Graphite working electrode

Description of Method. The amount of chlorpromazine in a pharmaceutical formulation is determined voltammetrically at a graphite working electrode in a nonstirred solution. Calibration is achieved using the method of standard additions. 

Is chlorpromazine oxidized or reduced at the graphite working electrode ... 

Anson and co-workers have shown that two Co ions were not necessary for four-electron 02 reduction.266 The mew-substituted complex porphyrin Co(TPyP) (42) complex bears four active pyridyl donors which readily react with four equivalents of [Ru(NH3)5(OH2)]2+ to produce the tetra-ruthenated derivative. The four Ru centers are sufficiently remote that their RuIII/n potentials coincide. Under steady state conditions [Co(TPyP)] Ru(NH3)5 4]8+ (43) adsorbed onto a pyrolytic graphite working electrode catalyzes the reduction of dioxygen (Figure 6). 

Figure 6 Steady state rotating ring-disk voltammograms of (A) compound (42) (B) compound (43) and (C) a Ru-bridged polymer of (43) each adsorbed to a graphite working electrode. Disk current shows reduction of 02 while ring current reveals the presence of H202 simultaneously reoxidised at the ring anode poised at +1.0 V (reproduced with permission of the American Chemical Society from Acc. Chem. Res., 1997, 30, 437-444).

Figure 22 Cyclic voltammograms recorded in aqueous solutions of Rieske fragments from (a) bci complex glassy carbon working electrode pH 7.2 (b) (recombinant) biphenyldioxygenase (basal) pyrolitic graphite working electrode (in the presence of the positively charged additive neomycin) pH 7.0. Scan rate 0.01 V s ...

Figure 56. Slow scan (10 /iV s ) voltammetry on a graphite working electrode (a) 1.0 M LiFAP in EC/DEC/ DMC (b) LiPEe in EC/DEC/DMC. Solid line pristine graphite. Dashed line after 1 week of cycling. (Reproduced with permission from ref 499a (Figure 4). Copyright 2003 The Electrochemical Society.)...

The electrochemical window of pure molten cryolite has not been expressly stated, but a voltammogram of purified cryolite recorded at a graphite working electrode exhibits very little residual current over the range of potentials extending from 0.4 to -1.9 V vs. a nickel wire quasi-reference electrode [7]. Physical property data for molten cryolite and phase equilibria for the AlF3-NaF melt system have been summarized [31,32]. The extremely high temperature of cryolite places severe constraints on the materials that can be used for cells. Platinum and boron nitride are the materials of choice. 

The different biosensors were obtained using thick-film SPEs produced by Biosensor Laboratory, University of Florence and commercialized by PalmSens. The electrochemical cell, consisting of a graphite working electrode and silver counter and pseudo-reference electrodes, was printed on a planar polyester substrate (Fig. 29.2). 

Neon light (two 15-W lamps) (Osram, Germany) for photopolymerisation of the PP2A/PVA-AWP mixture on the screen-printed graphite working electrode. 

The 2 x SSC buffer solution contained 300 mM of NaCl and 30 mM C3H5Na307 (pH 7.4). The acetate buffer solution (ABS) was prepared at the final concentration of 0.25 M, with 10 mM of NaCl (pH 4.7). All oligonucleotides, probes and complementary strands were purchased from Sigma Genosys (UK). All measurements were performed using screen-printed electrodes (SPEs). SPEs were used as disposable. The three-electrode system used was formed by a graphite working electrode, a counter electrode and a silver-based reference electrode. 

Fig. 2 Screen-printed electrodes produced in the author s lab the cell consists of circular graphite working electrode (diameter of 3 mm), a silver pseudo-reference electrode, and a graphite counter electrode. The cell is printed on a planar, polyester substrate (of thickness 450 micron). Each cell is pre-cut by a laser trim. The dimension of each cell is 0.8 cm x 4.5 cm. A standard connector of 2.45 mm pitch can be used with these cells. These sensors show a coefficient of variation (CV) of 5%...

Currently, work is being conducted on an in situ electrodeposition sampling device 20, 21, 22), It consists of a submersible, self-contained potentiostat, power supply, reference electrode, and working electrode. Metals are deposited on the 1-in. diameter, wax-impregnated, pyrolytic graphite working electrode 21, 22, 23) which can then be removed from the sampler at the surface and stored. The metal film can be either... 

Figure 20.5 Amperometric detection in HPLC and HPCE. (a) Two models of detector cells. The porous graphite working electrode have a large surface and operates under coulometric conditions. The flow of the mobile phase at the working electrode ensures renewal of the electroactive species (b) Detail of the end of a capillary in HPCE. The working electrode, placed on the cathodic side of the apparatus, is bathed by ions exiting the capillary. Apart from phenols, aromatic amines and thiols, few analytically important molecules are electroactive.

TCNQox immobilised on the surface of the graphite-working electrode is reduced by the thiocholine produced in the reaction of enzymatic hydrolysis of ACTh. TCNQ reoxidation is realized using DPV technique in the... 

Detector E, ESA Coulochem model 5100 A, two porous graphite working electrodes and associated palladium reference electrodes, +0.55 V for first electrode, +0.70 V for second (monitoring) electrode... 

The method used to measure the activity of immobilized biological materials can interfere with the operational activity. PSII complexes isolated Irom the thermophilic cyanobacterium Synechococcus elongatus and immobilized in BSA-glutaraldehyde on the surface of a screen-printed sensor composed of a graphite working electrode and Ag/AgCl reference electrode shown a weak operational half-life of about 8h if the electrodes were coupled and a good half-life (24h) with separated electrodes. The low stability with the coupled electrodes was caused by Ag ions released from the reference electrode, which were toxic for PSII activity. In the same way, the operational life of whole... 

Using graphite working electrodes, it has been demonstrated that in vivo measurements of physiologically important catecholamines and their metabolites, along with 5-hydroxtryptamine (serotonin) and its metabolite 5-hydroxyindole, are possible via their voltammetric oxidation signals. Adams has reviewed these in vivo electroanalytical techniques. An advantage... 

In voltammetry, current is measured while voltage between two electrodes is varied. (In amperometry, we held voltage fixed during the measurement of current.) Consider the apparatus in Figure 17-9 used to measure vitamin C (ascorbic acid) in fruit drinks. Oxidation of analyte takes place at the exposed tip of the graphite working electrode ... 

Cyclic voltammetry at a graphite working electrode has been used directly on white and red blood cells from human bone marrow one of the three irreversible anodic peaks observed with a bone marrow blood cell mixture was only present in leukemic patients [124]. Cyclic voltammetry has also been used directly on E. coli, rat jejunal mucosal tissue, and the enzyme lactate dehydrogenase to evaluate oxidative damage [125]. An earlier study showed that bacteria can be classified as gram-positive... 

Electrochemical detectors measure chemical properties of a compound and rely on chemical reactions in which electrons are transferred fi om one compound to another. There are two types of electrochemical detectors, amperometric or coulo-metric detectors. The latter one is commonly used because of its high surface of contact with a structure of porous graphite working electrodes giving 100 % of the analyte. The magnitude of the current is therefore directly proportional to the injected compounds, and conveniently the peak areas in an HPLC chromatogram represent the total current as a function of time. 

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