bluuebunny/crossref_metadata_2025 huggingface dataset:
A highly sensitive and selective catalytic method for the determination of ultratrace amounts of rhodium with oscillopolarographic detection
Authors: Zhi‐liang Jiang , Li‐sheng Wang
Published: May 2005

A novel, highly sensitive, and selective catalytic method with oscillopolarographic detection for quantifying trace rhodium is described. The method is based on experimental results that Rh(III) has a very strong catalytic effect on the slow redox reaction between thoron and periodate in acetate buffer (pH 4.2) solution at 100°C. Thoron exhibits a sensitive oscillopolarographic wave at −0.60 V (vs. SCE). Ascorbic acid was used as interference eliminator and a quenching reagent. The detection limit of 15 ppt and calibration plot from 3.0 × 10−2 to 1.6 ppb Rh(III) were obtained by a fixed‐time procedure. Rhodium was determined in catalysts by the method with good results.
Simultaneous determination of glucose and sucrose by a dual‐working electrode multienzyme sensor flow‐injection system
Authors: Zhang Xianen , Rechnitz Garry A.
Published: May 2005

A dual‐working electrode (K1 and K2) multienzyme sensor, made of carbon paste, glucose oxidase (GOD) membrane (on K1) and invertase (INV)/mutarotase (MUT)/GOD membrane (on K2), is proposed for simultaneous determination of glucose and sucrose. Interference to the K2 caused by H2O2 produced in the enzyme reaction on K1 can be eliminated by depositing a catalase (CAT) layer between K1 and K2. Acceleration of glucose mutarotation by MUT was found to be three times faster than by phosphate buffer. Glucose was determined directly from the response of K1, while sucrose was computed based on a formula derived from a two‐point calibration method. The maximum concentration of sucrose that could be determined depended strongly on the concentration of coexisting glucose. The activities of immobilized GOD, INV, MUT, and CAT were examined individually and found stable at room temperature for at least 1 month. The final loss of sucrose response activity was found to be due to denaturation of INV.
Amperometric biosensors for detection of L‐ and D‐amino acids based on coimmobilized peroxidase and L‐ and D‐amino acid oxidases in carbon paste electrodes
Authors: Kacaniklic V. , Johansson K. , Marko–Varga G. , Gorton L. , Jönsson–Pettersson G. , Csöregi E.
Published: May 2005

An apparent direct electron transfer between various electrode materials and peroxidases immobilized on the surface of the electrode has been reported in the last few years. An electrocatalytic reduction of hydrogen peroxide promoted by the immobilized peroxidase starts at about +600 mV (vs. Ag/AgCl) at neutral pH. The efficiency of the electrocatalytic current increases as the applied potential is made more negative and starts to level off it about −100 mV (vs. Ag/AgCl). Amperometric biosensors for hydrogen peroxide can be constructed with these kinds of peroxidase modified electrodes. By coimmobilizing a hydrogen peroxide‐producing oxidase with the peroxidase, amperometric biosensors can be made responding to the substrate of the oxidase within a potential range essentially free of interfering electrochemical reactions. Sensors for L‐ and D‐amino acids are shown based on coimmobilizing HRP with L‐amino acid oxidase (L‐AAOD) or D‐amino acid oxidase (D‐AAOD). The effects of the immobilization procedure, buffer (flow carrier), pH, taken amounts of enzymes, flow rate, and injection volume on the response were investigated. The addition of polyethylenimine (PEI) into the paste was found to increase the response considerably. All 20 of the most common L‐amino acids could be detected.
Resolution of ascorbic acid or catecholamine and indole alkaloid mixtures by pulse voltammetry at highly polished glassy carbon
Authors: Kamau Geoffrey N. , Rusling James F.
Published: May 2005

Metallographic polishing of glassy carbon electrodes (GCEs) yields well‐defined oxidation peaks for two‐ and three‐component mixtures of ascorbic acid, dopamine (DA), catechol, and hydroquinone. Linear calibration plots of differential pulse voltammetric current versus concentration were obtained for each component at a range of 0.4 to 10 μM, Deterioration of voltammograms was observed when highly, polished GCE was aged in solution, resulting in positive shifts and broadening of the peaks. Lower limits of detection (LLD) in water at pH 7 were about 0.01 μM, for DA and 1 μM for AA. Highly polished GCEs were further applied to mixtures of naturally occurring indole alkaloids.
Electrochemical study of iproniazid and its analytical determination by differential pulse polarography
Authors: Martín M. E. , Borges T. M. , Arias J. J. , González S.
Published: May 2005

Iproniazid was found to be irreversibiy reduced in two steps, involving the exchange of two electrons and two protons each, by using tast polarography, normal pulse polarography (NPP), and cyclic voltammetry (CV). The rate constants of these two steps were found to be 5.8 × 10−6 and 4.2 × 10−6 and 4.2 × 10−6 cm s−1, respectively, and their corresponding diffusion coefficients 4.5 × 10−5 and 8.3 × 10−5 cm2 s−1, Also, α, the coefficient of cathodic transfer, was found to be 0.20 to 0.25 for the first peak and 0.17 to 0.15 for the second. On the basis of the electrochemical study performed, a differential pulse polarographic method for the determination of iproniazid over the concentration range of 5 × 10−7 M to 1 × 10−4 M was developed.
Binding of cytochrome c with 4‐pyridyl derivatives modified on the gold electrode
Authors: Xie Yuanwu , Dong Shaojun
Published: May 2005

In this work, the adsorption or binding of cytochrome c with 4‐pyridyl derivatives modified on the gold electrode was studied. It was found that the concentrations of electrolyte had much influence on the adsorption of cytochrome c. At lower concentrations of electrolyte (i.e., 2 mmol/L), the binding of cytochrome c with 4,4′‐bipyridyl or 4‐mercaptopyridine on the modified electrode surface can be detected by using the long dipping method for 4,4′‐bipyridine or pretreating the bis(4‐pyridyl) disulfide modified electrode at more negative potentials for 4‐mercaptopyridine. When the concentrations of the electrolyte increase, the binding of cytochrome c with the 4‐pyridyl derivatives changes from irreversible to reversible.
Automatic coulometric titrator with optical indication for acidity number determination
Authors: Podhájecký Petr , Langmaier Jan , Trojánek Antonin
Published: May 2005

The automatic coulometric titrator with a colorimetric indication is described, and its use is demonstrated on acidity number (AN) determinations. Compared to the standard volumetric procedure, the automated procedure yields more accurate results at lower sample and reagents consumption.
Electrochemical behavior of formetanate and chlordimeform pesticides
Authors: Subbalakshmamma M. , Reddy S. Jayarama
Published: May 2005

The electrochemical behavior of formetanate and chlordimeform is studied by using dc polarography, cyclic voltammetry, ac polarography, and differential pulse polarography (DPP) in universal buffers of pH 2.0 to 12.0, including 1 M HCIO4 and 1 M HCl. The number of electrons is determined by millicoulometry. Kinetic parameters such as transfer coefficients, diffusion coefficients, and heterogeneous forward rate constant values are evaluated using these techniques. The results obtained suggest the nature and mechanism of the electrode process. Differential pulse polarography is used for the estimation of formetanate in formulation.
Voltammetry of macromolecular metal complexes involving a nonreversible process: The Ni(II)‐polymethacrylate system
Authors: Argudo M. , Esteban M.
Published: May 2005

The voltammetric behavior of Ni(II) in the presence of polymethacrylic acid (PMA) is studied by normal pulse polarography (NPP), differential pulse polarography (DPP), reverse pulse polarography (RPP), cyclic voltammetry (CV), and anodic stripping voltammetry (ASV), Results obtained seem to indicate the lability of the Ni/PMA complex. Because of the lack of a model for macromolecular metal systems including Mn+/M(Hg) couples with slow rate charge transfer the usefulness of a model assuming electrochemical reversibility has been applied to a metal ion as Ni(II) with a slow rate of charge transfer. The agreement of the experimental results with that theoretically expected upon the model allows us the determination of the apparent formation constant K of the Ni/PMA complex and its dependence on the counterion concentration and on the degree of dissociation of PMA.
Polarographic study of the herbicide metamitron
Authors: Olmedo Carlos , Deban Luis , Vázquez Dolores , Pardo Rafael , Palmero Susana
Published: May 2005

The electrochemical characteristics of the herbicide metamitron have been studied in the pH range 1 to 9 by applying several polarographic techniques, namely DCP, TAST, and DPP, adsorptive stripping voltammetry, and cyclic voltammetry with HMDE. The reduction of this molecule evolves in four processes in pHs lower than 3, and in two steps between pH 3 and 9. All processes involve two electrons, are irreversible, and imply the reduction of the functions CN and N‐NH2 that are present in the molecule. Also, an adsorption phenomenon was observed in several processes. The quantitative determination of metamitron can be carried out in an acetate medium (pH4.6), by applying DPP, with a detection limit of 50 μg/L and using adsorptive stripping voltammetry, reaching a detection limit of 0.5 μg/L. Assays of commercial samples are illustrated.
Conductometric biosensors based on cholinesterases for sensitive detection of pesticides
Authors: Dzydevich Serge V. , Shuľga Alexander A. , Soldatkin Alexei P. , Hendji Andre' M. Nyamsi , Jaffrezic‐Renault Nicole , Martelet Claude
Published: May 2005

Disposable conductometric microbiosensors based on immobilization of acetyl and butyrylcholinesterases (BuChEs) on interdigitated electrodes were fabricated. Enzymes were immobilized by crosslinking with bovine serum albumin and the differential output between the pair of electrodes covered with the enzyme membrane and the pair covered with albumin only was recorded. On the basis of these biosensors, a biochemical assay for pesticides in liquids was developed. Respective detection limits were 5 × 10−11 M for diisopropyl fluorophosphate (DFP), 10−7 M for trichlorfon, and 10−6 M for paracoxon‐methyl and paraoxon‐ethyl for the assays based on the enzymes tested. The presence of pesticides in the sample in concentration exceeding the detection limits can be detected after only 10 minutes of incubation, whereas, in order to extend the range of the determined pesticide concentration and to improve the accuracy of the assay, it is better to use incubation times longer than 30 minutes. Use of pyridin‐2‐aldoximide methiodide as reactivating agent allowed one to achieve the complete recovery of the sensor response when it was incubated in low‐concentrated pesticide solutions, e.g., less than 10−6 M for paraoxon‐methyl and during a short time, e.g., 10 to 20 minutes, for 10−5 M paraoxon‐methyl solution.
Characterization of a mediated amperometric biosensor for hypoxanthine using deflavo xanthine oxidase
Authors: Zhao Shishan , Luong John H. T.
Published: May 2005

Deflavo xanthine oxidase was prepared by removing the flavine adenine dinucleotide (FAD) group from the native enzyme using 2 M CaCl2. The deflavo enzyme was effectively stabilized by 5 mM EDTA in Tris buffer solution, pH 8, and retained about 80% of its activity after several days when stored in this medium at 4°C. The deflavo enzyme was then used for the development of a mediated amperometric electrode for hypoxanthine/xanthine using 1,1′‐dimethylferricinium as mediator, and its performance characteristics were compared to a native enzyme electrode. The resulting deflavo xanthine oxidase electrode was not noticeably sensitive to oxygen in the presence of hypoxanthin while its capability to interact with ferricinium remained intact. The electrode sensor with immobilized deflavo enzyme showed high operational and storage stabilities with a detection limit of about 0.1 μM. No significant sensitivity loss was observed on the enzyme electrode after 150 repeated analyses during a 7.5 hour operation. The deflavo enzyme electrode retained 80% of its sensitivity when stored at 4°C after a month.
Electrochemical determination of ultralow levels (<10−12 M) of mercury by anodic stripping voltammetry using a chemically modified electrode
Authors: Turyan Iva , Mandler Daniel
Published: May 2005

A glassy carbon electrode (GCE) coated with 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane, Kryptofix‐222, has been used for the very sensitive and selective analysis of very low levels of mercury. A detection limit lower than 10−12 M (<0.2 ppt) was obtained applying anodic stripping voltammetry (ASV). The parameters that governed the sensitivity and possible interferences by other ions have been examined in detail. The electrode has been successfully applied for determining mercury in seawater, wastewater, and also in human saliva and amniotic fluid. The modified electrode exhibited high stability and, therefore, could be used repeatedly without mechanical regeneration.
Polishable composite electrode based upon graphite powder modified with an electrochemically deposited catalyst
Authors: Cox James A , Lewinski Krzysztof
Published: May 2005

A polishable bulk‐modified electrode is described that contains polymeric‐mixed valent ruthenium oxide with cyano cross‐links (mvRuCN) as a catalyst. Because mvRuCN is not available as an isolated compound, it was electropolymerized on graphite powder that was subsequently formed into a conducting composite with epoxy. Except for promoting oxidations at a more positive potential, this composite behaved the same as mvRuCN films on glassy carbon. Electrocatalytic oxidation of various N‐nitrosamines, As(III), glutathione, isotocin, and myoglobin was observed. Flow‐injection analysis of 50 μM N‐nitrosodi‐n‐propylamine with amperometric detection at the bulk‐modified composite electrode yielded currents of 2.5 ± 0.1 μA (5 trials) when the carrier solution is pH 1.5 phosphate buffer. The use of a micellar carrier,pH 1.5 phosphate buffer in 0.01 M hexadecyltrimethylammonium chloride, decreased the sensitivity of the flow‐injection amperometric determination of N‐nitrosodi‐n‐phenylamine by 50%, but otherwise, the behavior of the electrode was unchanged. The major advantages of the bulk‐modified electrode over the surface‐modified electrode jras the long‐term stability (at least several months with dry storage) and polishability. Regarding trie latter, 19 replicates of the oxidation of As(III) yielded a relative standard deviation (RSD) of the current response of 3% when the surface was polished between each trial.
Electrochemical study of pyrazolone derivatives at the liquid/liquid interface
Authors: Wang Erkang , Wang Hanming , Yu Zemu
Published: May 2005

Pyrazolone derivatives, such as antipyrine, aminopyrine, and 4‐aminoantipyrine, can transfer across the water/nitrobenzene interface to produce a pair of well‐defined symmetric, reversible anodic‐cathodic peaks by cyclic voltammetry. The transfer mechanism has been studied as a result of the formation of complex of related pyrazolone derivatives with a proton. The protonated complex formed then transferred across the water/nitrobenzene interface. The effect of drugs' structure on the transfer behavior was discussed and parameters related to interfacial behavior were determined.
Electrochemical behavior of triazolobenzodiazepine derivatives
Authors: Arenaza Jesús , Gallo Blanca , Vicente Francisca , Dominguez Manuel
Published: May 2005

The electrochemical behavior of two novel triazolobenzodiazepines (adinazolam and U43.465F) has been studied in the pH range 3 to 13.5. Both compounds are reduced on the dropping mercury electrode and yield one reduction wave attributed to the azomethine group. The two‐electron transfer is polarographically reversible. However, the transfer is followed by a fast conversion of the elearolysis product by a chemical reaction with an irreversible global process. A weak adsorption of the reactant has been observed under certain conditions. Quantitative analysis has been performed, showing that adinazolam and U43,465F can be determined up to 1.1 × 10−6M using differential pulse polarography.
Liquid chromatography series dual‐electrode amperometric detection for aromatic nitro compounds
Authors: Lin Yuehe , Zhang Rongkun
Published: May 2005

A new design of dual‐electrode electrochemical detector for liquid chromatography is described utilizing two series generator/detector electrodes. The detector developed is based on the larger electrode area design compared with commercial ones and has higher electrolytic efficiency, which lead to a higher detection sensitivity when in a reductive‐oxidative series detection mode. Analytes are first reduced at the upstream electrode and the reaction products are then detected by oxidation at the downstream electrode. So, the influence of dissolved oxygen and trace amounts of heavy metals in the mobile phase and sample is eliminated. Thus, exhaustive removal of dissolved oxygen before analysis is not required, and the method can be easily automated. The technique is tested on seven aromatic nitro compounds. Under the optimized conditions, the assay is linear in a concentration range of 2.0 × 10−7 to 4.0 × 10−5 g/mL and has low detection limits of 1.0 to 2.0 ng using a 10 μL sample. The largest standard deviation was 5.2%. The recovery of the detection of water samples was 93 to 107%.
Reproducible, reliable and rugged Hg‐plated Ir‐based microelectrode for in situ measurements in natural waters
Authors: Tercier M.‐L. , Parthasarathy N. , Bufle J.
Published: May 2005

Construction of a reproducible, reliable and rugged iridium‐based microelectrode is described. Perfect electrical contact, Ir‐glass sealing and Ir disk morphology are the key points for obtaining reproducible voltammetric sensors. These points are discussed in detail and optimal fabrication conditions are given. Electron bombardment under vacuum yielded good soldering between Ir and Cu electrical cable. Reproducible polishing of the microelectrode to a mirror like Ir disk surface is obtained with silicon carbide pads and diamond paste using an automatic home made polisher. Cyclic voltammetry and optical microscopy have been used to characterize this microelectrode. Hgplated Ir‐based microelectrodes are prepared by electrodeposition of mercury on the iridium disk substrate. Reproducibility and reliability close to 100% have been obtained for Ir‐based microelectrode preparation, mercury layer deposition and trace metal measurements by differential pulse anodic stripping voltammetry (DPASV) and square wave anodic stripping voltammetry (SWASV) in synthetic solutions even at low ionic strength (10−3 M). Continuous measurements over long periods of time indicate that the Hg‐plated Ir‐based microelectrodes can be used for several days without renewal of the mercury layer. These microelectrodes were applied to lead and cadmium speciation studies directly in river waters by SWASV without any separation. The results show that free PbII and CdII concentrations as low as 0.5 nM and 0.1 nM respectively can be determined by direct measurements, without perturbing the medium. The lifetime of these microelectrodes in the present state of the art is more than 2 years.
Methylene‐green‐mediated carbon paste glucose biosensor
Authors: Kulys J. , Wang L. , Hansen H. E. , Buch‐Rasmussen T. , Wang J. , Ozsoz M.
Published: May 2005

An amperometric glucose bioelectrode based on the incorporation of methylene green (MG) within a glucose oxidase (GOD)‐containing carbon paste is described. The electrode generates an anodic current in the range of 0.0–0.6 V (vs. SCE). The optimum pH is 8.5. The apparent Michaelis constant for the Cali bration plot is 49.3 mM (at 0.5% MG and 5.0% GOD loadings). The electrode sensitivity is 18.1 μA/mM cm2. The electrode is insensitive to paracetamol and ethanol. At 0.068 V the response to ascorbic acid (40 μM) accounts for 2.4% of that of the normal physiological glucose level in blood. The performance was optimized by systematically altering the electrode composition and electrode potential. The electrode was used to measure glucose in a serum sample and gave an acceptable correlation with the reference method Eksan‐G results. Good stability was observed for storage in the dry state in the refrigerator.
Polarographic and electrochemical studies of some aromatic nitro compounds: Part VIII. Effects of solvents and surfactants on current–voltage curves obtained with DC and differential pulse polarography
Authors: Zuman P. , Rupp E.
Published: May 2005

Differential pulse polarography (DPP) is an excellent analytical method, but cannot be recommended for applications in the initial stages of mechanistic studies. Its application is also questionable in the analysis of samples containing varying concentrations of an organic cosolvent or of surface active compounds. The effect on limiting currents obtained by DC polarography and on peak currents obtained by DPP was demonstrated for reductions of various nitrobenzene derivatives. The similarity of changes in current for various nitrobenzenes enables the exclusion of the formation of adducts or micelles as the predominant effect. The decrease of the limiting currents in all cases is much smaller than the decrease of DPP peak currents, due to strong effects of the surfactants on the kinetics of electroreduction. For the analysis of natural products or of solutions containing varying amounts of organic cosolvent, the measurement of the DC polarographic limiting current is preferred. An addition of 30% ethanol minimizes the effects of the varying concentration of surfactant on both DC polarographic limiting and DPP peak currents.
Electrocatalytic oxidation of reduced nicotinamide coenzymes at organic dye‐modified electrodes
Authors: Chi Q. , Dong S.
Published: May 2005

Chemically modified electrodes (CMEs) were prepared by adsorbing different dyes, including methylene blue (MB), toluidine blue (TB) and brilliant cresyl blue (BCB), onto glassy carbon electrodes (GCE) with anodic pretreatment. The electrochemical reactions of adsorbed dyes are fairly reversible at low coverages. The CMEs are more stable in acid solutions than in alkaline ones, which is mainly due to decomposition of the dyes in the latter media. They exhibit an excellent catalytic ability for the oxidation of nicotinamide coenzymes (NADH and NADPH). The formation of a charge transfer complex between the coenzyme and the adsorbed mediator has been demonstrated using a rotating disk electrode. The charge transfer complex decomposition is a slow step in the overall electrode reaction process. Some kinetic parameters are estimated. Dependence of the electrocatalytic activity of the CMEs on the solution pH is discussed.
An amperometric study of the reactions of copper(I) and copper(II) oxides with barium peroxide in surfactant suspensions
Authors: Franklin T. C. , Nnodimele R. A. , Bui T.
Published: May 2005

A study was made of the amperometric titration of the reaction between barium peroxide and copper(I) and copper(II) oxides. It was shown that it was possible to titrate a solid with a solid in surfactant suspensions. The studies were made in aqueous and acetonitrile suspensions containing cationic surfactants. End points were obtained at molecular ratios of BaO2 to CuO of 1 : 1, 1 : 3, and 1 : 5; and molecular ratios of BaO2 to Cu2O of 1 : 1 and 2: 1. It was postulated that the reactions involving CuO were

The reactions involving Cu2O were postulated to be

.
Application of dual‐pulse staircase voltammetry for simultaneous determination of glucose and fructose
Authors: Fung Y.‐S. , Mo S.‐Y.
Published: May 2005

A new electroanalytical method, DPSV, employing dual pulses (0.7V and −0.8V) prior to anodic scan (using staircase voltammetry) is developed for simultaneous determination of glucose and fructose. The electrochemistry of both sugars was studied prior to optimizing the operational parameters. The linear ranges were found to be 0.01–2.0 mM for both sugars, precisions (mean = 0.10 mM and n = 8) 1.8% and 2.4% and detection limits (estimated by 3 times the standard deviation) 0.001 and 0.003 mM for glucose and fructose, respectively. To establish the reliability of the method, various food additives were tested and found to give no interference effect under normal concentrations. HPLC method was carried out in parallel with the method for analyzing food, drink and honey samples. No statistically significant difference in the results was obtained for methods.
Electrocatalytic oxidation of hydroquinone on a polypyrrole‐coated glassy carbon electrode
Authors: Vijayan M. , Krishnan V.
Published: May 2005

The electrochemical behavior of hydroquinone (H2Q) in 1 M H2SO4 on a polypyrrole‐coated glassy carbon electrode (PPy/GCE) has been studied using cyclic voltammetry. Hydroquinone undergoes oxidation at a lower anodic potential on a PPy/GCE compared to a bare GCE. Hydroquinone is oxidized catalytically on a PPy/GCE, and this has been found to be a diffusion‐controlled 2e− process. The effects of film formation potential, film thickness, and dopant anions on the catalytic behavior with respect to hydroquinone oxidation on a PPy/GCE are also discussed.
A study of riboflavin determination by square wave adsorptive stripping voltammetry on mercury film electrodes
Authors: Economou Anastasios , Fielden Peter R.
Published: May 2005

In this work riboflavin was determined by square wave adsorptive stripping voltammetry (SWASV): riboflavin was initially adsorbed on a mercury film electrode (MFE) at a potential of 0.0 V (vs. Ag/AgCl) and at pH 12; the subsequent reductive stripping step was carried out by applying a square wave potential‐time waveform on the electrode. Both a batch method (based on the rotating disk electrode configuration) and a flow approach [based on the wall‐jet flow‐through electrode and flow injection analysis (FIA)] were employed. Both instrumental and chemical parameters were investigated and optimized for analytical use of the technique. The limit of detection was 0.5 nmol L −1 (for 10 min of preconcentration), the precision was 8% for the batch system (at the 10 nmol L−1 level) and 6% for the flow system (at the 100 nmol L−1 level); the linear range depended on the preconcentration time and the mass transfer conditions during the accumulation step. Both methods were automated and applied to the determination of riboflavin in commercial pharmaceutical products with recovery values at over 90%.
Polarographic behavior and determination of oxamniquine in dosage forms
Authors: Belal F. , Aly F. A.
Published: May 2005

A highly sensitive method is described for the determination of oxamniquine in its pure form and in capsules. The proposed method depends upon the polarographic activity of oxamniquine in Britton–Robinson buffer, whereby a well‐defined cathodic wave, followed by a more negative ill‐defined one, was produced over the whole pH range. The first wave was characterized as being irreversible and diffusion‐controlled with limited absorption properties. The current–concentration relationship was found to be rectilinear over the ranges 1 × 10−5 to 5 × 10−4 and 1 × 10−6 to 5 × 10 −4 M in the direct current (DCT) and differential pulse polarography (DPP) modes, respectively, with a minimum detectability of 1 × 10−7 M. The number of electrons involved in the reduction process was established through coulometric measurement at an applied potential. The mechanism of the electrode reaction was verified and confirmed through chemical reactions of the electrolyzed solution. The proposed method was successfully applied to the determination of oxamniquine in capsules, and the results obtained were in accordance with those found using the United States Pharmacopeia (USP) XXII method.
Electrochemical behavior of 2‐ and 8‐quinolinethiol complexes with cobalt and nickel and their catalytic hydrogen evolution
Authors: Paneli Miropi G. , Voulgaropoulos Anastasios N.
Published: May 2005

2‐ and 8‐quinolinethiols catalyze hydrogen evolution at −1.500 V and −1.380 V vs. Ag/AgCl, respectively. The more positive potential for hydrogen evolution in the case of the latter is a result of its more acidic character. The addition of cobalt shifts the potential overvoltage for hydrogen evolution to more positive potentials in the presence of 2‐quinolinethiol, i.e., 1.400 V vs. Ag/AgCl; while in the presence of 8‐ quinolinethiol a significant increase in height of the hydrogen wave at −1.380V vs. Ag/AgCl is observed. In the former case, hydrogen evolution follows reduction of the CoII‐2‐quinolinethio1 complex, and for higher cobalt concentrations the wave splits into two Brdicka's peaks. In the latter case, reduction of the CoII‐2‐quinolinethiol complex takes place at the same potential as the hydrogen wave and, as a result, only one peak is observed; this peak can be used for the determination of cobalt with a detection limit of 0.50 nM and a relative standard deviation (RSD) of 3.8%.
Acetylcholinesterase‐based amperometric sensor
Authors: Stoytcheva Margarita
Published: May 2005

An amperometric sensor has been created using the hydrolysis of acetylthiocholine iodide, which is catalyzed by the acetylcholinesterase enzyme and generates an electroactive product. An electrochemically modified graphite electrode is used, with acetylcholinesterase covalently bonded directly to its surface. The characteristics of the sensor, such as the response time, repeatability, reproducibility, stability, dynamic range, activation energy, and temperature coefficient of the current are evaluated. The optimum working conditions (pH, temperature, and rotation speed) are established.
Complexation of lead with humic matter by stripping voltammetry. Prevention of adsorption on Nafion‐coated mercury film electrode
Authors: Capelo Sofia , Mota Ana M. , Gonçalves Maria L. S.
Published: May 2005

The complexation of humic matter with lead in natural water conditions was studied by differential pulse anodic stripping voltammetry (DPASV) using a mercury film of a Nafion‐coated mercury film as the working electrode. The results clearly show that the Nafion film greatly minimizes the adsorption of humics on the electrode. Besides adsorption, other effects on the voltammetic signal are discussed, such as the degree of lability, ligand heterogeneity, and the metal‐to‐ligand concentration ratio at the electrode surface.
Polarographic determination of diethyldithiocarbamate using kinetic and catalytic processes
Authors: Spataru Nicolae , Calusaru Aurelian
Published: May 2005

Diethyldithiocarbamate (Et2DTC) is not polarographically reducible, but in complex combination with cobalt two prewaves are formed in ammonia buffer. These prewaves are due to catalytic cobalt and hydrogen discharge and they are useful for analytical purposes in the determination of Et2DTC with high sensitivity (2 × 10−6−1 × 104 M). The effects of CoII, ammonium hydroxide, and ammonium chloride concentrations on the catalytic waves are described. A mechanism for the formation of the prewaves is proposed, in which adsorption plays a prominent part. Suitable conditions for analytical applications are described.
Determination of orthochlorophenol by stripping voltammetry
Authors: Manisankar P. , Prabu H. Gurumallesh
Published: May 2005

The present work reports on a differential pulse and square wave stripping voltammetric procedure for the determination of orthochlorophenol. The best conditions included using 0.1 M KOH solution, an accumulation potential of 0.4 V vs. Ag/AgCl electrode, a square wave amplitude of 60mV, a frequency of 50 Hz, a step potential of 4mV, and an initial scan potential of −1.0 V. Under these conditions, determination limits of ng/ml were achieved at a stationary glassy carbon electrode.
Fast voltammetric sensors for the measurement of soil water activity
Authors: Huang Huiliang , Dasgupta Purnendu K.
Published: May 2005

Small inexpensive soil water sensors and the necessary electronics package for fast voltammetry (l04 V/s scan rate) are described. The sensor consists of a blunt ended hypodermic needle cathode containing a concentric PTFE insulating tube and therein, a Pt‐wire anode. The sensing film is formed by dip‐coating a 1:7 blend of a perfluorosulfonate and a polyestersulfonate polymer at the tip of the needle. Atop this sensing film is a composite protective film of cellulose acetate and nylon that inhibits the passage of ionic or low MW constituents and allows the transport of water. The sensor is sheathed in a PTFE tube that protrudes beyond the sensor tip and the protrusion gap is filled with a paste of talc and BaSO4 which serves as a water conduit between the soil and the sensor proper. The sensor is capable of making reliable moisture measurements between the wilting point and the field capacity of the soil sample; the response behavior consists of the combination of two nearly linear segments, the sensor output increasing steeply between the wilting point and ca. 60% of the field capacity and then much more gradually to the field capacity. The sensors have been field tested. No effect on sensor performance is observed even after burial under soil for several months.
Detection of surface activity by voltammetric measurements
Authors: Komorsky‐Lovrić Šebojka , Lovrić Milivoj , Branica Marko
Published: May 2005

Influences of a nonionic detergent Triton X‐100 on square‐wave voltammetry and anodic stripping square‐wave voltammetry of Cd2+ in 0.5 M NaClO4 + 0.01 M HClO4 are measured at precisely controlled durations of adsorptive accumulation and surfactant concentrations. Diagnostic criteria for the presence of surface‐active substances in electrolytes are reported. A voltammetric method for the quantitative analysis of detergents is proposed. An ionic type of detergent can be recognized by the variation of the accumulation potential.
Electrochemical behavior of metallothioneins and related molecules. Part II: Lys–Cys–Thr–Cys–Cys–Ala thionein fragment [56–61] MT I in the presence of cadmium and/or zinc
Authors: Muñoz Amalia , Rodriguez Adela Rosa
Published: May 2005

An electrochemical study, using differential pulse polarography (DPP), of a peptide Lys–Cys–Thr–Cys–Cys–Ala Thionein Fragment [56–61] MT I (FT) was performed in order to compare the behavior of metallothioneins and that of this less complex molecule, intrinsic to the metallothionein structure. The influence of different parameters, such as the solution pH and the concentration of metal elements, cadmium and zinc was investigated. Two different electrochemical systems were distinguished: in the first one, the mercury electrode itself is involved in the charge transfer steps; in this case, peaks are attributed to the oxidation of the mercury electrode in the presence of the peptide acting as a chelating agent. The second electrochemical system corresponds to the reduction of metal cations, cadmium and zinc, at a dropping mercury electrode either as free ions or complexed by the peptide. The apparent stability constants for complexes of FT with cadmium, zinc and mercury were estimated. The order of affinity is: K′HgFT ≫ K′CdFT > K′ZnFT. The DPP response can be used for elucidation of the chemical forms of compounds (speciation).
A tubular graphite‐epoxy electrode incorporating horseradish peroxidase as a potentiometric sensor for hydrogen peroxide
Authors: Zulfikar  , Hibbert D. Brynn , Alexander Peter W.
Published: May 2005

A novel potentiometric peroxidase enzyme sensor based on a tubular graphite‐epoxy design is reported for the determination of hydrogen peroxide in an FIA system. The sensor was formed from horseradish peroxidase (40 mg), graphite (240 mg) and epoxy (780 mg). Hydrogen peroxide, injected into pH 7,0.05 M phosphate buffer at 26°C, was determined with a linear slope of 45.6 mV/decade in the concentration range 7.5 × 10−7 to 5.0 × 10−5 M. Acceptable reproducibility of 1.2% relative standard deviation was obtained in the flow injection analysis. The advantages of this sensor are low cost, simple electronic circuit design and better selectivity than amperometric sensors and a detection limit comparable with other methods.
Needle‐type glucose biosensor with an electrochemically codeposited enzyme in a platinum black matrix
Authors: Abdel‐Humid Ihab , Atanasov Plamen , Wilkins Ebtisam
Published: May 2005

In this study we report the development of a needle‐type glucose biosensor for the management of hemorrhagic shock. The immobilization technique depends on the electrophoretic deposition of the glucose oxidase enzyme in an electrochemically grown platinum black matrix. The sensor was coated with Nafion to decrease the effect of interferents. Preliminary tests were carried out to evaluate the sensor performance in vitro. These tests included the measurement of glucose levels in buffer solutions containing various potential physiological interferents, as well as in bovine serum. The preliminary results show the sensor to have inearity up to 33 mM and a diminished response to interferents. The advantages of this technique are its simplicity and high controllability.
Potentiometric potassium selectivity of polymer membrane electrodes prepared with organo‐phosphine ligands
Authors: Saleh M. B. , Taha F. , Aof G. S.
Published: May 2005

Potassium ion‐selective electrodes based on a new type of phosphine oxide compounds were prepared. The electrode based on tert‐butyl‐3‐p‐tolyl phosphine oxide cyclohexene gave a linear response with a Nernstian slope of 60 mV per decade within the concentration range 10−1–10−5 M KCl. The electrode exhibited good selectivity for potassium with respect to alkali, alkaline earth and other metal ions. The content of potassium ion in some plant and soil samples was determined using the prepared electrode and flame photometry. The electrode gave results very similar to those of flame photometry. Routine use of ion‐selective potentiometry for potassium determination can thus be recommended for plant and soil analysis.
Simultaneous voltammetric determination of antimony, copper, lead, and tin in steel using a hydrochloric acid–isopropanolic medium
Authors: Hofbauerová Helena , Labuda Ján , Fišera Miroslav , Vaníčková Mária
Published: May 2005

The problem of overlapping peaks of antimony and copper, as well as lead and tin, was solved by performing differential pulse anodic stripping voltammetry and differential pulse voltammetry in a 1.8 M HCl–80% isopropanol supporting electrolyte media. Arsenic (III) does not interfere in the alcoholic medium and it can be determined by differential pulse voltammetry in acidic aqueous solution. The procedure has been applied to the determination of trace metals in alloy steel.
Ferrocene‐containing polymers as electron transfer mediators in carbon paste electrodes modified with PQQ‐dependent aldose dehydrogenase
Authors: Smolander Maria , Gorton Lo , Lee Hung Sui , Skotheim Terje , Lan Hsing‐Lin
Published: May 2005

The aim of this work was to improve an aldose‐detecting biosensor based on quinoprotein aldose dehydrogenase (ALDH). Polymer‐bound ferrocene derivatives with four different structures were studied as electron transfer mediators between the coenzyme of ALDH, pyrroloquinoline qninone (PQQ), and the conducting electrode material. The ferrocene polymers were mixed into carbon paste, which was used for the preparation of aldose‐detecting electrodes by immobilizing ALDH on the carbon paste surface by adsorption. The current responses of the ferrocene polymer modified electrodes were studied and the effect of the polymer structure on the response was examined. The electrodes modified with all four polymers showed maximum response at the working potential around 300 mV (vs. Ag/AgCl). The operational stability of the ferrocene polymer modified electrodes was better than that of corresponding dimethylferrocene modified electrodes. The ferrocene polymer modified electrodes seemed to be suitable for the measurement of real samples.
A model of non‐nernstian response in the determination of aluminum ions by indirect potentiometry
Authors: Ngila J. Catherine , Alexander Peter W. , Hibbert D. Brynn
Published: May 2005

Flow analysis data of the response of an aluminum wire electrode to fluoride into which Al3+ is added is modeled assuming a logarithmic response of the electrode to F− and reaction of F− with aluminum ions to give a series of complexes [AlFq](3−q)+ when q = 1,2,3,4,5,6. The solutions were maintained at pH 5.0 with acetic acid/acetate buffer. Other species modeled were the hydroxo complexes of aluminum [Alm(OH)n](3m−n)+ when m = 1, n = 1,2,3,4; m = 2, n = 2; m = 3, n = 4; m = 13, n = 32, and the acetate complex [Al2(OH)2OAc]3+. Protonation of F− to HF and HF was also considered. Three coefficients were required to fit the data, a constant and slope of the response of the electrode to free fluoride and a dispersion factor in the flow analysis. Published stability constants were used and no account was taken of ionic strength. The model may be used to predict optimum analysis conditions given an approximate aluminum concentration.
Stripping voltammetry at microdisk composite electrode assembly
Authors: Wang Joseph , Armalis Saulius
Published: May 2005

The attractive stripping voltammetric performance of the recently developed RAM electrode, consisting of 3.5‐μm radius carbon microdisks embedded in epoxy resin, is described. The microdisk dimensions and interdisk spacings of the RAM surface lead to nonlinear diffusional flux and offer efficient metal deposition from quiescent samples. Coupled with large “collective” stripping currents, a wide potential window and a low background current, the new electrode yields low detection limit (e.g., 0.3 μg/L lead and cadmium for 2‐min deposition) and good precision (2.1–2.3% RSD, n = 15). Assays of drinking water are used for illustration.
Investigations on adsorption potentiometry. Part X: Derivative adsorption chronopotentiometry of chromium(III)
Authors: Jin Wenrui , Jia Xianglan , Lu Jianmin
Published: May 2005

The study concerns a very sensitive electroanalytical method, based on derivative chronopotentiometry of the chromium(III) complex with 2‐(5′‐bromo‐2′‐pyridylazo)‐5‐diethyl aminophenol (5‐Br‐PADAP) accumulated adsorptively on the surface of a hanging mercury drop electrode. The detection limit is 6 × 10−11 mol/L for a preconcentration time of 6 min. The mechanism of the electrode reaction has been investigated in detail.
Solid state electrochemical characterization of tungsten oxides and related heteropoly‐12‐tungstic acid single crystals
Authors: Karwowska Beata , Kulesza Pawel J.
Published: May 2005

Tungsten oxide, dihydrate (WO3 · 2H2O) and monohydrate (WO3 · H2O) pastes, as well as silico‐12‐tungstic acid single crystals (H4SiW12O40 · 31H2O) have been subjected to electrochemical investigations in solid‐state, i.e., in the absence of deliberately added external liquid electrolyte phase. Mobile protons, which exist in WO3 · H2O and H4SiW12O40 · 31H2O (but not in WO3 · H2O) bulk materials, are capable to support electron transport between WVI, V mixed‐valence sites (generated in the systems upon partial reduction). Silicotungstic acid can be reduced reversibly to heteropolyblue (HzSiW12O, where z is 1, 2 or 4), which is analogous to hydrogen tungsten oxide bronze (HxWO3, 0 < x < 0.35), i.e., blue nonstoichiometric WVI, V oxide. The values of z = 4 and x ≈ 0.35 are approximately equivalent because each silicotungstate structure consists of twelve WO3 surrounding the SiO4 group. There are similarities in the voltammetric behaviors of WO3 · 2H2O and H4SiW12O40 · 31H2O. Quantitative characterization of H4SiW12O40 · 31H2O has been achieved with the use of a carbon fiber ultramicrodisk electrode. Upon injection of four electrons per silicotungstate unit, the maximum concentration (6–7 M) of WVI, V redox sites is generated within the diffusional flux in the crystal. An effective diffusion coefficient for charge propagation is high (3–4 × 10−7 cm2 s−1), Injection of more electrons (z > 4) leads to irreversible redox transitions in the system. Silico‐12‐tungstic acid single crystal can be considered as a bulk, molecular, model for redox reactions in catalytic tungsten oxides.
Total anodic voltammetric waves of undiluted dimethylsulfoxide at Pt microelectrodes
Authors: Koncka Marta , Stojek Zbigniew
Published: May 2005

At least two total anodic voltammetric waves of DMSO, or voltammetric waves of undiluted DMSO, can be obtained at platinum microelectrodes. These waves are of roughly equal height. Linear scan‐ and reverse pulse voltammograms indicate that the first wave is a one‐electron wave. After the addition of water the formation of dimethylsulfone is possible and therefore a part of DMSO equivalent to water concentration is oxidized via the two‐electron process. This results in an increase of the wave height and can be used for analytical purposes. To determine water content, by using this increase, its concentration in DMSO should be higher than 0.1 mol/L.
Application of DPASV to the study of heavy metal complexation in colloidal latex dispersions
Authors: Díaz‐Cruz José M. , Wonders Jeannette H. A. M. , van Leeuwen Herman P.
Published: May 2005

Differential pulse anodic stripping voltammetry (DPASV) was applied to the study of the binding of ZnII, CdII and PbII by two kinds of polystyrene latex particles at different pH values and at different electrolyte concentrations. For the calculation of stability constants, the criterion of consistency between current and potential data was applied. For CdII and PbII, the application of DPASV yields qualitatively good results (in agreement with those previously found by DPP). However, from a quantitative point of view, the consistency criterion often reduces the applicability of the technique to quite narrow pH ranges, which increases the error in some calculations. In the case of ZnII, certain anomalies were found, rendering quantitative considerations impossible.
A new conducting polymer glucose sensor based on polythianaphthene
Authors: Compagnone Dario , Federici Giorgio , Bannister Joe V.
Published: May 2005

A glucose biosensor has been developed by entrapment of glucose oxidase in a polythianaphthene film formed onto a platinum surface. Glucose has been measured by H2O2 detection at +400 mV (vs. SCE). Electrochemical kinetic constants for the enzyme electrode have been calculated and indicated that in the unsaturated region the rate limiting step is the diffusion of the substrate through the polymer. The biosensor exhibited a linear response in the range 0.05–7.4 mmol/L with a response time of 30–60s and a relative standard deviation of 5.4%. The presence of the film onto the electrode prevents the oxidation of interfering agents such as ascorbic and uric acid. The use of additional polycarbonate membranes onto the electrode surface extended the linearity of the response allowing the probe to be used in blood glucose analysis, The amount of glucose in two control sera was measured using the biosensor. Results correlated well with the glucose nominal values.
The voltammetry of neuropeptides containing L‐tyrosine
Authors: Reynolds Norman C. , Kissela Brett M. , Fleming Lynda H.
Published: May 2005

Neuropeptides containing an N‐terminal tyrosine are irreversibly oxidized on glassy carbon electrodes using scan rates from 0.020 to 0.500 V/s. Despite variations in peptide length and amino acid composition from tyrosine to α‐neoendorphin 1–10, peak potentials occurred in a relatively narrow range from +0.925 V to +0.971 V (vs. Ag/AgCl). An inverse linear relationship of Ep vs. pH with a slope near −59 mV/pH unit suggests that the oxidation involves a one electron oxidation and a single proton transfer similar to the oxidation of simple para‐substituted phenols. Linear slopes between 0.790 and 0.933 of log Ip vs. log v suggest that surface processes contribute to the voltammetry on glassy carbon.