bluuebunny/crossref_metadata_2025 huggingface dataset:
Graphite‐teflon enzyme electrode
Authors: Wang Joseph , Reviejo A. Julio , Angnes Lucio
Published: May 2005

The fabrication and performance of graphite‐Teflon‐enzyme electrodes are described. The new bulk‐modified composite enzyme electrodes couple the advantages of renewable (polishable) surfaces, mechanical rigidity, fast response, and favorable signal‐to‐noise characteristics. The new fabrication strategy is illustrated for the immobilization of horseradish peroxidase and glucose oxidase, in connection with measurements of peroxide species and glucose, respectively. The incorporation of a ferrocene mediator to yield a reagentless device is also illustrated. Flow injection measurements of hydrogen peroxide with the graphite‐Teflon‐peroxidase detector are carried out at 120 samples/hour, to yield a detection limit of 2.5 × 10−6 M and a relative standard deviation of 2%. Applicability to organic‐phase biosensing is illustrated.
Determination of manganese using the method of electrochemical enrichment
Authors: Stara V. , Kopanica M.
Published: May 2005

Manganese was determined by differential pulse voltammetry in pre‐enriched solution. The metal was first deposited on the surface of a hanging mercury drop electrode by electrolysis, and after a short oxidation interval, the reformed manganese(II) ions were determined by differential pulse cathodic polarization scan. The detection limit (with 120 seconds deposition) was 2 μg L−1. The only interfering element was cobalt (when present at tenfold concentration excess). Compared with conventional stripping voltammetry the described method has a lower detection limit value, and the analysis is performed during a shorter time interval. The proposed method was applied for the determination of manganese in natural waters.
Electrochemical reduction and oxidation of two cephalosporin antibiotics: Ceftriaxone (rocephin) and cefoperazone (cefobid)
Authors: El‐Maali Nagwa Abo , Ali Azza M. M. , Ghandour Mahmoud A.
Published: May 2005

Two cephalosporin antibiotic derivatives, ceftriaxone (CFRX) and cefoperazone (CFPZ), have been studied by direct current, differential pulse polarography (DPP), and cyclic voltammetry. Both give rise to two irreversible two‐electron reduction steps. The characteristics of the corresponding electrode reactions are discussed. The electrooxidation of both drugs was also studied at the carbon paste electrode (CPE). Both drugs give rise to one oxidation peak at about +1.05 V vs. SCE (pH 1.6, phosphate buffer solution). Optimum pH ranges for the determination of these drugs at the CPE are also given. Linear calibration plots were obtained over the concentration ranges 0.49 to 99 μg/mL and 0.66 to 534 μg/mL for CFRX and CFPZ, respectively. Detection limits of 2.5 ng/mL and 0.13 μg/mL for CFRX and CFPZ, respectively, were readily achieved.
Determination of adenine by chronopotentiometric stripping analysis with nafion‐modified electrode
Authors: Litong Jin , Shenghui Liu , Zhuping Bai , Yuzhi Fang
Published: May 2005

The determination of adenine by chronopotentiometric stripping analysis with Nafion‐modified electrode is reported. Various conditions for the determination of adenine were explored. In the Britton‐Robinson (BR) buffer solution (pH 3.3), preconcentration was carried out at −0.2 V (vs. SCE) for 90 seconds by chronopotentiometric stripping analysis. The peak height was proportional to the adenine concentration between 2.5 × 10−7 and 8.0 × 10−6 mol/L. For 10 repetitive measurements, the relative standard deviation for 5 × 10−6 mol/L, adenine was 2.2%. The method was fairly free of interference, and the results of real samples were satisfactory.
Voltammetric waveshapes measured in flowing systems: Mass transport‐limited tafel analysis of some nonsimple systems
Authors: Compton Richard G. , Fisher Adrian C. , Sanders Giles H. W.
Published: May 2005

Analytical theory is presented which allows rigorous mass transport‐corrected Tafel analysis for the reversible electrode processes (1) 2B ⇄ A2 + 2e− and (2) B2 ⇄ 2A + 2e− occurring at electrodes in flowing systems. Predictions are compared with the conclusions of numerical finite‐difference modelling for both wall‐jet and channel flow cell geometries. Exceillent agreement is found.
Theory of ultramicroelectrodes
Authors: Aoki Koichi
Published: May 2005

This review describes the theory of mass transport at ultramicroelectrodes that have broken through several experimental limitations of electrochemical measurements. On the basis of the mathematical miniaturization, the ultramicroelectrode can be classified into a point electrode, a line electrode, and a plane electrode. Electrochemical features of these electrodes are described from a viewpoint of the mass transport, especially due to diffusion. Theoretical difficulty in ultramicroelectrodes is mainly due to nonuniform current distribution on the electrode surface. The expression for the time‐dependent diffusion‐controlled current at any electrode geometry, which predicts the current responding to any potential variation, is presented. Conditions of the steady‐state current are specified. The diffusional characteristic functions at a disk. a cylinder, and a band are presented, from which the theories of various electrochemical techniques can be derived analytically. Voltammetric peak currents at several ultramicroelectrodes are compared in light of the diffusional edge effect. The properties of the steady‐state current are described at a disk, a band array, a ring, and a recess electrode. The theory is extended to the current‐potential curves complicated by the heterogeneous kinetics at a disk, a cylinder, and a band‐array electrode.
Software development for improving the application of static semimicroelectrodes in voltammetric quantitative analysis of oligocomponent samples
Authors: Mesáaroš ŠTefan , Bustin Dušan
Published: May 2005

A computer procedure is proposed to improve the application of the nonsteady‐state voltammogram at a semimicroelectrode in quantitative analysis of oligocomponent samples. The technique is based upon the optimized order differentiation. The proposed computer routine offers the optimation of the differentiation order as well as accomplishment of the differentiation itself. The mutual independence of the analytical signal‐‐a prerequisite of quantitative application of semimicroelectrode voltammetry– was tested with a mixture of o‐dianizidine and 4‐amino‐4′‐methoxy diphenylamine. Pt‐disk (ø = 40 μm) and Pt‐fiber (ø = 40 μm, 15 mm in length) semimicroelectrodes were applied for the testing.
Postchromatographic electrochemical detection of carbohydrates at a silver oxide electrode
Authors: Tougas Terrence P. , Debenedetto Mark J. , Demott James M.
Published: May 2005

Silver electrodes, when conditioned at sufficiently positive potentials in the presence of a strong base, can be made to form a silver(I) oxide or silver(II) oxide surface. In the presence of this oxide surface, carbohydrates may be oxidized and quantitated by means of an electrocatalytic scheme. The current which flows to reoxidize the charge‐transfer mediator (silver oxide) is directly related to concentration of carbohydrate. Rectilinear response is obtained over at least two decades of concentration (104 M to 10−6 M). Design of a prototype electrochemical cell and studies of optimum cell conditions are discussed. The application of a high‐performance liquid chromatography (HPLC) detector for the separation of some common sugars is illustrated.
Elimination of zinc/copper intermetallic interference in the determination of zinc in wastewaters and seawater by potentiometric stripping analysis
Authors: Scollary Geoffrey R. , Cardwell Terence J. , Cattrall Robert W. , Nan Chen Guo , Vicente‐Beckett Victoria A. , Hamilton Ian C. , Roden Steve
Published: May 2005

A new approach to the elimination of Zn/Cu intermetallic interference in the determination of zinc by potentiometric stripping analysis is described. The method is based on the use of several enrichment/ stripping cycles, with each cycle using an enrichment time of 10 seconds or less and the stripping signal from each cycle being added to give the total stripping signal. The additive method compares favorably with the traditional “third element” approach based on the use of gallium, and it is demonstrated that, for an industrial sample containing oil and grease, the additive method has significant advantages over the gallium method. The advantages of potentiometric stripping analysis in monitoring zinc in industrial wastes and the applicability of the technique to zinc speciation studies are described.
Application of glassy carbon substrated cyanide‐sensitive electrodes in determination of cyanide and mercaptan levels of wastewater
Authors: Stankovic Slavka M. , Jovanović Momir S. , Jovanović Vladislava M. , Djikanović Milka
Published: May 2005

Quantities of free and complex cyanides and mercaptans were determined in wastewater. Levels of free and complex cyanides were determined after previous oxidation of mercaptans by hydrogen peroxide. The procedure used for cyanide determination relied on applying a laboratory‐made glassy carbon (GC) substrated melt‐coated Agl “cyanide‐sensitive” electrode. The level of mercaptans was determined by iodometric titration in bicarbonate solution. Iodine was coulometrically generated using the depolarization end point detection on a GC/saturated calomel electrode indicating a couple connected directly to the recorder.
Differential electrolytic potentiometric determination of caffeine in nonaqueous media
Authors: Abdennabi Abdalla M. S. , Sultan Salah M.
Published: May 2005

The application of direct current differential electrolytic potentiometry (dc DEP) to the titration of caffeine in acetic anhydride‐toluene mixture has been investigated. A very stable low current source has been constructed to polarize the antimony electrodes. The behavior of these electrodes during the titration of caffeine has been examined. Caffeine in commercial samples like tea, Pepsi as a beverage and Prontopyrin, a proprietary drug, was extracted in chloroform and determined by dc DEP.
Chronocoulometric interrogations of oxidase‐based enzyme electrodes for enhanced selectivity
Authors: Higson S. P. J. , Vadgama P. M. , Ward J. P.
Published: May 2005

Classical oxidase‐based enzyme electrodes rely on the amperometric determination of H2O2. Such electrodes are vulnerable to electroactive interferants found in biological solutions. Some interferants may be oxidized at anodic potentials, necessitating the use of permselective barrier membranes. Two generic chronocoulometric approaches to the interrogation of oxidase‐based enzyme electrodes have been developed. Both the chronocoulometric interrogation of H2O2 and the chronocoulometric interrogation of the reduction of O2 (formed from the anodic oxidation of H2O2) have allowed new correlations to be made with 0 to 20 mM glucose concentrations. Furthermore, the inter rogation of O2 has allowed a glucose sensor to be constructed that is virtually free from the effects of electroactive interferants.
Voltammetric investigations of the effect of triton X‐100 on copper processes in the presence of oxygen
Authors: Krznarić Damir , Plavšić Marta , Ćosović Božena
Published: May 2005

The influence of Triton X‐100 (T‐X‐100) on the redox processes of copper in NaCl solutions and in the presence of oxygen was investigated by anodic stripping alternating current voltammetry (ASacV), anodic stripping direct current voltammetry (ASdcV), and differential pulse anodic stripping voltammetry (DPASV). In the presence of oxygen, copper dissolution from amalgam is characterized by a catalytic process, resulting in a net cathodic current due to the oxidation of Cu(I) to Cu(II) by H2O2 formed on the electrode, and the subsequent reduction of Cu(II) back to Cu (I). Triton X‐100 blocks the catalytic process by hindering the formation of H2O2, by competing with CuCl and Cl− for the adsorption sites on HMDE surface, and by blocking the formation of Cu(I) and Cu(II) hydroxide deposit on the surface. Its presence also changes the redox processes of copper from reversible to quasireversible. At the same time, T‐X‐100 increases the oxidation current of copper, probably through disproportionation of Cu(I) to Cu(0) and Cu(II). This last effect was observed regardless of whether oxygen was present in the solutions or not.
Potentiometric ion‐pair titrations of metal ions forming complexes with 1,10‐phenanthroline and its derivatives
Authors: Vytřas Karel , Varmužová Ilona
Published: May 2005

Simple coated‐wire electrodes, prepared using an ordinary aluminum wire conductor covered with the plasticized poly(vinyl chloride) membrane, were used in potentiometric titrations of metal ions forming complexes with 1,10‐phenanthroline and its derivatives. The method precipitation of ion pairs formed by metal phenanthroline complexes and tetraphenylborate. Titractions were accompanied with titration curves yielding very sharp potential breaks, so that very reproducible results could be taken even in titrations of quite diluted solutions (down to 2.5 × 10−7 mol of the metal ion in the 25 cm3 of the sample titrated). Using the procedure described the following cations were titratable in forms of their 1.10‐phenanthroline complexes: Zn2+, Cd2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Vo2+, Ga3−, In3−, and Tl3−. Some of the metal ion solutions, prepared from the salts of analytical‐reagent‐grade purity, can be recommended for use in standardization procedures of the sodium tetraphenylborate titrant. 2.9‐Dimethyl‐1,10‐phenanthroline complexes of Zn2+, Cd2+, and Cu+ were also titrable, but the results were significantly erroneous. Metal 4,7‐diphenyl‐1,10‐phenathroline complexes were insoluble in water as well as in water/ethanol mixtures.
Fast‐pulsed amperometric detection at electrodes: A study of oxide formation and dissolution at platinum in 0.1 M NaOH
Authors: Roberts Richard E. , Johnson Dennis C.
Published: May 2005

Results of a potential‐step chronocoulometric study of oxide formation at a Pt‐rotated minidisk electrode (0.00785 cm2) indicate that the anodic charge (qa) grows ca. as a linear function of the log time (t) for t = ca. 2–30 ms. Furthermore, the slope of the linear qa – log (t/ms) plot is proportional to the applied overpotential for oxide formation. The anodic peak current observed during linear potential‐scan voltammetric experiments is nearly a linear function of scan rate (ϕ) for small ϕ (1000 < mV s−1) but shows substantial negative deviation from linearity for ϕ > 1000 mV s−1. The peak potential for oxide formation shifts in a positive direction for increasing values of ϕ, suggesting that this process is kinetically slow relative to large ϕ values. Reverse potential‐step chronocoulometric measurements demonstrate that the background current in so‐called “reverse‐pulsed amperometric detection (RPAD)” can be decreased by inhibiting the conversion of the hydrous oxide (PtOH) to the inert oxide (PtO). Data also indicate that the rate of cathodic dissolution of surface oxide is dependent on applied potential for t < 2 to 30 ms. Oxide reduction continues even for t > 1000 ms.
Design and evaluation of photoelectrochemical flow cells
Authors: Barisci J. N. , Wallace G. G.
Published: May 2005

Several photoelectrochemical flow cells have been designed and their analytical performances evaluated and compared. Two cell geometries, thin‐layer and wall‐jet, and three irradiation configurations differing in the relative position of the irradiation and detection points have been considered. In the first configuration (“adjacent”), the irradiation point is located upstream of the working electrode. In the second arrangement (“above”), the light irradiates the solution above the working electrode as well as the electrode surface. The third configuration (“on”) involves the use of an optically transparent electrode through which the light passes before irradiating the solution present on the electrode surface. The “adjacent” thin‐layer cell was found to be the most practical and useful design. The photoelectrochemical efficiency of this cell was optimized and evaluated in terms of window and channel size.
Studies on electrochemical reactions at metal‐oxide electrodes for combination with high‐performance liquid chromatography
Authors: Stitz Alfred , Buchberger Wolfgang
Published: May 2005

Various electrodes, such as nickel, copper, and cobalt metal electrodes and nickel‐, copper‐, and cobalt‐modified glassy‐carbon electrodes, are investigated for the oxidative amperometric detection of alcohols, polyols, and carbohydrates after separation by high‐performance liquid chromatography (HPLC). These electrode materials are compared with respect to stability, detection limits, and an eventual necessity of electrode surface pretreatment. Detection limits of 4 ng and 10 ng glucose injected can be achieved using a metallic copper electrode and a metallic nickel electrode, respectively. Investigations at the surface of a nickel electrode reveal the existence of a reversible layer of nickel oxide with higher valence which is formed in an alkaline medium at an applied potential of at least 400 mV versus Ag/AgCl/KCl(sat). Its thickness strongly depends on electrochemical pretreatment procedures. This layer can be converted into a layer of lower valence nickel oxide either electrochemically or chemically. Investigations of the electrode surface are carried out by in situ ultraviolet‐visible (UV‐vis) reflectance spectroscopy and by Fourier‐transform infrared spectroscopy (FTIR). Controlled‐potential experiments at various metal‐oxide electrodes and separation of the oxidation products on ion‐exchange columns reveal some of the reaction mechanisms for the oxidation of alcohols, polyols, carbohydrates, and similar organic compounds.
Voltammetric determination of piroxicam after incorporation within carbon pastes
Authors: Paniagua Ana Rosa , Vázquez Maria Dolores , Tascón Maria Luz , Sánchez‐Batanero Pedro
Published: May 2005

An accurate voltammetric method for the piroxicam determination at solid state, with a detection limit of 0.47 mg/g, is described. The method is based on the incorporation and oxidation of piroxicam within a carbon paste matrix bound with a nonconducting solvent. The method was successfully applied to the analysis of several pharmaceutical formulations.
Polarographic behavior of the β‐lactam antibiotic Cefuroxime and study of the reduction mechanism in acidic media
Authors: Bernacca Giuliana , Nucci Lamberto , Pergola Francesco
Published: May 2005

Polarographic behavior of the cephalosporin Cefuroxime (CFXN) in aqueous solutions of PH ranging from 1 to 10 was investigated. The reactant is strongly adsorbed in acidic media, while in neutral and alkaline solution, electrode reaction is not affected by adsorption phenomena. A kinetic study of the methoxyimino group electroreduction to methanol and an aminic derivative in acidic media was carried out. The overall electrode process is controlled by the heterogeneous protonation step preceded by a fast electronation step in the pH range 1 to 3, whereas for 3 < pH < 5, the rate determining step (rds) is the first electronation step. Moreover, a fast protonation precedes the rds in the whole acidic medium. The best experimental conditions for the detection of CFXM in differential pulse plarography (DPP)were found. Owing to its high adsorptivity, CFXM is detectable at a concentration as low as 1 × 10−8 M at a pH of about 2.
Liquid chromatography/electrochemical detection of hydroxylamines by oxidation at a cobalt phthalocyanine chemically modified electrode
Authors: Qi Xiaohe , Baldwin Richard P.
Published: May 2005

Chemically modified electrodes (CMEs) containing a polymeric cosating of cobalt phthalocyanine (CoPC) were shown to catalyze the electrooxidation of hydroxylamine (NH2OH) and its N‐mono‐, N,N‐di‐, and O‐substituted derivatives. All of these compounds were oxidized at unmodified glassy carbon electrodes only at potentials higher than +1 V (vs. Ag/AgCl) but gave substantial anodic currents between +0.25 and +0.55 V at the CoPC‐coniaining surface. On the basis of exhaustive electrolysis experiments, the number of electrons transferred for the oxidations was found to vary between 1.2 and 1.6 depending on the particular hydroxylamine compound and the specific condition, of the electrolysis; and the products included oximes, azoxy compounds, and dimeric species. These observations were consistent with an electrocatalytic mechanism involving oxidation of the hydroxylamine by electrogenerated Co(III)PC and subsequent reaction of the initially formed oxidatior products by several pathways. When the CoPC CME was used as the sensor in amperometric detection following liquid chromatography, the detection limits obtained at +0.55 V ranged from 0.4 pmol for hydroxylamine itself up to 40 pmol for N,O‐dimethylhydroxylamine. By maintaining the applied potential at +0.20 V, the detection could be made selective for hydroxylamine and N‐mono‐substituted hydroxylamine compounds only.
Partial characterization in vitro of glucose oxidase‐modified poly(phenylenediamine)‐coated electrodes for neurochemical analysis in vivo
Authors: Lowry John P. , O'Neill Robert D.
Published: May 2005

Glucose oxidase (GOx) modified poly‐phenylenediamine (PPD) coated 250 μm Pt‐disk electrodes were prepared by electropolymerization in phenylenediamine solutions containing GOx. Bothorthoandmetamonomers were tested, and theorthoisomer was found to give better glucose responses. The response of Pt/o‐PPD/GOx electrodes to glucose was well behaved with a rapid response time and displaying Michaelis‐Menten kinetics. The behavior of these electrodes in vitro to ascorbic acid (a principal interferant in brain tissue) was complex in that the sensitivity was concentration dependent. At low ascorbate concentrations (<50 μM), the sensitivity was similar to that of bare Pt (72 ± 13 nA/ mM, n = 10) whereas at higher levels it decreased sharply to 0.2 ± 0.1 nA/mM (n = 3) at 1 mmol/L ascorbate. At still higher concentrations (1 to 10 mmol/L), the sensitivity was concentration independent, 0.14 ± 0.02 nA/mM (n = 3). Calibrations for another potential interferant, uric acid, were linear in the range studied (0 to 100 μM) with a slope of 0.41 ± 0.03 nA/mM (n = 3), indicating negligible interference by this substrate for concentrations present in brain extracellular fluid. Surprisingly, the permeability of both substrates was greater in PPD films containing no GOx. The results are discussed in terms of the suitability of these electrodes for monitoring brain glucosein vivo.
The electrochemical processes of copper in the presence of triton X‐100
Authors: Plavšić Marta , Krznarić Damir , Ćosović Božena
Published: May 2005

In this work, the redox processes of copper ions were studied by electrochemical methods in NaCl and NaClO4solutions in the absence or in the presence of nonionic surfactant Triton X‐100 (T‐X‐100). The enhancement of the anodic peak current of copper in the presence of T‐X‐100 in sodium chloride solutions was observed depending on the Concentrations of T‐X‐100 and copper (II) ions. This is the consequence of destabilization of the otherwise stabile CuClcomplex in chloride solutions by the presence of T‐X‐100. The process involves disproportionation of formed copper (I) species to copper (0) and copper (II).
Contribution to the electrochemical behavior study of piroxicam in different aqueous‐orgarnic media and electrodes by using polarographic and voltammetric techniques
Authors: González Mercedes , Vázquez Maria Dolores , Tascón Maria Luz , Sánchez‐Batanero Pedro
Published: May 2005

A study of the electrochemical behavior of piroxicam has been carried out by dc polarography, classical and differential pulse mode voltammetric techniques, as well as by classical and differential pulse mode adsorptive cathodic stripping voltammetry (AdCSV), in methanol/H2O(20/80% v/v) and acetonitrile/H2O(20/80%‐6 v/v) media. Several parameters, such as pH, temperature, scan rate, ad‐accumulation potential, and accumulation time, elucidate the piroxicam reduction mechanism and establish analytical methods, mainly by AdCSV, obtaining a detection limit of 2.4 × 10−11 M.
Electronic configurations in potentiostats for the correction of ohmic losses
Authors: Souto Ricardo M.
Published: May 2005

Recent trends in the design of potentiostats capable of correcting for ohmic losses occurring in electrochemical cells are reviewed. The various effects of ohmic drop occurrence and their influence on diverse electroanalytical techniques are considered, as well as potentiostat configurations and stability, with emphasis in the three‐electrode cell configuration. Electronic correction methods are discussed according to the following classifications: (1) positive feedback, (2) negative impedance, (3) current pulse, (4) analogic subtraction, and (5) current interruption.
Enzyme chronopotentiometry
Authors: Uhe B. , Schuhmann W. , Janker G. , Schmidt H.‐L. , Janata J.
Published: May 2005

Chronopotentiometry (CP) with enzyme electrodes is a new approach to overcome inherent problems of steady‐state potentiometric processes. The developed procedure is presented on the example of a glucose oxidase (GOD) electrode. Electrochemically generated mediator helps to overcome traditional difficulties arising from poorly defined mixed potentials in the presence of oxygen during an analysis. Transition times are automatically evaluated by using computerized calculation programs. The technique can be used for determining substrate concentrations; moreover, it is particularly promising as an effective tool to study electrode processes with biochemical systems on an electrode surface.
Differential pulse voltammetric determination of lead(II) with benzoin oxime‐modified carbon paste electrodes
Authors: Tuzhi Peng , Zhe Tang , Guoshun Wang , Baoen Shen
Published: May 2005

A new chemically modified electrode (CME) for determining lead(II) with high sensitivity and selectivity is reported. The electrode is constructed by adding benzoin oxime into a carbon paste mixture. The lead(II) is accumulated on the electrode surface by the formation of the complex in an open circuit, and then the resulting surface is characterized by medium exchange, potential reduction, and differential pulse anodic stripping voltammetry. In 10 deposition/measurement/regeneration cycles with a single surface, the response could be reproduced with 5.7% relative standard deviation. Quantitation of lead(II) from the peak current of the anodic wave for a 10 minute deposition time gives a detection limit of 8 × 10−9 M (1.6 ppb). Linear calibration plots are obtained for lead(II) concentrations ranging from 10−7 to 10−8 M. The modified electrode preferentially accumulates lead from the solution, while most of the metal ions do not interfere with the determination. The mechanism of the accumulation of lead on the benzoin oxime‐modified electrode has been explored. Application to the determination of lead in wastewater is illustrated.
Observed redox interferences of poly(pyrrole)‐based perchlorate‐selective electrodes
Authors: Hulanicki Adam , Michalska Agata , Lewenstam Andrzej
Published: May 2005

The responses of the poly(pyrrole)‐based ion‐selective perchlorate electrode were investigated in both perchlorate and redox buffers media. Sensitivity of tested electrodes both to the changes of perchlorate on concentrations and redox potential of the solution were observed. Slopes were characteristic −51.3 mV/dec in the case of perchlorate ion solutions and 61 mV/dec in the case of redox calibration. Potentiometric redox sensitivity of the tested poly(pyrrole) layers was observed in presence of 1 M sodium perchlorate. Potentiometric redox sensitivity of the bare platinum electrode and perchlorate‐sensitive electrode based on poly(pyrrole) in presence of 0.1 M NaClO4 were compared.
Pulse polarography of azobenzene
Authors: Komorsky‐Lovrić ŠEbojka , Lovrić Milivoj
Published: May 2005

Pulse polarography is applied to measure adsorption of azobenzene and hydrazobenzene in a wide acidity range between 5 M HClO4 and 0.5 M NaClO4 buffered to pH 7. The solvent is 20% v/v aqueous acetonitrile. In 5 M HClO4 the adsorption of azobenzene is weaker, while at pH 7 it is stronger than the adsorption of hydrazobenzene. In weakly acidic and neutral NaClO4 solutions, the surface protonization of azobenzene is a rate‐determining step of the redox reaction. When the polarographic pulse is very short, the unprotonated azobenzene is reduced directly and at potentials which are more negative than the potentials at which the monoprotonated azobenzene is reduced if pulses are longer. The rate constants of benzidine rearrangement of adsorbed hydrazobenzene are measured in concentrated HClO4 solutions: k = 52 s−1, 115 s−1, and 224 s−1 for 1, 3, and 5 M HClO4, respectively.
Voltammetric investigations on carbon paste electrodes as supports for mercury films
Authors: Švancara Ivan , Pravda Miloslav , Hvizdalová Marie , Vytřas Karel , Kalcher Kurt
Published: May 2005

Different carbon paste electrodes (CPEs) were investigated for their ability to act directly as supports for mercury films formed “in situ” by electrodeposition. A CPE, containing tricresyl phosphate as a pasting liquid, was found to be especially suitable for this purpose. The mercury film on this support exhibited a more negative potential limit than mercury films deposited onto common carbon pastes or glassy carbon. Thus, the mercury film electrode (MFE) with the tricresyl phosphate‐based carbon paste support proved to be advantageous for differential pulse anodic stripping voltammetry (DPASV) of Zn(II). The effects of various supporting electrolytes, and of the concentration of Hg(Il) ions on the response of zinc, were studied in detail together with an optimization of voltammetric parameters. Interferences from metal ions such as Ni(II), Co(II), Mn(II), and Cu(II), were also investigated. For quantitative evaluations, Zn(II) was accumulated from a 0.1 M ammonia buffer containing 2 × 10−5 M Hg(II), with an accumulation potential of –1.5 V (vs. Ag/AgCl). The current response of Zn(II) was linear for a concentration range from 2 × 10−7 to 2 × 10−5 mol/L with a detection limit of 1 × 10−7 mol/L (accumulation time 180 seconds). The method was applied to the determination of Zn(II) in drinking water and deionized water.
Effect of interference on amperometric glucose biosensors with cellulose acetate membranes
Authors: Vaidya Rajesh , Wilkins Ebtisam
Published: May 2005

A new enzyme electrode concept featuring glucose oxidase (GOD) immobilized on fine carbon powder in a fluid state and a cross‐linked GOD enzyme layer has been developed. This enzyme electrode has been tested in vitro at 37°C and has a lifetime of 3 months after which it can be recharged with fresh enzyme. In vitro interference tests carried out on this sensor used with cellulose acetate membranes are described. Sulfur‐free EDTA‐treated cellulose acetate membranes (molecular weight cutoff at 1000) were used, some of which were coated with positively and negatively charged hydrogel layers. The sensors showed a stable and linear response to glucose concentrations >300 mg/dL, in the presence of glucose alone in the phosphate buffer medium and in the presence of interferences. The effects of ascorbic acid, bilirubin, creatinine, L‐cysdne, glycine, uric acid, and urea on the amperometric signal of the sensor were studied. The cellulose acetate membrane coated with the negatively charged hydrogel layer provided good protection for the enzyme electrode, especially in the presence of uric acid, bilirubin, and L‐cystine.
Determination of copper in seawater by adsorptive voltammetry with 1,2‐dihydroxyanthraquinone‐3‐sulfonic acid
Authors: Quentel François , Elleouet Catherine , Madec Christian
Published: May 2005

A method is described for the determination of copper in seawater by adsorptive stripping voltammetry after accumulation of a 1,2‐dihydroxyanthraquinone‐3‐sulfonic acid (DASA) complex. The effects of various operational parameters (pH, ligand concentration, potential, and accumulation time) on the reduction current of the adsorbed chelate are discussed. A linear current concentration relationship was observed up to 5 × 10−8 M. The detection limit is 0.3 nM.
Fish Liver Tissue‐Based Membrane Electrode for Uric acid in Serum
Authors: Deng Jiaqi , Wang Qing
Published: May 2005

A novel tissue‐based membrane electrode for uric acid in serum is constructed by coupling of fish liver to an oxygen electrode. The oxygen signals decrease with the concentrations of uric acid, and the linear range of the calibration graph is 2.0 × 10−5 to 3.0 × 10−4 mol/L. The biosensor has a lifetime of at least 3 months. Optimum conditions of preparing the sensor and measuring uric acid were explored. Its application in serum was compared with two methods of pure enzyme, and satisfactory results were obtained.
Electrocatalytic activity of cytochrome c for the reduction of nitric oxide
Authors: Miki Koujiro , Ikeda Tokuji , Kinoshita Hideaki
Published: May 2005

Sodium nitrite in acidic solutions produces a voltammetric cathodic wave starting from −0.5 V (vs. Ag/AgCl) in the presence of a small amount of cytochrome c (cyt c), in which cyt c works as a catalyst for the electroreduction of nitric oxide produced by the disproportionation reaction of nitrite. Hemoglobin (Hb) and myoglobin (Mb) are also effective as catalysts for this type of reaction.
The linear sweep voltametric method: An application to the study of reversible and irreversible processes
Authors: González‐Velasco J.
Published: May 2005

The theory of the linear sweep voltametric method has been the object of a series of articles in which useful solutions for current versus scan rate (I vs. v) relationships and for the diagnostic criteria for different kinds of reacting systems have been found. Some difficulties remain in order to clarify these concepts. This article is an attempt to introduce clearer ideas about how to deduce I vs. v and I vs. E relationships for the method mentioned above as applied to the study of reversible and irreversible electrochemical processes. Some new equations are given which have been deduced under consideration of the numerical solutions obtained by Nicholson and Shain [4]. Variations of Co(O, t) and CR(O, t) with the potential value have been found, and an unambiguous definition of k°′ for irreversible processes is given, which allows the determination of k° values from linear voltammograms recorded in the study of such processes. Also, the values of δN, the thickness of the diffusion layer, have been calculated as a function of the potential and sweep rate.
The oxidation of cyclic diols on a gold elecrode structure‐reactivity relationships
Authors: Luczak Teresa , Holze Rudolf , Beltowska‐Brzezinska Maria
Published: May 2005

The electrooxidation of the three isomeric 1,2‐, 1,3‐, and 1,4‐cyclohexanediols at a gold electrode in contact win an alkaline electrolyte solutior has been studied with cyclic voltammetry. Signficant differences in the electrochemical activity of the isomers were found. The 1,2‐diol is by far the most active one. Its trans‐isomer is more reactive than the cis‐isomer. These differences are rationalized based on the molecular structure and the different elearosorption properties.
Differential pulse polarographic determination of omeprazole in pharmaceutical preparations
Authors: Özaltin Nuran , Temizer Aytekin
Published: May 2005

A new electroanalytical method was developed for the analysis of omeprazole. Various polarographic techniques and supporting electrolytes were examined. Best results were obtained with differential pulse polarography (DPP) in borate buffer (pH 9.0) solution. Linear response was observed from 2.0 × 10−7 M to 2.0 × 10−5 M. The peak potential was observed at –1.28 V (vs. Ag/AgCl). The developed method was applied to two different commercial hard gelatin capsules, containing enteric‐coated granules, preparations. The relative standard deviations were found to be 3.04% (brand A) and 2.88% (brand B).
Electroanalytical applications in occupational and environmental health
Authors: Ashley Kevin
Published: May 2005

Electroanalytical chemistry has been used for years in the occupational and environmental health fields. Portable sensors and analytical devices based on electrochemical (EC) methods are commonly used on‐site in the workplace. Laboratory EC methods also have been used extensively for the analysis of industrial hygiene and related samples. Recent advances in electroanalytical methodology may lead to new analytical applications in the occupational health arena, both in the laboratory as well as on‐site in the workplace. Applications in heavy metals analysis, analysis for inorganic and organic species, and bioanalysis are exemplified. This article provides an overview of the history of EC analysis for industrial hygiene purposes, and also summarizes current and newly developed applications of electroanalytical methods in occupational and environmental health.
The electrochemistry of dibutyltin at mercury electrodes in aqueous media
Authors: Turoczy Nicholas J. , Carter Rodney J. , Bond Alan M.
Published: May 2005

The electrochemical reduction of dibutyltin (Bu2Sn2+) at mercury electrodes has been investigated in aqueous media containing nitrate and chloride electrolytes using the techniques of direct current (DC) polarography, differential pulse (DP) polarography, DP voltammetry, and cyclic voltammetry. In 0.10 M nitrate media, the initial charge transfer process occurs at approximately –0.7 V (vs. Ag/AgCl) and is described by the equation

in which a reversible charge transfer occurs with completely surface‐confined dibutyltin. However, when longer time domains at a hanging mercury drop electrode (HMDE) are used, the complexity of the electrochemistry increases, which is attributed to the occurrence of butyl exchange processes with the electrode mercury and consequent disruption of the film of adsorbed dibutyltin. In 0.50 M chloride media, the extent of adsorption is considerably less, and the processes, but not necessarily the postulated mechanism, correspond more closely to that described by previous workers for the reduction of dibutyltin compounds in ethanol‐water mixtures.
Redox reaction of peroxidase at poly(o‐phenylenediamine) modified electrode
Authors: Deng Qing , Dong Shaojun
Published: May 2005

The redox conversion of heme‐containing protein horseradish peroxidase (HRP), which has a molar mass of 40,000 was studied. The conversion was obtained at an electrochemical polymerized ophenylenediamine (PPD) film‐modified platinum electrode. Optical thin‐layer spectroelectrochemical techniques were applied to determine the characteristics of the electrochemical processes. The modified film can mediate the redox conversion of the HRP.
Investigations on adsorption potentiometry: Part 4. Derivative adsorption chronopotentiometry of the bismuth‐2‐(5′‐bromo‐2′‐pyridyeazo)‐5‐diethylaminophenol system
Authors: Jin Wenrui , Wang Junying
Published: May 2005

Derivative adsorption chronopotentiometry of the bismuth complex with 2‐(5′‐bromo‐2′‐pyridylazo‐5‐ diethylaminophenol (5‐Br‐PADAP) has been described. The theory of derivative adsorption chronopotentiometry for the complex system and the method of determination of the composition, the conditional stability constant, as well as the number of electrons transferred by the electroactive complex adsorbed on the surface of the electrode have been discussed. In 0.025 mol/L NaOH, the linear range of the method is 2 × 10−9 to 1.1 × 10−7 mol/L for the preconcentration time of 120 seconds. This method has been used to determine the bismuth content in food.
Simultaneous determination of lead, copper, and mercury at a modified carbon paste eletrode containing humic acid
Authors: Jeong Euh‐Duck , Won Mi‐Sook , Shim Yeon‐Bo
Published: May 2005

The modified carbon paste electrode (CPE) responding simultaneously to lead(II), copper(II), and mercury(II) ions has been constructed by incorporating humic acid (HA) into the graphite powder with Nujol oil. Simple immerging of the electrode into the measuring solution containing these metal ions led to the chemical deposition of the ions onto the electrode through the complexation of the ions with HA. Cyclic and differential pulse voltammetry (DPV) characterized the modified electrode's surfaces. Several cyclings of the potential regenerated the electrode (from more positive than the stripping potential of reduced Hg to more negative than the reduction of Pb(II)ion), which was then used for another deposition. After five deposition/measurement/regeneration cycles, the peak current of voltammograns of the analyte decreased slightly. The response reproduced with a 5.1% relative standard deviation. We also applied ihe differential pulse technique to the previously mentioned system. Here, the detection limit tor Pb(II), Cu(II), and Hg(II) ions were 5.0 × 10−9 M 8.0 × 10−9 M, and 8.0 × 10−9 M, respectively, for 20 minutes of deposition time. After pretreatment of silver(I) ion with KC1, we could not observe any interference by other metal ions on the determination of the test ions in aqueous solution. Satisfactory results were acquired for the determination of the test metal ions in certified standard urine reference material SRM's 2670 (trace elements in urine).
Amoxycillinium‐Selective plastic membrane electrodes based on amoxycillinium‐phosphotungstate ion associate
Authors: Shoukry A. F. , Issa Y. M. , Rizk M. S. , Abdel‐Aal M. M.
Published: May 2005

The (1:3) (phosphotungstate:amoxycillinum) ion associate is used as the ion exchanger in preparing conventional and coated wire plastic‐membrane electrodes for amoxycillin (Am). The performance characteristics of the electrode are as follows: presoak time, 30 minutes; average slope: 59 ± 0.8 mV/ concentration decade, at 25°C, for 24 hours of continuous soaking; usable concentrations range, 1.96 × 10−4 to 1.5 × 10−2 M (Am); working pH range 3 to 9, and mean isothermal coefficient, 2.25 × 10−3 mV/°C. The electrode displays very good selectivity for Am toward a large number of inorganic and organic cations. The standard addition method and potentiometric titration are used to determine Am in pure solutions and in pharmaceutical preparations.
The electrocatalytic oxidation of D(+)‐glucose by a cis‐dioxoruthenium complex
Authors: Lai Yip‐Kai , Wong Kwok‐Yin
Published: May 2005

The ruthenium oxo complex electrogenerated from Cis‐[RuL2 (OH2)2]2+ (L = 6,6′‐dichloro‐2,2′‐bipyridine) is an active catalyst for the oxidation of D(+)‐glucose in solution. The second‐order rate‐constant for the reaction between cis [RuL2O2]2+ and D( + )glucose in 0.1 M CF3CO2H evaluated by rotating disk voltammetry is (1.2 ± 0.2) × 102 dm3 mol−1s−1. The chemically modified electrode prepared by immobilization of the ruthenium complex inside a Nafion film on the pyrolytic graphite electrode surface is capable of catalyzing glucose oxidation at potentials comparable to other reported modified electrodes.
Amperometric microbiosensors for detection of hydrogen peroxide and glucose based on peroxidase‐modified carbon fibers
Authors: Csöregi Elisabeth , Gorton Lo , Marko‐Varga György
Published: May 2005

A mediatorless amperometric microbiosensor can be constructed by immobilizing horseradish peroxidase (HRP) onto the surface of carbon fibers Several types of carbon fibers were tested. The best microelectrode, constructed by immobilizing HRP on high modulus. type (GH) carbon fibers, presented a linear response range between 20 μM and 2.5 mM H2O2 and a detection limit of 0. 2 μM H2O2 calculated as twice the signal‐to‐noise ratio. When HRP was coimmobilized with hydrogen peroxide‐producing glucose oxidase (GOD), a glucose sensor could be constructed with a linear potential range between 20 and 160 μM glucose, with a detection limit of 20 μM. The detection of the substrates was performed at a working potential of 0 mV (vs. SCE) at pH 6.0.
The preparation in situ of a silver–silver chloride reference electrode
Authors: Kulys Juozas , Munk Jens A , Buch‐Rasmussen Thomas , Hansen Henrik E.
Published: May 2005

The preparation in situ of a silver‐silver chloride reference electrode includes anodic‐cathodic pretreatment of a silver electrode in a phosphate buffer solution comprising 0.1 M sodium chloride. At pH 7.0 and 25°C and with optimally pretreated electrodes, the potential of the Ag/AgCl electrode was 45.0 mV (vs. SCE) with a reproducibility of 0.2%. In a period of 30 seconds following a delay of 2 to 10 seconds, the electrode shows a very stable potential that changes only 0.2 to 0.3%. The electrode potential changes 0.3 mV/°C. The electrode shows nernstian dependence of the potential to the sodium chloride concentration. At the physiological level, the only electrochemically active compound that significantly influences the potential of the electrode is reduced glutathione. Paracetamol (0.2 mM) and uric acid (0.27 mM) after slightly the electrode potential. The electrode parameters in plasma are close to those of phosphate buffer solution, whereas in artificial blood, the reproducibility and the stability of the potential decrease. The reproducibility and stability of the electrode potential in capillary blood was 1.4 and 3.7%, respectively.
Field‐Effect transistors as transducers in biosensors for substrates of dehydrogenases
Authors: Vering Thomas , Schuhmann Wolfgang , Schmidt Hanns‐Ludwig , Mikolajick Thomas , Falter Thomas , Ryssel Heiner , Janata Jiri
Published: May 2005

A specially designed field‐effect transistor (FET) with a significantly enlarged gate area was applied in a classical urea enzyme FET (ENFET). The resulting high stability and sensitivity toward pH shifts make it predestinated for the measurement of H+ produced in the equilibrium of NAD+ ‐dependent enzymatic reactions, especially when the equilibrium is shifted by a subsequent reaction. As a model, the glucose dehydrogenase (GDH) reaction connected to an ion‐sensitive field‐effect transistor (ISFET) is demonstrated by which glucose could be determined in the range from 1 to 40 mM. A platinum electrode on the gate of the FET permits the measurement of reduction equivalents (NADH) by means of the recently, reported chronopotentiometrical methods. Thus, in principle, a way toward a redox ENFET is shown.
Evaluation of mediators for development of amperometric microbial bioelectrodes
Authors: Kaláb TomáŠ , Skládal Petr
Published: May 2005

The microbial biosensors were constructed from carbon paste electrodes (CPEs) modified with insoluble mediators and immobilized membrane vesicles or whole cells of the bacterium Paracoccus denitrificans. The best results were obtained with membrane vesicles and ferrocene (FC). This system could serve for determination of succinate, D‐lactate, and L‐lactate. Significant increase of signal was obtained when competitive flux of electrons to oxygen was blocked by inhibiting terminal oxidases using cyanide.
Electroanalytical study of the antioxidant tert‐butylhydroquinone (TBHQ) in an oil‐in‐water emulsified medium
Authors: González‐Cortés Araceli , Armisén Pilar , Asunción Ruiz M. , Yáñez‐Sedeño Paloma , Pingarrón José M.
Published: May 2005

An electroanalytical study of the oxidation of tert‐butylhydroquinone (TBHQ) by differential pulse polarography (DPP) and square‐wave voltammetry (SWV) in an emulsified medium formed with ethyl acetate and Pluronic F‐68 is carried out. The optimization of the chemical variables of the emulsions by DPP allowed the choice of the following working conditions: pH 9.0, 0.04% Pluronic F‐68, 2.0 mL of ethyl acetate and 3 minutes as ultrasonic stirring time. The demonstrated reversibility of the electrode process at the mercury electrode makes it suitable for the application of SWV. The influence of the square‐wave (SW) characteristic parameters on the TBHQ net peak current at the hanging mercury drop electrode (HMDE) was tested. Calibration graphs were obtained within the ranges 1.0 × 10−5 to 1.0 × 10−4, 1.0 × 10−6 to 1.0 × 10−5, and 1.0 × 10−7 to 1.0 × 10−6 mol L−1. An improved sensitivity with respect to that obtained by DPP was produced. The limit of detection was found to be 6.2 × 10−8 mol L−1. Interferences from tert‐butylhydroxyanisole, tert‐butylhydroxytoluene, propylene glycol, citric acid, propyl gallate, and ascorbic acid were tested. The proposed method was applied with good results to the determination of TBHQ in spiked popcorn samples by direct emulsification of the ethyl acetate sample extract.