodiphenylamine) released via amidolysis from a specific peptide substrate contained in the solution. Analysis of the voltammetric current response as a function of time showed that the Lineweaver‐Burk type treatment could apply, in good agreement with theoretical predictions. From the experimental data, the heterogeneous catalytic rate and the apparent Michaelis constant were deduced. The global kinetics were satisfactorily interpretated in terms of a competition existing between catalysis and transport of the substrate toward the electrode.
Fundamentals and limitations for the application of the carbon paste electroactive electrode in the electroanalysis of solids
Authors: Gruner Wolfgang , Kunath Jürgen , Kalnishevskaja Ljubov N. , Posokin Juri V. , Brainina Khjena Z.
Published: May 2005

Experimental conditions for the qualitative and quantitative application of the carbon paste electroactive electrode (CPEE) in the analysis of powders and pulverizable materials are demonstrated for two substances (Cu and TiC) with different reaction schemes in sulfuric acid. The selection of the carbon powder, the type and content of the organic binder, and the paste preparation was done with respect to homogeneity and reproducibility. The influence of the size and shape of the sample particles as well as of the graphite particles on the analytical result is discussed.
Voltammetric reaction of the sulfide/disulfide system with oxygen at mercury electrodes
Authors: Fedurco Milan , Veselá Věra , Heyrovský Michael
Published: May 2005

On the voltammetric curve in the potential range where the first step of the reduction of oxygen at the hanging mercury drop electrode is inhibited by a surfactant, the presence of cystine or other disulfides in the solution produces a reduction peak, the height of which is greatly enhanced by oxygen.
Benzoquinone‐mediated glucose/glucose oxidase reaction at pyrolytic graphite electrode
Authors: Murthy A. Surya N. , Anita
Published: May 2005

In view of the high reversibility of the p‐benzoquinone/hydroquinone couple at a pyrolytic graphite (PG) electrode (compared to platinum or carbon paste electrodes) the glucose‐glucose oxidase (GOD)‐benzoquinone coupled reaction was examined on a pyrolytic graphite surface in homogeneous solution and kinetic data obtained.
Tensammetric techniques for electroanalysis
Authors: Lukaszewski Zenon
Published: May 2005

The following tensammetric schemes, alternating current (ac) polarography of fundamental harmonic and second harmonic, phase‐sensitive ac, square wave tensammetry, differential pulse and normal pulse tensammetry, Kalousek commutator technique, derivative chronopotentiometry, and several other techniques, are reviewed. Thermodynamic background and kinetic limitations of tensammetric analytical signals are discussed. Special attention is given to the behavior of mixtures and to the consequences of association of the analyte as well as to applications of different tensammetric techniques.
On the adsorption voltammetry of the boron‐Beryllon III system: Part I. Determination of boron in plants and soils
Authors: Jin Wenrui , Jiao Kui , Metzner H.
Published: May 2005

A very sensitive electrochemical adsorptive voltammetric procedure for trace measurements of boron(III) in plants and soils is described. The complex of boron(III) with Beryllon III is adsorbed on a dropping mercury electrode (DME) with a long lifetime, and the reduction current of the accumulated complex is measured by linear sweep voltammetry. In order to form the boron(III) complex with Beryllon III, it is necessary to boil the solution for 15 minutes. The electrochemical behavior of the complex is explored. The size of the complex peak, which appears at a position between two peaks of reduction of the ligand, is proportional to the boron concentration. Optimum experimental conditions include 0.05 M HOAc/0.25 M NaOAc as supporting electrolyte, 1 × 10−4 M Beryllon III, solution pH 4.4, and an initial potential of −0.30 V (versus SCE). The linear range of the determination of boron is 4 × 10−5 −1 × 10−5 M. The relative standard error of the method is 0.76% for 3 × 10−6 M boron (III) and 3.4% for 6 × 10−7 M boron (III), respectively.
On the adsorption voltammetry of the boron‐Beryllon III system: Part II. Mechanism of the electrochemical reduction of Beryllon III and its complex with B(III) in acetate buffer
Authors: Jin Wenrui , Jiao Kui , Metzner H.
Published: May 2005

The adsorptive and voltammetric characteristics of Beryllon III and its complex with B(III) at a mercury electrode have been investigated in acetate buffer. The adsorption phenomena were observed by sampled dc polarography, normal pulse polarography, linear sweep voltammetry, and drop time curve measurement. It was found that (1) the reactant was an azo‐group in Beryllon III or its complex with B(III) adsorbed on the surface of the mercury electrode; (2) for reduction of Beryllon III, the product was a hydrazo compound and it was also adsorbed on the surface of the electrode; two electrons and two protons were irreversibly transferred in the overall reaction and the apparent transfer coefficient αn (= 1.8) was measured experimentally; the irreversible electron transfer was followed by a chemical reaction; (3) for reduction of Beryllon III complex with B(III), the product was a hydrazo compound; two electrons and two protons were transferred reversibly in the reaction; the hydrazo compound was desorbed from the surface of the electrode, and the reversible electron transfer was followed by a chemical reaction.
A square‐wave voltammetry of Europium(III)‐humic acid complex
Authors: Mlakar M. , Branica M.
Published: May 2005

The reduction process of Europium(III) in the presence of humic acid was investigated by squarewave (SW) voltammetry. The Eu(III)‐humate complex is reduced reversibly, and both the reactant and product of the redox reaction are adsorbed at the electrode surface. The relationship between the properties of the SW response and the parameters of a charge transfer and of the excitation signal are discussed. The SW voltammograms of the Eu‐humate complex are analyzed according to the theoretical predictions.
Simplified treatment of differential pulse polarography
Authors: Fatouros N. , Krulic D. , Rouelle F. , Champagne G. Y.
Published: May 2005

The expression for the current of differential pulse polarography (DPP), in the case of reversible systems, has been established using the diffusion layer model without resolving the diffusion equations. Criteria for the reversibility of the electrochemical reaction, inherent to DPP, are also discussed.
A comparative spectroelectrochemical study of the electrosorption of benzonitrile and benzylcyanide on a silver electrode
Authors: Holze Rudolf
Published: May 2005

The electrosorption of benzonitrile (BN) and benzylcyanide (BC) on a polycrystalline silver electrode from aqueous electrolyte solutions was studied with surface‐enhanced Raman spectroscopy (SERS). Spectra, obtained with the potential of the electrode within a potential range where, according to simultaneously performed cyclic voltammetry, solely adsorption occurs, showed bands clearly attributable to molecules adsorbed on the silver electrode. The results imply both end‐on adsorption via the nitrile group and edge‐on orientation, depending mostly upon the composition of the supporting electrolyte solution.
Polarographic behavior and determination of some S‐triazine herbicides
Authors: Ignjatović Ljubiša M. , Marković Dragan A. , Veselinović Dragan S. , Bešić Borislav R.
Published: May 2005

The possibility for differential pulse polarography (DPP) determination of S‐triazine has been shown and compared with gas‐chromatographic (GC) measurements. Good agreement was found between GC and DPP measurements in analyzing 20 samples of industrial wastewater. It was found, using controlled potential coulometry (CPC), that four electrons take part in electrochemical reduction steps. On the basis of this and polarographic measurements, the mechanism of electrochemical reduction of S‐triazine was postulated.
Bilayer lipid membranes for electrochemical sensing
Authors: Nikolelis Dimitrios P. , Krull Ulrich J.
Published: May 2005

Bilayer lipid membranes (BLMs) are described as selective and sensitive electrochemical transducers for inorganic ions and organic species. The electrostatic properties of BLMs, which are significant in controlling ion permeation processes, and the possible mechanisms for signal generation are presented herein. Operation of a BLM‐based transducer hinges on a selective interaction between analyte in aqueous solution and membrane‐embedded receptors; as a result, the electrostatic fields and/or the physical phase structure of the membrane alters, leading to an analytical signal (most commonly conductivity changes) which can be related to the analyte concentration. Examples of electrochemical sensors based on this principle and efforts to stabilize these bilayer membranes are presented in this review article.
Nafion‐crown ether modified carbon fiber electrodes: New microbiosensors for detection of neurotransmitters in vitro and in vivo
Authors: Baumeyer Thomas , Dittrich JÜRgen , Crespi Francesco
Published: May 2005

Based on experience in in vivo voltammetry with Nafion carbon fiber electrode coated (CFE), a new kind of modification, was developed based on mixing Nafion and crown ether (dibenzo‐18‐crown‐6) solutions. Nafion‐crown ether electrodes (NA‐CRO‐CFEs) offer higher sensitivity to dopamine than Nafion‐CFEs. The improvement of detection limit is caused by enrichment of the neurotransmitter in polymermembrane by interaction of oxygen atoms of the crown ether and the positively charged amino group of catecholamine. With NA‐CRO‐CFEs one is able to detect dopamine and serotonin in physiological basal concentrations in vitro and in vivo without overlapping of oxidation peaks of ascorbic acid or metabolites. Identification of in vivo peaks is discussed with in vitro and in vivo experiments.