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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Electroanalysis 3 (1991), S. 87-95 
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The intracellular response of ultrasmall carbon ring electrodes has been investigated. Adsorption of high molecular weight species (e.g., proteins, lipids, sugars) on the electrode surface appears to result in deterioration of the amperometric signal, making in vivo voltammetric measurements difficult. Assuming a linear dependence between the degree of electrode fouling and the number of scans taken in the neuronal microenvironment, an analytical method based on both pre- and postcalibration data is presented to evaluate the response obtained at deteriorating ultrasmall carbon ring electrodes during intracellular voltammetry. Additionally, poly(ester sulfonic acid)-coated carbon ring electrodes have been used in an attempt to increase selectivity in intracellular voltammetry and to reduce the effects of electrode fouling. In vitro results obtained in solutions of dopamine, dihydroxyphenylacetic acid, and ascorbic acid indicate some exclusion of anionic species from the electrode by the negatively charged polymer film. Moreover, use of polymer-coated electrodes in vivo result in such a decrease in the percentage of electrode fouling that the degradation of the response is only 45%. This leads to a more reproducible response and better detection limits compared to results from naked electrodes.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 3 (1991), S. 141-145 
    ISSN: 1040-7685
    Keywords: capillary electrophoresis ; copper electrode detection ; amino acids ; catecholamines ; peptides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of a copper wire amperometric detector for capillary electrophoresis is reported. Detection is accomplished by use of a porous glass joint, which allows amperometric detection at a copper wire electrode inserted in the end of the capillary. An anodic current is produced by a change in the copper oxide film solubility, resulting from complexation of copper ions with certain analytes at the electrode surface. This copper/copper oxide electrode has been used to detect nonelectroactive native amino acids and dipeptides. Subfemtomole detection limits in picoliter injection volumes have been obtained without solute derivatization. In addition, simultaneous analysis of nonelectroactive amino acids and electroactive catecholamines has been demonstrated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 6 (1994), S. 263-268 
    ISSN: 1040-7685
    Keywords: capillary electrophoresis ; scanning electrochemical detection ; voltammetric detection ; catecholamines ; peptides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Scanning electrochemical detection has been combined with capillary electrophoresis to increase the resolving power for closely eluting solutes. This detection mode has been characterized and provides voltammetric information for easily oxidized solutes with linear detection over concentrations in the 10-3 to 10-5 M range. Detection limits for catechols range from 360 amol to 740 amol (2.3 μM to 6.6 μM concentrations). Finally, two neutral solutes, catechol and tryptophan, co-elute under zone electrophoresis conditions, but are resolved with scanning detection.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1040-0397
    Keywords: Ring Microelectrode ; 5-Hydroxytrypton ; Voltammetry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ultrasmall gold ring electrodes have been constructed by electrodeposition of gold onto carbon ring electrodes. Electrodes thus formed show similar adsorption/desorption peaks for oxygen in H2SO4 solution compared to those obtained at conventional-sized electrodes. These electrodes have been used in conjunction with linear scan voltammetry and subsequent cleaning pulses to obtain repeatable quantitative results for the electochemical oxidation of 5-hydroxytrptamine and 5-hydroxyindoleacetic acid. This technique involves the use of a linearly scanned applied potential, followed by a large positive potential to clean the electrode oxidatively and negative potential for electrode activation. The result of the cleaning pulses is that oxidation products of 5-hydroxytryptamine are cleaned off the electrode and reproducible voltammograms are obtained.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1040-0397
    Keywords: Electrodeposition ; Poly(oxyphenylene) ; Carbon fiber ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By varying the conditions of an electrodeposition solution containing phenol and 2-allylphenol, thin poly(oxyphenylene) films can be formed. These films have been used to insulate flame-etched carbon fiber electrodes to produce smaller electrode tip diameters. Experiments have been performed to test both the insulating properties and the film thickness of this poly(oxyphenylene) copolymer at pH 5.0, 7.0, and 9.0. The effects of monomer concentration on the polymer insulation integrity and film thickness have also been investigated. These experiments show that a decrease in pH results in thinner insulating films. It is also shown that monomer concentration can be decreased to 12 mM phenol/18 mM 2-allylphenol without causing an appreciable change in the insulating properties of the copolymer film; however, as the concentration is decreased, the pH appears to have less influence on the copolymer thickness.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Electroanalysis 6 (1994), S. 746-751 
    ISSN: 1040-0397
    Keywords: Electrochemical treatment ; Adenosine ; Carbon fiber ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Voltammetry of adenosine after electrochemical treatment is explored. The activations scheme includes an anodic potential (+2.2 V) for 125 ms and a cathodic potential (-1.0 V) for 75 ms. Subsequent staircase voltammetry can be used to obtain both qualitative and quantitative information. This activation procedure has been applied to 11 μm carbon-fiber microelectrodes to obtain reproducible voltammograms for adenosine. To characterize this activation procedure, the effect of the magnitude and duration of both the anodic and the cathodic potentials have been studied. Data obtained suggest that the magnitude of the applied potential pulse is critical to proper electrode activation, whereas duration and total charge passed have minimal effects.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Electroanalysis 3 (1991), S. 899-907 
    ISSN: 1040-0397
    Keywords: Microelectrodes ; electrochemical treatment ; carbon ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrochemical anodic treatment at ultrasmall carbon ring electrodes appears to result in the formation of an oxide film that displays charge-selective and pH-dependent enhancements following treatment. Voltammetry after treatment in pH 7.4 citrate-phosphate buffer is more Nernstian for dopamine (DA) and less Nernstian for 3,4-dihydroxyphenylacetic acid (DOPAC). However, oxidation in pH 2.8 buffer gives rise to voltammetry that is less Nernstian for both DA and DOPAC. Extensive surface oxidation in potassium hydroxide apparently forms a thick layer that acts like a thin layer reservoir for adsorbed analyte. Voltammetry following extensive treatment is attenuated and peak shaped. Minimal surface oxidation in KOH results in more Nernstian sigmoidal voltammetry with only light current attenuation. The data suggest that an oxide layer formed following anodic treatment is non-uniform and leaves sites of activated carbon exposed on the surface. Furthermore, it appears that this layer has cation-exchange properties giving rise to charge transfer selectivity. A model of the surface formed following anodic oxidation is consistent with previous models involving both surface cleanliness and carbon structure orientation.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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