Carbon fiber electrodes Voltammetr

R. Cespuglio, H. Faradji, Z. Hahn, and M. Jouvet, Voltammetric detection of brain 5-hydroxyindo-lamines by means of electrochemically treated carbon fiber electrodes chronic recordings for up to one month with movable cerebral electrodes in die sleeping or waking rat, in Measurements of Neurotransmitters Release in Vivo (C.A. Marsden, ed.), Wiley, Chichester (1984). 

A major advantage of carbon fiber electrodes is the possibility of using fast voltammetric scan rates (> 100 V/s) due to small electrode area [48]. Even though internal resistance can be significant for carbon fibers (see later), the... 

Electrochemical detectors for liquid chromatography have reached a level of maturity in that thousands of these devices are used routinely for a variety of mundane purposes. Nevertheless, the technology is advancing rapidly in several respects. Multiple electrode and voltammetric detectors have been developed for more specialized applications. Small-volume transducers based on carbon fiber electrodes are being explored for capillary and micropacked columns. Recently, electrochemical detection has also been coupled to capillary electrophoresis [47]. Finally, new electrode materials with unique properties are likely to afford improved sensitivity and selectivity for important applications. 

The results described in the previous paragraph suggest that extracellular dopamine levels in the rat striatum are indeed higher than the detection limits available with carbon fiber electrodes. Under resting conditions, however, the voltammetric signal from dopamine is obscured by a large background current. Nevertheless, this result implies that there may be many more opportunities than we... 

Fig. 48. Dopamine-dependent CV current at brain-implanted carbon fiber electrode. Stimulus signal lasting 5 s at 60 Hz frequency voltammetric signals applied in 100 ms intervals (see B) Ej = -0.4 V, Er = -f 0.8 V vs. SCE, scan rate 300 V s . Adapted from [172].

Cheng, Design of an Intelligent Voltammetric System and Fabrication Optimisation of Its Carbon Fiber Electrode, PhD. Thesis., NCKU Tainan Taiwan, 2003... 

Aguei L, Vega-Montenegro D, Yanez-Sedeno P et al (2005) Rapid voltammetric determination of nitroaromatic explosives at electrochemically activated carbon-fiber electrodes. Anal Bioanal Chem 382 381-387... 

The need to measure concentrations in very small volumes is not restricted to biological systems. For example, open tubular columns for liquid chromatographic separations offer the advantage of increased resolution, but because their internal diameters may be as small as 15 pm, the amount of material in the eluted peaks is very small. Thus, the use of these columns requires detectors that can be used with low concentrations in small volumes. Jorgenson and co-workers showed that this could be accomplished by the insertion of a 10-pm-diameter, cylindrical electrode made from a carbon fiber into the end of the column [4]. The close fit between the column wall and the fiber ensured that a large fraction of the eluting molecules were electrolyzed. When the electrochemical data were collected in a voltammetric mode, the resolved compounds could be classi-... 

A recent study by Xi et al. (1998) utilized single carbon fiber instead of multiple fiber electrodes and a fast-scan voltammetry instead of chronoamperometry. An additional difference was that the rats were first trained to acquire stable rates of heroin selfadministration and then were implanted with the electrodes. Under these conditions 60% of the rats responded to self-injection of 0.06A).l mg/kg of heroin with a monophasic increase, 20% with a biphasic increase/decrease and 20% with a biphasic decrease/ increase of the electrochemical signal (Xi et al., 1998). Only monophasic increases were observed with doses of 0.2 mg/kg of heroin. Tonic monophasic increases in signal were observed also by chronoamperometry with stearate-coated electrodes in a comparative study of cocaine and amphetamine self-administration in parallel with microdialyis (Di Ciano et al., 1995). From this study, however, it appears that, although the effect of drug self-injection on dialysate DA and on the tonic voltammetric signal is qualitatively... 

When a voltammetric scan is initiated at a bare carbon electrode placed in a solution of 10 mM ascorbate/1 mM DOPAC, the peaks due to the oxidation of the two compounds are poorly resolved (24-26). If, however, a PNVP-coated electrode is placed in the same solution, the two peaks are partially resolved, as illustrated in the upper square wave voltammogram shown in Figure 5. Because the concentrations of the two species are more nearly equal close to the electrode surface, the oxidative signals are partially resolved. If the electrode potential is held sufficiently positive to oxidize both species for several minutes, and another scan is acquired, the lower voltammogram shown in Figure 5 is obtained. In this case, ascorbate was oxidized with subsequent rapid hydrolysis to an electroinactive form whereas DOPAC was oxidized to its ortho-quinone form. When the potential was stepped back to a more negative value, the DOPAC quinone was reduced back to the dihydroxy- form. Thus the lower scan shown exhibits a peak due primarily to oxidation of DOPAC since the ascorbic acid present in the film was oxidatively depleted. We have recently reported similar results obtained at gamma-irradiated, PNVP-coated, carbon fiber ultramicroelectrodes (24,25). 

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