摘要:

AbstractAlthough many electrochemical gas sensors have been reported, electrochemical gas sensors based on liquid collection constitute a smaller subset. Minimally, a liquid interface based electrochemical gas sensor is composed of two electrodes and an ion conducting electrolyte. There is a large number of possible arrangements of these parts, and many choices exist for their composition and preparation methods. This results in a diverse and rich technology now available for gas sensing. The measurement of some analyte gases of interest, notably ozone, nitrogen oxides, hydrogen peroxide, formaldehyde, ammonia, sulfur dioxide and hydrogen sulfide are specifically discussed. Finally, the recent reviews that are likely to be the most relevant to the further development of electrochemical detection approaches for gases with a liquid collection interface are cited and discussed.

ISSN:1040-0397    

DOI:10.1002/elan.1140090802

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe behavior of (ferrocene)amylose (FA), in the presence of amylolytic depolymerases (α‐amylase fromAspergillus oryzaeand human saliva), has been investigated by cyclic voltammetry at a rotating disk electrode (CVA/RDE). Growth of the limiting current with time in the presence of the enzymes is proportional to the amount of enzyme introduced. The quantitative data treatment to assay the endoamylolytic activity of enzymes at CVA/RDE involves plotting (idt/id0)4.5against time; the slope of the linear plot being equal to (rate)Mn0C−1, whereidtandid0are the limiting currents at timetand 0, respectively, (rate) is the enzymatic activity,Mn0is the number averaged molecular weight of FA att= 0, andcis its concentration. The comparison of CVA/RDE with the 3,5‐dinitrosalicylic acid and the Somogyi–Nelson reducing saccharides procedures shows advantages of the former, especially in assaying small quantities of enzymes. Also the CVA/RDE approach is simpler and takes place under much milder conditions. The main disadvantage of CVA/RDE is the inhibiting effect of Triton X‐100 in the reaction between FA and the amylases which is not observed in the case of native, ferrocene‐free amylose. In general, CVA/RDE appears to be an attractive analytical method for monitoring diverse enzymatic depolymerizati

ISSN:1040-0397    

DOI:10.1002/elan.1140090803

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractCyclic voltammetry was used to investigate the electrochemical behavior of nitrite at a platinum‐modified glassy carbon electrode (Pt‐CME) in phosphate buffer (pH 4.5). Experiments in flow injection analysis and ion‐chromatography (IC) were performed to characterize the electrode as an amperometric sensor for the determination of nitrite ions. The effects of several common interferences on the amperometric signal were estimated. The electrode stability, precision, limit of detection, and linear range were evaluated at a constant applied potential of 1.1 V. Calibration plots were linear from 0.03 μM to 0.5 mM with a slope of about 21 μA/mM and a correlation coefficient of 0.9987. The limit of detection (LOD) was 15 nM (0.7 ppb) in a 100 μL injection. The electrode response was sufficiently stable: over 6 h of operating time a 2.8% signal loss was observed. The determination of nitrite in milk and pear juices was achieved by IC and the relevant results were compared with those obtained with a standard spectrophotometri

ISSN:1040-0397    

DOI:10.1002/elan.1140090804

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractMembrane glassy carbon electrodes modified with cation‐exchangers (Eastman AQ‐29D, laponite, or polystyrene sulfonate) entrapped between the membrane and the carbon surface were used to study the electrochemical behavior of herbicides and plant growth regulators from the quaternary ammonium family. Cations are shown to incorporate in the entrapped solutions containing negatively charged cation‐exchangers, because of favorable electrostatic interactions. In the case of nonelectroactive cations, collection of mepiquat, chlormequat and difenzoquat from the bulk solution is assessed from the competition in ion‐exchange equilibrium between one of the above‐mentioned cations and the electroactive diquat cation. An attractive property results from the use of spinach ferredoxin as cation‐exchanger inside the membrane electrode. Promotion of ferredoxin is shown to be evidenced as a result of the collection of nonelectroactive cations from the bulk solution. Prospects of such modified membrane electrodes in the environmental field ar

ISSN:1040-0397    

DOI:10.1002/elan.1140090805

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe electrochemical study of the peptidic fragment Lys‐Cys‐Thr‐Cys‐Cys‐Ala [56–61] MT I (FT) alone and in the presence of cadmium was performed, by cyclic voltammetry using a hanging mercury drop electrode, in order to enable comparisons between the behavior of Cd, Zn metallothioneins and that of this less complex molecule, intrinsic to the metallothionein structure. The influence of the equilibration time, of the scan rate, and of the solution pH was investigated. The influence of the addition of cadmium with different Cd–FT ratios was also studied. Samples containing both Cd and FT give complex voltammograms showing different peaks. Several electrochemical systems were distinguished: the mercury electrode itself is involved in the charge transfer step in the presence of thiol groups coming from the FT structure; another system can be attributed to the oxido‐reduction of cadmium either as free ion or complexed by the peptide. The adsorption phenomena play an important role in the electrochemical process. Both dissolved and adsorbed species ar

ISSN:1040-0397    

DOI:10.1002/elan.1140090806

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe possibility of producing polymer‐coated electrodes containing complexing agents capable of collecting metal ions was investigated. The organic ligands 2‐mercaptobenzimidazole and 2‐mercaptobenzothiazole were used as monomers for electropolymerization on glassy carbon electrodes. The electroanalytical applicability of the modified electrodes was evaluated for Hg2+ions, by applying a chemical preconcentration step with subsequent measurement by differential pulse voltammetry. The influence of some electropolymerization parameters, such as scan rate, monomer concentration and the number of cyclic scans, on the voltammetric response of mercury(II) was studied. A 5 min preconcentration period allowed the detection of 0.08 mg/L (4.0 × 10−7mol L−

ISSN:1040-0397    

DOI:10.1002/elan.1140090807

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe advantages of microelectrodes such as the improvement of signal‐to‐noise ratio, the ability to perform electrochemical measurements in high resistive solutions and small RC‐time constants give the possibility of an extended use for voltammetric and chronoamperometric techniques in analytical chemistry. In this comparative study, the microelectrode properties of three selected electrodes were examined. The characterization of a RAM‐microarray electrode, an epoxy‐impregnated carbon electrode and a conventional glassy carbon macroelectrode was performed by cyclic voltammetry at different scan rates, by DP‐voltammetric measurements using different concentrations of supporting electrolyte and by transient measurements. It could be shown, that in comparison to the microarray electrode and to the glassy carbon macroelectrode, respectively, the results obtained by using the epoxy‐impregnated carbon electrode are caused by its semimicroelectr

ISSN:1040-0397    

DOI:10.1002/elan.1140090808

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe electrochemical reduction of secnidazole has been carried out in aqueous solution in the pH range of 2.0–12.0 by DC polarography, AC polarography and cyclic voltammetry. Two well‐defined reduction waves appear in acidic media, whereas at higher pHs the two waves overlap. The variation ofE1/2orEpandIlimorIpwith pH was studied. The diffusion‐controlled nature of the waves was established and the irreversibility of the electrode process was verified by different criteria. The mechanism of reduction was discussed. A method for the detemination of secnidazole by DC polarography at pH 8.5 which allows quantitation over the 1 × 10−5M‐4 × 10−4M range was proposed and applied to the determination of secnidazole in tablets. The mean recovery was 99.67% and the relative standard deviation was 0.89%. Excipients did not interfere in the

ISSN:1040-0397    

DOI:10.1002/elan.1140090809

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractPotentials for the one‐electron reduction of a series of substituted benzo‐ and naphthoquinones were measured in 10 aprotic solvents by cyclic voltammetry and used to construct Hammett plots. Hammett reaction constants, ρ, were determined in each solvent and used as indicators of the solvent‐mediated stabilization of the charged radical‐anion product of the reduction reaction. Correlations of Hammett ρ values with solvent parameters suggest that the Lewis acidity of the solvent, in particular the solvent's ability to donate a partially positive proton, is a consistent predictor of the degree of charge stabilization of the quinone radical anion. Other mechanisms of charge stabilization, including solvent–solute charge transfer complexes and dipole–dipole interactions involving the molecular dipole moment (or an induced dipole moment) of the solvent, were found to be inconsistent predictors of the effect of solvent on one‐electron quinone reduction i

ISSN:1040-0397    

DOI:10.1002/elan.1140090810

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractAn electrochemical method for the simultaneous determinations of HgIIconcentration and total AsIIIand AsVconcentration has been developed. The method does not require the additional preliminary step of the chemical reduction of AsVto AsIII, or oxidation of AsIIIto AsVbefore stripping analysis takes place. Also, the method for the simultaneous determination of HgIIconcentration and AsIIIconcentration is described. Measurements were performed in 0.1 M HCl using a gold‐plated graphite electrode as sensor. Detection limits for both methods are below 0.4 ppb. Relative standard deviation did not exceed 15%. The possible interference by other trace metals was investigated. Analyses of natural water and industrial solutions were made using proposed methods and AAS. Thet‐test demonstrates that there was no significant difference between the results obtained with these methods. Proposed methods decrease the time of analysis because concentrations of the HgIIand arsenic ions were measured simultaneously. Also, the removal of the additional step of chemical reduction of AsVto AsIIIor oxidation of AsIIIto AsVdecreases analysis time, and also reduces the chance of contamination due to the use of additional reage

ISSN:1040-0397    

DOI:10.1002/elan.1140090811

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY