bluuebunny/crossref_metadata_2025 huggingface dataset:
The amperometric titration of copper(II) sulfate with potassium permanganate in surfactant suspensions
Authors: Franklin Thomas C. , Nnodimele Remi A.
Published: May 2005

It has been demonstrated that it is possible, in the presence of a cationic surfactant, to oxidize copper(II) sulfate (CuSO4. 5H2O) with potassium permanganate in aqueous sodium hydroxide solutions and to oxidize the solid copper(II) sulfate with solid potassium permanganate in methylene chloride. Presumably the surfacant solubilizes the solids and protects the unusual valence from reaction with water. In both solvents, the rate of reaction was fast enough to be followed with an amperometric titration. The stoichiometric reactions in these solvents were found to involve one potassium permanganate for three copper(II) sulfates, indicating that copper(II) was oxidized to in copper(III) while permanganate was reduced to manganese(IV). The results show that both ions and solids, suspended and coated with surfactants, can react rapidly enough for the reactions to be used in titrations and that copper(III) can be formed by chemical reaction and stabilized by a cationic surfactant film.
Catalytic determination of traces of uranium in rocks by chronocoulometry
Authors: Cantagallo Maria Inês C. , Gutz Ivano G. R.
Published: May 2005

The chronocoulometric method for the determination of trace levels of uranium based on the catalytic reduction of nitrate described in a preceding article, was applied and evaluated with real and synthetic samples Samples with complex matrixes like rocks were first solubilized in h9ot acid (HF+ HNO3) by digestion under pressure in a PTFE bomb. When necessary, liquid‐liquid exraction with tri‐n‐ butyl phosphate (TBP) followed by reversion to aqueous phase was used for previous separation of interferents. Results for a feldspar, a phosphorite, and three granitic rock in the range of 2 to 100 ppm, are in good agreement with those obtained by other tedhniques such as X‐ray fluorescence, isotopic dilution‐mass spectrometry (ID‐MS), and instrumental activation analysis (differences of 4 to 16% in relation to the unweighted mear for different techniques).
A high‐speed computerized polarographic system for cathodic stripping voltammetry in seawater
Authors: Hernández‐Brito J. J. , Cardona‐Castellano P. , Siruela‐Matos V. , Pérez‐Peña J.
Published: May 2005

A low‐cost computer‐controlled high‐speed polarographic system has been devised to determine heavy metals in seawater using adsorptive stripping voltammetry. The system consists of a potentiostat that has been developed in our Department, a 303A PAR polarographic cell, a personal computer with an I/O digital board PIO‐96, and a hp7440 plotter. The potentiostat operates between –2.5 and +2.5 V, with a multirange selection current between ±100 nA and ±1000 μA. There are various outlet channels with different time constants and noise levels. The quickest channel can detect processes in a 10 μs range with a noise level of ±4 nA (seawater matrix), while for a range of 30 ms, the noise is ±100 pA. The software controls different signal patterns, techniques, and a complete set of operations and has been developed in the C language to accelerate the data acquisition. The system has been successfully applied to high‐speed cathodic stripping voltammetry (HSCSV) on seawater samples, showing promising results in that there is an increase in the sensitivity over standard methods in the presence of oxygen and in stirred solutions. The analysis time can be reduced significantly at a high speed, and also, determinations aboard a ship are improved.
Ultrasensitive adsorptive–catalytic stripping voltammetry of iron in the presence of hydroxamic acids and hydrogen peroxide
Authors: Lu J. , Wang J. , Yarnitzky C.
Published: May 2005

An ultratrace catalytic–adsorptive stripping voltammetric procedure for the determination of trace amounts of iron is reported. The method is based on the interfacial accumulation of the iron‐N‐benzoyl‐N‐phenylhydroxylamine complex on the hanging mercury drop electrode, followed by catalytic reduction of the adsorbed complex in the presence of hydrogen peroxide. The presence of hydrogen peroxide greatly amplifies the adsorptive stripping response. Optimum experimental conditions have been explored to give an extremely low detection limit of 1.8 × 10−10 M (10 ng/L) iron following 10min accumulation. Analogous improvements are reported for other hydroxamic acid complexes of iron. Such acids hold great promise for developing additional adsorptive stripping procedures.
Differential pulse polarographic investigation of the nickel(II)–orotic acid complex
Authors: Blázquez L. Calvo , Gil E. Pinilla , Carra R. M. García‐Moncó , Misiego A. Sánchez
Published: May 2005

Differential pulse polarographic studies illustrate that the NiII ion forms a complex with orotic acid (aqueous medium, pH = 9.5, ionic strength μ = 0.2). The stiochiometric composition of this complex has been determined, and a method for its determination in an aqueous medium is proposed.
Dual enzyme amperometric biosensor for putrescine with interference suppression
Authors: Yang X. , Rechnitz G. A.
Published: May 2005

A putrescine biosensor has been developed. Putrescine oxidase, peroxidase, and bovine serum albumin were cross‐linked directly on the surface of a graphite electrode by glutaraldehyde. The sensor was used to determine putrescine at 0 mV (vs. Ag/AgCl reference electrode) in a potassium phosphate buffer (pH 7.4) solution containing 4 mM dopamine (3‐hydroxytyramine). The response of putrescine was linear up to 600 μM with a standard deviation of 2.8%. The detection limit was 5 μM. The response time was around 30 s. The lifetime was over 30 days when the electrode was used every day. The interferences of cadaverine and spermidine could be eliminated by added dopamine which, apparently, inhibits the enzymatic conversion of these substrates more strongly than that of putrescine.
Kinetic and mechanistic study of the copper(II)–oxamate complexation, monitored by the CuII solid state ion selective electrode
Authors: Karayannis M. I. , Veltsistas P. G. , Merkoci A. X.
Published: May 2005

The complexation process of copper(II) with oxamates was followed by the use of a copper solid state ion selective electrode. The shape of the recorded potential vs. time was interpreted on the basis of the known kinetic expressions for a two step reaction, monitoring the consumption of the reagent. The potential changes of the electrode are attributed to a decrease in the copper concentration. The curves are of an exponential form with two distinct parts, the first due to the intermediate activated complex, which is produced very rapidly, and the second is due to the slow formation of the soluble chelate. The effects of various parameters are studied in relation to the retardation of the first step. The reaction rate constant k, the equilibrium constant K* for the first step, the stability constant K, the activation energy Ea, the change in enthalpy, and the product (pZ) of the frequency and steric factors were determined. On the basis of the above data, a mechanistic scheme for this complexation reaction is proposed.
Cation determination in aqueous solution using the methyl viologen‐doped zeolite‐modified carbon paste electrode
Authors: Walcarius A. , Lumberts L. , Derouane E. G.
Published: May 2005

Methyl viologen (MV2+) initially exchanged in a zeolite Y modified carbon paste electrode (ZMCPE) is reduced after being exchanged for the supporting electrolyte cation. The use of an electrolyte cation that cannot enter zeolite channels to a great extent does not give rise to appreciable currents while a non‐size‐excluded cation allows liberating MV2+ from zeolite particles and their subsequent reduction at the electrode–solution interface. Following those observations, the MV2+‐based ZMCPE has been used for the constant potential (−0.85 V) amperometric detection of nonreducible:, non‐size‐excluded cations in aqueous medium. The performance of this electrode was investigated in both batch injection analysis (BIA) and flow injection analysis (FIA). The great advantage of BIA coupled to the amperometric detection is the ability to use electrolyte‐free sample solutions. For FIA experiments, dissolved oxygen was eliminated by using an electrochemical scrubber containing porous carbon electrodes. With the MV2+‐doped ZMCPE, alkali and alkali‐metal cations can be detected at the submillimolar level for both batch and flow injection analysis.
Determination of metal–organic complexation in natural waters by SWASV with pseudopolarograms
Authors: Lewis B. L. , Luther G. W. , Lane H. , Church T. M.
Published: May 2005

A novel electrochemical method is described for the examination of metal–organic complexation in natural waters. The technique is based upon the comparison of square wave anodic stripping voltammetry (SWASV) ‘pseudopolarograms’ (current vs. deposition potential plots) for natural samples with those obtained for metal complexation with selected ‘model’ binding ligands at constant ionic strength. For electrochemically active zinc species in seawater, the pseudopolarogram approach allowed the estimation of thermodynamic stability constants (KML) within a stability constant window of approximately 104–106 M−1 up to ≥ 1015 M−1. For a natural rainwater sample, the pseudopolarogram indicated only one zinc class, probably a mixture of ‘free’ and/or inorganically complexed species. In an application to a coastal seawater sample, three species were identified: (1) weakly complexed, log KZnL = 4.14 ± 0.92 M−1; (2) moderately complexed, log KZnL = 7.77 ± 0.62 M−1; (3) strongly complexed, log KZnL = 11.45 ± 0.95 M−1. Results are compared to those obtained using complexometric titration with SWASV at a thin mercury film–glassy carbon rotating disk (TMF–GCRD) electrode. The latter detected a single strong complexing ligand (or ligand class), with [L′] = 15.25 ± 0.04 nM and log K′ZnL ≥ 10.9 M−1.
Carbon paste electrodes with electrolytic binder: Influence of the preparation method
Authors: Ramírez M. T. , Palomar M. E. , González I. , Rojas‐Hernández A.
Published: May 2005

A method for the construction of carbon paste electrodes (CPE) is described. Here ferrocene is used as the insoluble electroactive species, graphite powder as conductor and sulfuric acid as binder. The CPE thus prepared prevents ferrocenium ions from diffusing towards the bulk solutions. Voltammetric, chronopotentiometric and chronoamperometric experiments performed with these CPEs show that the different preparation methods yield different electrochemical parameters for the ferrocene–ferrocenium system.
Oxidative behavior of aminohalogenbenzophenones – indirect determination of benzodiazepinooxazoles
Authors: Fernández M. C. , Alonso R. M. , Jiménez R. M. , Rodríguez F. J.
Published: May 2005

An electroanalytical study of three aminohalogenbenzophenones: 2‐amino‐5‐chlorobenzophenone (MCB), 2‐amino‐2′,5‐dichlorobenzo‐phenone (DCB), and 2‐amino‐5‐bromo‐2′‐fluorobenzophenone (BrFB); metabolites of the psychotropic drugs benzodiazepinooxazoles and benzodiazepines, has been carried out at a glassy carbon electrode using different voltammetric techniques. The compounds studied are electrooxidizable in a hydroalcoholic medium (MeOH:H2O, 10 : 90), 0.5 M KC1, and a pH range of 1–13. The oxidation processes are irreversible and predominantly diffusion controlled. On the basis of the oxidation process, voltammetric methods have been developed that allow the determination of aminohalogenbenzophenones from 0.2 to 15ppm for MCB and BrFB, and 0.2 to 14ppm for DCB; with a reproducibility in terms of relative standard deviation (RSD) lower than 5.2% for 10 determinations of 10 ppm solutions of MCB, DCB, and BrFB. Detection limits of 200ppb (μg/L) for MCB and DCB, and 100ppb for BrFB were obtained. The voltammetric method developed for DCB has been applied to the indirect determination of Cloxazolam in tablets.
Polarographic behavior of 2‐carboxybenzaldehyde thiosemicarbazone and the indirect trace determination of palladium(II) ions in catalysts
Authors: Cabanillas Augustina Guiberteau , Espinosa‐Mansilla Anunciación , Salinas Francisco , López‐de‐Alba Pedro L.
Published: May 2005

The electrochemical characteristics of 2‐carboxybenzaldehyde thiosemicarbazone (2CBTSC) have been studied by differential pulse polarography (DPP) and cyclic voltammetry (CV) at a mercury electrode. This new thiosemicarbazone is reduced in a two‐electron irreversible step at the nitrogen double bond of the side chain at pH 1.82. An anodic peak situated very close to the oxidation response of mercury has been observed by DPP in neutral and alkaline media. Determination of 2CBTSC based on the reduction peak is possible in the range of 5 × 10−8 M to 8 × 10−6 M, with a relative standard deviation of 2.3% in the middle of the range and a detection limit of 7.6 × 10−9 M (1.7 ng/mL). The decrease in the reduction peak of the thiosemicarbazone after the addition of Pd(II) has been used for the development of precise and sensitive amperometric determination of palladium in catalysts with an average relative error of 1.1% and a determination limit of 6ppb of Pd(II) (5.6 × 10−7 M).
Stripping measurements of hydrogen peroxide based on biocatalytic accumulation at a horseradish peroxidase/ferrocene/carbon paste electrode
Authors: Ciszewski Aleksander , Górski Zbigniew
Published: May 2005

Carbon paste electrodes containing horseradish peroxidase and ferrocene accumulate charge in the presence of hydrogen peroxide, the discharge of which gives the chronoamperometric stripping current. Hence a 50‐fold enhancement of the response for 50 nM hydrogen peroxide is obtained following 60s preconcentration. The hydrogen peroxide measurements were made in 0.05 M phosphate buffer of pH 7.4. The relative standard deviation at the 50 nM level is 9.8%. The electrode is useful for hydrogen peroxide determination for more than two days.
The electrochemistry of hydrogen peroxide on evaporated gold/palladium composite electrodes. Manufacture and electrochemical characterization
Authors: Johnston David A. , Cardosi Marco F. , Vaughan D. Huw
Published: May 2005

A thin‐film composite metal electrode is described for the amperometric measurement of hydrogen peroxide. By thermally evaporating a 27 μM layer of gold/palladium through a copper mask onto a plastic substrate a number of chemically equivalent sensing elements can be prepared. On these electrodes, hydrogen peroxide can be oxidized at a voltage of 0.4V (SCE). A model for the oxidation of peroxide at these electrodes is described based upon reversible binding of hydrogen peroxide to electrochemically generated palladium oxide sites.
Electrocatalytic amperometric detection of hydroxylamine with a palladium‐modified carbon paste electrode
Authors: Cai Xiaohua , Kalcher Kurt , Lintschinger Josef , Neuhold Christian G. , Tykarski Janusz , Ogorevc Bozidar
Published: May 2005

Carbon paste electrodes (CPEs), modified by addition of Pd powder to the paste and electroactivation, exhibited electrocatalytic activity towards hydroxylamine. Electrogenerated palladium(0) at the electrode surface was found to be involved in the electrocatalytic oxidation of NH2OH. The electrode was employed as an amperometric detector for flow injection systems. Repeated injections (60) of hydroxylamine (5 ng) showed a relative standard deviation of 4.0%. Linear relation between the current and the analyte concentration was found between 0.1 and 10 ng of hydroxylamine. The detection limit was 20pg NH2OH (3σ). The applicability of the method to the determination of hydroxylamine in river water was investigated.
New polycrystalline solid state responsive electrodes for the determination of the selenite ion
Authors: Zareh Mohsen M. , Amin Alaa S. , Abdel‐Aziz Manar
Published: May 2005

New electrodes for the selective determination of selenite were constructed by compressing either HgSeO3 or a mixture of HgSeO3 and Hg2Cl2. The linear concentration range was 6.0 × 10−5−10−1 M with a slope of 29.5 mV/concentration decade. The usable pH range for both electrodes was wide (3–10) and their life span was up to 8 days. Selectivity coefficient values were determined for various anions and no significant interferences were observed for most of them. The solubility products of some sparingly soluble selenite salts were determined using the latter electrode.
Anodic stripping voltammetry for the determination of trace iodide
Authors: Guanghan Lu , Min Yang , Qifang Zheng , Ailan Wang , Zexiang Jin
Published: May 2005

A carbon paste electrode is used for stripping voltammetry of trace iodide in a Britton–Robinson (B–R) buffer containing cetyltrimethyl ammonium bromide(CTMAB). The electrochemical behavior of I2BrR is described. In a solution containing 0.1 μg/mL iodide, the relative standard deviation for ten determinations is 3.3%, the peak height also varies linearly with the concentration of iodide over the range 0.05–0.25 μg/mL, and the detection limit is 0.03 μg/mL. This method has been used for the determination of iodide in table salt samples with 88–104% recovery.
Coulometric stripping potentiometry
Authors: Jagner Daniel , Wang Yudong
Published: May 2005

The combination of a novel electrode design and a new experimental approach to coulometry permits the analysis of microliter amounts of samples without prior calibration. The technique has been applied to the determination of lead in whole blood standards. The time for one analysis is 4min and the relative precision approximately 5%. The mass detection limit for cadmium is 3 fmol, the lowest mass detection limit hitherto reported for any electroanalytical technique. The measurements are based on the principle of constant current stripping potentiometry. Amalgamated analytes are re‐oxidized by a Combination of an applied constant current and spontaneous chemical oxidation. Equations making it possible to apply Coulomb's law are presented.
Control of selectivity and electroactivity on underoxidized polypyrrole film electrodes
Authors: Zhao Shishan , Luong John H. T.
Published: May 2005

Neutral (or under‐oxidized) PPY film electrodes were directly prepared by electropolymerization and elimination of the subsequent oxidation of the deposited PPY layers during the polymerization process. Electroactivity and selectivity could be established on these nonconducting, densely packed neutral PPY film electrodes through controlled oxidation. Development of electroactivity for different redox solutes was concluded to be a combination of the creation of conducting areas and the opening of transport channels in the neutral PPY network by the oxidation. Selectivity of the PPY film electrode was controlled by selection of electrolyte counter‐anion, management of molecular size, and change of pH.
Insoluble inorganic salts as carbon paste electrode modifiers for preconcentration and voltammetric determination of oxalic acid
Authors: Cai Xiaohua , Ogorevc Božidar , Tavˇar Gabrijela , Kalcher Kurt
Published: May 2005

A novel approach for chemical modification of carbon paste electrodes (CPEs) has been investigated. Selected water‐insoluble inorganic salts as modifiers were found to exhibit preconcentration capability for oxalic acid under open‐circuit conditions in a pH 4.3 buffered solution. After medium exchange to a pure electrolyte (Britton–Robinson buffer, pH 8), the accumulated oxalate was measured by square‐wave anodic stripping voltammetry with a peak current response at 1.2 V (vs. Ag/AgCl). The water‐insoluble inorganic salts as modifiers were active through the interfacial accumulation of insoluble oxalate by the exchange of anions. The candidate inorganic salts should be, therefore, less insoluble than the corresponding oxalates, whereas, the differences in solubility between the modifiers and the corresponding oxalates are of minor importance. Among the investigated inorganic salts, lead sulfate produced the highest response under the employed conditions and was therefore exploited as accumulating material for oxalic acid. With suitable preconcentration times, a linear calibration graph from 0.7 mg/L to 42.8 mg/L of oxalic acid in the analyte solution was obtained, and a detection limit of 0.3 mg/L at a preconcentration time of 5min was achieved. The lead sulfate‐modified CPE was used to determine oxalic acid in orange juice without pre‐separation.
Adsorptive stripping voltammetry in dispersed media. Application to the determination of the herbicide terbutryn
Authors: Pedrero Maria , Alonso M. Rosa , de Villena F. Javier Manuel , Pingarrón Jose M.
Published: May 2005

The possibility of applying adsorptive stripping voltammetry (AdSV) in dispersed media has been evaluated. Sensitive methods for the determination of the herbicide terbutryn at nanomolar levels by AdSV at the hanging mercury drop electrode in micellar and emulsified media are proposed. The anionic surfactant sodium pentanesulfonate was chosen as the most suitable agent for micellar solutions and oil–water emulsions. On the other hand, ethyl acetate was used as the organic solvent to form terbutryn emulsions. A systematic study of the various experimental parameters that affect the stripping response was carried out by differential pulse voltammetry. When working in a 0.1 mol L−l perchloric acid medium with an accumulation potential of −0.60 V, terbutryn could be determined over the 6.0 × 10−9−4.0 × 10−7 and 6.0 × 10−9−2.0 × 10−7 mol L−1 ranges in micellar (50s accumulation time) and emulsified (70s accumulation time) media, respectively. The limits of detection were 2.2 × 10−9 and 1.1 × 10−9 × mol L−1, and the relative standard deviations (n = 10) were 6.3 and 4.3% in micellar and emulsified media, respectively. The effect of other coexisting herbicides on the terbutryn stripping peak was evaluated. Finally, the developed method in emulsified medium was applied to the determination of terbutryn in spiked tap waters.
Electrochemical behavior of metallothioneins and related molecules. Part I: Lys–Cys–Thr–Cys–Cys–Ala thionein fragment [56–61] MT I
Authors: Mendieta Jesús , Chivot Jacques , Muñoz Amalia , Rodríquez Adela Rosa
Published: May 2005

In order to obtain a better understanding of the electrochemical behavior of the Metallothionein (MT), the peptidic fragment Lys–Cys–Thr–Cys–Cys–Ala [56–61] MT I (FT) compound constitutive of the proteic structure has been studied. The elucidation of the electrochemical mechanism at the electrode could be reached from comparison with other mechanisms proposed for similar molecules. This study stems from a more complete work. Under our experimental conditions, with a low concentration of the substance (< 5 × 10−5 M) and the use of a dropping mercury electrode, a diffusion controlled mechanism is suggested for the electrochemical behavior of FT. In this case the mercury electrode itself is involved in the charge transfer step and the polarographic response is attributed to the oxidation of the mercury electrode in the presence of the chelating agent FT. This hypothesis was supported by the lack of modification of the electrocapillary curves in the presence of low concentration of FT in relation to those obtained with the supporting electrolyte alone and by the linear relationship between the polarographic intensity and the concentration at a low concentration of FT. The influence of the pH of the solution on the behavior of FT was investigated using DC and DPP methods. The variation of i1, ip and Ep with pH was determined. From these results the apparent acid‐base dissociation constant of the FT was evaluated, corresponding to the dissociation of protons from the thiol groups. Likewise the apparent stability constants of the Hg–FT were estimated as a function of the pH. It was assumed that the main complex of Hg–FT possessed a stoichiometry of 1 : 1 but it is probable that two or more different complexes coexisted.
Electrochemical behavior of metallothioneins and related molecules. Part III: Metallothionein
Authors: Muñoz Amalia , Rodríguez Adela Rosa
Published: May 2005

The electrochemical behavior of Cd–Zn Thionein from rabbit liver and horse kidney with respect to pH of the solution at the dropping mercury electrode was studied, using differential pulse polarography (DPP). At pH 7.5 three well defined peaks were observed at a potential different from the potentials corresponding to pure Cd2+ and Zn2+. Two different electrochemical systems are involved: the oxidation of the mercury electrode in the presence of thiol groups contained in the metallothionein and the reduction of either free (pH < 4) or complexed (pH > 6) metal ions. The apparent acid‐base dissociation constant of metallothionein was estimated. The apparent stability constants of the complexes CdT, ZnT and HgT were estimated at different pH values. Cadmium forms at least two complexes with thionein exhibiting different stabilities and probably different structures. Modifications in the polarograms with the addition of Cd, Zn and the peptidic fragment [56–61] MT I, a molecule intrinsic to the metallothionein structure, were studied. A diagram showing the oxido‐reduction potentials corresponding to twelve diflerent electrochemical species is given. DPP allows one to distinguish the chemical forms of compounds (speciation).
Metformin‐selective polyvinyl chloride (PVC) membrane electrode based on the metforminium phosphomolybdate ion pair
Authors: Rizk Mahmoud S.
Published: May 2005

The (1:1) (phosphomolybdate : metforminium) ion pair was used as the ion exchanger in preparing conventional plastic membrane electrodes for metformin (Mf) and their performance characteristics were studied. The electrode exhibited a linear response with a Nernstian slope over a relatively wide concentration range. The calibration‐plot slope was constant for up to 5 days with continuous soaking at 57 mV/concentration decade at 25°C; it subsequently decreased as the time of soaking increased, reaching 42mV/decade after 20 days. The change in pH did not affect the electrode performance within the range 3.0–10.5. The standard electrode potentials were determined at different temperatures and were used to calculate the isothermal coefficient of the electrode (0.000695 V/°C). The electrode displayed good selectivity for Mf with respect to a large number of inorganic and organic cations. The standard addition method and potentiometric titration were used to determine Mf in pure solutions and in pharmaceutical preparations.
Chemically amplified detection of catecholamines by liquid chromatography using an L‐ascorbic acid carrier
Authors: Uchiyama Shunichi , Itoi Naoyuki , Husehe Yusushi
Published: May 2005

The oxygen consumed during the tyrosinase reaction is significantly amplified by L‐ascorbic acid due to a substrate recycling process; the substrates have to be separated in order to obtain individual amplified current responses of each substrate. In this work, the chemically amplified current responses of catecholamines were obtained individually by liquid chromatography using an immobilized tyrosinase reactor and an L‐ascorbic acid carrier solution. The highly sensitive determinations of L‐dopa, dopamine, and norepinephrine were carried out individually using a Clark type oxygen electrode detector. The amplification factors of 1 × 10−7 M L‐dopa, norepinephrine, and dopamine were found to be 224, 357, and 568, respectively, when 5 × 103 M L‐ascorbic acid solution was used as a carrier; the detection limit for dopamine was found to be 5 × 10−9M.
Attempts to modify an electrode with a conducting platinum cluster compound
Authors: Xu Liang , Li Fenglei , Dong Shaojun
Published: May 2005

A conducting platinum cluster compound K1.64Pt(C2O4)2 was electrochemically synthesized on a glassy carbon electrode through the electrooxidation of K2Pt(C,2O4)2 in an aqueous medium using single potential step and cyclic voltammetry methods. The precursor K2Pt(C2O4)2 was prepared by a ligand exchange reaction between C2O42− and PtCl42−. During single potential step experiments, the electrolytic current corresponding to the oxidation of K2Pt(C2O4)2 increased dramatically after a sharp decrease at the beginning (due to the formation of conducting K1.64Pt(C2O4)2 on the surface of the working electrode). Two kinds of mechanism account for the current transients at the different applied potentials. Cyclic voltammetry was conducted with K1.64Pt(C2O4)2 on the surface of the working electrode and a steady‐state diffusion current was observed. Since the material grew in a fibrous manner, each conducting fiber which was in contact with the electrode could serve as an ultramicroelectrods. The behavior of the working electrode was thus changed from a plain to an ultramicroelectrode array.
Investigation of batch measurements with immobilized enzyme reactors and amperometric electrodes
Authors: Amine Aziz , Palleschi Giuseppe
Published: May 2005

The optimization of all parameters which govern the response of a biosensor is generally very difficult. Flow‐injection analysis with an immobilized enzyme reactor (IER) is considered as a complementary method or possibly an alternative to a biosensor. Similarly, the proposed batch experiments with an IER, can in many instances advantageously replace the biosensor. The principle consists of successive insertions of appropriate IERs into the cell solution after a steady‐state current output has been recorded from the interfering species present in the solution. Selected examples of enzymatic assays in food samples, aimed either at eliminating electrochemical interferences or allowing multi‐substrate determinations are reported and discussed.
Polymer membrane‐based polyion sensors: Development, response mechanism, and bioanalytical applications
Authors: Fu Bin , Bakker Eric , Yun Jong H. , Wang Enju , Yang Victor C. , Meyerhoff Mark E.
Published: May 2005

Polymer membrane type ion‐selective electrodes (ISEs) are now used routinely to measure clinically important ions (e.g., Na+, K+, Ca2+) in undiluted blood. However, efforts to develop similar sensors suitable for the direct detection of larger biomolecules have been less successful owing to the difficulty in identifying appropriate membrane chemistries that yield a significant and selective response toward the desired macromolecular analytes. Recently, we have found that poorly plasticized polymer membranes (PVC) doped with lipophilic anion and cation exchangers exhibit unexpectedly large and reproducible potentiometric responses to low levels (< 1 μM) of certain biomedically important macromolecular polyionic species (heparin and protamine). This article provides data demonstrating how the specific membrane formulation and electrode geometry used influence the magnitude of the polyion EMF responses observed. The results suggest a non‐ equilibrium/steady‐state polyion extraction process is responsible for the potentiometric heparin and protamine responses exhibited by appropriately formulated membranes. The practical utility of these sensors for monitoring heparin levels in blood as well as heparin/ protamine binding to other biologically important macromolecules will be described. Further, the prospects of adapting the same polyion extraction chemistry to devise optically sensitive thin polymer films for monitoring heparin will also be addressed.
Flow‐injection liposome immunoanalysis (FILIA) with electrochemical detection
Authors: Edwards Alison J. , Durst Richard A.
Published: May 2005

An automated flow‐injection liposome immunoanalysis (FILIA) system with electrochemical detection has been developed to measure the herbicide alachlor. The computer‐controlled system is composed of commercially available components, with the exception of the reusable immunoreactor column packing material (glass beads) which is covalently coated with antibody specific for the analyte of interest. Use of such components affords full automation while simplifying the construction of, and modifications to, the system. The assay is based on competition in the immunoreactor column between alachlor‐tagged liposomes containing an electroactive marker, ferrocyanide, and free alachlor, with quantitative signal amplification provided by lysis of bound liposomes with surfactant to release the marker. An optimized assay permits the detection of 0.5 ng alachlor in a spiked water sample. The electrochemical detector is operated in the controlled‐potential, amperometric mode in which ferrocyanide is oxidized at low potential (+ 0.330 V vs. Ag/AgCl), thus minimizing electroactive interferences. The relationships among the various operational parameters (e.g., potential, flow rate, assay time, composition of solutions) are discussed, and the optimization of these parameters is presented.
From molecular recognition to analytical information using chemical sensors: Development of a combined catheter gastric pH‐probe
Authors: Spichiger Ursula E. , Aiping Xu , Citterio Daniel , Bühler Hans , Chaniotakis Nik , Rusterholz Bruno , Simon Wilhelm
Published: May 2005

The best possible performance of a sensor can be described in terms of information theory according to Shannon, and is based on the reduction in entropy of a system. The relevant quantity is the maximum yield in information. The maximum yield in information can be related directly to the analytical performance and the selectivity of the recognition process. A combined catheter electrode for potentiometric intraluminal pH‐measurement of 3 mm outer diameter was developed and tested in gastric juice. The sensor described is based on the neutral chromoionophore ETH 2418 incorporated into a liquid membrane of variable composition. The sensor was optimized to obtain maximum yield in information relevant to medical intragastric applications. The influence of different types of polymers, plasticizers, additives and carriers, and of varying their concentrations was studied. Studies focused on: extending the dynamic pH range; showing a sufficient pH‐resolution and accuracy by eliminating the interference of the drug Dormicum. The combined catheter electrode showed a wide dynamic range, high long‐term potential stability and good reproducibility, as well as a fast response time in aqueous solutions [15]. The maximum yield in information for 9 decades of H+‐activity was calculated as to be 7.94 bits. The loss in information for one decade loss in dynamic range from 9 to 8 decades of H+‐activity and constant reproducibility is 0.17 bits. This measure allows the comparison of required and achieved quality of different probes, accuracy not respected.
Electrically ‘wired’ tyrosinase enzyme inhibition electrode for the detection of respiratory poisons
Authors: Robinson Gemma , Leech Dónal , Smyth Malcolm R.
Published: May 2005

The use of the solution redox species, [Os(bpy)2Cl2]+/0, [Os(bpy)2(MeIm)Cl]2+/+ and [Fe(CN)6]4−/3−, where bpy is 2,2‐bipyridine and MeIm is N‐methylimidazole, as electron mediators in the enzymatic reduction of oxygen by tyrosinase is investigated. Co‐immobilization of both enzyme and an osmium redox mediator in a hydrogel on glassy carbon electrodes results in a biosensor for the ‘reagentless’ addressing of enzyme activity, consuming only oxygen present in solution. Immobilized enzyme inhibition biosensors can thus be constructed for the detection of tyrosinase inhibitors, such as sodium azide, using this approach. The enzyme inhibition biosensor can detect levels of azide as low as 5 × 10−6 mol dm−3 in solution and may be useful in environmental monitoring applications and as an early warning poison sensor.
Some peculiarities observed in voltammetric studies of different glassy carbon electrodes in nonaqueous media
Authors: Bjelica Luka J. , Jovanović Ljiljana S. , Rehák Nándor L.
Published: May 2005

Cyclic voltammograms for the ferric/ferrous reaction in prevailingly nonaqueous solutions, recorded with three electrochemically pretreated (ex situ) glassy carbon electrodes (GCEs) of low heat‐treatment temperature (HTT), showed an unexpected increase in peak separations (ΔEp) with an increasing content of DMF or ethanol in the solution. This deactivating effect, which was minor with the Tokai was extremely pronounced with the GCEs of low HTT. In contrast to this, the ΔEp values obtained with these GCEs after their polishing with alumina showed a dramatic decrease with increasing content of the organic solvent. On the other hand, the ΔEp values for the voltammograms of the ferrocene/ferricinium reaction were practically independent of the nature and content of the organic solvent, electrode pretreatment mode, or the HTT value.
Variation in PED response at a gold microelectrode as a function of waveform parameters when applied to alditols and carbohydrates separated by capillary electrophoresis
Authors: Roberts Robert E. , Johnson Dennis C.
Published: May 2005

Results are presented from a systematic study of the noise (N) and peak‐to‐noise ratio (P/N) obtained for pulsed electrochemical detection (PED) at a gold micro‐wire electrode applied to a mixture of alditols and monosaccharides separated by capillary electrophoresis (CE). The electrode potentials and time periods for oxidative cleaning and reductive reactivation of the electrode were held constant in the PED waveform at minimum allowable values and the time period for digital integration of electrode current (tint) was varied from 50 to 800 ms by 50‐ms intervals. The value of N was virtually independent of tint and P/N increased approximately as a linear function of tint in the range 50–200 ms corresponding to waveform frequencies in the range 4.5–2.7 Hz. A detection limit of 9 fmol glucose was determined for a 4‐nL injection using tint = 200 ms.
An enzyme‐containing ink for screen‐printed glucose sensors
Authors: Nagata Ryohei , Yokoyama Kenji , Durliat Hélène , Comtat Maurice , Clark Susan Anne , Karube Isao
Published: May 2005

A glucose sensor employing ferrocene‐bound glucose oxidase was fabricated by the screen printing technique. In order to obtain high GOD activity, glucose oxidase (GOD) was modified with ferrocenecarboxylic acid (fc) as an electron mediator. Simultaneous spectroscopic and electrochemical analyses showed that ferrocene‐bound GOD (fc‐GOD) displayed an increase in catalytic current. The ferrocene acts as an electron transfer relay between the active center of the enzyme and the gold electrode. The screen printing process was used to print successfully the unique fc‐GOD containing ink onto the gold electrode patterned on the glass plate. The fc‐GOD containing ink was specially developed to be suitable for the printing apparatus. The printed glucose sensor was shown to offer a stable calibration profile and stable electrochemical properties.
Metal‐dispersed screen‐printed carbon electrodes
Authors: Wang Joseph , Pedrero Maria , Pamidi Prasad V. A. , Cai Xiaohua
Published: May 2005

Nickel‐, cobalt‐, copper‐, and palladium‐dispersed carbon inks are used for screen printing of electrocatalytic sensors. The resulting strips couple the advantages of mass‐producible disposable electrodes and effective catalytic surfaces. The dispersed metal particles lead to a marked decrease in the oxidation potential for carbohydrates, amino acids, aldehydes or alcohols. Characterization of the electrocatalytic behavior and the analytical (sensing) performance are reported. Applicability to wine samples is illustrated.
Thin‐layer composite enzyme electrodes for glucose determinations
Authors: Zawodzinski Thomas A. , Campbell Carmen , Davey John , Gottesfeld Shimshon , Serach James , Wilson Mahlon , Rishpon Judith
Published: May 2005

We have prepared amperometric glucose sensitive electrodes with a composite active layer consisting of Nafion, glucose oxidase, and carbon‐supported platinum particles. A particularly advantageous configuration results from the use of such a film on a gas diffusion electrode. We demonstrate that the gas diffusion electrode configuration enables us to supply oxygen from the back of the electrode, thus providing the capability of operating the sensor independent of dissolved oxygen. The insensitivity to solution oxygen concentration has been demonstrated by monitoring the glucose response of the electrode after extensive deoxygenation of solution. Cast composite layers yield mechanically robust coatings with high enzyme loadings, and thus high sensitivity to glucose. The electrode responds rapidly and is stable over a long period (90% activity after more than half a year) when stored in solution. We have optimized the composition of the sensitive layer with respect to Nafion to C/Pt ratio and enzyme loading.
Reinvestigation of a ferric ion‐selective electrode based on the chalcogenide glass FexSe60Ge28Sb12(x = 1–10)
Authors: Koenig Christian E. , Graber Erich W.
Published: May 2005

A ferric ion‐selective electrode based on the iron containing chalcogenide glass FexSe60Ge28Sb12(X = 1–10) was reinvestigated in order to optimize the electrode characteristics and to elucidate the mechanism of the potential determining process. By modifying the preparation procedure of the chalcogenide glass described in the literature and of the electrode configuration highly stable sensors were obtained. These sensors show super‐Nernstian slopes of the calibration plots of about 65 mV/decade, selectivity coefficients of about 10−4for several heavy metal ions and a potential drift of 3–4 m V/h due to some slow corrosion process occuring at the electrode surface. Furthermore the data of impedance, cyclovoltammetric, and XPS experiments show that the conditioning process of the electrode leads to a modified surface layer which behaves like a specific ion exchanger for Fe3+ ions. In contact with a Fe3+ containing electrolyte, the exchange of Fe3+ ions between the electrolyte and the modified surface layer leads to the injection of holes from the surface layer into the bulk of the chalcogenide glass. Thus the fermi level of the material is shifted, causing the observed potential change.
An indirect voltammetric approach for the determination of cyanide at a chemically modified electrode
Authors: Sousa Maria de Fátima B. , Godinho Oswaldo E. S. , Aleixo Luiz M.
Published: May 2005

An indirect voltammetric procedure for measuring free cyanide ions, using a chemically modified carbon‐paste mercury‐sensitive electrode, is described. The method is based on competitive HgII‐complex formation reactions between an organic ligand at the electrode surface and CN− ions in solution. A linear decrease of the peak current of mercury in a solution of a defined Hg2+ concentration was observed, when the cyanide concentration was increased from 8.0 to 49.0 mg/L (0.3‐1.9 × 10−6M). The relative standard deviation for five independent measurements was 8%.
Optimization by experimental design of the adsorptive stripping voltammetric parameters in the determination of cinoxacin
Authors: Gratteri Paola , Furlanetto Sandra , Pinzauti Sergio , Leardi Riccardo , Corti Piero
Published: May 2005

The quinolone antibacterial agent cinoxacin was studied by adsorptive stripping voltammetry making use of its controlled interfacial accumulation on a static mercury drop electrode. Measurements were obtained in differential pulse mode and optimized by experimental design. The chemometric approach allowed the identification of a strong interaction between pH and pulse amplitude. The dynamic linear range of calibration was extended from 0.4 to 9 × 10−8 M. Analyses of cinoxacin capsules and spiked human urine sample were carried out without the need of previous extraction or filtration. A cleanup procedure was required to separate cinoxacin from the human plasma matrix prior to adsorptive stripping analysis.
Ultrasonic extraction and field‐portable anodic stripping voltammetry of lead from environmental samples
Authors: Ashley Kevin
Published: May 2005

Ultrasonic extraction of lead from environmental samples, followed by anodic stripping voltammetric (ASV) analysis using a field‐portable ASV instrument, was evaluated. Representative lead‐containing standard reference materials were subjected to ultrasonic agitation in dilute nitric acid, and the lead subsequently determined by ASV. Recoveries of lead were found to be statistically equivalent to those obtained previously by means of hotplate concentrated acid digestion and atomic spectrometric analysis. Laboratory‐prepared air filter samples were also analyzed for lead content by using the ultrasonic extraction/portable ASV analytical protocol. For duplicate laboratory‐prepared air filter samples, results from microwave digestion and atomic absorption analysis compared well with those from ultrasonic extraction and portable ASV analysis. The lower detection limit for the ultrasound/portable ASV method was found to be less than 1 ppb Pb in solution, or < 0.1 μg Pb/filter. The results suggest that the method may allow for the on‐site determination of lead in environmental samples such as paint, dust, soil and workplace air.
Biosensors based on cross‐linking of biotinylated glucose oxidase by avidin
Authors: Vreeke Mark S. , Rocca Patrick
Published: May 2005

Avidin, having four biotin binding units, cross‐links and immobilizes glucose oxidase (GOX) labeled with multiple biotins (B‐GOX) when solutions of B‐GOX and avidin are mixed on an electrode. The H2O2 flux generated in the B‐GOX catalyzed oxidation of glucose by dissolved O2 is measured as an electroreduction current at a horseradish peroxidase (HRP) redox conducting hydrogel electrode poised at +100 mV (Ag/AgCl). The sensitivity of the resulting glucose sensor is 0.14 A cm−2 M−1 with a linear range up to 2mM glucose.
Determination of casein by square‐wave voltammetry using electrocatalytic reduction of nickel(II)
Authors: Perez Ambrosio Sanchez , DelgadoZamarreño Maria M. , Mendez Jesús Hernandez , Turrion Nieves María B.
Published: May 2005

The catalytic peak produced at −0.80 V (vs Ag/AgCl) by the presence of casein in the reduction of NIII on a dropping mercury electrode in sodium acetate medium was explored using square‐wave voltammetry (SWV). The effects of the electrochemical variables on SW voltammograms were studied and optimum operating conditions were established (10−2 M NiII, 1 M sodium acetate, pH 7.0 and temperature of 23° C). Good linearity between the SW voltammetric peak current and casein concentrations in the 0–128 mg L−1 range was obtained. An electrocatalytic method is proposed for the determination of casein with rapid and precise results (relative standard deviation of 5.2 %).
Submersible bioprobe for continuous monitoring of peroxide species
Authors: Wang Joseph , Cepría Gemma , Chen Qiang
Published: May 2005

A peroxidase‐based biosensor, coupled to a newly designed remote probe, is used for monitoring peroxide species at large sample‐instrument distances. The new bioprobe can operate over a broad pH and ionic‐strength ranges relevant to natural water conditions. Measurements of micromolar levels of hydrogen peroxide and 2‐hutanone peroxide in untreated river and groundwater samples are demonstrated, and prospects and challenges for remote field applications are discussed.
Determination of metals in a multicomponent system by differential pulse and alternating current anodic stripping voltammetry
Authors: Locatelii Clinio , Vasca Ermanno , Bighi Corrado , Fagioli Francesco , Garai Tibor
Published: May 2005

A combination of sensitive and selective voltammetric methods, namely differential pulse (DPASV) and fundamental and second harmonic alternating current anodic stripping voltammetry (ACASV) were found to be very suitable techniques for the simultaneous determination of metal species having half‐wave potentials close to one another. The simultaneous determination of traces of CuII, BiIII, SbIII, PbII, CdII and SnII is described using 0.1 M HCl as the supporting electrolyte with the subsequent addition of 0.02 M EDTA or 1.0 M NaOH (for the analysis of CuII, SbIII and SnII, respectively). A semistationary mercury electrode (long lasting sessile drop mercury electrode) was used as the working electrode. A saturated calomel electrode (SCE) and a platinum electrode were used as the reference and auxiliary electrodes, respectively. The analytical procedure was verified with the analysis of standard reference material NBS‐SRM 631 Spectrographic Zinc Spelter LVl. Precision and accuracy, expressed as relative standard deviation and relative error, respectively, were 3 to 5%, while the detection limits were of the order of 10−8 to10−10 M in the case of element examined.