Electrode carbon fibre

This can be carried out in vitro (in brain slices, cultured cell preparations) or in vivo and involves penetrating the experimental tissue with a carbon-fibre electrode of 5-30 pm in diameter (Fig. 4.9). This serves as an oxidising electrode and the Faradaic current generated by the oxidation of solutes on the surface of the electrode is proportional to their concentration. Obviously, only neurotransmitters which can be oxidised can be measured in this way so the technique is mainly limited to the study of monoamines and their metabolites. The amplitude of each peak on the ensuing voltammogram is a measure of solute concentration and individual peaks can be identified because different... 

B. Fabre, S. Burlet, R. Cespuglio, and G. Bidan, Voltammetric detection of NO in the rat brain with an electronic conducting polymer and Nafion bilayer-coated carbon fibre electrode. J. Electroanal. Chem. 426, 75-83 (1997). 

F. Gonon, M.F. Suaud-Chagny, and M. Buda, Fast in vivo monitoring of electrically evoked dopamine release by differential pulse amperometry with untreated carbon fibre electrodes, in Proceedings of Satellite Symposium on Neuroscience and Technology (A. Dittmar and J.C. Froment, eds), p. 215. Lyon... 

Determination of S02 reactions as a function of pH and its detection at modified carbon-fibre electrodes... 

Scheme of the flow-through cells with (1) [Fe(ll)TSPcE modified carbon-fibre electrode, (2) glass tubes to immobilise the carbon fibre, (3) reference electrode, (4) flow-through pipeline and (5) metallic tube acting as counter electrode. 

Voltammetric curves of the electrodeposition of [FedDTSPc]4- at a carbon-fibre electrode in pH=7.4 buffer containing 1x10 3mol I- [FedDTSPcF v=100mVs- number of scans is 25. 

Figure 12.9 shows current-potential curves, recorded at carbon-fibre electrodes modified with [Fe(II)TSPc]4, with increasing concentrations of sulphur dioxide in a l.Omoll1H2S04 solution. Similar curves were obtained... 

Besides these main waves, three other waves are observed in Fig. 12.9. Waves I and II are attributed to oxidation of reaction products formed in wave V. This was proved by cycling the potential between -0.3 and 0.6 V vs. AglAgCl where waves I and II were absent. By addition of sodium dithion-ite to the solution, waves I and II again appeared, indicating that the reaction product formed in wave V is dithionite. Waves I and II were also observed at a bare-carbon-fibre electrode after addition of sodium dithionite. Therefore, it is not clear whether these reactions are electrocatalysed by [Fe(II)TSPc]4. However, when cycling between -0.3 and 0.6 V vs. AglAgCl, wave III still occurred under these conditions, indicating that this wave can be attributed to a species in solution. 

Electroluminescence in anthracene as a result of the injection of holes by a field-enhanced tunnelling through a surface barrier when a gold electrode is employed has been investigated (Sworakowski et al., 1974), and recombination has also been reported following injection from carbon fibre electrodes (Williams et al., 1972). In all cases, because of the difference in hole and electron drift mobilities, maximum light emission occurs near the positive electrode. 

Agui, L., Vega-Montenegro, D., Yanez-Sedeno, P. and Pingarron, J. M. (2005), Rapid voltam-metric determination of nitroaromatic explosives at electrochemically activated carbon-fibre electrodes. Anal. Bioanal. Chem., 382(2) 381-387. 

Figure 4. Stability of 100 repetitive measurements of 3 ppm TNT at submersible carbon fibre electrode assembly.

Fig. 19. Potentiostatic transient for the growth of mercury nucleus on a carbon fibre electrode from a 0.1 M solution of Hg2(N03)2 in aqueous KN03 at - 200mV. (After Scharifker and Hills [25].)...

Amperometric electrodes that are extremely thin (<1 pm diameter) are called ultramicroelectrodes and have a number of advantages over conventional electrodes. Being narrower than the diffusion rate thickness, mass transport is enhanced, the signal-to-noise ratio is improved and the measurements can be made in resistive matrices such as nonaqueous solvents. These have huge applications in medicine as they can lit inside a living cell. Carbon fibre electrodes are coated in insulating polymer and plated with a thin layer of metal at the exposed tip to prevent fouling of the carbon itself. These can then be used to measure analytes of interest in various cells and membranes of the human body. 

Fig.7. ESR-spectrum of the p-phenylenediamine cation radical formed at carbon fibre electrode at -fO.35 V in 0.1 M Na2S04.

Both these results prove that the carbon fibre electrode can be used for sensitive ESR-electrochemical measurements. The problem with the carbon electrode is the stability with respect to the ESR spectroscopy. It has been found during this study that the change between anodic and cathodic treatment of the carbon electrode creates the carbon signal at such a level that can be detected under conditions of the highly resolved spectrum. It is the change from... 

Taking this behaviour into account it is preferable to use two types of carbon fibre electrodes for ESR spectroscopy - one for cathodic and the other for anodic processes. Care must be taken in the field of signal accumulation where a background signal abstraction is preferable with carbon electrodes. 

Methods for the removal of low concentrations of species from effluent which involve either oxidation or adsorption will clearly require a cheap but high-surface-area electrode structure, and several carbon bed and carbon fibre electrode cells have been described. The latter are prepared from 5—15 fxm diameter carbon fibre which has a specific area of 260 m g and hence permits a high throughput of effluent. Such a cell has been used for treatment of paper mill effluent and a 70% reduction of BOD with a 95% removal of highly toxic chlorinated phenols has been claimed. 

Suaud-Chagny, M.F. In vivo monitoring of dopamine overflow in the central nervous system by amperometric techniques combined with carbon fibre electrodes. Methods 33(4), 322-329 (2004)... 

CE with end-column amperometric detection (33 pm diameter carbon fibre electrode, +0.65 V vs Ag/AgCl) has also been used to detect isoprenaline enantiomers in microdialysates of rat plasma. Analyses were performed at 20 kV in fused-silica capillaries (65 cm x 50 mm i.d.). The analysis buffer consisted of aq. lithium acetate (100mmolpH 4.75), methyl-O-P-cyclodextrin (100gL ) and disodium EDTA (0.5 mmolL ). Samples were introduced by electrokinetic injection (18 kV, 3 s) or by pH-mediated stacking (electrokinetic injection, 18kV 15 s, followed by electrokinetic injection of 0.1 mol L aq. hydrochloric acid, 18kV, 20 s). Inclusion of DHBA as the internal standard was claimed to increase the precision of the analysis from 3.2 to 1.4% RSD. The LoD was 600ngL (S/N = 3, 1 pL sample). 

Antoniadau S, Jannakoudakis AD, Theodoridou E (1989) Electrocatalytic reactions on carbon fibre electrodes modified by hemine II. Electro-oxidation of hydrazine. Synth Met 30 295-304... 

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