摘要:

AbstractThis article describes a coulometric measurement device for glucose based on thin‐layer bulk electrolysis. The analysis is carried out in a specially constructed cell, the electrochemical capillary fill device, which has a total volume of less than 20μl. Once the sample enters the cell by capillary action, the freeze‐dried assay components (glucose oxidase, ruthenium (III) hexamine, buffer salts, etc.) become solubilized and quickly disperse throughout the volume of the cell. After a period of one min, the time taken for the enzyme catalyzed oxidation of glucose to gluconic acid to reach completion, a potential step is applied and the current transient, resulting from the oxidation of reduced mediator at the working electrode, integrated over a period of 60 s. From the resultant charge value, the concentration of glucose in the sample can be unambiguously determined. The response of the sensor is both linear and accurate over the range 2–30 mM, which covers the normally accepted range for blood glucose levels in diabetic patients. The second order rate constant for the reaction between reduced glucose oxidase and ruthenium (III) hexamine was evaluated by conducting a numerically based analysis that was designed to separate the diffusional and catatytic components of current tran

ISSN:1040-0397    

DOI:10.1002/elan.1140040104

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe polarographic method proved suitable for investigation of adsorption of acifluorfen (I) (5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2′‐nitrobenzoic acid) on lignin. Polarographic reduction of acifluorfen in aqueous buffers (pH7 is attributed to a decrease in protonation rate of the reduction intermediate. Unsubstitutedp‐nitrophenyl phenyl ether (II) shows an analogous behavior. Reduction wave of the nitro group can be used for determination of aciflurofen (I), fluorodifen (III), oxyfluorfen (IV), and bifenox (V) in the 1 × 10−5to 5 × 10−4M range. Adsorption of acifluorfen depends on th

ISSN:1040-0397    

DOI:10.1002/elan.1140040105

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe electrochemical oxidation of cadmium amalgam was studied in the nonaqueous solvents CH2Cl2, 1,2‐C2H4Cl2and propylene carbonate. Significant coordination effects were observed between the electrogenerated Cd(II) ions and 18‐membered macromonocyclic ligands, each containing six Lewis bases heteroatoms: 18‐O6, 18‐S6, 18‐N2O4, and 18‐N6. The stoichiometries and the stabilities of the resulting complexes were determined. These stabilities increase from 18‐O6or

ISSN:1040-0397    

DOI:10.1002/elan.1140040106

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractAn amperometric enzyme electrode for the determination ofL‐glutamine was developed. The probe consisted of a platinum electrode that senses hydrogen peroxide produced from the reactions catalyzed by glutaminase and glutamate oxidase, which are co‐immobilized on a preactivated Immobilon‐AV Affinity membrane. Protective membranes eliminated interferences fromL‐glutamate and most compounds electroactive at a similar potential. The response of the probe was linear over the concentration range 1 × 10−6M to 7.5 × 10−4M.L‐Glutamine in serum samples obtained from healthy volunteers was determined using the probe, and the results correlated well with previously

ISSN:1040-0397    

DOI:10.1002/elan.1140040107

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe blank response at glassy carbon electrodes in a flow injection system consists of a transient component and a steady state (residual current) component. The transient response is attributed to nonfaradaic current and faradaic current from the oxidation‐reduction of electroactive surface functional groups on glassy carbon. The magnitude of the transient response was dependent on the potential applied to the electrode, temperature, ionic strength and pH of the injected sample solution, and independent of the flow rate. A linear relationship exists between the transient response and the difference in concentration of ionic species or pH between injected sample and the carrier. A differnce of 0.01 M ionic concentration or 0.04 pH unit between carrier and injected sample could change the transient charge by ca. 0.038 μC/cm2. The shape of the transient response due to pH difference at high positive potential indicates that some changes occur on glassy carbon surface in this potential regi

ISSN:1040-0397    

DOI:10.1002/elan.1140040108

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractA silicone‐based calcium potentiometric sensor is described, with improved hemocompatibility, as desired for continuous monitoring of clinical samples. The favorable dynamic properties of the new electrode are illustrated in a flow operatio

ISSN:1040-0397    

DOI:10.1002/elan.1140040109

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe present work reports on an adsorptive stripping voltammetric procedure for the determination of tetramethrin. The best conditions found were pH 4 in 0.2 mol/L acetic acid/acetate buffer solution, and accumulation potential of −0.5 V (vs. Ag/AgCl electrode), an accumulation time of 60 s, frequency 120 Hz, step potential (Es) 2 mV. Under these conditions, determination limits of 1.7 ng/mL−1(8.5 10−9M) are ach

ISSN:1040-0397    

DOI:10.1002/elan.1140040110

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractIon‐selective microelectrodes were prepared by coating a matrix containing the crown ether benzo‐18‐crown‐6 or one of five polyether ring‐substituted benzo‐18‐crown‐6 derivatives on a preconditioned silver wire in a flow cell. Responses of the electrodes toward lithium, sodium, potassium, magnesium, calcium, strontium, and lead were measured. Selectivity coefficients were obtained by the matched potential, fixed interference, and separate solution methods. Compared with benzo‐18‐crown‐6, the nature of the side arm in the lariat ether derivatives was found to influence the selectivities in different ways. For specific ionophores, high selectivities of potassium over lithium, sodium, magnesium, calcium, and strontium, of strontium over magnesium and calcium, and of lead over magnesium, calcium, and stront

ISSN:1040-0397    

DOI:10.1002/elan.1140040111

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe electrochemical behavior of several calcium antagonists of the dihydropyridine family has been investigated in aqueous buffered solution using a glassy carbon electrode. Both oxidation of the dihydropyridine ring and the reduction of the nitro or benzoxadiazole moiety are observed using cyclic voltammetry and the shape of the voltammograms depending on the initial scan direction. Each process may interfere with the other. The single reduction peak corresponds to a four‐electron transfer giving rise to the hydroxylamine. Reversing the scan leads to the nitroso derivative, its reversibility depends on the 2‐ or 3‐position of the nitro group. Oxidation of the dihydropyridine ring proceeds through a two‐electron exchange. However, nicardipine, which possesses a dialkylbenzylamine side chain, exhibits two additional peaks; the first due to the methoxylation of the side chain, and the second attributed to the oxidative chlorination of this moiety. Potentials are pH dependent. A general EC mechanism is proposed for the overall

ISSN:1040-0397    

DOI:10.1002/elan.1140040112

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe sensitivity of the determination of iron in natural waters, including seawater, using cathodic stripping voltammetry (CSV) with adsorptive collection of complexes with 1‐nitroso‐2‐naphthol is greatly enhanced by catalytic reoxidation in the presence of hydrogen peroxide. The limit of detection is lowered to 0.16 nM Fe (using an adsorption time of 60 s) and further to 0.03 nM Fe by increasing the adsorption time to 10 min. Interference from an increase in the background current, brought about by catalysis of the hydrogen evolution, is overcome by addition of an anionic surfactant (sodium dodecyl sulfate (SDS)). Optimal conditions include a hydrogen peroxide concentration of 1.8 mM and 5 ppm SDS. Procedures to purify the reagents from contaminant levels of iron are described. The method is successfully applied to certified seawater and samples from the North Atl

ISSN:1040-0397    

DOI:10.1002/elan.1140040113

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY