摘要:

AbstractSugars and alditols undergo an electrocatalytic oxidation in alkaline solution at cobalt‐oxide‐based glassy carbon (Co/GC) electrodes. The catalytic deposit was investigated by cyclic voltammetry and scanning electron microscopy (SEM). It is pointed out that, at relatively low coverage of cobalt, two main redox processes, CoII→ CoIIIand CoIII→ CoIV, are observed in 0.2 M NaOH. The redox behavior of the Co/GC electrode is strongly dependent on hydroxide ion concentration, and no electrocatalytic activity is observed at pH lower than 11.5. Under voltammetric conditions the modified electrode exhibits anon‐Nernstianpotential/pH shift (−88 ± 3 mV per pH unit). A reasonable explanation of theE/pH behavior in alkaline solution is given and an oxidation mechanism of CoIIto CoIIIis proposed in terms of hydrous cobalt oxides. No detrimental effects on the electrocatalytic oxidation of polyhydric compounds are observed in the presence of high acetonitrile concentrations (up to 40%). Inspection by SEM of the cobalt‐based deposit evidenced the presence of grain‐like microcrystallites on the glass

ISSN:1040-0397    

DOI:10.1002/elan.1140070402

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe voltammetric behavior in alkaline solution of a nickel‐based chemically modified electrode (Ni‐CME) prepared by oxidative electropolymerization of a nickel–tetraazaannulene complex (NiIIL) was investigated. After electrochemical deposition of the (NiIIL)nfilm in dichloromethane on a conducting substrate, the modified electrode was continuously cycled in alkaline solution until a steady voltammetric profile was obtained. Although upon electrochemical treatment in basic solutions the nickel–nitrogen tetracoordination of the (NiIIL)nfilm is probably lost, the nickel species remain entrapped inside the polymeric skeleton and exhibit stable redox behavior resembling that of the nickel hydroxide electrode. This makes it possible to prepare very thin films of nickel‐based modified electrodes. In cyclic voltammetry experiments the Ni‐CME exhibits a pH dependence of the peak potentials typical of the α‐Ni(OH)2/γ‐NiOOH redox process, and a separation between anodic and cathodic peak potentials of 64mV at pH 13.2 and 10 mVs−1. The redox catalysis at Ni‐CMEs of representative compounds that are not easily electrooxidized, such as choline, cadaverine, γ‐amino butyric acid (GABA), benzyl alcohol, and glycine, is demonstrated. The good stability of these nickel‐based modified electrodes makes them attractive

ISSN:1040-0397    

DOI:10.1002/elan.1140070403

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractAnalytical procedures are described for the solid state phase microanalysis of synthetic and natural tin‐, arsenic‐, and antimony‐bearing sulfosalts and sulfides of thallium, tin, lead, and silver. In these procedures, abrasive stripping voltammetry and coulometry of the solid phases are applied. Trace amounts of the sample compounds were transferred onto the surface of a graphite electrode and the electrochemical reduction or oxidation was followed by voltammetric techniques. The most valuable technique for distinguishing different mineral phases is to record the anodic dissolution voltammograms after a preliminary electrolytic reduction of the sulfides or sulfosalts to the elementary metals which are still confined to the electrode surface. For various compounds an approach was developed in which the ratio of charges consumed during reduction and oxidation of the solid phases is used for unambiguous identification. Coulometric measurements are also used for the determination of the quantitative composition of the solid p

ISSN:1040-0397    

DOI:10.1002/elan.1140070404

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractAmperometric determination of electroactive species not requiring calibration described in this work is based on separation of linear and spherical parts of limiting diffusion current of a determined substance to the hemispherical Hg‐semimicroelectrode (radius 37.5 μm). Charges transfered by these two components of current during experiment are comparable for semimicroelectrodes and the determination error is acceptably low (<10%) for concentration interval 50–500 μmol dm−3. The calibrationless amperometric determination was verified with cadmium and lead. A new way of calculating optimum value of electrode radius to minimize the determination error is also pr

ISSN:1040-0397    

DOI:10.1002/elan.1140070405

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe synthesis, characterization, and sensor application of the novel redox polymer [Os(bipy)2(PS)7.5(DMAP)2.5Cl]Cl, where bipy = 2,2′‐bipyridyl, PS = polystyrene, and DMAP = poly[4‐(N‐methyl‐N‐p‐vinylbenzylamino) pyridine], are described. The charge transport properties of electrodes modified with the redox material are investigated using cyclic voltammetry and chronoamperometry. The modified electrode behaves as an efficient electrocatalyst for the outer‐sphere reduction of FeIII, with the cross‐exchange reaction occurring at the surface of the polymer (Sk″) at concentrations less than 1.0 × 10−3mol dm−3FeIII, with a change over to theSte, kinetic regime at higher substrate concentrations. Direct agreement was observed between the kinetic behavior at rotating disk electrodes and in thin‐layer flow cells. Application of the modified electrodes for the determination of iron in pharmaceutical formulations and the long term stability of the electrodes are investigated. The results obtained are compared with those reported for the analogous metallopolymer [Os(bipy)2(PVP)10Cl]Cl, where P

ISSN:1040-0397    

DOI:10.1002/elan.1140070406

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA palladium‐dispersed carbon paste electrode was used for the electrocatalytic reduction of hydrogen peroxide. After cycling the potential between 0.4 and −0.8V (vs. SCE) in pure dilute alkaline solution (10−3M NaOH), the resulting electrode surface exhibited stable and sensitive electrocatalytic response for hydrogen peroxide. The involved catalytic mechanism was thoroughly investigated. The electrocatalytic effect was attributed to electrogenerated elemental palladium at the electrode surface. The catalytic reduction of hydrogen peroxide proceeds via the hydroxyl radical, OH·. Dissolved oxygen can also be catalytically reduced in a similar way to hydrogen peroxide. The height of the cathodic catalytic current peak, as obtained by linear sweep voltammetry (LSV) was directly proportional to the hydrogen peroxide concentration over a very wide concentration range (0.1–600mgL−1). The detection limit (3σ) was calculated as 5

ISSN:1040-0397    

DOI:10.1002/elan.1140070407

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe preparation of a polymer based microarray system is described. The technique utilizes electropolymerization to form a nonconductive polymeric layer on a conductive substrate. Provided appropriate electrochemical conditions are used, microarray behavior can be obtained for the resultant modified electrode substrate.

ISSN:1040-0397    

DOI:10.1002/elan.1140070408

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractSome characteristics of bi‐ligand systems, important for the design and performance of studies on mixed‐ligand complex formation, are given. The problem of the optimum ligand concentration is discussed using published results. In the experimental work the concentration range of the stronger complexant (at a constant level of the weaker) seems to be critical. The measurements should start under conditions where the increase in the half‐wave potential shift (with respect to the situation in the presence of only the weaker ligand) is virtually absent and finish at concentrations where it is pronounced. Small changes at the beginning reflect the ‘contribution’ of ternary species to the composite signal, whereas the big shifts at higher concentrations are mainly produced by simple species with only a minor contribution from mixed‐ligan

ISSN:1040-0397    

DOI:10.1002/elan.1140070409

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA flow‐through coulometric titration technique is described which can be applied for the determination of a wide variety of compounds. If necessary, the sample can be transformed in the measuring system into a form which can be titrated. Thus an enzyme‐catalyzed reaction can also be used as a sample pretreatment step. In this article a measurement technique and apparatus are described in which an enzyme‐catalyzed reaction is used for the fast and reliable determination of penicillin compounds. The principle of the technique is that an enzyme reactor is built into the sample line of the measurement system used for performing coulometric triangle programmed titrations. One of the components of the reaction mixture leaving the reactor (in this case penicilloic acid) is determined by coulometric acid–base titration. This technique is especially useful for the analysis of large sample

ISSN:1040-0397    

DOI:10.1002/elan.1140070410

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA novel strategy for enhancing the sensitivity of alcohol‐dehydrogenase amperometric biosensors, based on biocatalytic accumulation of the mediator, is described. By performing the biochemical/chemical step under open‐circuit conditions, it is possible to accumulate the reduced form of the Meldola blue mediator, prior to the chronoamperometric quantitation of the enriched layer. Such temporal separation of the recognition and transduction events offers a 35‐fold sensitivity enhancement (following a 5‐min accumulation). Factors influencing the response are explored and applicability to various wine samples is illustrated. The new amplification strategy can be extended to biosensors based on other nicotinamide‐cofactor dependent dehyd

ISSN:1040-0397    

DOI:10.1002/elan.1140070411

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY