Carbon paste electrode conductivity

Although the carbon-paste electrode is quite effective for readily oxidizable analytes, a full range of electrochemical response is only available with the mercury electrode, particularly the versatile version called dropping mercury electrode. Witli this electrode, analyses are conducted at a frequently renewed mercury... 

Conducting carbon polymer ink, which filled a UV-ablated microchannel, was used to construct the integrated microelectrode on a plastic chip. Both chronoamperometry and CV were employed to detect a model compound (fer-rocenecarboxylic acid) down to 3 iM, corresponding to 0.4 fmol within a volume 120 pL [758], In another report, a carbon-paste electrode was constructed by filling a laser-ablated (PET or PC) channel with C ink. The whole structure was then cured at 70°C for 2 h [189]. 

Modified electrodes for this analytical purpose have mostly been formed by electrode adsorption of the mediator systems on the electrode surface or by electropolymerization [24,116]. Recently, for example, NAD(P)H oxidations have been performed on platinum or gold electrodes modified with a monolayer of pyrroloquinoline quinone (PQQ) [117] or on poly(methylene blue)-modified electrodes with different dehydrogenases entrapped in a Nafion film for the amperometric detection of glucose, lactate, malate, or ethanol [118]. In another approach, carbon paste electrodes doped with methylene green or meldola blue together with diaphorase were used for the NADH oxidation [119]. A poly(3-methylthio-phene) conducting polymer electrode was efficient for the oxidation of NADH [120]. By electropolymerization of poly(aniline) in the presence of poly(vinylsulfonate) counterions. 

A carbon paste electrode modified with Cu -doped clinoptilolite powder has been evaluated as an amperometric sensor for non-electroactive in flow injection analyses [48]. The conductivity of heulandite single crystals parallel to [100] has been studied under isothermal conditions as a function of the H2O content, small polar organic molecule concentration, and charge compensating cations. Results indicate that heulandite electrodes will be applicable for analytical purposes in aqueous solution [49]. 

Performance improvement of polysulfone ultrafiltration membrane has been achieved by blending with PANI-NFs [457]. Conducting blends of nanostruetured PANI and PANI-clay nanocomposites with ethylene vinyl acetate as host matrix have been prepared [458]. A new conducting hybrid biocompatible composite material of PANI-NFs well dispersed in a collagen matrix was fabricated with various PANI-NFs/eoUagen ratios [459]. PANI-NFs doped by protonic acids can be efficiently dispersed in vinylidene fluoride-trifluoroethylene copolymers [460]. Fabrication of MWCNTs/PANI-NF nanocomposites via electrostatic adsorption in aqueous colloids has been reported [143]. A PANI-NFs/ carbon paste electrode was prepared via dopping PANI-NFs into the carbon paste [461]. 

AuE gold electrode CCPE chitosan-entrapped carbon paste electrode CV cyclic voltammetry 3D-CPNE three-dimensional conducting polymer nanorods electrodes DPASV differential pulse anodic stripping voltammetry DPV differential pulse voltammetry GCE glassy carbon electrode SPE screen-printed electrode SWV square wave voltammetry. 

Polymeric films can be prepared at the surface of metal, glassy carbon, as well as carbon paste electrodes. The preparation of conducting polymers at the surface of carbon electrodes employed in biosensors is already reviewed [1]. The methods mostly used are solvent casting, spin coating, and electropol5mierization. 

The physical combination of immobilized enzymes and electrodes can be realized in several different ways. The most common are those in which the enzyme is immobilized in a membrane that is held in close proximity to the electrode surface, immobilized directly on the electrode surface with retained activity, or immobilized in an electrically conducting paste comprising a carbon-oil mixture, known as a carbon paste electrode. The enzyme substrate (and cosubstrate, if required) will diffuse from the... 

Wang, J., Martinez, T., Yaniv, D.R., and McCormick, L. (1990) Characterization of the microdistribution of conductive and insulating regions of carbon paste electrodes with scanning tunneling microscopy. /. Electroanal. Chem., 286, 265-272. 

Mixtures of conductive particles with an electrode modifier have also been carried out using carbon paste electrodes. A recent example is the incorporation of PVP, which was protonated and exposed to ferrocyanide (113). The PVP-modified carbon paste electrode behaved similarly to a surface-modified electrode. The advantage of such a system is that the surface could be renewed simply by exposing a fresh layer of modified carbon paste by mechanically removing the surface layer. 

Apart from UV detection, there are two other alternative detection methods for trace analysis of nitrite. A very sensitive detection method for nitrite is DC amperometry at +1.1 V on a carbon paste electrode. In this case, amperometry and suppressed conductivity detection can be applied simultaneously by directing the conductivity cell effluent through the amperometric celL Figiu-e 10.17 exemplifies this with a surfiice water sample that was injected imdiluted [26]. As can be seen firom this chromatogram, nitrite concentrations in the lowest micro-gram/Liter range can be detected without any problem. 

Carbon nanotubes can be grown on conducting Si, Au, Pt, and glass. The first three substrates are useful for making nanotubes into electrochemical electrodes. There are three ways nanotubes have been configured as an electrochemical electrode. First, nanotubes have been made into the equivalent of a carbon paste electrode by dispersion into mineral... 

Conductivity detection and DC amperometry can be used simultaneously. In a non-suppressed system the conductivity cell effluent is directed to the amperometric cell in a suppressed system the positioning of the amperometric cell depends on the electrode material. The carbon paste electrode, for example, is positioned between the suppressor and the conductivity cell, so that electroactive anions can be detected together with standard anions [14]. An example of applications involving a carbon paste electrode is shown in Fig. 7-8. The separation of nitrite, thiosulfate, and iodide is performed in an acidic medium with a... 

Metal nanoparticle-doped sol-gel silica nanocomposites do not possess the required conductivity to fabricate bulk or screen-printed electrodes. Inspired by the well-known resorcinol/formaldehyde sol-gel process, which can be pyro-lyzed to get a conductive amorphous carbon matrix, we have synthesized a nanocomposite material made of a carbon xerogel doped with bismuth nanoparticles and fabricated a carbon paste electrode for heavy metal analysis (Figure 46.11) [24]. The resulting sensor is very sensitive to several heavy metals. Extremely low detection limits for Pb " and Cd of around 0.5 ppb were achieved using a nanocomposite paste electrode containing 6 wt. % of bismuth. 

Electrochemical oxidation of thermally denatured single-stranded DNA (ssDNA) was studied on a room temperature ionic liquid N-butylpyridinium hexafluorophosphate (BPPFg) modified carbon paste electrode (IL-CPE) by Sun et al. [27]. The presence of IL layer on the surface of CPE showed the ability of ionic conductivity and cation exchange extraction. 

A hydroxyl functionalized ionic liquid (IL) l-(3-chloro-2-hydroxy-propyl)-3-methylimidazolium tetrafluoroborate (PMIMBF4) was used for the preparation of bulky-modified carbon paste electrode (IL-CPE) by Guo et al. [31] and it was applied to the sensitive detection of adenosine-5 -diphosphate (ADP). Due to the specific characteristics of IL such as high ionic conductivity and strong adsorption ability, IL-CPE showed remarkable redox catalysis effect on the oxidation of ADP. By using (DPV) the oxidation peak current was linearly dependent on the ADP concentration in the range from 10.0 to 1000.0 pmol L with the detection limit as 3.23 pmol L (3o). 

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