摘要:

AbstractAn amperometric biosensor for the determination of fish freshness has been developed by immobilizing 5′‐nucleotidase (NT), nucleoside phosphorylase (NP) and xanthine oxidase (XO) enzymes on a Nafion‐paraquat chemically modified glassy‐carbon working electrode. The sensing principle is based on the oxygen consumption in the enzymatic reaction catalyzed by xanthine oxidase immobilized in the matrix. The quantity of hypoxanthine (Hx), the combined amount of inosine (HxR) and Hx and the total quantity of inosine 5′‐monophosphate (IMP), HxR and Hx can be determined, respectively, by changing the medium conditions. This sensor system can be used to determine the freshness of fish. An indicator of fish freshness,K1, is defined asK1= {[HxR] + [Hx]}/{[IMP] + [HxR]+ [Hx]}. This biosensor prowides a reliable means for determining of Hx, HxR and IMP in fish samples and the freshness of th

ISSN:1040-0397    

DOI:10.1002/elan.1140091602

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractPeroxidase (POD) was entrapped on a ferrocene (Fc)‐embedded carbon paste (CP) electrode with a dialysis membrane to construct a POD‐Fc‐CP electrode for the reductive amperometric determination of hydrogen peroxide (H2O2). The electrode allowed the H2O2detection down to 10 nM (under stirring), with a linear relation up to 15 μM, and without change of the response over one month. On the other hand, a plastic‐formed carbon (PFC) electrode can donate electrons to POD without any specific mediator. The POD‐entrapped PFC electrode produced a relative current density of 24% compared with the POD‐Fc‐CP electrode. The reductive detection of H2O2with the POD‐Fc‐CP electrode was applied to the determination of creatinine and creatine in serum and urine using sarcosine oxidase, creatine amidinohydrolase, and creatinine amidohydrolase as the reagents. The significance of the membrane‐covered POD‐Fc‐CP electrode in the coupling of the oxidase re

ISSN:1040-0397    

DOI:10.1002/elan.1140091603

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe processes of oxide film formation and ion adsorption on gold electrodes were monitored by the simultaneous measurement of electrochemical potential scanning voltammetry and surface plasmon resonance (SPR) condition. The time differential of the SPR incident angle was used for the analysis of the surface reactions of the gold electrode. Each stage of oxide film formation on the sputtered gold electrodes and anion adsorption/desorption was clearly detected by this method and directly correlated to the current. SPR is sensitive to the surface adsorbate while the electrode current reflects the overall electrochemical process. This difference was used to separate adsorption from the diffusion process under different hydrodynamic conditions.

ISSN:1040-0397    

DOI:10.1002/elan.1140091604

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe formal redox potentials of 9‐substituted anthracenes (9XA) were measured by means of a fast scan cyclic voltammetry (FSCV) with a microelectrode. Because the FSCV depresses the influence of subsequent fast reactions, the redox potentials could be measured for a series of substituents in both the oxidation and the reduction processes. The correlation of the redox potentials with the results of molecular orbital calculations were demonstrated, in particular with the PM3 method. The plots of the redox potential versus the energy difference between the redox states gave better correlat on than those versus the energy levels of the HOMO and LUM

ISSN:1040-0397    

DOI:10.1002/elan.1140091605

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe ligand cupferron is used for the simultaneous adsorptive stripping voltammetric measurements of several trace metals. Experimental variables affecting such multielement capability, including the cupferron concentration, adsorption time or metal concentration are explored. Adequate resolution is demonstrated for up to five metals (FeIII, UVI, CrVI, VV, and BiIII), present at the ppb concentration level. Possible changes in peak heights, associated with competition for the complexing ligand and/or coadsorption effects, are explored. Different concentration ratios of the mixture components can be tolerated. Applicability to groundwater or river‐water samples is illustrate

ISSN:1040-0397    

DOI:10.1002/elan.1140091606

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA novel transducer design is proposed based on a electrocatalyst for hydrogen peroxide oxidation (platinum black) electrodeposited on the inner wall of a stainless steel needle which serves as a working electrode, and an external Ag/AgCI reference/counter electrode. Electropolymerized 1,3‐diaminobenezene (1,3‐phenylenediamine) is employed as a protective layer for the platinum black as well as an interference eliminating layer. This configuration uses the Pt electrocatalyst in its most active dispersed form and ensures good mechanical ruggedness and protection of the catalytic and biological components. The design also provides the possibility to obtain high enzyme loading and hence an extended sensor life‐time. Two types of glucose sensors were constructed based on this novel design concept. The enzyme (glucose oxidase) was immobilized either in a hydrophilic gel matrix inside the needle body (i) or cross‐linked on the inner needle surface (ii). Cellulose triacetate, polycarbonate, and Nafior were used as external diffusion control layers, which extended the linear range of the sensor response to over 25 mM glucose. These biosensors demonstrated diminished response to interferences from oxidizable compounds present in body fluids and a life time of at least three

ISSN:1040-0397    

DOI:10.1002/elan.1140091607

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractGlassy carbon electrodes (GCE's) modified with phthalocyanine complexes of Rh, Ru and Os are employed for the catalytic oxidation of cysteine. When cyanide and dimethylsulfoxide (DMSO) are used as axial ligands giving (DMSO)(Cl)RhIIIPc, [(CN)2RhIIIPc]−, (DMSO)2OsPcII, and [(DMSO)2Ru(II)Pc]·2DMSO complexes, the peak currents for the oxidation of cysteine increase after each scan, indicating an increase in the catalytic activity of the electrode with repetitive scanning. This improvement in the catalytic activity of the GCE after the first scan is attributed to the formation of dimeric π cation radical species at the electrode surf

ISSN:1040-0397    

DOI:10.1002/elan.1140091608

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractCarbon fiber ultramicroelectrodes have been used in anodic stripping voltammetry (ASV) of trace gold. The advantageous characteristics of ultramicroelectrodes combined with ASV resulted in a fast, selective, sensitive and reproducible method. An electrochemical pretreatment was necessary for analytical determinations. The combination of supporting electrolyte (HCl 0.1 M) and electrodeposition potential (0.0 V) gave a high selectivity. A calibration plot from 1.00 × 10−8M to 1.60 × 10−6M (r= 0.9994) was achieved with a detection limit of 5.94 × 10−9M and a relative standard deviation (RSD) of 2.87% at 3.0 × 10−7M. AgI, CuII, PbIIand HgIImetals in the concentration of 1.00 × 10−6M were not found to interfere with the ASV of gold (3.00 × 10−7M) when carried out under optimum conditions. The procedure was applied to the determination of gold in two tap water

ISSN:1040-0397    

DOI:10.1002/elan.1140091609

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractAlkylated α, β and γ cyclodextrins have been incorporated in ion‐selective electrodes as neutral ionophores and used for the detection of the tricyclic antidepressants imipramine, desipramine and trimipramine as their hydrochloride salts. Nernstian response and excellent potentiometric limits of detection were observed with each of the three alkylated cyclodextrins examined. Interference from ‘serum’ levels of Na+, K+and Ca2+ions was very low. Interference from organic molecules such as glycine, L‐histidine and nicotinamide was also low in most cases (see text for exceptions). Electrodes suitable for amperometric measurements were assembled by depositing alkylated cyclodextrins on screen printed electrode substrates. Inclusion of the tricyclic antidepressants in the cyclodextrin cavity aided by controlled potential electrolysis, allowed subnanomolar levels of the analyte to be monitored by square wave voltammetry. Mechanistic studies indicated that, by preconditioning the modified electrodes at approximately +0.6 V in phosphate buffer, the appropriate radical cation was formed, which, on further conditioning at approximately −0.2 V rapidly formed the dimer which possessed a lower oxidation potential of approximately +0.18 V. Monitoring the redox wave at 0.18 V afforded a powerful analytical handle for trace analysis of these tricyclic antidepressants. This redox wave is observable only in the presence of aqueous phosphate which may be attributed to the formation of a hydrogen‐bonded surface ion‐pair including the substrate and a phos

ISSN:1040-0397    

DOI:10.1002/elan.1140091610

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractCyclic voltammetry was used to characterize the oxidation‐reduction behavior of a series of novel hexacoordinate silicon(IV) porphyrin complexes. Each (Por)SiX2[Por = the dianions of the porphyrins: tetrakis(p‐tolyl)porphyrin (TTP), tetraphenylporphyrin (TPP), tetrakis(p‐trifluoromethylphenyl)porphyrin (TTFP), octaethylporphyrin (OEP), × = F, Cl, O3SCF3] complex undergoes one to two oxidations and one to two reductions, all occurring at the porphyrin ring. No silicon(IV) reduction is observed for any of the porphyrin complexes. The effects of solvent, supporting electrolyte, substituents on the porphyrin ring, axial ligands, certral metal, and ruffling of the porphyrin ring are des

ISSN:1040-0397    

DOI:10.1002/elan.1140091611

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY