Chemically modified carbon electrode

The HOPG (highly oriented pyrolytic graphite) carbon electrode chemically modified with (5[-phenylalanine at the basal surface led to 2% ee in the reduction of 4-acetylpyridine [377]. A cathode modified with a chiral poly(pyrrole) reduced 4-methylbenzophenone or acetophenone in DMF/LiBr and phenol as proton donor to 1-phenylethanol with up to 17% ee [382]. Alkyl aryl ketones have been reduced to the corresponding alcohols at a Hg cathode in DMF/water in the presence of (1R,2S)-A,A-dimethylephedrinium tetrafluorobo-rate (DET), producing (5 )-l-phenylethanol with 55% ee from acetophenone. Cyclovoltammetry supports an enantioselective protonation of the intermediate (PhCOH(CH3)) [383]. 

M.A.T. Gilmartin, R.J. Ewen, J.P. Hart and C.L. Honeybourne, Volt-ammetric and photoelectron spectral elucidation of the electrocatalytic oxidation of hydrogen-peroxide at screen-printed carbon electrodes chemically-modified with cobalt phthalocyanine, Electroanalysis, 7 (1995) 547-555. 

J.P. Hart and I.C. Hartley, Voltammetric and amperometric studies of thiocholine at a screen-printed carbon electrode chemically modified with cobalt phthalocyanine studies towards a pesticide sensor, Analyst, 119 (1994) 259-263. 

Wring, SA., Hart, J.P., Bracey, L. 8c Birch, B.J. (1990). Development of screen-printed carbon electrodes, chemically modified with cobalt-phthalocyanine, for electrochemical sensor applications. Anal. Chim. Acta. 231, 203-212... 

The stripping voltammetric determination of pertcchnetatc by means of a glassy carbon electrode, chemically modified with a tctraphenylarsonium chloride loaded copolymer film, was reported. A detection limit of 10 M TCO4 was achieved after a 5 min enrichment time [101]. 

Thiols can be oxidised at a variety of solid electrodes, such as noble metals, carbon and carbon with chemically modified surfaces. Mefford and Adams found that relatively high voltages, greater than -1-1 V, were required to oxidise GSH and cysteine at glassy carbon electrodes. Chemically modified surfaces can reduce the oxidation potentials required and hopefully increase specificity and sensitivity. Halbert and Baldwin used cyclic voltammetry to study the electrochemistry of cysteine, homocysteine, A -acetylcysteine and GSH at both unmodified and cobalt phthalocyanine-modified carbon paste electrodes. This non-chromatographic technique was used to measure the relatively high concentrations of GSH in whole blood. The electrochemistry of thiols has been reviewed. ... 

S.A. Wring, J.P. Hart and B.J. Birch, Development of an improved carbon electrode chemically modified with cobalt phthalocyanine as a re-usable sensor for glutathione, Analyst, 1989, 114, 1563-1570. 

Based on AA oxidation to dehydroascorbic acid in acidic medium using iodine-iodide solution as oxidizing reagent. The iodine amount consumed in the redox reaction was detected Electrocatalysis of AA on a glassy carbon electrode chemically modified with polyaniline films AA was determined at a vitreous C electrode modified with 3,4-dihydroxybenzaldehyde AA was determined with a chemically modified with methylene green (electron mediator) carbon paste electrode... 

Casella, L G. and M. R. Guascito. 1997. Electrocatalysis of ascorbic acid on the glassy carbon electrode chemically modified with polyaniline films. Electroanalysis 9 1381-1386. 

Electrodes doped with mediators are also successful in analyses using NAD (P)-dependent dehydrogenases (86-88). In these cases, the mediator is firmly adsorbed to the electrode. The cofactor is oxidized by the mediator, which becomes reduced. The mediator is reoxidized by an electrochemical process on the electrode. This technology makes it possible to reduce the amount of cofactor needed, for example, in flow injection analysis and also eliminates the need for enzymatic regeneration systems. A further successful development uses a carbon paste chemically modified with a dehydrogenase, the coenzyme, and a phenoxazine mediator. This complex structure is then coated with a polyester sulfonic acid cation exchanger (86). The mediators used are of aromatic polycyclic structure and are firmly bound to graphite or other carbon electrodes (Fig. 2) (89). 

Microelectronic technologies have also been used in nitrite biosensors and electrochemical sensors (Suzuki and Taura, 2001 Adhikari and Majumdar, 2004). Ameida et al. (2013) have also developed a method of electrochemical nitrite measurement by means of a gold working electrode covered with 1,2-diaminobenzene (DAB) integrated in a FIA system. This sensor helps improve selectivity, repeatability, stability, and sensitivity. A Nafion/lead-ruthenate pyrochlore electrode chemically modified for determination of NO2 oxidation and NO reduction based on AC-impedance spectroscopy and FIA has also been tested (Zen et al., 2000). Quan and Shin (2010) also tested an electrochemical nitrite biosensor based on co-immobilization of copper-containing nitrite reductase and viologen-modified chitosan (CHIT-V) on a glassy carbon electrode (GCE). 

In other work, Guo and Khoo (1765) developed a method for the quantitative detection of cysteine in the 10 -10 -mol range using carbon paste electrodes chemically modified with [Cu(S2CNEt2)2]. 

Diewald W, Kalcher K, Neuhold C, Cai X-H, Magee RJ (1993) Voltammetric behavior of thallium(III) on carbon paste electrodes chemically modified with an ani[Pg.113]

Dopamine, a neurotransmitter, was covalently coupled, via an amide bond, to a modified polystyrene having A-(2-(3,4-dihydroxyphenyl)ethyl) isonicotinamide units. The dopamine-coupled polymer was coated onto glassy carbon electrodes. In aqueous electrolyte solutions (pH 7), cathodic current caused cleavage of the amide linkage and release of dopamine at potentials more negative than 0.9 V [41]. The chemical scheme for the amide bond cleavage is presented in Figure 18. 

A.A. Ciucu, C. Negulescu, and R.P. Baldwin, Detection of pesticides using an amperometric biosensor based on ferophthalocyanine chemically modified carbon paste electrode and immobilized bienzymatic system. Biosens. Bioelectron. 18, 303-310 (2003). 

S. Wring and J. Hart, Chemically modified screen-printed carbon electrodes. Analyst 117, 1281-1286 (1992). 

M.S. Lin and B.I. Jan, Determination of hydrogen peroxide by utilizing a cobalt(II)hexacyanoferrate-modified glassy carbon electrode as a chemical sensor. Electroanalysis 9, 340-344 (1997). 

Several approaches have been undertaken to construct redox active polymermodified electrodes containing such rhodium complexes as mediators. Beley [70] and Cosnier [71] used the electropolymerization of pyrrole-linked rhodium complexes for their fixation at the electrode surface. An effective system for the formation of 1,4-NADH from NAD+ applied a poly-Rh(terpy-py)2 + (terpy = terpyridine py = pyrrole) modified reticulated vitreous carbon electrode [70]. In the presence of liver alcohol dehydrogenase as production enzyme, cyclohexanone was transformed to cyclohexanol with a turnover number of 113 in 31 h. However, the current efficiency was rather small. The films which are obtained by electropolymerization of the pyrrole-linked rhodium complexes do not swell. Therefore, the reaction between the substrate, for example NAD+, and the reduced redox catalyst mostly takes place at the film/solution interface. To obtain a water-swellable film, which allows the easy penetration of the substrate into the film and thus renders the reaction layer larger, we used a different approach. Water-soluble copolymers of substituted vinylbipyridine rhodium complexes with N-vinylpyrrolidone, like 11 and 12, were synthesized chemically and then fixed to the surface of a graphite electrode by /-irradiation. The polymer films obtained swell very well in aqueous... 

Lorenzo E, Alda E, Hernandez P, et al. 1988. Voltammetric determination of nitrobenzene with a chemically modified carbon-paste electrode Application to wines, beers, and cider. Fresenius Z Anal Chem 330 139-142. 

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