摘要:

AbstractTungsten oxide, dihydrate (WO3· 2H2O) and monohydrate (WO3· H2O) pastes, as well as silico‐12‐tungstic acid single crystals (H4SiW12O40· 31H2O) have been subjected to electrochemical investigations in solid‐state, i.e., in the absence of deliberately added external liquid electrolyte phase. Mobile protons, which exist in WO3· H2O and H4SiW12O40· 31H2O (but not in WO3· H2O) bulk materials, are capable to support electron transport between WVI, Vmixed‐valence sites (generated in the systems upon partial reduction). Silicotungstic acid can be reduced reversibly to heteropolyblue (HzSiW12O 404−, wherezis 1, 2 or 4), which is analogous to hydrogen tungsten oxide bronze (HxWO3, 0

ISSN:1040-0397    

DOI:10.1002/elan.1140071102

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractAt least two total anodic voltammetric waves of DMSO, or voltammetric waves of undiluted DMSO, can be obtained at platinum microelectrodes. These waves are of roughly equal height. Linear scan‐ and reverse pulse voltammograms indicate that the first wave is a one‐electron wave. After the addition of water the formation of dimethylsulfone is possible and therefore a part of DMSO equivalent to water concentration is oxidized via the two‐electron process. This results in an increase of the wave height and can be used for analytical purposes. To determine water content, by using this increase, its concentration in DMSO should be higher than 0.1

ISSN:1040-0397    

DOI:10.1002/elan.1140071103

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractResults are presented from a systematic study of the noise (N) and peak‐to‐noise ratio (P/N) obtained for pulsed electrochemical detection (PED) at a gold micro‐wire electrode applied to a mixture of alditols and monosaccharides separated by capillary electrophoresis (CE). The electrode potentials and time periods for oxidative cleaning and reductive reactivation of the electrode were held constant in the PED waveform at minimum allowable values and the time period for digital integration of electrode current (tint) was varied from 50 to 800 ms by 50‐ms intervals. The value ofNwas virtually independent oftintandP/Nincreased approximately as a linear function oftintin the range 50–200 ms corresponding to waveform frequencies in the range 4.5–2.7 Hz. A detection limit of 9 fmol glucose was determined for a 4‐nL injection usin

ISSN:1040-0397    

DOI:10.1002/elan.1140071104

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe electrochemical response mechanism of a previously reported potentiometric oxygen (O2) sensing system based on thin films of copper sputtered on single crystal Si(100) is examined. The potentiometric O2response of such films is shown to depend on sample stirring rate as well as the pH, ionic strength and nature of the buffer salts within the test solution. XPS studies of the copper films exposed to solution for several days confirm the presence of compper corrosion products on the surface. These findings, in conjunction with cyclic voltammetric measurements, suggest that the potentiometric O2response originates from slow corrosion of copper and simultaneous reduction of O2at the surface of the thin films. A steady‐state situation exists when the rates of these two reactions are equal, resulting in a corrosion potential (also referred as rest potentialErfor the system) that varies in a near Nernstian (1 e−) manner with the partial pressure of O2in solution. A mathematical formulation for this type of response, based on the Butler–Volmer equation, is presented. The analytical implications of these findings with respect to devising useful potentiometric O2sensors based on copper films are disc

ISSN:1040-0397    

DOI:10.1002/elan.1140071105

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA glucose sensor employing ferrocene‐bound glucose oxidase was fabricated by the screen printing technique. In order to obtain high GOD activity, glucose oxidase (GOD) was modified with ferrocenecarboxylic acid (fc) as an electron mediator. Simultaneous spectroscopic and electrochemical analyses showed that ferrocene‐bound GOD (fc‐GOD) displayed an increase in catalytic current. The ferrocene acts as an electron transfer relay between the active center of the enzyme and the gold electrode. The screen printing process was used to print successfully the unique fc‐GOD containing ink onto the gold electrode patterned on the glass plate. The fc‐GOD containing ink was specially developed to be suitable for the printing apparatus. The printed glucose sensor was shown to offer a stable calibration profile and stable electrochemical p

ISSN:1040-0397    

DOI:10.1002/elan.1140071106

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractNickel‐, cobalt‐, copper‐, and palladium‐dispersed carbon inks are used for screen printing of electrocatalytic sensors. The resulting strips couple the advantages of mass‐producible disposable electrodes and effective catalytic surfaces. The dispersed metal particles lead to a marked decrease in the oxidation potential for carbohydrates, amino acids, aldehydes or alcohols. Characterization of the electrocatalytic behavior and the analytical (sensing) performance are reported. Applicability to wine samples is il

ISSN:1040-0397    

DOI:10.1002/elan.1140071107

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractWe have prepared amperometric glucose sensitive electrodes with a composite active layer consisting of Nafion, glucose oxidase, and carbon‐supported platinum particles. A particularly advantageous configuration results from the use of such a film on a gas diffusion electrode. We demonstrate that the gas diffusion electrode configuration enables us to supply oxygen from the back of the electrode, thus providing the capability of operating the sensor independent of dissolved oxygen. The insensitivity to solution oxygen concentration has been demonstrated by monitoring the glucose response of the electrode after extensive deoxygenation of solution. Cast composite layers yield mechanically robust coatings with high enzyme loadings, and thus high sensitivity to glucose. The electrode responds rapidly and is stable over a long period (90% activity after more than half a year) when stored in solution. We have optimized the composition of the sensitive layer with respect to Nafion to C/Pt ratio and enzyme loadin

ISSN:1040-0397    

DOI:10.1002/elan.1140071108

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA theory to describe the enhancement of the transition time and change in peak shape for the chronopotentiometric reduction of an adsorbed species caused by the reduction of an electroactive diffusing species is presented. The equations were derived for planar, cylindrical and spherical electrodes and verified for the chronopotentiometric reduction of adsorbed cystine, as mercurous cysteine thiolate, on a hanging mercury drop electrode in the presence of dissolved oxygen.

ISSN:1040-0397    

DOI:10.1002/elan.1140071109

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA study of the response characteristics of some fluoride selective electrodes based on three lanthanide fluoride single crystal membranes (LnF3; Ln = La, Ce and Nd) is reported. There is little difference between the response of these three membranes in buffered fluoride solutions except that CeF3shows a slightly faster response and a slightly lower detection limit. The effect of the hydroxide ion on the response to fluoride is examined and is shown to be particularly severe for the CeF3membrane. It is demonstrated that hydroxide ion interference on these membranes is due to the formation of hydroxo‐complexes which form within a gel layer at the membrane surface. A mechanism is proposed for the response of the electrodes to the hydroxide io

ISSN:1040-0397    

DOI:10.1002/elan.1140071110

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractAn electrochemical hydrogen sensor has been constructed, based on two platinum electrodes that differ in their true‐to‐geometrical surface area ratios and that are in contact with Nafion. The electrodes attain different mixed potential values in air containing hydrogen and thus the sensor does not require a reference atmosphere (pure air). The potential difference between the electrodes can be used for potentiometric or amperometric detection of hydrogen. The detection sensitivity strongly depends on the relative humidity (RH) of the test air. Within a hydrogen concentration range from 40 to 4000ppm (v/v) and with RH varying between 33 and 95%, the sensitivity of potentiometric detection decreases with increasing RH from 149 to 113 mV per concentration decade, while that for amperometric detection increases from 0.67 to 1.25 nA/ppm. On a step change in the hydrogen concentration, a value of 95% of stationary response is attained within ca. 140 s for potentiometric detection and ca. 50s for amperometric measurem

ISSN:1040-0397    

DOI:10.1002/elan.1140071111

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY