摘要:

AbstractThe mechanical and physicochemical techniques for activation of solid voltammetric electrodes—that is, polishing, chemical, and electrochemical treatment and modification of the electrode surface by heat or electromagnetic radiation—are briefly surveyed and critically evalua

ISSN:1040-0397    

DOI:10.1002/elan.1140040902

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThis review article assesses the status of electroanalysis in the food industry. Modern trends in electroanalysis, which offer unique possibilities for assays of foods and drinks, and for monitoring food production processes, are discussed. Particular attention is given to the utility of new biocatalytic sensors, stripping techniques, and electrochemical flow detectors in the food industry. More than 90 references are given and future prospects are discussed.

ISSN:1040-0397    

DOI:10.1002/elan.1140040903

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe potentiometric response to anions of glassy carbon electrodes coated with thin unmetallated poly(tetrakis(p‐aminophenyl)porphyrin) (poly(H2(p‐TAPP))) films is examined. The polymer films are introduced onto the glassy carbon surface by constant‐potential anodic electrolysis of the porphyrin monomer from a solution of dichloromethane containing a quaternary ammonium perchlorate salt. The thickness of the film is the controlled by the electrodeposition time. Oxidized poly(porphyrin) modified electrodes exhibit near Nernstian response to iodide in the concentration range of 5 × 10−5– 1 × 10−1M with significant selectivity over a wide range of other anions tested. The mechanism of the electrode's iodide ion response is considered in light of its response to other redox‐active anions, and a recent literature report describing the selective iodide response of electrodes coated with electropolymerized poly(3‐methylthiophene) films. Spectroelectrochemical studies with poly(porphyrin)‐modified tin oxide electrodes are used to confirm the redox‐type response mechanism of the sensors toward iodide. The analytical limitations of using such polymer film‐modified electrodes for potentiometric io

ISSN:1040-0397    

DOI:10.1002/elan.1140040904

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractElectrochemical enzyme cells for glutamate and aspartate analysis have been assembled and used in continous‐flow and in flow‐injection analysis. The enzymes, glutamate oxidase (GOD) and aspartate amino‐transferase (AST), were co‐immobilized on an Immobilon Immuno‐affinity membrane, which was placed into a three‐electrode, flow‐through cell. Additional protective membranes were used to reduce the electrochemical interferences and to protect the immobilized enzymes. Thin‐layer and walljet cells were used and compared. Calibration curves for glutamate and aspartate showed a linearity range of 1–500 μmol/L and 10–500 μmol/L respectively. The sensitivity was higher using the flow‐through system with a response time of 2 min. Better reproducibility was achieved using the FIA procedure with a response time of less than 1 min. Glutamate in foodstuffs and asparatate in some pharmaceutical products were analyzed. Results were compared and correlated well

ISSN:1040-0397    

DOI:10.1002/elan.1140040905

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractGlucose‐oxidase (GOD) and glucose‐dehydrogenase (GDH) immobilized cylindrical microelectrodes were fabricated, and their characteristics were evaluated by using 1,4‐benzoquinone and ferricyanide as electron mediators, respectively. Each enzyme was immobilized in a photocrosslinkable polymer on a cylindrical microelectrode of 2 μm diameter. A linear range in the calibration plot of the GOD‐based micro‐glucose sensor was observed to be wider than that obtained using a disk electrode of 1 mm diameter. The mediated response of the 2 μm glucose sensor was compared with the response resulting from hydrogen peroxide detection. This result showed that a higher response and a wider linear range were observed at a highly concentrated mediator. For the GDH‐immobilized 2 μm microelectrode, a much higher response was obtained when not only ferricyanide but also diaphorase were employed to reoxidize NADH produced by the enzyme reaction of GDH. The GDH‐based micro‐glucose sensor was found to be unaffected by dissolved ox

ISSN:1040-0397    

DOI:10.1002/elan.1140040906

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractUltrasmall gold ring electrodes have been constructed by electrodeposition of gold onto carbon ring electrodes. Electrodes thus formed show similar adsorption/desorption peaks for oxygen in H2SO4solution compared to those obtained at conventional‐sized electrodes. These electrodes have been used in conjunction with linear scan voltammetry and subsequent cleaning pulses to obtain repeatable quantitative results for the electochemical oxidation of 5‐hydroxytrptamine and 5‐hydroxyindoleacetic acid. This technique involves the use of a linearly scanned applied potential, followed by a large positive potential to clean the electrode oxidatively and negative potential for electrode activation. The result of the cleaning pulses is that oxidation products of 5‐hydroxytryptamine are cleaned off the electrode and reproducible voltammograms are o

ISSN:1040-0397    

DOI:10.1002/elan.1140040907

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe reduction of mono‐ and dinitropyrazoles and of nitroimidazoles follows the general pattern of reduction of aromatic nitro compounds: The nitro group is reduced in a four‐electron step to a hydroxylamino group and the protonated form of the hydroxylamino group is—in the lower pH range—further reduced to an amine. This reduction differs from that of nitrobenzenes in participation of a second hydrogen ion probably involved in protonation of the heterocyclic ring. This second proton is for nitroimidazoles transferred before the uptake of the first electron, for nitropyrazoles probably after this uptake. The transfer of the second electron is indicated to be the potential determining step. The two sequences are H+, H+, e, H+, e, 2e, H+and H+, e, H+, H+, e, 2e, H+, respectively. For nitropyrazoles and nitroimidazoles without an alkyl substituent on the ring nitrogen, the reduction process is further complicated by the dissociation of the NH‐group in the heterocyclic ring. For 1‐alkyl‐5‐nitroimidazoles, for 4(5)‐nitroimidazole and for N‐unsubstituted‐4‐ and 3(5)‐ nitropyrazoles (but not for 2‐nitroimidazoles, 1‐alkyl‐4‐nitroimidazoles and 1‐alkylnitropyrazoles) the hydroxylamino derivative formed in the first four‐electron step undergoes a base catalyzed dehydration yielding a quinone‐like ketimine. Easy reduction of this species results in alkaline solutions in a limiting current which is significantly higher than corresponds to a four‐electron and limits to a six‐electron reduction. Such dehydration reactions occur considerably faster for dihydroxylamino derivatives formed in the reduction of dinitropyrazoles resulting in two wave

ISSN:1040-0397    

DOI:10.1002/elan.1140040908

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

Abstract1, 2‐Dialkyl‐4‐nitroimidazoles are reduced between pH 0 and 13 in a four‐electron wave. The resulting arylhydroxylamine is stable and in acidic media reduced further to the amine. 1,2‐Dialkyl‐5‐nitroimidazoles and 2‐alkyl‐4(5)‐nitroimidazoles are reduced in alkaline media with the number of electrons approaching six. The hydroxylamine derivative formed in these reductions can be dehydrated and yields an easily reducible, quinone‐like ketimine. The rate of the dehydration governs the heights of the first step and is base catalyzed. The sequence of electron and proton transfers for 2‐ alkylsubstituted nitroimidazoles is the same as that observed for corresponding desalkyl compounds.1‐Alkyl‐4‐amino‐5‐nitroimidazoles, as well as 1‐alkyl‐4‐nitro‐5‐aminoimidazoles, are reduced in a single wave, the height of which approaches that of a six‐electron process. The dehydration of the hydroxylamino derivative is favored, probably due to an internal base catalysis. The shifts of half‐wave potentials with pH differ principally from those of all other nitroimidazoles and indicate the predominant

ISSN:1040-0397    

DOI:10.1002/elan.1140040909

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe theoretical treatment of derivative potentiometric stripping analysis and differential potentiometric stripping analysis is presented. The latter term refers to the technique employing the derivative of time with respect to potential vs. the potential function as the measured signal. The mathematical expressions obtained were also verified experimentally.

ISSN:1040-0397    

DOI:10.1002/elan.1140040910

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractLidocaine transfer across the water/1,2‐dichloroethane and the water/nitrobenzene interfaces has been investigated by chronopotentiometry with linear current scanning and cyclic voltammetry. The irreversible hydrolysis occurring in the phase transfer of dicaine at the water/nitrobenzene interface is discusse

ISSN:1040-0397    

DOI:10.1002/elan.1140040911

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY