bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractCarbon 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

AbstractA 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

AbstractCarbon 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

AbstractNew 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

AbstractA 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

AbstractThe 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

AbstractNeutral (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

AbstractA 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

AbstractThe 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

AbstractIn 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

AbstractThe 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

AbstractThe (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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractPolymer 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

AbstractAn 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

AbstractThe 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

AbstractThe 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

AbstractCyclic 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.