Carbon paste electrode chemically modified

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]

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). 

CNT randomly dispersed composites Many soft and rigid composites of carbon nanotubes have been reported [17]. The first carbon-nanotube-modified electrode was made from a carbon-nanotube paste using bromoform as an organic binder (though other binders are currently used for the paste formation, i.e. mineral oil) [105]. In this first application, the electrochemistry of dopamine was proved and a reversible behavior was found to occur at low potentials with rates of electron transfer much faster than those observed for graphite electrodes. Carbon-nanotube paste electrodes share the advantages of the classical carbon paste electrode (CPE) such as the feasibility to incorporate different substances, low background current, chemical inertness and an easy renewal nature [106,107]. The added value with CNTs comes from the enhancement of the electron-transfer reactions due to the already discussed mechanisms. 

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. 

S. Hu, C. Xu, J. Luo, J. Luo and D. Cui, Biosensor for detection of hypoxanthine based on xanthine oxidase immobilized on chemically modified carbon paste electrode, Anal. Chim. Acta, 412(1-2) (2000) 55-61. 

Stability of Prussian blue modified screen-printed electrodes The operational stability of all the PB-modified sensors is a critical point, especially at neutral and alkaline pH. A possible explanation for reduced stability could be the presence of hydroxyl ions at the electrode surface as a product of the H202 reduction. Hydroxyl ions are known to be able to break the Fe-CN-Fe bond, hence solubilising the PB [21]. An increased stability of PB at alkaline pH was first observed by our group after adopting a chemical deposition method for the modification of graphite particles with PB for the assembling of carbon paste electrodes [48]. 

Some derivatives with mediating properties are suitable to form chemically modified electrodes (CMEs) with catalytic properties for NADH oxidation (55). Various attempts have been tried with different classes of mediators to immobilize the mediator onto solid electrodes or in carbon paste electrodes since the first deliberately made CME for electrocatalytic oxidation of NADH was described by Tse and Kuwana in 1978 (56), see Table I. They and others (67-72) based their CMEs on immobilized ortho-quinone derivatives. However, these CMEs were rapidly inactivated in the presence of NADH, probably because of side reactions in the catalytic process (72). For some other immobilized mediators one major reaction route could be proposed as the CME turned out to be quite stable in the presence of NADH. The catalytic reaction sequence comprizes two steps, one chemical between NADH and the immobilized mediator (reaction (6)) and one electrochemical between the mediator and the electrode (reaction (7)). The sequence is given below for the simplest case ... 

Surface complexation — is complexation of metal ions by ligands immobilized on the electrode surface (-> electrode surface area). The ligands may be incorporated in the structure of a -> carbon paste electrode, covalently bound to the surface of a chemically modified electrode (-> surface-modified electrodes), or adsorbed (-> adsorption) on the electrode surface etc. Surface complexation is not confined to electrodes. It can occur on many surfaces, e.g., minerals, when in contact with metal ion solutions or solutions containing complexing ions (in the first case, the surface provides the ligand and the solution the metal ion, whereas in the second case, the surface provides the metal ion and the solution the ligand). Surface complexation can be an important step in the dissolution of solid phases [ii]. 

Hydrophobic organic ligands added to a carbon-paste electrode, or immobilized on a chemically modified electrode, can be used for the accumulation of metal ions by the surface-complexation mechanism [89-91], The same goal can be achieved by immobilized ion exchangers such as natural or synthetic zeolites [89], clay minerals [92], silica [93], and ion exchange resins [94] ... 

Various chemically modified electrode configurations have been investigated to optimize the current response and lower the overpotential. A hypox-anthine biosensor has been reported based on a glassy carbon paste electrode modified with Au nanoparticles and XO. The enzyme modified electrode shows catalytic activity at +500 mV vs. Ag/AgCl, which is 250 mV less positive than in the absence of the Au nanoparticles. Pundir and coworkers have extensively studied an XO-based biosensor with several nanomaterials and xanthine concentrations were determined by the measurement of H2O2 produced at +600 mV vs. Ag/AgCl. The biosensor was used for quantification of xanthine in tea leaves, coffee powder and fish meat. 

Nitrite Nitrite is an important indicator of fecal pollution in natural waters as well as a potential precursor of carcinogenic species. A rush of flow and sequential injection spectrophotometric method based on Griess-type reactions has been proposed, also coupled to online sorbent enrichment schemes. The catalytic effect of nitrite on the oxidation of various organic species constitutes the basis of fairly sensitive spectrophotometric methods. Fluorometric methods based on the formation of aromatic azoic acid salts, quenching of Rhodamine 6G fluorescence, and direct reaction with substituted tetramine or naphthalene species have been also reported. Indirect CL methods usually involve conversion into nitric oxide and gas-phase detection as mentioned in the foregoing section. The redox reaction between nitrite and iodide in acidic media is the fundamental of a plethora of flow injection methodologies with spectrophotometric, CL, or biamperometric detection. New electrochemical sensors with chemically modified carbon paste electrodes containing ruthenium sites, or platinum electrodes with cellulose or naphthalene films, have recently attracted special attention for amperometric detection. 

Apart from this variety and the individual nuances, chemical modification of CPEs leads to qualitatively new configurations termed chemically modified carbon paste electrodes (CMCPEs [4, 5,8,9]). 

Kalcher, K. (1990) Chemically modified carbon paste electrodes in voltam-metric analysis. Electroanalysis, 2, 419-433. 

Ravichandran, K. and Baldwin, R.P. (1981) Chemically modified carbon paste electrodes. / Electroanal Chem., 126, 293 - 300. 

Aglan, R., Mohamed, G., and Mohamed, FL (2012) Chemically modified carbon paste electrode for determination of cesium ion by poten-tiometric method. Am. J. Anal. Chem., 3, 576-586. 

At carbon electrodes, purine bases produce well-defined oxidation peaks within a wide pH range (0-12.5) [142,143]. Purine nucleosides and nucleotides are oxidized at potentials more positive than the parent bases [144]. Signals corresponding to the oxidation of purine bases, nucleotides, and nucleotides have also been obtained using chemically modified carbon electrodes [145,146] (for more details see Sect. 12.4.3). Recently, Cai and coworkers [147] proposed a method for trace A determination using an electrochemically/chemically modified (in alkahne sodium nitrate solution) carbon paste electrode (CPE). Pyrimidines are considered to be electroinactive on carbon electrodes however, Oliveira-Brett and Matysik recently reported [148] specific anodic peaks observed in solutions of T and C bases (but not their nucleosides). Sugar components of nucleotides can be oxidized at copper electrodes [149]. 

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. ... 

K. Kalcher. Chemically Modified Carbon Paste Electrodes in Voltammetrie Analysis." Eleciroanalysis 2... 

A. Safavi, M. Pakniat, and N. Maleki. Design and construction of a flow system for determination of Cu(II) ions in water by means of a chemically modified carbon paste electrode. Analytica Chimica Acta 335 275-, 1996. 

---