摘要:

AbstractThe electrochemical properties of carbon paste electrodes (CPEs), including unmodified and modified with protein and polycations, were investigated by impedance spectroscopy (IS) using ferricyanide and ferrocene monocarboxylic acid (FcMA) as redox probes. Various electrochemical pretreatments were applied to the unmodified CPE. The heterogeneous charge transfer rate constant of ferro/ferricyanide couple is enhanced by 2 to 10 times compared with that obtained at untreated electrodes. It was found that for ferricyanide the more suitable pretreatments are successive cyclic voltammetric scans, cathodization and a square wave‐like stepping rather than high‐potential anodization. However, the pretreatment only exhibits a slight effect on the kinetics of FcMA. At the CPEs containing modifier, the electron transfer rate of the redox couple depends more on the pH of electrolyte solution if ferro/ferricyanide is used. The results can be explained by the differently charged states of the CPEs that were caused by the protonation or deprotonation of the modifiers in various pH solutions and demonstrate the importance of the electrostatic interaction on the kinetics of the highly polar species such as ferricyanide. The different adsorptive behavior of ferricyanide and FcMA is also discus

ISSN:1040-0397    

DOI:10.1002/elan.1140090502

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe development of an amperometric biosensor for the determination of phenolic compounds is described, using quinoprotein glucose dehydrogenase. The enzyme is integrated into carbon paste and its ability to donate electrons to oxidized phenolic compounds during glucose oxidation is exploited. The sensor response is based on electrochemical oxidation of the phenolic compound followed by its enzymatic regeneration when the bulk solution contains glucose and the electrode is potentiostated at +500 mV (vs. Ag/AgCl/0.1 mol/L KCl). As the result of the catalytic analyte regeneration the electrodes offer very sensitive measurements of redox species likep‐aminophenol and hydroquinone and catecholamines such as epinephrine, norepinephrine, and dopamine. The sensor performance is characterized for the different substrates. Highest sensitivity is achieved forp‐aminophenol which could be determined at sub‐nanomolar

ISSN:1040-0397    

DOI:10.1002/elan.1140090503

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractAn amperometric biosensor for hypoxanthine determination has been developed. The sensor uses a Nafion‐paraquat chemically modified glassy‐carbon electrode. It detects the oxygen consumed by the enzymatic reaction catalyzed by xanthine oxidase which is immobilized on the electrode surface. The sensor responds linearly to hypoxanthine over the concentration range of 1 × 10−6M −2 × 10−4M. The biosensor can be reused for more than 100 times without significant deterioration in performance. After 32 days storage at 3–5°C, the sensor response remains at 68% of the initial level. The high sensitivity, selectivity and stability of this biosensor demonstrates its practical applicability for a simple, rapid and economical determination of hypoxanthine i

ISSN:1040-0397    

DOI:10.1002/elan.1140090504

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractSquare wave voltammograms of methyl viologen (MV2+) were recorded at a renewable Nafion‐loaded carbon paste electrode immersed in 20 mL of phosphate buffer solution (pH 7.4) contained in a beaker‐type electrochemical cell (Pyrex glass; contact area = 33 cm2). From the calibration plot obtained in the concentration range 0.01–2.4 μM, it could be concluded that the maximum surface excess of MV2+adsorbed on Pyrex glass (0.24 nmol cm−2) was reached at concentrations above 1.4 μM. The adsorption isotherm presented a sigmoidal shape characteristic of attractive interaction. From this plot, it was evaluated that the maximum depletion of MV2+in solution (28%) did not occur at the lowest concentrations, but in nearly micromolar solutions. This result emphasizes the unavoidable and random errors which are involved when MV2+solutions are purposely diluted in Pyrex glassware. The MV2+adsorption proceeds to a less extent on Duran borosilicate glass and/or in acid or alkali

ISSN:1040-0397    

DOI:10.1002/elan.1140090505

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractAnalytical and numerical methods are used to establish concentration distributions around channel microband electrodes both in isolation and as part of multi‐electrode arrays. The importance of axial diffusion in addition to convection and diffusion normal to the electrode surface is stressed. In particular, downstream depletion effects are shown to occur over many electrode lengths, so that the diffusion fields of electrodes within arrays overlap and interfere. A simple analytical expression is derived to describe this depletion and permits the design of practical arrays in which electrodes operate essentially independently of each othe

ISSN:1040-0397    

DOI:10.1002/elan.1140090506

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

Abstract(4S)‐4′‐diisopropyl‐2,2′‐bithiazoline (DPT) is an electroactive organic chiral compound giving two reduction responses in square‐wave voltammograms at potentials about −0.2 and −0.4 V by forming a complex with mercury which deposits at the electrode surface. By the addition of copper(II) ion to the solution of DPT a third peak appears between them at about −0.3 V, which corresponds to the reduction of adsorbed Cu‐DPT complex. Optimal pH for the investigation of those redox processes was found to be 2.8. By square‐wave voltammetric measurements it was interpreted that these redox reactions were quasireversible with immobilized reactants. By plottingip/fvs. frequency a quasireversible maximum was obtained, and the apparent standard reaction rate constants were calculated: log (ks)DPT=(0.91 ± 0.9) and 1

ISSN:1040-0397    

DOI:10.1002/elan.1140090507

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractAn electrochemical biosensor for the specific detection of short DNA sequences from theE. colipathogen is described. This hybridization device relies on the immobilization of a 25‐mer oligonucleotide probe, from theE. coli lacZgene, onto a screen‐printed carbon electrode. Chronopotentiometric detection of the Co(bpy)3+3indicator is used for monitoring the hybridization event. Numerous variables of the assay protocol, including those of the probe immobilization step, the hybridization event, and the indicator association/detection, are characterized and optimized. Hybridization times of 2‐ and 30‐min are sufficient for detecting 300‐ and 50 ng/mL, respectively, of theE. coliDNA target. Applicability to analysis of untreated environmental water samples is illustrated. Such single‐use electrochemical sensors hold great promise for decentralized environmental and food testing for theE. c

ISSN:1040-0397    

DOI:10.1002/elan.1140090508

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA semi conducting polymer‐modified glassy carbon electrode was fabricated by cyclically sweeping in the potential range of −0.4–1.2 V(vs. SCE) or by electrolyzation at constant potential of 1.4 V in 0.5 M sulfuric acid solution containing 1.0 mM Nile Blue. This redox active polymer could successfully be used for the amperometric determination of hemoglobin. The effect of pH was studied for the polymerization of Nile Blue. It was found that the polymerization did not occur in neutral or basic solutions. The formal potential of this film is −410 mV (pH 7.0) which is more negative than that obtained at the bare electrode in the Nile Blue bulk solution. The electrochemical characteristics of this polymer are discussed. The modified electrode could electrocatalyze the reduction of hemoglobin, and a good linear amperometric response could be obtained over the range of 0.05–7.0 mg/mL (correlation coefficient: 0.985). This modified electrode exhibited good stability and reproducibility for long

ISSN:1040-0397    

DOI:10.1002/elan.1140090509

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe modification of carbon paste matrices with fibrinogen is reported. The effect of the pH of the solution on the CV peak currents of positively or negatively charged redox analytes was examined at the fibrinogen‐modified carbon paste electrode. In the presence of the coating, pH‐dependent selectivity in electrochemical detection of charged species was demonstrated depending on the sign of the supported charge. Above the isoelectric pH attributed to the immobilized protein (5.5), the current response of anionic redox probes [Fe(CN) 63−/Fe(CN) 64−] was impeded while the response was almost totally restored below this pH. Opposite trends were observed with the Ru(NH3) 63+/Ru(NH3) 62+cationic

ISSN:1040-0397    

DOI:10.1002/elan.1140090510

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe utility of potentiometric stripping analysis (PSA) for studying the interaction of fulvic acid with CuIIand PbIIat pH 1.8 and 4.8 was assessed. The impact of fulvic acid on both the deposition and stripping steps was considered. In contrast to results obtained by anodic stripping voltammetry, fulvic acid influenced both these steps in PSA, and to different degrees. Surface active substances have been claimed to have self‐compensatory effects in PSA; this work shows that this is not valid for heterogenous natural complexants such as fulvic aci

ISSN:1040-0397    

DOI:10.1002/elan.1140090511

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY