摘要:

AbstractThe time dependent backwards implicit method is used to simulate the shape and position of the stripping peaks in DC (linear scan) anodic stripping voltammetry at mercury thin film hydrodynamic electrodes for electrochemically irreversible and quasireversible systems assuming that the electrode diffusion layer thickness is uniform, as in the case of a rotating disk electrode. The effect of the electrochemical rate constant in influencing both the peak potential and peak shape is examined and the conditions identified under which electrochemically reversible behavior is approached.

ISSN:1040-0397    

DOI:10.1002/elan.1140091702

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe voltammetry of the molybdosilicate and molybdophosphate complexes, formed by the addition of hexafluorosilicate and phosphate to anacidic sodium molybdate solution, have been defined at gold microdisk electrodes. It is shown that the reaction conditions influence both the kinetics of formation of the complexes and their voltammetry. It is possible to find conditions where the steady state amperometric response of the Au microdisk electrodes allows a rapid and convenient method for the determination of silicate and phosphate at concentrations in the range 1–1000

ISSN:1040-0397    

DOI:10.1002/elan.1140091703

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe potentiometric and AC impedance characteristics of all solid‐state sodium‐selective electrodes based on planar screen‐printed Ag/AgCl electrodes are described. Two solid‐state designs have been investigated. The first was based on the deposition of a sodium‐selective PVC membrane directly on top of a screen‐printed Ag/AgCl electrode. The second design included a NaCl doped hydrogel layer, between the PVC and Ag/AgCl layers. The hydrogel provides a mechanism to relieve any blockage to charge transfer occurring when PVC membranes are used directly on top of Ag/AgCl and also improves adhesion between the two layers. Results suggest the electrodes display fast ion exchange kinetics, low noise and drift. The performance compares favorably to that of a conventional ion‐selective electrode with internal fil

ISSN:1040-0397    

DOI:10.1002/elan.1140091704

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractAppropriately formulated polymeric membrane electrodes are shown to exhibit analytically useful nonequilibrium potentiometric responses to biologically important polyanions with high phosphate content, including polyphosphates and nucleic acids, in the μg/mL concentration range This response is dependent on the charge density, lipophilicity, and molecular weight of the polyanion species. The application of these electrodes for monitoring enzymatic activities is also demonstrated, using acid phosphatase/polyphosphate as a model system. The detection limit of this assay was found to be 0.9 ± 0.4 mU/mL with a linear range of 5–100 mU/mL. A similar electrochemical assay scheme can be utilized to monitor ribonuclease activity, using a RNA homopolymer as the substr

ISSN:1040-0397    

DOI:10.1002/elan.1140091705

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractNonactin andN,N‐dioctadecylmethylamine ionophores, each in an epoxydiacrylate polymer, were photo‐cured on silver wires (0.8 mm i.d.) and evaluated as ammonium and hydrogen (pH) coated wire electrodes. The photo‐cured membranes prepared in this study exhibited excellent adhesion to the metal substrate and improved mechanical strength compared to PVC based membranes. The ammonium electrode exhibited a Nernstian response over a concentration range between 0.01 mM and 100 mM with a detection limit of 0.0005 mM. The ammonium electrode exhibited improved selectivity against most common interfering ions, including potassium compared to previous studies. The hydrogen selective electrode exhibited a near‐Nernstian slope of 55.9 ± 0.8 mV change/loga (H +)between pH 4.0 and pH 11.0 in the steady‐state mode. The ammonium and pH sensors each responded quickly reaching 90% of steady‐state value in<5 s, making these coated wire sensors ideal for flow injection potentiometry measurements. In the FIP mode, both the photo‐cured ammonium and pH electrodes exhibited near‐Nernstian responses of 49.2 ± 1.0 mV change/activity decade and 50.2 ± 0.4 mV change/loga (H +), respectively, over a similar concentration range as in the steady‐state mode. The photo‐cured ammonium and pH electrodes were used simultaneously in the analysis of hydroponic nutrient solutions and waste water samples obtained from a local greenhouse grower in the flow

ISSN:1040-0397    

DOI:10.1002/elan.1140091706

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA new microsystem, integrating microdialysis sampling and glucose oxidase immobilized on a tungsten wire inserted into the lumen of the microdialysis probe, has been developed. The microsystem, coupled with amperometric detection, has proved to be viable for glucose determination in food samples. The immobilization procedure, based on the formation of an insoluble net formed by the enzyme with a polyanhydride (in the presence of polyethyleneimine), yielded a very stable enzyme layer that maintained about 75% of its initial activity after one month of daily use. Complex sample matrices (milk, juices) were successfully analyzed with little or no sample pretreatment using the fully automated flow system.

ISSN:1040-0397    

DOI:10.1002/elan.1140091707

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractTraces of sulfide ion produce a cathodic peak on the HMDE at about −1.50 V (vs. SCE) after preconcentration at −0.5 V in the borax buffer containing 0.01 mM CoII. This peak is due to the catalytic hydrogen evolution, as demonstrated by the influence of the buffer concentration, the effect of water substitution by deuterium oxide and by the formation of hydrogen bubbles on the electrode. The effect of sulfide ion concentration, deposition time and deposition potential demonstrate that a positively charged cobalt complex is adsorptively accumulated during the deposition step. The reduction of CoIIin this species produces a catalytically active compound which is involved in the reduction of the hydrogen ion according to the proposed mechanism. The potential analytical applications of this process for the determination of the sulfide ion have been assessed. The peak current is directly proportional to the concentration of the sulfide ion enabling the application of the standard addition method. The detection limit (using either normal or derivative LSV) is about 1 nM for 10 min accumulation time. The accuracy and reproducibility are fairly good and some of the common interferences in CSV of sulfide ion are removed or at least diminis

ISSN:1040-0397    

DOI:10.1002/elan.1140091708

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA series of metalloporphyrins (CuTMpyP, CuTMAP. CuTPPS, NiTMpyP, ZnTMpyP and CdTMpyP) reacting with DNA were compared. The interaction of metalloporphyrin with DNA shows different binding modes and electrochemical behavior when either the metal ion or porphyrin ligand is different. Due to electrostatical repulsion interaction between the anionic substitute group and a phosphate group on DNA molecular backbone, it is difficult for the anionic porphyrin to interact with DNA. The ability of cationic porphyrins to react with DNA depends on the size of the substitute group and the metal ion in the porphyrin plane center. Metalloporphyrin with or without axial ligand, which depends on the metal ion, results in outside binding or intercalating modes, and shows different interaction capability with DNA. The conditional binding constants of NiTMpyP, CuTMpyP and CuTMAP, which mainly show intercalating mode to DNA, were evaluated.

ISSN:1040-0397    

DOI:10.1002/elan.1140091709

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThis article describes a general method for stabilizing microdroplets of mercury on thick‐film screen printed electrodes (SPEs). Electrodes modified with nickel metal powder are compared with amalgam stabilized mercury SPEs. Application of the electrodes to the measurement of organic materials is demonstrated by the electrochemical determination of 2‐furaldehyde, a marker for power transformer condition monitoring. The electrodes were characterized by cyclic voltammetry and subsequently a square‐wave voltammetric method was used to extend the detection limit of the measurement. The resulting cathodic currents for the reduction of 2‐furaldehyde was proportional to the concentration of 2‐furaldehyde. Plots of 2‐furaldehyde concentration against response at a nickel‐modified carbon SPE gave linear regions for concentrations in the range 3.7–14.3 ppm (regression equation;Y= 0.99 + 0.15x,r= 0.999,n= 3), and linear regions at mercury‐coated silver‐modified carbon SPEs in the range 8.9–36.4 ppm (regression equation;Y= 1.71 + 0.14x,r= 0.999,n= 3) and in the range 0.9–8.9 ppm (regression equation;Y= 1.34 + 0.17x,r= 0.980,n= 3), respectively. A particular advantage of using the mercury‐modified SPE rather than the nickel‐modified base card is that the well‐defined electrochemistry of furan derivatives allow them to be individually distinguished. The half‐wave potentials at the mercury SPE for 2‐furaldehyde (E1/2= −1.15 V vs. Ag/AgCl) and two possible interferents 2‐acetyl‐furan and 5‐methyl‐2‐furaldehyde (E1/2= −1.2 and −1.31 V vs. Ag/AgCl) are sufficiently well separated to allow the individual components to be resolved whereas at a

ISSN:1040-0397    

DOI:10.1002/elan.1140091710

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA 20% (w./w.) polystyrene‐based heterogeneous membrane of inorganic ion‐exchanger, cerium(IV) vanadate, has been prepared and used as a bismuth(III) selective electrode. The electrode gives linear potential response in the concentration range 8.0 × 10−5‐1.0 × 10−1mol L−1with a slope of 19.2 mV per decade of concentration and a fast response time of 50s. The electrode functions well in the pH range 2.0–4.0, in partially nonaqueous media up to 25% (v./v.) alcoholic content and was used over a period of 4 months without any significant drift in potentials. It exhibits selectivity for Bi3+over a large number of metal ions and can be used as an indicator electrode to determine Bi3+by potentiometric titr

ISSN:1040-0397    

DOI:10.1002/elan.1140091711

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY