摘要:

AbstractThis review deals with the use of pyridine‐nucleotide dependent dehydrogenase enzymes in amperometric biosensor design. The electrochemistry of the nicotinamide coenzymes, their mechanism and the challenges associated with their direct oxidation on solid electrodes are discussed. In addition, a survey of the different solutions proposed in the literature for addressing these problems and some of their applications are presente

ISSN:1040-0397    

DOI:10.1002/elan.1140090302

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe amperometric and cyclic voltammetric detection of α‐melanocyte stimulating hormone (MSH), β‐endorphin, and corticotropin‐like intermediate lobe peptide (CLIP), all proopiocortin (POC) derived peptides secreted from melanocytes of the pituitary intermediate lobe, at carbon fiber microelectrodes was investigated. For amperometry, it was found that all of these peptides could be detected; however, fouling of the electrodes reduced the response of the electrode after successive application of the peptide in flow injection experiments. The fouling was apparently due to oxidation of tyrosine in the peptides as similar results were found for tyrosine but not tryptophan. The effect of fouling could be reversed if the electrode was electrochemically treated by scanning from −1.0 V to +1.0 V at 300 V/s for 2 min between application of the peptides. Using cyclic voltammtery at 800 V/s, it was possible to distinguish MSH, which had a peak shaped voltammogram, from the other POC peptides, which had relatively flat voltammetric waves at this scan rate. The scan rate dependence of the peak current for MSH revealed that the voltammetry was adsorption controlled. As a result, in a monitoring application, where voltammograms are continuously obtained with a fixed interval between them, decreasing the interval increases the temporal resolution but decreases the sensitivity for MSH. It was found that when monitoring the current in the potential range of 0.90 to 1.00 V, the temporal response to MSH was dependent upon the potential window used for scanning. Using high scan rates and a potential window 0 to 1.2 V, it was possible to monitor exocytosis from single melanocytes and use the voltammogram to demonstrate detection of MSH from

ISSN:1040-0397    

DOI:10.1002/elan.1140090303

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThin‐film gold electrodes were produced by radio‐frequency sputtering using a polyvinyl chloride foil as substrate. The voltammetric behavior was characterized in various electrolyte solutions. In alkaline and neutral aqueous solutions reliable voltammetric measurements can be performed while in acidic media some nondefined phenomena occur. A novel type of electrode for batch injection analysis (BIA) is presented which is produced from circular pieces of the thin‐film material. This electrode can be used for BIA in conventional voltammetric cells. Pulsed amperometric detection is demonstrated to be viable with thin‐film gold electrodes and shows analytical advantages over constant‐potential detection in the BIA of hydrogen

ISSN:1040-0397    

DOI:10.1002/elan.1140090304

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractElectrocatalytical reduction of hydrogen peroxide and oxygen was performed by horseradish peroxidase, recombinantCoprinus cinereusperoxidase,Polyporus pinsituslaccase andBotrytis cinerealaccase on carbon paste electrodes containing a paraffin soluble mediator. The electrocatalytical process proceeded at 0.0V (vs Ag/AgCl; in situ electrode). The electrode responses had maximum values at pH 6.4 and 5.5 for the horseradish peroxidase and laccases catalyzed reactions, respectively. The sensitivity for horseradish peroxidase and recombinantCoprinus cinereusperoxidase was 23.4 and 5.4 μC nM−1cm−2, respectively. A detection limit of 7.5 fmol horseradish peroxidase could thus be achieved. Systems based on laccases showed lower sensitivity. The model of electrocatalytical reduction of hydrogen peroxide and oxygen included a permanent liberation of mediator from the carbon paste and it's biocatalytical conversion in the diffusion layer. The model was analyzed by comparing kinetic data in homogeneous solution with the electrode response. Mass transport effects were studied by using rotating carbon paste electr

ISSN:1040-0397    

DOI:10.1002/elan.1140090305

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA channel flow cell specifically designed for ultraviolet‐visible spectroelectrochemical experiments is described. The performance of the cell was characterized using the oxidation ofN,N,N′,N′‐tetramethyl‐p‐phenylenediamine in aqueous electrolytes and excellent agreement between theory and experiment was obtained. The technique was applied to study the dimerization rate of methyl viologen radical cations. The mechanistic results confirm that the electrogenerated methyl viologen radical cation dimerizes rapidly in aqueous solution and a previously unknown dimerization rate constant close to 104M−1s

ISSN:1040-0397    

DOI:10.1002/elan.1140090306

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA method for the voltammetric determination of vanadium(v) using a carbon paste electrode in situ modified with cetyltrimethylammonium bromide (CTAB) is described. Vanadium is preconcentrated at the electrode surface via its anionic oxalate complex from acidic solution (0.01 M oxalic acid, 0.25 mM CTAB, pH 2.2) at a potential of −0.9 V [vs. the saturated calomel electrode (SCE)]. Simultaneously during accumulation, vanadium(v) in the complex is reduced to its tetravalent state. Differential pulse anodic stripping voltammetry exploiting the reoxidation can be used for the determination of trace levels of vanadium(v). Linearity between current and concentration exists for a range of 5 to 200 μg.L−1Vvwith a preconcentration time of 1 min. The limit of detection (calculated as 3 σ) is 0.07 μg.L−1with a preconcentration time o

ISSN:1040-0397    

DOI:10.1002/elan.1140090307

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe diffusion coefficient values of GaIIIin potassium nitrate and potassium chloride supporting electrolytes have been obtained polarographically. The half‐wave potential,E1/2, andE3/4‐E1/4values have also been determined. TheE3/4‐E1/4values confirm the irreversibility of GaIIIreduction in KNO3and KCl electro

ISSN:1040-0397    

DOI:10.1002/elan.1140090308

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe adsorptive stripping voltammetric determination of zeatin at a carbon fiber electrode is optimized and characterized. Applicability to assays of vegetable extracts is illustrated.

ISSN:1040-0397    

DOI:10.1002/elan.1140090309

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe preparation of carbon paste electrodes (CPEs) modified with the hexacyanoferrate ion attached to synthetic hydrotalcite, a solid anion exchange resin Wofatit SBW and a liquid anion exchanger tris‐octylamine (TOA) used as pasting liquid, is described. Stability of the electrodes and their electrocatalytic properties were investigated. The surface‐modified hexacyanoferrate‐TOA‐CPE can be prepared and renewed in a simple and reproducible manner. The sensor was applied to the determination of ascorbic acid in real samples using a mediator accumulation/chronoamperometric detection

ISSN:1040-0397    

DOI:10.1002/elan.1140090310

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe tensammetric determination of the total concentration of mixtures of nonionic and anionic surfactants is desribed. By taking advantage of the different accumulation behavior of nonionic and anionic surfactants on the surface of the hanging mercury drop electrode (HMDE), it has been possible to determine the total concentration of nonionic surfactants without contribution from anionic surfactants. After subtraction of nonionic surfactant concentration from total, the concentration of anionic surfactants can be determined indirectly. Detection limits of 10 to 100 μg L−1for single compounds and 100 μg L−1for mixtures were calculated. Humic acids, relevant complexing reagents (like EDTA) and different cations do not interfere in the determination when they are present in typical concentrations found in surface waters. The method has been applied to several mixtures of surfactants. The possibility of solid‐phase‐extraction (SPE) for sample pretreatment has been inv

ISSN:1040-0397    

DOI:10.1002/elan.1140090311

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY