摘要:

AbstractExtensive studies of the characteristics of electrochemically pretreated, Nafion‐coated carbon fibers used for in vivo electrochemistry are summarized. While electrochemical pretreatment provides high sensitivity for the monitoring of catecholamine neurotransmitters, it causes fibers to respond slowly. The ionomer film, which confers selectivity, adds relatively little to the electrode time constant. In terms of sensitivity and time constant changes, serious interactions occur during the course of the in vivo experiments while the electrodes are exposed to brain tissue. Fortunately, selectivity characteristics do not change during in vivo experiments. Postcalibration procedures and other measurement techniques that provide reliable experimental measurements are discusse

ISSN:1040-0397    

DOI:10.1002/elan.1140020303

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractUltramicroelectrodes are shown to be extremely useful for investigating fast electrochemical kinetics due to the effects of decreased ohmic drops obtained by reducing electrode dimensions. Scan rates above 1 MV/s can be reached.

ISSN:1040-0397    

DOI:10.1002/elan.1140020304

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractBattery‐powered, complementary metal oxide semiconductor (CMOS) devices have been used to develop a programmable function generator. When used in conjunction with commercially available, battery‐powered potentiostats or electrometers and recording devices, the technique of field‐based direct current stripping voltammetry becomes available. The instrumental performance of a range of modular, battery‐powered instruments has been evaluated with conventional and microsized electrodes and compared with ac‐powered laboratory instruments using conventionally sized electrodes. Stripping experiments with the field‐based instrument and with microelectrodes can be carried out under linear potential sweep conditions because the limit of detection is similar to that obtained with transient techniques at conventional sized electrodes. Other simplifications to the instrumentation and voltammetric procedures that are valuable in field‐based studies (e.g., neither stirring nor deoxygenation of the solutions is required) also are achieved by using microelectrodes and are illustrated by the determination of copper in a river

ISSN:1040-0397    

DOI:10.1002/elan.1140020305

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractCyclic voltammetry involving amalgam formation at mercury microelectrodes is described experimentally and theoretically for reversible systems. Silver microdisks were used to support the mercury deposit during the preparation of electrodes. The ratio of the mercury film thickness to the disk radius is much lower than 1 (e.g., a 1 μm thick layer of Hg on a silver disk with a radius of 15 μm) justifies the namemercury film microelectrode.When the substrate is present in the solution, the original shape of the cyclic voltammograms (one or more cathodic waves followed by one or more anodic symmetrical peaks) is the result of the combination of spherical diffusion in the solution and restricted diffusion in the mercury film. When the substrate is present initially in the mercury phase, an anodic symmetrical peak is followed by a negligibly small cathodic peak. The alternate dimension implicit and the alternate direction Galerkin methods were used in the calculation

ISSN:1040-0397    

DOI:10.1002/elan.1140020306

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractAn elecrochemical microband thin‐layer flow cell that incorporates a thin glassy carbon electrode was fabricated and tested. The microband, tested with ferrocyanide and catecholamine oxidation, exhibited properties of a microelectrode with excellent electroactivity and signal‐to‐noise (S/N) response. For the chromatographic determination of several catecholamines at the 100 fmol level, the relative standard deviation as measured by the peak height ranged from 3–8%. The detection limit for DOPAC was 5 fmol (S/N = 3). The microband thin‐layer cell gives an improved S/N ratio at an applied potential of 0.6 V vs. Ag/AgCl compared to that of a conventionally sized glassy carbon electrode. The small surface area of the microband allows rapid stabilization of chromatographic background (baseline) following the application of the potential. The microband thin‐layer flow cell has a volume of 5 μL and exhibits a flow‐rate‐independent response, reduced ohmic drop, and gradient elution capability. The microband cell has great potential for commercialization as a universal detector for liqui

ISSN:1040-0397    

DOI:10.1002/elan.1140020307

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractLight produced by the electrogenerated chemiluminescence reaction of luminol in alkaline peroxide was monitored with a sensitive imaging system. The light images were taken to represent the level of microscopically local activity on the electrode surface with a spatial resolution in the submicrometer domain. The temporal resolving capabilities of the imaging system permitted the construction of time‐sequenced images and intensity‐potential profiles, the latter being equivalent to a microscopically local voltammogram. Spatial variation in luminol oxidation kinetics were observed at porphyrin‐coated glassy carbon, carbon paste, and anodized glassy carbon electrodes. Implications for other composites and microelectrodes are disc

ISSN:1040-0397    

DOI:10.1002/elan.1140020308

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe manual recording of near‐steady‐state diffusion currents at inlaid disk or shrouded hemispherical microelectrodes provides a simple and accurate analytical method for a variety of electroactive species in the micromolar and millimolar concentration ranges. The only instrumentation needed is a battery, a chain of resistors, and a battery‐powered picoammeter. A two‐electrode cell suffices. Ferrocene in an acetonitrile solution can be analyzed at concentrations as low as 2.0 μM, but the detection limits are higher in aqueous solutions. Using a simple microcell, as little as 100 pmol of ferrocene could be detected. This work resembles some of the earliest voltammetric studies, but the use of smaller electrodes provides a firmer theoretical foundation to the exp

ISSN:1040-0397    

DOI:10.1002/elan.1140020309

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractAnalytical equations for steady‐state current‐potential curves at interdigitated microarray electrodes (IDA) were derived by the conformal mapping of the complex variable theory when the electrode reaction was quasi‐reversible and totally irreversible. In this technique, curved current lines in the IDA could be transformed into a set of parallel lines, as in a thin‐layer cell at a faced twin electrode. The current‐potential curves were a function ofko(we+wg)/D and were almost independent of the geometrical parameter,wg/(we+wg), wherekois the reaction rate constant,weis the common width of each microband anode or cathode,wgis the width of the gap between the anode and the cathode, andDis the diffusion coefficient. The quasi‐reversible domain was 0.2

ISSN:1040-0397    

DOI:10.1002/elan.1140020310

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractFlexible ultramicroline electrodes have been made from a variety of materials, including Au, Pt, Ir, and C. The thickness of these materials ranges from 3.5 nm (approximately 13 atoms thick) to 700 nm. The smallest electrodes are comparable to the smallest rigid line electrodes produced by other techniques. The electrode material is sandwiched between flexible polymer supports, and the bottom is cut with a scalpel to produce the working face of the ultramicroline electrode. The special method of attaching the films to the polymer support allows a high degree of electrode flexibility without causing fractures and concomitant increases in resistance and altered electrode characteristics. The flexibility of these electrodes offers the potential for easy fabrication of a variety of electrode configurations, including spirals, rings, concentric rings, linear arrays, and ring‐disc electrodes. Examples of the electrochemical behavior of ultramicroline and ultramicroring electrodes are described and are similar to those of rigid ultramicroelectrodes that are produced using other technologies. The carbon ultramicroline electrodes are somewhat more susceptible to mechanical damage than the metallic electrodes when they are flexed, and the resistivity increases on bending, thus indicating some fracturing of the film. Nonetheless, they can still be bent into various geometries and are electrochemically usefu

ISSN:1040-0397    

DOI:10.1002/elan.1140020311

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractA comprehensive view of in vivo electrochemistry (voltammetry) is presented with a detailed evaluation of electrodes and waveforms. Special attention is given to specific kinds of electrode fabrication. The article is presented in an historical format to emphasize both the progression of the electrochemical technology and the inherent stability of the technique. Future prospects relevant to voltammetry are discussed, and 189 references are included.

ISSN:1040-0397    

DOI:10.1002/elan.1140020312

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY