bluuebunny/crossref_metadata_2025 huggingface dataset:
Reverse pulse voltammetry with waiting period at conventional disk electrodes: Theory
Authors: Stojek Zbigniew , Jaworski Aleksander
Published: May 2005

Regeneration of the initial concentrations at a solid, stationary disk electrode after each reverse pulse in the reverse pulse voltammetry simplifies interpretation of the experimental data but requires modification of the waveform. The modification examined in this work involved inserting a waiting period after each reverse pulse at the potential where the initial concentrations could be reproduced. For conventional disk sizes and a wide range of τ, which is the sum of generating time and pulse time, the minimum length of the waiting time was found theoretically to be 12τ.
The anodic dissolution of dental amalgams studied with abrasive stripping voltammetry
Authors: Scholz Fritz , Rabi Fazil , Müller Wolf‐Dieter
Published: May 2005

The recently described technique abrasive stripping voltammetry was used to study the corrosion behavior of five commercial dental amalgams. Abrasive stripping voltammetry of these amalgams reveals details of the anodic dissolution of the alloys that are not accessible by other methods. Systematic studies of SnHg alloys, SnAg alloys, and dental amalgams lead to a method that allows the identification of the γ2‐phase in dental amalgams. It can be shown that the non‐γ2 amalgams have a higher stability than γ2‐containing amalgams only in solutions of very low complexation ability. In cases of more aggressive solutions such as lemon juice, non‐γ2 and conventional amalgams exhibit identical behavior during the anodic oxidation.
LCEC of underivatized polypeptides and proteins at copper electrodes
Authors: Luo Peifang , Baldwin Richard P.
Published: May 2005

Constant potential amperometric detection of underivatized polypeptides and proteins can be carried out at metallic copper electrodes. When coupled with liquid chromatography, this approach provides a sensitive and selective method of analysis for these compounds. Two different detection mechanisms can be employed: a neutral pH, low potential oxidation process attributed to enhanced dissolution of the electrode by peptide species capable of forming soluble Cu(II) complexes and a high pH, high potential electrocatalytic oxidation of the analytes. Of the two approaches, the latter process was found to be more attractive for LCEC applications as it was useful for a wider range of peptides and proteins and gave substantially larger currents and lower detection limits. The compounds exhibiting useful electrocatalytic response at the copper electrode ranged from oligopeptides such as enkephalins and bradykinin to very large proteins such as glucose oxidase (F.W. 160,000) and catalase (F.W. 240,000). The response was not dependent on the presence of tyrosine, tryptophan, or cysteine amino acid units and was shown to be compatible with both ion‐exchange and reverse‐phase separation schemes.
Convection independent detection with voltammetric single microdisk electrodes
Authors: Matysik Frank‐Michael , Emons Hendrik
Published: May 2005

A new cell construction for voltammetric investigations at microdisk electrodes in flowing solutions is described. A platinum microdisk electrode can be arranged inside a small tube facing the flowing solution. Systematic investigations were carried out with electrodes ranging from 0.7 μM to 114 μm in diameter. It is demonstrated that the voltammetric response for continuous flow detection, as well as for flow injection measurements, does not depend on convection if the disk diameter of the electrode is equal to 0.7 μm. In addition, detection limits for the determination of ferrocene in continuously flowing acetonitrile solutions and under flow injection conditions were determined at electrodes with various diameters.
Renewable alcohol biosensors based on alcohol‐dehydrogenase/nicotinamide‐adenine‐dinucleotide graphite epoxy electrodes
Authors: Wang Joseph , Gonzalez‐Romero Elisa , Ozsoz Mehmet
Published: May 2005

Alcohol dehydrogenase (ADH) and nicotinamide adenine dinucleotide (NAD+) have been incorporated within rigid graphite epoxy matrices to yield renewable (by polishing) alcohol sensors. The enzyme and cofactor retain their bioactivity on confinement in the graphite epoxy, with the oxidation current of the NADH formed serving as the response. Because of the intimate contact between the biocatalytic and sensing sites, the reagentless sensor produces steady‐state signals within 15–30s. The influence of various experimental variables is explored for optimum analytical performance. Common polishing procedures are used to regenerate fresh bioactive surfaces.
Simultaneous flow injection analysis of L‐lactate and L‐malate in wine based on the use of enzyme reactors
Authors: Yoshioka Shuichi , Ukeda Hiroyuki , Matsumoto Kiyoshi , Osajima Yutaka
Published: May 2005

The simultaneous determination of L‐malate and L‐lactate, by enzyme‐supported flow injection analysis (FIA), was developed using two enzyme reactors in parallel and a single oxygen electrode. NADH formed in the reaction of malate dehydrogenase (MDH) was regenerated to NAD+ with dissolved oxygen, using vitamin K3 and diaphorase (DI). L‐Lactate was determined using the enzyme lactate oxidase (LOD). When sample solutions were simultaneously injected into the two reactors (the MDH‐DI‐reactor and the LOD‐reactor) with a controlied residence time, a “train” of two peaks corresponding to L‐lactate and L‐malate were seen in the FIA‐gram. The peak currents were linearly related to the L‐malate and L‐lactate concentration in the range 0.05–1.2 mM and 0.01–0.5 mM, respectively. The present system was applied to the determination of L‐lactate and L‐malate in wine. The results showed good agreement with those obtained using a conventional method (F‐kit method), suggesting that this system may be applicable to the monitoring of malo‐lactic fermentation during wine production.
The use of the reference element method for stripping voltammetric analysis of natural waters
Authors: Brainina Khiena Z. , Vilchinskaya Elena A. , Khanina Rosa M. , Kalnishevskaya Lyubov N.
Published: May 2005

An internal standard method is proposed in the stripping analysis of natural waters. The method consists of the introduction into the sample solution of a reference element and subsequent calculation of the concentration of several elements by the increase in the analytical signal from the reference element. Criteria of the reference element selection are given. Calculated proportionality factors k obtained with the use of solutions simulating sea and river waters under the same experimental conditions can be applied to the determination of copper(II), lead(II), and cadmium(II) in natural waters. The use of the internal standard method allows one to substantially shorten the time of analysis (3–5 minutes instead of 30–50 minutes) and to improve accuracy and reproducibility of the analytical data.
Bombyx mori silk fibroin‐based immobilization method for preparation of urea electrode
Authors: Fang Yao , Shao Zhengzhong , Deng Jiaqi , Yu Tongyin
Published: May 2005

A novel method for enzyme immobilization was developed. This system represents the first successful use of silk fibroin (obtained directly from Living Bombyx mori) as immobilization materials for the construction of an urea electrode. It is based on the structural transition of the silk fibroin membrane from α‐helix and random coil to antiparallel β‐sheet. Operational conditions and response characteristics of the resulting urea electrode were investigated, including immersion time, pH, buffer, response time, calibration curve, recovery, thermal stability, and lifetime.
Voltammetric study of cadmium complexation in halogenide mixtures of high ionic strength
Authors: Zelić Marina , Branica Marko
Published: May 2005

Cadmium complexation in chloride‐bromide and chloride‐iodide mixtures of a high ionic strength (I = 4 mol/L) was studied by polarographic/voltammetric methods. In the first case, statistically expected formation constants of mixed‐ligand complexes were confirmed. The presence of iodide ions, however, makes interpretation of the experimental data more difficult because the electrode process becomes complex. In addition to CdI2, which is a well‐known surface‐active species, CdClaI2a− seems to be adsorbed at the mercury surface.
Fast pulsed amperometric detection at noble metal electrodes: A study of oxide formation and dissolution kinetics at gold in 0.1 M NaOH
Authors: Roberts Richard , Johnson Dennis C.
Published: May 2005

The anodic charge (qa) for oxide formation, obtained by potential‐step chronocoulometry at a Au minidisk electrode, is nearly a linear function of log (t/ms) for t = ca. 3–30 ms with a slope proportional to the applied overpotential for oxide formation. It was demonstrated that, contrary to popular opinion based on voltammetric observation at slow scan rates (ϕ), the anodic current for oxide formation obtained using a linear potential‐scan waveform is not a linear function of ϕ at large values of ϕ. It was also demonstrated that a reverse potential‐step waveform can be used to interrupt the rapid oxide growth and, perhaps, inhibit the conversion of the hydrous oxide (AuOH) to the inert oxide (AuO). This result has probable significance for decreasing the background current during anodic pulsed amperometric detection of amines and sulfur compounds whose oxidation mechanisms are believed catalyzed by AuOH but not by AuO. The cathodic charge (qc) for oxide dissolution is approximately a linear function of t with a slope that is proportional to the applied potential.
Stripping measurements of hydrogen peroxide based on biocatalytic accumulation at mediatorless peroxidase/carbon paste electrodes
Authors: Wang Joseph , Ciszewski Aleksander , Naser Najih
Published: May 2005

Biocatalytic accumulation, followed by chronoamperometric detection, is shown to greatly enhance the sensitivity of mediatorless biosensing of hydrogen peroxide at horseradish peroxidase (HRP)/carbon paste bioelectrodes. The mixed carbon paste, with its close proximity between the biocatalytic and graphite sensing sites, promotes the mediatorless accumulation of the oxidized form of HRP. Hence, a 28‐fold enhancement of the response for 10 μM hydrogen peroxide is obtained following 3‐minute preconcentration. The relative standard deviation (surface‐to‐surface) at the 10 μM level is 3.3%. The effect of experimental variables, such as the preconcentration time, measuring potential, or paste composition, are explored. Analogous observations are reported for tissue (horseradish root)‐based carbon pastes, for mediated HRP detection, and for monitoring of organic peroxides. Future prospects of the bioamplification approach are discussed.
Polarographic and electrochemical studies of some aromatic and heterocyclic nitro compounds, part I: General mechanistic aspects
Authors: Zuman Petr , Fijalek Zbigniew , Dumanovic Dragica , Sužnjević Desanka
Published: May 2005

Comparing reduction potentials of aromatic nitro compounds with those of corresponding nitroso compounds, by studying shifts of half‐wave and peak potentials with pH and by following the decrease of limiting current in buffered 35% DMF‐water mixtures, the sequence of protons and electrons in the four‐electron reduction step was proved to be: H+, e, H+, e, 2e, 2H+. Arylhydroxylamines formed in the four‐electron reduction of nitro compounds can be protonated and further reduced, they can undergo dehydration (provided that the dehydration product is stable), they can undergo chemical reactions with intermediates of the reduction of the nitro group, like ArNO\documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\mathop 2\limits^.} $\end{document}, they can be electrooxidized to nitrosobenzenes (which can undergo chemical reactions) or they can react with carbonyl groups when present. Stabilization of the dehydrated form can occur in quinonemethide (nifedipine) or in some quinone‐like heterocyclic derivatives. Side reactions of ArNHOH and ArNO are demonstrated by smaller peaks in CV and by controlled potential electrolysis. Reactions of ArNHOH with carbonyl groups were observed by formation of new waves of nitrones in the reduction of nitrobenzenaldehydes.
Polarographic and electrochemical studies of some aromatic and heterocyclic nitro compounds, part III: Electroreduction of mono‐ and dinitropyrazoles and ‐imidazoles
Authors: Dumanović D. , Jovanović J. , Sužnjević D. , Erceg M. , Zuman P.
Published: May 2005

The reduction of mono‐ and dinitropyrazoles and of nitroimidazoles follows the general pattern of reduction of aromatic nitro compounds: The nitro group is reduced in a four‐electron step to a hydroxylamino group and the protonated form of the hydroxylamino group is—in the lower pH range—further reduced to an amine. This reduction differs from that of nitrobenzenes in participation of a second hydrogen ion probably involved in protonation of the heterocyclic ring. This second proton is for nitroimidazoles transferred before the uptake of the first electron, for nitropyrazoles probably after this uptake. The transfer of the second electron is indicated to be the potential determining step. The two sequences are H+, H+, e, H+, e, 2e, H+ and H+, e, H+, H+, e, 2e, H+, respectively. For nitropyrazoles and nitroimidazoles without an alkyl substituent on the ring nitrogen, the reduction process is further complicated by the dissociation of the NH‐group in the heterocyclic ring. For 1‐alkyl‐5‐nitroimidazoles, for 4(5)‐nitroimidazole and for N‐unsubstituted‐4‐ and 3(5)‐ nitropyrazoles (but not for 2‐nitroimidazoles, 1‐alkyl‐4‐nitroimidazoles and 1‐alkylnitropyrazoles) the hydroxylamino derivative formed in the first four‐electron step undergoes a base catalyzed dehydration yielding a quinone‐like ketimine. Easy reduction of this species results in alkaline solutions in a limiting current which is significantly higher than corresponds to a four‐electron and limits to a six‐electron reduction. Such dehydration reactions occur considerably faster for dihydroxylamino derivatives formed in the reduction of dinitropyrazoles resulting in two waves with total transfer of up to 12 electrons.
Polarographic and electrochemical studies of some aromatic and heterocyclic nitro compounds, part IV: Polarographic reduction of 2‐alkylnitroimidazoles and aminonitroimidazoles
Authors: Dumanović D. , Jovanović J. , Sužnjević D. , Erceg M. , Zuman P.
Published: May 2005

1, 2‐Dialkyl‐4‐nitroimidazoles are reduced between pH 0 and 13 in a four‐electron wave. The resulting arylhydroxylamine is stable and in acidic media reduced further to the amine. 1,2‐Dialkyl‐5‐nitroimidazoles and 2‐alkyl‐4(5)‐nitroimidazoles are reduced in alkaline media with the number of electrons approaching six. The hydroxylamine derivative formed in these reductions can be dehydrated and yields an easily reducible, quinone‐like ketimine. The rate of the dehydration governs the heights of the first step and is base catalyzed. The sequence of electron and proton transfers for 2‐ alkylsubstituted nitroimidazoles is the same as that observed for corresponding desalkyl compounds.

1‐Alkyl‐4‐amino‐5‐nitroimidazoles, as well as 1‐alkyl‐4‐nitro‐5‐aminoimidazoles, are reduced in a single wave, the height of which approaches that of a six‐electron process. The dehydration of the hydroxylamino derivative is favored, probably due to an internal base catalysis. The shifts of half‐wave potentials with pH differ principally from those of all other nitroimidazoles and indicate the predominant role of the amino group in the proton transfer.
Theory of derivative and differential potentiometric stripping analysis and stripping chronopotentiometry
Authors: Garai Tibor , Nagy Zoltán , Mészáros Lajos , Bartalits Liliana , Locatelli Clinio , Fagioli Francesco
Published: May 2005

The theoretical treatment of derivative potentiometric stripping analysis and differential potentiometric stripping analysis is presented. The latter term refers to the technique employing the derivative of time with respect to potential vs. the potential function as the measured signal. The mathematical expressions obtained were also verified experimentally.
Design and electrochemical evaluation of an optically transparent thin‐layer electrode flow cell
Authors: Brett Ana Maria C. F. Oliveira
Published: May 2005

A new thin‐layer spectroelectrochemical cell with an optically transparent thin‐layer electrode (OTTLE) has been designed and characterized using ferro/ferricyanide in aqueous solution with potassium chloride supporting electrolyte as a model system. The optical configuration is directed perpendicularly through the OTTLE and solution. The cell is equipped with two semi‐transparent tin dioxide coated glass windows at a distance of 50–150 μm; that is, smaller than the semi‐infinite electrochemical diffusion layer thickness, and can be used either in a stationary mode or in a continuous‐flow system. Design is such that platinum wire or tin dioxide can be used as working electrode, the reference being Ag/AgCl. The formal potential obtained for the ferro/ferricyanide system is in good agreement with that expected; the difference between the anodic and cathodic peak potentials in cyclic voltammograms is less than 10 mV which suggests a good cell design. It is intended to apply the cell to in situ spectrophotometric monitoring of UV/vis/near‐IR absorbance changes due to electrode reactions of biologically electroactive compounds. The complementary information from the two techniques should be valuable in elucidation of reaction rates and mechanism.
Rotating ring‐disk electrode studies of polypyrrole‐glucose oxidase biosensors
Authors: Bélanger Daniel , Nadreau Jocelyn , Fortier Guy
Published: May 2005

A rotating ring‐disk electrode, (RRDE) of which the platinum disk was coated with a polypyrrole‐glucose oxidase (PPy‐GOD) film by electrochemical polymerization and the ring was left bare, has been used to characterize the PPy‐GOD electrode. Polypyrrole‐GOD films of various thicknesses grown in the presence of 100 and 500 U/ml of GOD in the deposition solution were used. The amperometric current generated at 0.7 V versus saturated calomel electrode (SCE) by the electrochemical oxidation of hydrogen peroxide, generated by the enzymatic reaction, has been evaluated at both the coated disk and uncoated ring at various rotation speeds. The collection efficiency of the RRDE was 22% and was used to evaluate the total current of the PPy‐GOD electrode. The total current of a polypyrrole electrode was defined as the sum of the disk current and the total ring current taken as the observed ring current divided by the collection efficiency of the RRDE. From this study, it clearly appears that the biotransformation of glucose takes place mainly at the polypyrrole film/solution interface independently of the rotation speed and that the catalysis is not limited by oxygen. The Eadie‐Hofstee type plots obtained for disk current with 10–225 mM of glucose show a strong positive deviation for glucose concentrations higher than 100 mM. On the other hand, linear plots are obtained when the total current of the enzyme electrode is considered. No definitive explanation can be given for these behaviors, except that at a higher glucose concentration, the flux of glucose is high enough to permit the diffusion of glucose deeper in the film, where it can be oxidized by the enzyme. Thus, the catalytic reaction is taking place in a thicker layer of the film.
Exploitation of the nitrite catalytic effect to enhance the sensitivity and selectivity of the adsorptive stripping voltammetric method for the determination of cobalt with dimethylglyoxime
Authors: Bobrowski Andrzej , Bond Alan M.
Published: May 2005

A highly sensitive, catalytic adsorptive stripping voltammetric (AV) method for the determination of ultratrace cobalt concentrations in the supporting electrolyte consisting of ammonia buffer, dimethylglyoxime (DMG), and NaNO2 has been evaluated and compared with the well‐known AV method with DMG and other dioximes. Conditions for maximal sensitivity and the simultaneous determination of Co and Ni are described. The sensitivity of the cobalt‐DMG complex method is improved about 20‐fold by exploitation of the catalytic effect observed in the presence of nitrite. The detection limit of the method is 4 × 10−11 M. As a result of the selective nature of the catalytic response for cobalt, the method is more sensitive and selective against Ni and Zn than the commonly used classical DMG method (without nitrite). The method, which uses inexpensive and widely available reagents (DMG, NaNO2), is suitable for the determination of Co in the 10−10 M–10−9 M concentration range even when the Ni concentration is 10 to 50 times higher, as is the case in many practical situations. The method is also advantageous when the background current from sources other than Ni makes the use of the less sensitive method with DMG impossible. However, the selectivity of the method over the Ni and Zn responses is inferior than obtained with previously published but more expensive catalytic methods based on nioxime‐NaNO2 or α‐benzil dioxime‐NaNO2 systems.
Adsorptive stripping voltammetric measurements of trace niobium levels following chelation with cupferron
Authors: Wang Joseph , Lu Jianmin , Taha Ziad
Published: May 2005

Trace levels of niobium can be determined by adsorptive stripping voltammetry, with controlled interfacial accumulation of the niobium/cupferron complex onto the hanging mercury drop electrode. Optimal conditions (5 times; 10−6 M cupferron in acetate buffer (pH 4.0), a preconcentration potential of −0.2 V, and differential pulse stripping) allow convenient quantitation of μg/L (ppb) concentrations. The detection limit is 83 ppt (10 minute preconcentration); the response is linear over the 0–20 ppb range: and the relative standard deviation (at the 5 ppb level) is 2.0%. Most cations do not interfere in the determination of niobium. Complexation with cupferron also allows analogous trace measurements of vanadium.
Electrochemical detection of carbohydrates at nickel‐copper and nickel‐chromium‐iron alloy electrodes
Authors: Marioli Juan M. , Kuwana Theodore
Published: May 2005

Nickel‐copper and nickel‐chromium‐iron alloy electrodes are employed in the amperometric detection of carbohydrates after anion‐exchange liquid chromatographic separation. The sugars are oxidized at the Ni(III) oxyhydroxide sites formed on the electrode surface at potentials of approximately 0.45 V (versus Ag/AgCl reference electrode). The set potential for the electrochemical detection of carbohydrates is optimized on a signal‐to‐noise (S/N) ratio analysis at different potential values. The detection limits for glucose, based on an S/N ratio of 3, are 15 and 1 picomoles at the nickel‐copper and the nickel‐chromium‐iron alloy electrodes, respectively. The electrodes' response was also assessed with respect to the detection of sugar alcohols, mono‐, and disaccharides.
Square‐wave voltammetry at spherical and disk microelectrodes as a function of electrode radius and frequency
Authors: Komorsky‐Lovrić Š. , Lovrić M. , Bond A. M.
Published: May 2005

Square‐wave voltammograms obtained with small spherical electrodes and influenced by electrode kinetics have been analyzed theoretically as a function of electrode radius and frequency for a reduction reaction involving a soluble reactant and product. If the redox reaction is reversible, or totally irreversible, dimensionless peak currents depend linearly on the parameter y = (D0/ƒ)1/2/r, where r is the electrode radius, D0 the diffusion coefficient of the oxidized species, and ƒ the square‐wave frequency. The variation of electrode size or frequency enables the determination of the charge transfer coefficient α or the kinetic parameter ks/D1/2 of an irreversible reaction (ks = standard heterogeneous charge transfer rate constant) if its reversible peak potential is known. Differences between square‐wave voltammograms at spherical and inlaid disk microelectrodes are considered theoretically and shown to be small under most conditions. As expected, in the limiting case where steady‐state mass transfer conditions prevail at microelectrodes, both the square‐wave current and peak potential become independent of the frequency. Steady‐state voltammetry, which is readily achieved at a slow d.c. scan rate of potential, may be more suitable than square‐wave voltammetry for kinetic measurements at microelectrodes, although the latter is likely to be the more sensitive technique in the analytical sense. This is in contrast to conventionally sized electrodes where the square‐wave method is likely to be superior in all contexts. Criteria of reversibility are proposed and confirmed by square‐wave voltammetric measurements on the reversible oxidation of ferrocene and quasi‐reversible reduction of ferricyanide at an inlaid gold microdisk electrode.
Polarographic and electrochemical studies of some aromatic and heterocyclic nitro compounds: Part VI. Polarographic, voltammetric, and controlled potential reduction of ortho‐nitrobenzaldehyde anthranil
Authors: Fijalek Zbigniew , Zuman P.
Published: May 2005

In acidic media, at pH < 7, the nitro group, in ortho‐nitrobenzaldehyde (I) is reduced in a four‐electron step to ortho‐formylphenylhydroxylamine (II). The protonated form of II is reduced by two electrons to ortho‐aminobenzaldehyde (IV), which is further reduced in a two‐electron process to ortho‐aminobenzylalcohol. At pH > 7, the arylhydroxylamine (II) condenses to form a nitrone, which is further reduced in two two‐electron waves, corresponding to the cleavage of the N‐O bond and reduction of the azomethine bond. At pH 7, formation of anthranil (III) from II is a relatively slow process: in cyclic voltammetry (CV) and d.c. polarography, II is further reduced to IV; in controlled potential electrolysis at a mercury pool electrode, the same products are obtained at 0° C, but at 25° C, III is the predominant product.
Determination of paraquat by cathodic stripping voltammetry after accumulation through the formation of an ion pair on a hanging mercury drop electrode
Authors: Macias J. M. Pinilla , Hernández L. Hernández , Sobrino J. M. Moreno , Escribano M. T. Sevilla
Published: May 2005

The formation of ion pairs is used to greatly enhance the sensitivity of cathodic stripping measurements at the hanging mercury drop electrode (HMDE). Such a scheme is illustrated for the trace determination of paraquat. Factors affecting the response are explored.
Determination of cefobid using adsorptive stripping voltammetric technique in different media
Authors: Ali Azza M. M. , El‐Maali Nagwa Abo , Ghandour Mahmoud A.
Published: May 2005

A sensitive voltammetric method has been developed for the cephalosporin antibiotic, cefoperazone monosodium salt (cefobid). The method is based on controlled adsorptive preconcentration of cefobid on the hanging mercury drop electrode (HMDE), followed by voltammetric determination of the surface species by cathodic stripping voltammetry. Cyclic voltammetry was used to examine the interfacial behavior of the drug. The electroanalytical techniques used were direct current stripping voltammetry (DCSV) and differential pulse stripping voltammetry (DPSV). The adsorptive stripping response was evaluated with respect to preconcentration dependence, possible interferences, and other variables. The drug is strongly adsorbed in acidic media, with maximum adsorption at pH2. The detection limit found by DPSV was 2 × 10−9 M (1.33 ppb), with 240 second preconcentration. The relative standard deviation at the 1 × 10−7 M level was 3.2%. The interference of uric and ascorbic acids and copper and calcium ions has been studied. The method was applied to the determination of cefobid in urine.
Nickelocene‐mediated glucose oxidase electrode
Authors: Atanasov P. , Kaisheva A. , Gamburzev S. , Iliev I. , Bobrin S.
Published: May 2005

Nickelocene is investigated as an electrochemical mediator in glucose oxidase (GOD) amperometric electrodes. It is found that the adsorbed nickelocene mediates the charge transfer between the electrode and glucose oxidase adsorbed on the electrode surface. The quasi redox potential of a nickelocene/nickelocenium couple adsorbed on an electrochemically activated pyrolytic graphite electrode is experimentally estimated (−0.105 V vs. Ag/AgCl). The steady‐state amperometric response of nickelocene‐mediated glucose electrode is investigated as a function of the glucose concentration, applied potential, and solution pH of the electrolyte. The working potential of a nickelocene‐mediated glucose electrode is 0.00 V (vs. Ag/AgCl).
Flow‐injection potentiometric determination of creatinine in urine using sub‐Nernstian linear response range
Authors: Matuszewski Wojciech , Trojanowicz Marek , Meyerhoff Mark E. , Moszczyńska Anna , Lange‐Moroz Elzbieta
Published: May 2005

A novel split‐stream flow‐injection system is described for the determination of creatinine in urine samples. The system is based on the use of a microreactor with immobilized creatinine iminohydrolase and downstream potentiometric detection of ammonium ions using a nonactin‐based membrane electrode. Splitting of the sample into two branches of the flow system, with the concomitant addition of alkali metal ions to the carrier solution, allows for simple correction of endogeneous ammonia and alkali metal ion levels via operation of the electrode in the sub‐Nernstian linear response range. The analytical utility of the system developed is illustrated by accurate creatinine determinations in urine samples.
Study of the electrode process of hemoglobin at a polymerized azure A film electrode
Authors: Dong Shaojun , Chu Qinghui
Published: May 2005

The electrochemically polymerized azure A film electrode is reported. The resulting film on a platinum electrode surface was analyzed with electron spectroscopy for chemical analysis (ESCA). The heterogeneous electron transfer processes of hemoglobin at the polymerized azure A film electrode have been investigated using in situ UV‐visible spectroelectrochemistry. The formal potential (E°′) and electron transfer number (n) of hemoglobin were calculated as E = 0.088 V versus NHE (standard deviation ±0.5, N = 4) and n = 1.8 (standard deviation ±0.5, N = 4). Exhaustive reduction and oxidation electrolysis are achieved in 80 and 380 seconds, respectively, during a potential step between −0.3 and +0.3 V. A formal heterogeneous electron‐transfer rate constant (ksh) of 3.54(±0.12) × 10−6 cm/s and a transfer coefficient (α) of 0.28(±0.01) were obtained by cyclic voltabsorptometry, which indicated that the poly‐azure A film electrode is able to catalyze the direct reduction and oxidation of hemoglobin.
Determination of chromium(VI) and chromium(III) by using a diphenylcarbazide‐modified carbon paste electrode
Authors: Paniagua A. R. , Vazquez M. D. , Tascon M. L. , Batanero P. Sanchez
Published: May 2005

A carbon paste electrode modified with diphenylcarbazide has been prepared in order to improve the analytical determination of chromium(VI) and chromium(III) using voltammetric techniques. Several parameters, such as carbon/diphenylcarbazide ratio, carbon/Nujol ratio, scan rate, accumulation time, etc., have been explored. A voltammetric study of both chemical species and an explanation of the chemical and electrochemical mechanism are presented. When applied to assays of soil samples, the results compared favorably to those of a polarographic method.
Adsorptive stripping tensammetry of motor oils in aqueous solutions
Authors: Kovac Martin , Kalvoda Robert , Novotny Ladislav , Berka Antonin
Published: May 2005

Adsorptive stripping tensammetry at a hanging mercury drop electrode is described for aqueous solutions of various motor oils. The method can be used for the determination of oils in polluted waters in the concentration range from 0.4–0.8 to 3.5–7 ppm, dependent on the type of oil. Distinction between “pure” and “used” motor oil is made.
A voltammetric phosphate sensor based on heteropolyanion formation at the nitrobenzene/water interface
Authors: Osakai Toshiyuki , Himeno Sadayuki , Saito Atsuyoshi , Katano Hajime
Published: May 2005

A novel voltammetric sensor for phosphate ion has been developed. This sensor relies on electrochemical formation of a heteropolyanion at the interface between an aqueous sample solution and a nitrobenzene solution containing hexamolybdate anion (Mo6) and on the subsequent detection of the voltammetric current due to the interfacial transfer of the heteropolyanion formed. Under optimal conditions, the voltammetric current is proportional to the phosphate concentration in the range from 0.02 to 0.5 mM. Though silicate ion interferes with the determination of phosphate ion, arsenate and germanate ions cause no significant interference.
Study of polypyrrole film as redox electrode
Authors: Michalska Agata , Lewenstam Andrzej , Ivaska Ari , Hulanicki Adam
Published: May 2005

The potentiometric redox sensitivity of different polypyrrole membranes is studied. Good Nernstian responses are observed for polypyrrole membranes polymerized on platinum substrate. The analytical use of such films as redox sensors is demonstrated.
Platinized carbon ultramicroelectrodes as glucose biosensors
Authors: Reynolds Eugene R. , Yacynych Alexander M.
Published: May 2005

Miniaturized glucose biosensors were constructed by all‐chemical means from disk‐shaped carbon ultramicroelectrodes (UMEs) (diameter = 8 μm). These ultramicrobiosensors (UMBs) are capable of direct measurement of glucose in the presence of interfering species. Carbon UMEs were partially platinized by the electrochemical reduction of a platinum (IV) complex. Platinization of the carbon UMEs gave an increased current response to hydrogen peroxide and allowed the modified electrode to be operated at a lower oxidative potential. Glucose oxidase (E.C. 1.1.3.4.) was immobilized either by glutaraldehyde cross‐linking or by direct covalent attachment to the electrode surface using carbodiimide. Response time (100% response) was 15–45 seconds. Response was linear over the range of 3–7 mM glucose. An electropolymerized film of poly(1,3‐diaminobenzene) was used to prevent interfering species.
Cupric hexacyanoferrate colloid doped polypyrrole film modified electrode
Authors: Li Yijun , Zhang Wenbin , Dong Shaojun
Published: May 2005

Anionic colloid cupric hexacyanoferrate (CuHCF) was incorporated into polypyrrole (PPy) films in the course of electrochemical polymerization of pyrrole from aqueous solution containing pyrrole and CuHCF colloid. The films obtained were dark brown in color. Three redox peaks appeared in the cyclic voltammogram (CV). The peaks around 0.7 V (vs, SCE) showed cation‐selective properties. X‐ray photoelectron spectroscopic analysis and ultraviolet‐visible (UV‐vis) spectroscopic properties of the film were investigated.
The electrochemical oxidation of penicillins on gold electrodes
Authors: Koprowski Lisa , Kirchmann Eric , Welch Lawrence E.
Published: May 2005

Penicillins can be electrochemically oxidized on gold electrodes in the presence of a catalytic surface oxide. Although oxidation can occur throughout a wide range of pH values, an acetate buffer solvent was selected to maximize the sensitivity and stability. Several amperometric waveforms were tested for penicillin detection using flow injection analysis. The use of pulsed amperometric detection (PAD) allowed the penicillins to be monitored either directly or indirectly depending on the specified waveform. Direct detection using standard PAD proved to be the optimal detection method, featuring excellent reproducibility and detectability to 4 × 10 −7 M for penicillin G.
Direct ion‐selective determination of boron in gallium arsenide
Authors: Lanza Pietro
Published: May 2005

The behavior of the Orion fluoroborate‐selective electrode (Model 93‐05) has been investigated under several working conditions. Long response time and slow shift of the potential can cause serious difficulties in practical applications. In spite of these facts, after a suitable conditioning of the electrode in solutions whose composition is similar to that of the solutions of the samples, sufficiently reproducible results are possible. Samples of GaAs, containing at least 1 μg/g of boron, can be analyzed with a precision (relative standard deviation) of about 5% (n = 5).
In situ fourier transform infrared reflection spectroscopic studies of ferricyanide/ferrocyanide on graphite electrode
Authors: Zhang Jiujun , Yin Qiguang , Cai Shengmin , Fujishima Akira
Published: May 2005

The electrochemical reactions of Fe(CN) and Fe(CN) on basal plane graphite electrode were studied using cyclic voltammetry and in situ Fourier transform infrared (FTIR) reflection spectroelectrochemistry. The IR band near 2080 to 2067 cm−1 was found to be an intermediate for Fe(CN) reduction and the band near 2058 to 2067 cm−1 for Fe(CN) oxidation. The possible mechanisms of reduction and oxidation and structure of intermediate are discussed.
Liquid chromatography and electrochemical detection of organic peroxides by reduction at an iron phthalocyanine chemically modified electrode
Authors: Qi Xiaohe , Baldwin Richard P.
Published: May 2005

Chemically modified carbon paste electrodes containing incorporated iron phthalocyanine (FePC) exhibited an electrocatalytic response for the reduction of organic peroxides. In pH 2 phosphate buffer, reduction at the FePC chemically modified electrode (CME) occurred at +0.1 to +0.2 V (vs. Ag/AgCl) for all peroxides examined except for dialkyl compounds. Because this potential was 100 mV more positive than that required for oxygen reduction at this electrode, amperometric detection of peroxides by this approach was possible in flow injection and high‐performance liquid chromatography without deoxygenating the sample or mobile phase solutions. In flow injection, the detection limit using this approach was 5 picomole (pmol) for hydrogen peroxide and varied from less than 1 pmol to as high as several hundred pmol for other peroxides. Cyclic voltammetry (CV) and visible spectroscopy experiments were consistent with a two‐step electrocatalytic mechanism involving the Fe(III)PC/Fe(II)PC couple.
Effect of polymer composition on the detection of electroinactive species using conductive polymers
Authors: Sadik Omowunmi A. , Wallace Gordon G.
Published: May 2005

Previous workers have demonstrated that conducting electroactive polymers can be used to detect electroinactive species. In this work, the effect of polymer composition, the nature of the eluent, and the electrochemical waveform on the selectivity of this detection process have been investigated.
A polytryptophan‐modified electrode
Authors: Narasaiah D. , Mitra Chanchal K.
Published: May 2005

A conducting polymer film has been formed on a Pt‐wire mesh by electrochemical oxidation of tryptophan from acidic and alkaline solutions. The electrochemical characteristics of the film have been studied both by cyclic voltammetry and impedance studies. For both p‐benzoquinone and potassium ferrocyanide, the peak currents are only slightly lower compared to bare electrode, but the background currents are considerably reduced. The polymer film is not acting as a mediator and is chemically stable, but it is electrochemically unstable outside the potential range of −700 to 800 mV (vs. SCE). Possible uses of this modified electrode in biosensors are discussed.
The polarographic behavior of the antitumor agent tauromustine and assay of its tablets
Authors: Belal F.
Published: May 2005

Tauromustine was found to be reducible at the dropping mercury electrode (DME) over the whole pH range in Britton‐Robinson (BR) buffers. A well‐defined cathodic wave was produced in the acid range, followed by an ill‐defined, more negative additional wave starting from pH 4.0. The main reduction wave was characterized as being diffusion‐controlled, although adsorption phenomena played a limited role in the electrode process. Using either direct current or differential pulse polarographic modes, the limiting current‐concentration plot is linear over a convenient range with a minimum detectability of 5 × 10−8 M using the latter technique. Tablets containing tauromustine (20 and 50 mg) were successfully analyzed adopting the United States Pharmacopoeia (USP) content uniformity test.
The study of differential pulse adsorptive stripping voltammetry of co(II)/1‐nitroso‐2‐naphthol chelate
Authors: Han Jilin , Chen Hongyuan , Gao (H. Kao) Hong
Published: May 2005

Cobalt (II)/1‐nitroso‐2‐naphthol chelate in citrate/ammonium citrate (pH 8.6) buffer solution is studied by adsorptive stripping voltammetry on a static mercury drop electrode (SMDE). The adsorbed chelate yields one distinct peak at −0.51 V, which can be utilized to quantify trace cobalt. The interfacial and redox behavior are evaluated by cyclic voltammetry and pulse polarography. The effect of accumulation potential, accumulation time, and concentration of ligand on the reduction peak currents of the chelate have been discussed. Possible interference metal ions are also investigated. The peak current is proportional to the concentration of cobalt in the range of 10−7 to 10−9 M (correlation coefficient 0.998). The relative standard deviation is 2.6% at the concentration of Co(II) 2.2 × 10−8 M (n = 7). The detection limit of Co(II) is as low as 0.05 ppb (2‐minute accumulation).
Electrochemical determination of oxygen permeability of isolated stratum corneum membranes
Authors: Wilson Alicia L. , Emons Hendrik , Heineman William R. , Pickens William L. , Hoath Steven B.
Published: May 2005

The mammalian stratum corneum is a thin, highly organized polymeric membrane which is relatively impermeable to water but permeable to some gases including oxygen. Isolated stratum corneum membranes from perinatal Sprague‐Dawley rats were mounted under electrodes used to determine the rate of diffusion of oxygen through the membrane. These membranes were consistently found to be permeable to oxygen, which could be quantitatively determined at a gold electrode at −0.6 V (vs. a Ag/AgCl electrode). The stratum corneum membrane was found to be anisotropic, with greater oxygen permeability when the gas diffused toward the electrolyte from the side of the membrane which would be oriented toward the exterior of the animal than when it diffused in the opposite direction. There is also evidence of anatomic site heterogeneity in the permeability of the membranes.
Amplified vitamin C sensor based on the cyclic reaction between L ‐ ascorbic acid and dehydroascorbic acid
Authors: Uchiyama Shunichi , Hasebe Yasushi , Suzuki Shuichi
Published: May 2005

The current response of L‐ascorbic acid at an ascorbate‐oxidase membrane electrode (detecting the decrease of oxygen) has been amplified by adding dithiothreithol into the sample solution. The signal amplification is based on the cyclic reaction between L‐ascorbic acid and dehydroascorbic acid, which leads to the regeneration of L‐ascorbic acid. The amplification factor was increased up to 22.5 (at pH 7.5) when 5 × 10−3 M dithiothreithol solution was used. This amplification system enables the determination of not only L‐ascorbic acid but dehydroascorbic acid, and the detection limit for vitamin C was found to be 2 × 10−7 M.
Hydrogen peroxide‐sensitive electrode based on horseradish peroxidase‐modified platinized carbon
Authors: Cardosi M. F.
Published: May 2005

Elearodes are described based on horseradish peroxidase (HRP) modified platinized carbon particles which are capable of reducing hydrogen peroxide at 0.0 V (vs. SCE). The HRP was covalently attached to the surface of the carbon particles via cyanuric chloride. Energy‐dispersive X‐ray analysis confirmed the presence of cyanuric chloride on the surface of the carbon. Electrochemical studies on these electrodes indicated that they were stable for extended periods and that the bound HRP was capable of mediating the electrocatalytic reduction of hydrogen peroxide.
Use of calixarenes as modifiers of carbon paste electrodes for voltammetric analysis
Authors: Arrigan Damien W. M. , Svehla Gyula , Harris Stephen J. , McKervey M. Anthony
Published: May 2005

The use of calixarene‐based chemically modified carbon paste electrodes (CMCPEs) in voltammetric analysis is reported here. A polymeric calixarene I was incorporated successfully and used for the accumulation of lead (II), copper(II), and mercury(II) ions with subsequent anodic stripping voltammetry as the determination step. The electrode response depended on the calixarene content, the electrolyte, and the preconcentration time and analyte concentration as well as the constituents of the sample matrix. The presence of alkali metal ions in the sample solution was found to have an adverse effect on electrode response, due to the preferable binding of these ions by the calixarene units immobilized in the carbon paste. Attempts to overcome this interference employed a nonpolymeric sulfur‐containing calixarene, the thioamide II, in the electrode. The stripping current was not enhanced by introduction of this compound as an electrode modifier, perhaps due to adsorption of the calixarene on the carbon partnicles via its metal ion binding site. However, the application of calixarenes to voltammetric methods of analysis is demonstrated and provides an additional use of calixarenes in electroanalysis.
The auto‐drop static mercury electrode—a novel concept
Authors: Yarnitzky Chaim N. , Rosenzveig Mirit
Published: May 2005

Smoothed operation of the SMDE is achieved by activating the mercury valve, detecting the natural mercury drop fall, and closing the valve after a predetermined interval. Constant area static mercury drops are obtained by this protocol without the need to resort to a mechanical knocker. This technique has proven very useful for flow electrochemical detection systems.
Computer elimination of voltammogram deformations by catalytic reaction to improve their signal for quantitative analysis. Determination of catalytic rate constant
Authors: Rievaj Miroslav , Korgová Elena , Mesároš Štefan , Bustin Dušan
Published: May 2005

Chemical reactions coupled with the electrode process lead to the change of shape and/or height of the measured voltammogram, thus complicating its application in quantitative analysis. This article describes a fractional differintegration procedure which corrects voltammograms for interference by catalytic reactions while simultaneously providing a value for the catalytic rate constants. A peocedure is proposed which utilizes the change of the shape of a reversible charge transfer voltammogram caused by slow and moderately fast catalytic reaction to the elimination of its influence on the analytical signal. It is based upon computer symmetrization of the voltammogram by fractional differentiation of the optimized order and the following correction of the signal. The procedure also enables an advantageous determination of the catalytic reaction rate constant. Since the height of the symmetrized signal is more sensitive to the catalytic process than the height of the original voltammogram, it is of special importance for lower rate constant values. Both elimination of catalytic influence and the determination of rate constant were tested with the Ti(III) NH2OH catalytic system.
Polarographic, voltammetric, and HPLC‐EC of pharmaceutically relevant cyclic compounds
Authors: Bersier Pierre M. , Bersier J.
Published: May 2005

This review gives a survey of the polarographic and voltammetric behavior of selected pharmaceuticals and substances of pharmaceutical relevance of various ring sizes (3–7, 14‐membered rings, polyring drugs), besides macrocyclic compounds and their determination by polarography, voltammetry, and liquid chromatography–electrochemical detection (HPLC–EC) in the practical laboratory.