ISSN:1040-0397    

DOI:10.1002/elan.1140070102

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA review is presented dealing with the use of carbon paste as an electrode maaterial for electrochemical sensors (311 references). It covers mainly publications which appeared during the period 1990–1993; numerous applications demonstrate the widespread applicability of carbon paste in the field of electrochemical analysis, such as voltammetry, amperometry, and potentiometry, but also as an electrode for electrochemical detectors in flow system

ISSN:1040-0397    

DOI:10.1002/elan.1140070103

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA review is presented dealing with the use of carbon paste amperometric electrodes for electroanalytical purposes, with either the surface or the bulk being modified with biologically derived material such as enzymes, tissues, and cells. It covers virtually all the publications which have appeared from the very first enzyme‐modified carbon paste electrode up to early 1994 and includes 220 reference

ISSN:1040-0397    

DOI:10.1002/elan.1140070104

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractSelf‐assembled monolayers of cystamine and cysteine chemisorbed on gold electrode surfaces have been used as a support for covalent immobilization of some phenoxazine and phenothiazine derivatives. The covalent attachment was achieved after previous functionalization of the free amino groups on the electrode surface with bifunctional reagents (terephthaloyl chloride and 1,6‐hexamethylene diisocyanate) able to react with the imino form of the amino group in position 3 of the phenoxazine and phenothiazine derivatives.In every case, a shift of the redox potentials between 130 and 180 mV towards more positive potentials, as well as an increase in the peak‐topeak separation between anodic and cathodic peaks was observed after covalent attachment. The surface coverages (10−11<Γ<10−10mol/cm2) obtained from the cyclic voltammograms were those for a not densely packed monolayer and varied depending on the redox compound immobilized. The surface‐modified electrodes obtained were afterwards used for the electrocatalytic oxidation of NADH.UV‐vis spectroscopy was used to monitor the successive steps of surface modification using gold semitransparent electrodes. The total surface coverage of redox mediator on the electrode surface could also be calculated from the optical difference spectra between the oxidized and the reduced state obtained ‘in situ’ in a spectroel

ISSN:1040-0397    

DOI:10.1002/elan.1140070105

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractConstruction of a reproducible, reliable and rugged iridium‐based microelectrode is described. Perfect electrical contact, Ir‐glass sealing and Ir disk morphology are the key points for obtaining reproducible voltammetric sensors. These points are discussed in detail and optimal fabrication conditions are given. Electron bombardment under vacuum yielded good soldering between Ir and Cu electrical cable. Reproducible polishing of the microelectrode to a mirror like Ir disk surface is obtained with silicon carbide pads and diamond paste using an automatic home made polisher. Cyclic voltammetry and optical microscopy have been used to characterize this microelectrode. Hgplated Ir‐based microelectrodes are prepared by electrodeposition of mercury on the iridium disk substrate. Reproducibility and reliability close to 100% have been obtained for Ir‐based microelectrode preparation, mercury layer deposition and trace metal measurements by differential pulse anodic stripping voltammetry (DPASV) and square wave anodic stripping voltammetry (SWASV) in synthetic solutions even at low ionic strength (10−3M). Continuous measurements over long periods of time indicate that the Hg‐plated Ir‐based microelectrodes can be used for several days without renewal of the mercury layer. These microelectrodes were applied to lead and cadmium speciation studies directly in river waters by SWASV without any separation. The results show that free PbIIand CdIIconcentrations as low as 0.5 nMand 0.1 nMrespectively can be determined by direct measurements, without perturbing the medium. The lifetime of these microelectrodes in the present state of the art is more

ISSN:1040-0397    

DOI:10.1002/elan.1140070106

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractCathodic stripping voltammetry of copper, based on the accumulation and reduction of its complex with 1,10‐phenanthroline (phen), has been studied. The complex is reduced in two steps from CuI–phen and CuII–phen to copper amalgam at potentials of −0.43 and −0.62 V vs. Ag/AgCl, respectively. The reduction processes are strongly dependent on the pH of the solution, as well as on the concentration of the metal ion and ligand. The reduction mechanism of both complexes was established. The detection limit for copper in 0.55 mol/LNaCl with 20 min accumulation at 0.0 V vs. Ag/AgCl, measuring the reduction peak of the CuI–phen complex at −0.43 V vs. Ag/AgCl by SWV, was found to be about 5 × 10−10mol/L. The reaction parameters were calculated by square‐wave voltammetry (SWV), i.e., transfer coefficients α Cu I‐phen= 0.31 and α Cu II‐phen= 0.45, and the maximum surface concentrations Γ Cu I‐phen= (2.02 ± 0.08) × 10−11mol/cm2and Γ Cu I‐phen= (2.83 ± 0.12) × 10−12mol/cm2. Measurements of the copper cont

ISSN:1040-0397    

DOI:10.1002/elan.1140070107

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractFour different polymer‐modified mercury film electrodes (MFEs) on a glassy carbon substrate were tested for their ability to determine lead and cadmium in the presence of surfactants. The polymers used for electrode modification were: Nafion, polyaniline, base‐hydrolyzed cellulose acetate, and base‐hydrolyzed poly(ethyl 3‐thiophene acetate). Triton X‐100, sodium dodecyl sulfate, dodecyl pyridinium chloride, and bovine serum albumin were chosen as representatives of surface active compounds. It is shown that polymer‐covered electrodes are useful in surfactant‐containing media in some instances, but none of them remained unaffected by any of the four surfactants. The cellulose acetate electrodes seem to be less affected by proteins than the bare MFE and other modified electrodes. The Nafion and cellulose acetate‐coated electrodes were used for the determination of lead in filtered and acidified, but otherwise untreated, water samples from a sewage treatment plant. The results obtained with the cellulose acetate‐coated electrode were in good agreement with those from atomic absorp

ISSN:1040-0397    

DOI:10.1002/elan.1140070108

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractAn 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 × 10−10M(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 strippin

ISSN:1040-0397    

DOI:10.1002/elan.1140070109

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA flexible glucose biosensor was constructed by immobilizing glucose oxidase within a gold‐coated, hydrophilic polytetrafluoroethylene membrane. All reagents and materials used were harmless and nontoxic. Enzyme immobilization was improved using a mesh mask during gold deposition, the grid pattern permitting better access into the membrane. The masked sensors had greatly improved output currents and linearity. The sensor was linear up to 662 mgL−1, the range covering the concentrations encountered in normal and diabetic human tear fluids. The current was proportional to the square of the electrode area, hence an electrode of known dimensions can be used without precalibration. Sterilization using 80% ethanol had a negligible effect on its response. The sensor is well suited to the detection of glucose or other analytes in body fluids, such as tears, airway mucus, sweat, and sal

ISSN:1040-0397    

DOI:10.1002/elan.1140070110

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractSeveran organic peroxides were studied by differential pulse polarography (DPP) in water and water–solvent media, and compared to hydrogen peroxide. Reduction occurred usually between −0.1 and +0.3 V vs. SCE, except for the peroxides containing atert‐butyl group adjacent to the OO function. In this case, reduction was more difficult and was shifted to the −0.9 to −1.1 V vs. SCE range. Diffusion coefficients were determined and are in the 4 − 9 × 10−10m2s−1range. The detection limits are generally no lower than 5 × 10−5mol l−1, due to the high irreversibility of the reduction process. Calibration plots from 5 × 10−5to about 5 × 10−4m

ISSN:1040-0397    

DOI:10.1002/elan.1140070111

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY