摘要:

AbstractThis article overviews the fundamentals of the phenomenon of direct electron transfer in enzyme‐catalyzed electrode reactions and the development of electroanalytical applications of the bioelectrocatalytic systems. A brief description of the enzymes capable of catalyzing electrochemical reactions by means of direct electron transfer is given. The physico‐chemical background of bioelectrocatalysis is discussed in terms of the different concepts underlying the mechanism of electron transfer. The concept of a “molecular transducer” is introduced to designate a complex, formed by the electrocatalytically active enzyme on the electrode‐electrolyte interface, which is directly responsible for the transduction of the chemical signal to an electric one. The role of this “molecular transducer” in enzyme electrodes and immunoelectrodes is discussed. The analytical applications of bioelectrocatalysis are categorized as systems employing either amperometric or potentiometric detection. Discussion focuses on the advantages of systems based on enzyme‐catalyzed direct electron transfer as opposed to other enzyme‐catalyzed electroanalytical devices. In conclusion, the trends towards upcoming practical applications are suggested as well as some directions in fundamental studies of bioelectrocatalysi

ISSN:1040-0397    

DOI:10.1002/elan.1140090902

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe electrochemical oxidation of full‐size heparin (13–15 kDa) is demonstrated in 1 M H3PO4at a glassy carbon electrode coated with a ruthenium oxide film. The pathway apparently is analogous to chemical oxidation by periodate. By comparison to currents from inorganic species, it is apparent that only about 2 electrons per mole are involved. Flow injection analysis (FIA) allowed determinations down to 2 μM heparin, but the calibration plot was nonlinear. Low molecular weight heparin (5–6 kDa) was not electroactive with this system. In basic solution at a glassy carbon electrode that is modified with a film of Cu2O, both full‐size and low molecular weight heparin are oxidized. The pathways involved oxidative desulfation and attack on saccharide units with evolution of CO2. Linear calibration plots which extended into the sub‐μM level were obtained by FIA. The detection limits, which were based on a value of 3 for the ratio of the signal to the standard deviation of replicates, were 9 nM for full‐size and 20–30 nM for various low molecular weight

ISSN:1040-0397    

DOI:10.1002/elan.1140090903

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

ISSN:1040-0397    

DOI:10.1002/elan.1140090904

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe concentration of antimony in copper plant electrolyte needs to be known at the ppm level. Spectroscopic techniques for trace metal determination in this electrolyte, such as atomic absorption and inductively coupled plasma (ICP) spectrometry only enable total antimony to be determined, whereas ideally the concentration of both the antimony(III) and antimony(V) oxidation states needs to be known. For the determination of antimony(III) and antimony(V) by differential pulse anodic stripping voltammetry (DPASV), the similar stripping peak potentials of −0.37 V(vs. Ag/AgCl) for copper and −0.27 V(vs. Ag/AgCl) for antimony in 5 M HCl mean that concentrations of copper greater than 6 times that of antimony cause difficulties in resolving the antimony and copper stripping peaks. In this article, a simple procedure is reported for the determination of antimony(III) and (V) in copper plant electrolyte after separation of antimony from copper by passing an ammoniacal solution of plant electrolyte through a column of Chelex‐100 ion‐exchange resin. Most of the copper is retained on the column so that the determination of antimony(III) and (V) by DPASV is possible after addition of hydrochloric acid to the eluent. Total antimony is determined in 5 M HCl and antimony(III) in 0.1 M HCl. Total antimony concentrations correlate well with data obtained by ICP and recoveries of antimony in both oxidation states

ISSN:1040-0397    

DOI:10.1002/elan.1140090905

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe electropolymerization of a flavin reductase (Fre) – amphiphilic pyrrole ammonium mixture previously adsorbed on the electrode surface provides an efficient bioelectrode for the amperometric detection of NADH and NADPH. The bioelectrode response was based on the oxidation at −;0.1 V vs. SCE of the enzymically generated dihydroriboflavin. The sensitivity and detection limit of the bioelectrode were 29 mAM−1cm−2and 0.2 μM for NADH and 15.8 mAM−1cm−2and 0.4 μM for NADPH. The coimmobilization of Fre and a lactate dehydrogenase leads to a dehydrogenase‐based bioelectrode for the determination of lactate in the presence of riboflavin and NAD+. With laponite additives into the polypyrrole host matrix, the sensitivity and the detection limit of the bioelectrode for lactate are 11.7 mAM−1cm−2and 1 μM respectively. Owing to the negative value of the applied potential for the oxidation of riboflavin, the response of the bienzyme electrode remains insensitive to interferents like ascorbate, ura

ISSN:1040-0397    

DOI:10.1002/elan.1140090906

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA new class of modified sol‐gel carbon composite electrodes, based on the encapsulation of complexing ligands, is described. Such modified electrodes couple the versatility and tunability of sol‐gel processes with the advantages of the preconcentration/voltammetric strategy. The incorporation of the ligand dimethylglyoxime (DMG) within the carbon‐silicate ceramic network is used to illustrate the new concept in connection with the voltammetric sensing of trace nickel. The sol‐gel carbon composite serves as a favorable host matrix for DMG, which retains its nickel binding characteristics. Factors influencing the sensor response, including the sol‐gel hydrolysis time, DMG loading or preconcentration time are explored. The electrode displays good linearity up to 800 μg/L nickel, a detection limit of 15 μg/L (following a 5 min accumulation), and a relative standard deviation of 7.7%. Applicability to assays of river water is illustrated. Doping of other ligands into sol‐gel carbon composites should result in similar voltammetric sensors for other imp

ISSN:1040-0397    

DOI:10.1002/elan.1140090907

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractSignificant improvements in selectivity for amperometric detection in flow analysis are achieved at covalently modified glassy carbon electrodes. Flow detectors modified withp‐alkylbenzene (alkyl = methyl, decyl) andp‐phenylacetate monolayers demonstrate how selectivity may be obtained on the basis of solute hydrophobicity and charge. The modified electrodes are stable under hydrodynamic conditions and in aqueous and mixed aqueous/organic carrier stre

ISSN:1040-0397    

DOI:10.1002/elan.1140090908

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe PbII‐N,N′‐di‐2‐picolylethylenediamine (DPA‐2) system was studied by differential pulse polarography (DPP) and glass electrode potentiometry (GEP) at fixed total‐ligand to total‐metal concentration ratio and varied pH. The polarographic experimental complex formation curve (ECFC) and calculated complex formation curve (CCFC) are used for modeling of a metal‐ligand system and the refinement of stability constants. The ECFC is used instead of a shift in the peak potential plotted vs. pH and it appears to be a characteristic function for a particular metalligand system. The CCFC is a theoretical curve calculated for the assumed metal‐ligand model from mass‐balance equations. The final model of metal species formed is the one which is accepted by these two experimental techniques and for which stability constants of metal complexes obtained from DPP and GEP differ the least. Four lead complexes Pb(HL), PbL, PbL2(OH) and PbL(OH)2and their stability constants as log β found from DPP 12.67 ± 0.08, 9.68 ± 0.07, 16.12 ± 0.08 and 14.88 ± 0.06, respectively, are reported. Results obtained from GEP and DPP differ only within experimental errors ty

ISSN:1040-0397    

DOI:10.1002/elan.1140090909

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe silica modified carbon paste electrode (SMCPE) was applied to the voltammetric detection of copper(II) at trace level after its accumulation under open‐circuit conditions. As demonstrated by cyclic voltammetric experiments, silica particles displayed an attractive ability to efficiently preconcentrate trace copper(II) from ammonia solution, according to a combined acid‐base and complexation reaction: 2 (SiOH) + Cu(NH3) 42+⇌ (SiO)2Cu(NH3)2+ 2 NH 4+. The analytical procedure involved four successive steps: the preconcentration during a given period of time at open circuit in the ammoniated analyte solution, the medium exchange of the electrode (washed with water) to a pure electrolyte solution (0.1 M HNO3), a 30 s electrolysis for reducing the accumulated CuIIspecies, and the square wave voltammetric determination. Experimental parameters affecting either the uptake of copper(II) or its voltammetric detection at SMCPE were explored, including the solution pH and ionic strength, the ammonia concentration in the preconcentration medium, the preconcentration time, the deposition potential and duration, the anodic stripping scan mode or the silica loading into the paste. A detection limit of 2 × 10−9M has been achieved after 10 min preconcentration (from a 0.5 M NH3medium), as determined for a signal‐to‐noise ratio of 3, and a linear calibration plot was obtained in the 5 × 10−9M to 5 × 10−6M concentration range. The relative standard deviation (n= 8) for the determination of a 5

ISSN:1040-0397    

DOI:10.1002/elan.1140090910

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe first electrodeposition in situ of C70‐salt films in a mixed solvent on a microdisk electrode is reported. The deposition conditions of these films were optimized and then the electrochemical behaviors of these films were investigated, displaying three one‐electron oxidation peaks with the characteristics of surface reactions. The electron‐transfer coefficients (α) of the three surface reactions were also dete

ISSN:1040-0397    

DOI:10.1002/elan.1140090911

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY