摘要:

AbstractAn overview of the analytical applications of conducting polymers is given. Examples of methods based on the change in electrically conductivity of the polymer membrane, exchange of the doping anion, determination of metals by deposition and stripping, incorporation of neutral compounds in the polymer membrane, and the novel properties of a polymer surface are presented and discussed.

ISSN:1040-0397    

DOI:10.1002/elan.1140030403

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractChemically modified electrodes exhibit unique behavior that can greatly benefit electrochemical sensing. In this article we review the development and applications of modified electrodes for chemical sensing. After a general introduction, different strategies for surface modification, as employed in chemical sensing, are discussed in detail. Special attention is given to permselective coatings, which offer controlled access at the sensor surface or the surface immobilization of biological entities that specifically recognize the analyte. Better, understanding of these modified electrodes is achieved by using high resolution surface characterization techniques. Future prospects are evaluated.

ISSN:1040-0397    

DOI:10.1002/elan.1140030404

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractA definition of electrogenerated luminescence (ECL) is given. Chemiluminescent reactions of different kinds are cited, as well as various types of pathway to the formation of the emitting excited state. After a consideration of the energetic and kinetic requirements for ECL‐producing reactions, the experimental conditions are examined. The important concept of ECL efficiency is introduced, as well as the feasibility of elucidating the mechanisms of ECL reactions. Some interesting new ECL systems are mentioned, together with examples of analytical applications of such scheme

ISSN:1040-0397    

DOI:10.1002/elan.1140030405

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe shapes of normal and reverse flow injection (nFI and rFI) signals have been studied using single‐channel manifolds, amperometric and visible spectrophotometric detection, and small and large (>1.5 mL) injection volumes. The shapes of nFI and rFI signals are fundamentally different because in rFI the sample, being the carrier stream, is present in essentially infinite volume. For this reason, rFI signals are broader and are prone to double‐peak formation at lower injection volumes than are nFI signals. Contributions to the final signal from dispersion at the front and rear boundaries of the injected bolus frequently are, or appear to be, unequal. With loop injection, the rear boundary travels further than the front boundary and is dispersed more: injection by stream switching removes this factor. With spectrophotometric detection, correction for large and opposite refractive index effects at the two boundaries may be required. In amperometric detection, differences in acidity of carrier stream and injectate can cause significant changes in background current on switching and can distort the signal at low concentrations of monitorand. When these factors are eliminated, however, other factors causing peak height and peak shape differences remain: differences in dispersion rates of reactants, and of reaction rates, appear to be the major fact

ISSN:1040-0397    

DOI:10.1002/elan.1140030406

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractA new enzymatic amperometric sensor for hydrogen peroxide based on a modified carbon paste electrode is described. Horseradish peroxidase and ferrocene mediator were immobilized by dissolution or dispersion in a graphite–paraffin oil paste. To prevent losses of immobilized chemicals under operational conditions, the electrode surface was coated with a Nafion membrane. The device exhibits a relatively fast response time (42 s for 95% of the steady‐state response) and yields currents linearly related to the hydrogen peroxide concentration over the 10−7to 10−5mol/L range in both static and flow injection operations. The slope of the calibration plot remained constant for more than 20 days. Flow injection assays of hydrogen peroxide at a sampling rate of about 70 injections per hour, with a relative standard deviation of 1.4%, are possible. An easy and low cost preparation procedure is de

ISSN:1040-0397    

DOI:10.1002/elan.1140030407

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractCharacteristics of ion‐selective field effect transistors (ISFETs) and ion‐selective electrodes (ISEs) with solvent polymeric membranes were compared for slope, selectivity, drift, and hysteresis. Drift and hysteresis of ISFETs were significantly inferior to those of analogous ISEs. Experiments using conventional ISEs with internal electrolyte solutions and ion‐selective liquid membranes of different kinds indicate that both primary ion and ionophore are necessary in the internal electrolyte solution and the ion‐selective membrane, respectively, to achieve small drift and small hysteresis. It is, therefore, concluded that to realize highly reliable membrane‐solid contact devices, the interface between the membrane and the solid in membrane–solid contact devices like ISFETs and coated wire electrodes (CWEs) should be electrochemica

ISSN:1040-0397    

DOI:10.1002/elan.1140030408

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractA numerical simulation is performed to calculate the amperometric response for a porous coating on an electrode surface to a Gaussian concentration plug in a flowing stream. The amperometric response is considered as a function of the layer thickness, the diffusion coefficient of the analyte through the layer, and the width of the Gaussian concentration profile. We consider the effect of the first two parameters on the magnitude of the current response and the lag time, which is the time delay between the time at which the peak of the concentration profile reaches the outer edge of the porous layer and the time of the peak current response. However, although it is not possible to decouple the magnitudes of the layer thickness and the diffusion coefficients from experimental measurements, it is possible to determine one parameter if the other is known. The width of the amperometric response varies linearly with that of the incident Gaussian concentration profile.

ISSN:1040-0397    

DOI:10.1002/elan.1140030409

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractComplex formation of Zn(II) and Cd(II) with polymethacrylic acid (PMA) and polyacrylic acid (PAA) is studied by sampled direct current, normal pulse, reverse pulse, and differential pulse polarography and by differential pulse anodic stripping voltammetry (DPASV). Titrations of Zn(II) or Cd(II) with partially neutralized PMA or PAA by DPASV allow the precise determination of the apparent formation constantKof the four systems. The two Zn(II) systems appear to be labile on the different time scales of the several techniques, without remarkable complications due to secondary phenomena. TheirKvalues, determined by all techniques, agree satisfactorily. The two Cd(II) systems, and especially the Cd/PAA system, show rather involved behavior, which tends to normality when the degree of neutralization αnof the polycarboxylates increases. Both slow kinetics and ligand adsorption coupled with induced Cd(II) adsorption (evidenced by maxima on the normal pulse polarograms) seem to be present. For all αnvalues, DPASV yields higher estimates ofKthan do polarographic technique

ISSN:1040-0397    

DOI:10.1002/elan.1140030410

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractComplex formation of Cd(II) with alginic and polygalacturonic acids is studied by normal pulse (NPP), reverse pulse (RPP), and differential pulse polarography (DPP), as well as by cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV). Titrations of Cd(II) with partially neutralized alginic or polygalacturonic acids, at different ionic strengths, by DPP and DPASV allow the precise determination of the apparent formation constantKof both systems. The systems appear to be labile on the different time scales of the various techniques. Adsorption of both polysaccharides, and the further induced adsorption of Cd(II), is evidenced clearly by NPP. On the other hand, the induced adsorption of Cd(II) is minimized under the conditions of RPP. The reversibility of the redox couple Cd2+/Cd(Hg) is not strongly affected by the presence of polysaccharides. Dependence of the apparent formation constants on the total ionic strength is reported.

ISSN:1040-0397    

DOI:10.1002/elan.1140030411

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe construction and performance of new carbon paste enzyme electrodes as amperometric sensors is described. Xanthine oxidase and alkaline phosphatase have been adsorbed on a carbon paste electrode (CPE), and physically entrapped with a semipermeable membrane. The product of enzymatic reaction, uric acid or p‐nitrophenol, was electrochemically oxidized versus an Ag/AgCl electrode at +0.4 or +0.8 V, respectively, yielding a steady‐state current directly related to the substrate concentration. Response characteristics as well as kinetic parameters have been evalua

ISSN:1040-0397    

DOI:10.1002/elan.1140030412

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY