摘要:

AbstractA putrescine biosensor has been developed. Putrescine oxidase, peroxidase, and bovine serum albumin were cross‐linked directly on the surface of a graphite electrode by glutaraldehyde. The sensor was used to determine putrescine at 0 mV (vs. Ag/AgCl reference electrode) in a potassium phosphate buffer (pH 7.4) solution containing 4 mM dopamine (3‐hydroxytyramine). The response of putrescine was linear up to 600 μMwith a standard deviation of 2.8%. The detection limit was 5 μM. The response time was around 30 s. The lifetime was over 30 days when the electrode was used every day. The interferences of cadaverine and spermidine could be eliminated by added dopamine which, apparently, inhibits the enzymatic conversion of these substrates more strongly than that of putre

ISSN:1040-0397    

DOI:10.1002/elan.1140070202

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe complexation process of copper(II) with oxamates was followed by the use of a copper solid state ion selective electrode. The shape of the recorded potential vs. time was interpreted on the basis of the known kinetic expressions for a two step reaction, monitoring the consumption of the reagent. The potential changes of the electrode are attributed to a decrease in the copper concentration. The curves are of an exponential form with two distinct parts, the first due to the intermediate activated complex, which is produced very rapidly, and the second is due to the slow formation of the soluble chelate. The effects of various parameters are studied in relation to the retardation of the first step. The reaction rate constantk, the equilibrium constantK*for the first step, the stability constantK, the activation energyEa, the change in enthalpy, and the product (pZ) of the frequency and steric factors were determined. On the basis of the above data, a mechanistic scheme for this complexation reaction is proposed.

ISSN:1040-0397    

DOI:10.1002/elan.1140070203

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe dependence of the peak height on the concentration of surfactant, the preconcentration time, and the preconcentration potential was examined. The behavior of the Triton X series fits the general scheme of the behavior of ethoxylates. Tritons having a lower number of ethoxylene subunits (EO) (1–12.5) form wide, analytically useful peaks within the range of the growing section on the calibration plot. A further increase in the concentration causes complicated transformations to appear on the tensammetric curve, which are caused by association. The wide peak is shifted irregularly in the negative direction and finally disappears, being transformed into a vertical line. An additional, usually needle‐shaped peak appears instead. Surfactants having a higher EO (30–40) form a narrow double peak, which is an analytically useful signal; this transforms into a single narrow one when the concentration increases. The higher the EO in Tritons, the broader the range of potentials for their adsor

ISSN:1040-0397    

DOI:10.1002/elan.1140070204

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractMethyl viologen (MV2+) initially exchanged in a zeolite Y modified carbon paste electrode (ZMCPE) is reduced after being exchanged for the supporting electrolyte cation. The use of an electrolyte cation that cannot enter zeolite channels to a great extent does not give rise to appreciable currents while a non‐size‐excluded cation allows liberating MV2+from zeolite particles and their subsequent reduction at the electrode–solution interface. Following those observations, the MV2+‐based ZMCPE has been used for the constant potential (−0.85 V) amperometric detection of nonreducible:, non‐size‐excluded cations in aqueous medium. The performance of this electrode was investigated in both batch injection analysis (BIA) and flow injection analysis (FIA). The great advantage of BIA coupled to the amperometric detection is the ability to use electrolyte‐free sample solutions. For FIA experiments, dissolved oxygen was eliminated by using an electrochemical scrubber containing porous carbon electrodes. With the MV2+‐doped ZMCPE, alkali and alkali‐metal cations can be detected at the submillimolar level for both batch and flow

ISSN:1040-0397    

DOI:10.1002/elan.1140070205

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe performances of Nafion‐coated thin mercury film electrodes and Nafion‐coated glassy carbon electrodes loaded in aqueous solutions of Yb3+or UO 22+, respectively, are examined in relation to their use for the electrocatalytic voltammetric detection of nitrate.Electrocatalytic reaction between the incorporated, reduced species, namely Yb2+and U3+, and the NO 3−, substrate is observed in both cases; however, the rapid inactivation of the ytterbium‐based sensor prevents its use for practical purposes. More promising results were obtained for the uranyl‐based sensor, since a more stable, modified electrode is obtained which can be used for the detection of nitrate in the 2–400 μMconcentration range; however, problems connected to the slow release of the catalyst from the coating remain to be solved. Finally, the limitations and possible development of such a voltammetric sensor are crit

ISSN:1040-0397    

DOI:10.1002/elan.1140070206

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractDifferential pulse polarography (DPP) is an excellent analytical method, but cannot be recommended for applications in the initial stages of mechanistic studies. Its application is also questionable in the analysis of samples containing varying concentrations of an organic cosolvent or of surface active compounds. The effect on limiting currents obtained by DC polarography and on peak currents obtained by DPP was demonstrated for reductions of various nitrobenzene derivatives. The similarity of changes in current for various nitrobenzenes enables the exclusion of the formation of adducts or micelles as the predominant effect. The decrease of the limiting currents in all cases is much smaller than the decrease of DPP peak currents, due to strong effects of the surfactants on the kinetics of electroreduction. For the analysis of natural products or of solutions containing varying amounts of organic cosolvent, the measurement of the DC polarographic limiting current is preferred. An addition of 30% ethanol minimizes the effects of the varying concentration of surfactant on both DC polarographic limiting and DPP peak currents.

ISSN:1040-0397    

DOI:10.1002/elan.1140070207

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA method is described for the voltammetric determination of palladium(II) using a carbon paste electrode modified with thioridazine. The modifier was added to the analyte solution and adsorbed onto the electrode surface under closed circuit conditions. Palladium could be preconcentrated onto the electrode surface and determined by differential pulse voltammetry without medium exchange. The dependence between the current response and the concentration of palladium(II) was linear within a range of 1 to 450 μg L−1with preconcentration times between 0 and 120 seconds. The influence of parameters such as modifier concentration and pH‐value on the determination of palladium were investigated. The applicability of this method for the voltammetric determination of palladium in fresh water and in catalysts used for synthetic organic reactions is demonstr

ISSN:1040-0397    

DOI:10.1002/elan.1140070208

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractGlucose, uric acid, and cholesterol in serum were assayed simultaneously in a flow injection system by using a 16‐way switching valve and a parallel configuration of three immobilized enzyme reactors. Nafion film‐coated and Nafion/cellulose acetate film‐coated platinum electrodes were used to selectively detect the hydrogen peroxide generated enzymatically in the enzyme reactors, without any interferences from electroactive species such asL‐ascorbate and proteins present in the serum. The signal current was linearly related to the glucose concentration in the range of 5–700 mg/dL, to the urate concentration in the range of 1–80 mg/dL, and to the cholesterol concentration in the range of 5–100 mg/dL. The precision (coefficient of variation) was better than 2.8% for the simultaneous assay of the three species in human control serum. The assay speed was up to 32 sam

ISSN:1040-0397    

DOI:10.1002/elan.1140070209

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractChemically modified electrodes (CMEs) were prepared by adsorbing different dyes, including methylene blue (MB), toluidine blue (TB) and brilliant cresyl blue (BCB), onto glassy carbon electrodes (GCE) with anodic pretreatment. The electrochemical reactions of adsorbed dyes are fairly reversible at low coverages. The CMEs are more stable in acid solutions than in alkaline ones, which is mainly due to decomposition of the dyes in the latter media. They exhibit an excellent catalytic ability for the oxidation of nicotinamide coenzymes (NADH and NADPH). The formation of a charge transfer complex between the coenzyme and the adsorbed mediator has been demonstrated using a rotating disk electrode. The charge transfer complex decomposition is a slow step in the overall electrode reaction process. Some kinetic parameters are estimated. Dependence of the electrocatalytic activity of the CMEs on the solution pH is discussed.

ISSN:1040-0397    

DOI:10.1002/elan.1140070210

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA study was made of the amperometric titration of the reaction between barium peroxide and copper(I) and copper(II) oxides. It was shown that it was possible to titrate a solid with a solid in surfactant suspensions. The studies were made in aqueous and acetonitrile suspensions containing cationic surfactants. End points were obtained at molecular ratios of BaO2to CuO of 1 : 1, 1 : 3, and 1 : 5; and molecular ratios of BaO2to Cu2O of 1 : 1 and 2: 1. It was postulated that the reactions involving CuO were\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {{\rm BaO}_{\rm 2} + {\rm CuO} \to {\rm BaCuO}_{\rm 3}} \\ {{\rm BaO}_{\rm 2} + {\rm 3CuO} \to {\rm Cu}_{\rm 3} {\rm O}_{\rm 4} + {\rm BaO or BaCu}_{\rm 3} {\rm O}_{\rm 5}} \\ {{\rm BaO}_{\rm 2} + 5{\rm CuO} \to {\rm BaCu}_{\rm 5} {\rm O}_{\rm 7} {\rm or BaO} + {\rm Cu}_{\rm 5} {\rm O}_{\rm 6}} \\ \end{array} $$\end{document}The reactions involving Cu2O were postulated to be\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {{\rm BaO}_{\rm 2} + {\rm Cu}_{\rm 2} {\rm O} \to {\rm BaCu}_{\rm 2} {\rm O}_{\rm 3}} \\ {{\rm 2BaO}_{\rm 2} + {\rm Cu}_{\rm 2} {\rm O} \to {\rm Ba}_{\rm 2} {\rm Cu}_{\rm 2} {\rm O}_{\rm 5}} \\ \end{array} $$\end{document}.

ISSN:1040-0397    

DOI:10.1002/elan.1140070211

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY