摘要:

AbstractPlant materials of the genusSphagnumhave long been known to absorb cations preferentially from dilute solutions. Preconcentrating modified electrodes based on the incorporation of peat moss within carbon paste matrices, have been designed for bioaccumulating copper ions prior to their voltammetric quantitation. Operational conditions, such as paste composition, solution pH or ionic strength, accumulation time, and voltammetric waveform are characterized and optimized to allow quantitation of submicromolar concentrations. The surface is regenerated by placing the electrode in a hydrochloric acid solution, allowing the use of a single electrode in multiple determinations (RSD of 6% for 15 repetitions). The plant modifiers also strongly bind and retain multiple charged counterions. These surface‐bound ionic metal complexes are able to mediate electron transfer with solution species (such as hydrogen peroxide). The approach could be extended to other plant‐material modifier/analyte systems, as well as for preconcentration for other trace techniques. Preliminary data are given for the Spanish moss/silver sys

ISSN:1040-0397    

DOI:10.1002/elan.1140040114

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe incorporation of mercury into a conducting poly(3‐methylthiophene) [P3MT] film results in an effective electrode for the analysis of lead in aqueous media. Mercury “films” were deposited electrochemically following the electropolymerization step. The resulting surfaces were characterized by cyclic voltammetry, scanning electron microscopy, and X‐ray analysis techniques. The analytical performance of the electrode was examined for the determination of lead (II) ions in aqueous media. The differential pulse peak current, at −0.59 V, is ca 10‐fold larger than the corresponding peak at the plain platinum electrode. Linear calibration curves are obtained for lead concentrations ranging from 0.1 to 0.8 ppm. The detection limit is 0.05 ppm. The relative standard deviation (at the 0.3 ppm level) is 2%. Interference effects were also studied. The new polymer modified electrode showed great promise toward resistance to surfact

ISSN:1040-0397    

DOI:10.1002/elan.1140040115

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractOptimum conditions for the mercury electrodeposition onto glassy carbon electrodes and the optimum alternating current (AC) adsorptive stripping signals of folic acid (vitamin B12) were found. The film was characterized by electron microscopy and the results obtained in the analysis of the vitamin were compared with those previously reported using conventional mercury electrodes (static or hanging). The mercury thin film electrode (MTFE) has shown more sensitive signals for folic acid with good performance and reproducibility. A detection limit down to 10−12M could be reached by using 300 s accumulation tim

ISSN:1040-0397    

DOI:10.1002/elan.1140040116

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractA platinum microelectrode with a radius of 12.5 μm was employed for determining the acidity of crude bovine milk samples by voltammetric titration. Solutions of sodium hydroxide and of several acids of different strengths were used as titrants. The relative standard deviation (RSD) was within 3%, regardless of the type of titrant agent employed. The data found with this approach were compared with those obtained by the classical methods commonly employed for the determination of the titrable acidity of milk

ISSN:1040-0397    

DOI:10.1002/elan.1140040117

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractA chemically modified mercury thin‐film electrode (MTFE) is presented that employs an electrochemically generated nonconducting polymer (poly‐N‐ethyltyramine), which has been derivatized with surface dithiocarbamate groups. Mercury is deposited chemically onto the electrode by complexation and, following electrochemical reduction of the mercury, is used as a substrate for anodic stripping voltammetry (ASV) of cadmium, lead, and copper. The properties of a conventional MTFE are compared with the modified elec

ISSN:1040-0397    

DOI:10.1002/elan.1140040118

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe oxidation of nicotinamide‐adenine dinucleotide phosphate (reduced form, NADPH) at glassy carbon electrodes modified with different enzymes has been studied. It was found that NADPH yielded a well‐defined anodic peak about +0.70 V (vs. Ag/AgCl) at glassy carbon electrodes coated with three different enzymes, glutathione reductase, glutathione peroxidase, and glucose oxidase, in 1.4 M potassium phosphate supporting electrolyte. It was confirmed that the enzymes immobilized at the working electrode surface reduced the overpotential for the oxidation of NADPH. This method provides a way to study the mechanism of some enzymatic reacti

ISSN:1040-0397    

DOI:10.1002/elan.1140040119

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractA polarographic study of the organochlorine pesticides dieldrin, heptachlor, endosulfan, and endosulfan sulfate in an emulsified medium formed with ethyl acetate and a mixture of two surfactants, Hyamine 2389 and Triton X‐405, as emulsifying agent, is reported. Well‐defined peaks were obtained by differential pulse polarography (dpp). Neither preceding acid‐base equilibria nor mechanism changes are involved in the reduction processes. The characteristics of the electrode processes were examined at pH 8.0 for heptachlor and at pH 6.0 for the other pesticides. The diffusion coefficients were calculated as well as the kinetic parameters αnaandk f, h0. The mechanisms of the polarographic reduction processes are proposed and the different behavior of heptachlor is discussed. Linear calibration plots were obtained using dpp over different concentration ranges; the analytical characteristics of the methods were determined. The effect of the presence of the other pesticides on theipandEpvalues of each one of the four pesticides was studied. Simultaneous determination of heptachlor and endosulfan sulfate was

ISSN:1040-0397    

DOI:10.1002/elan.1140040120

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractPeroxidase‐mediated oxidation of diethylstibestrol (DES), a synthetic estrogen, has been proposed as a pathway in DES‐induced carcinogenicity. However, the transient nature of the DES oxidation product, DES‐quinone (DES‐Q), requires a rapid method such as cyclic voltammetry to study its stability and reactivity. Thus, the irreversible tautomerization of DES‐Q into dienstrol form (Z, Z‐DIES) is described by a two step mechanism. Tautomerization kinetics are studied as a function of pH and temperature. A significant descrease of half‐life for DES‐Q is observed in the presence of the glutathione thiolate form. Furthermore, voltammetric investigations were performed in dimethylformamide to detect the semiquinone radical of DES‐Q, a suspected

ISSN:1040-0397    

DOI:10.1002/elan.1140040121

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractA voltammetric investigation of the direct electro‐oxidative decarboxylation ofD‐gluconate ion toD‐arabinose on spectroscopic graphite electrode from methanol–water mixtures as well as from aqueous solutions is described. Practically a 100% yield inD‐arabinose and and 80% yield in current were realized. The kinetic behavior points to a rate‐determining release of the first transferring electron from the gluconate anion to the electrode, followed by a cleavage of the C‐1–C‐2 bond and by the resultin

ISSN:1040-0397    

DOI:10.1002/elan.1140040122

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

ISSN:1040-0397    

DOI:10.1002/elan.1140040126

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY