Copper , amperometric detection

Copper electrodes have been used to determine amino acids and carbohydrates [10]. Metal oxide electrodes (including thin-film semiconductors) show some promise, but nothing of substance has yet been published with regard to LCEC. Pulsed amperometric detection (PAD) takes advantage of metal oxides formed in situ. This approach is discussed later. 

Other materials were also employed to construct electrodes for amperometric detection. For instance, a boron-doped diamond (BOD) electrode was used for amperometric detection of nitroaromatic explosives, organophosphate nerve agents, and phenols. The BOD electrode offers enhanced sensitivity, lower noise, negligible adsorption of organic compounds, and low sensitivity to oxygen [760], In addition, a copper particle-modified carbon composite electrode was used for amperometric detection of glucose in a PDMS chip [761]. 

Figure 6.12 shows the detection of carbohydrates by amperometric detection at a constant potential (0.6 V versus Ag/AgCl) with a cylindrical copper wire electrode65 (25 pun in diameter). Because the pK values of most sugars are in the vicinity of 12-13, they are ionized at high pH and separated by CZE under such conditions, without prior derivatization or complexation procedures. 

Adamic and Bartak [6] used high pressure aqueous size exclusion chromatography with reverse pulse amperometric detection to separate copper(II) complexes of poly(amino carboxylic acids), catechol and fulvic acids. The commercially available size exclusion chromatography columns were tested. Columns were eluted with copper(II) complexes of poly(aminocarboxylic acids), citric acids, catechol and water derived fulvic acid. The eluent contained copper(II) to prevent dissociation of the labile metal complexes. Reverse pulse electrochemical measurements were made to minimise oxygen interferences at the detector. Resolution of a mixture of DTP A, EDTA and NTA copper complexes was approximately the same on one size exclusion chromatography column as on Sephadex... 

Zhang S, Sun W-l, Xian Y-z, Zhang W, Jin L, Yamamoto K, Tao S, Jin, J (1999) Multichannel amperometric detection system for liquid chromatography to assay the thiols in human whole blood using the platinum microelectrodes chemically modified by copper tetra aminophthalocyanine. Anal Chim Acta 399(3) 213-221... 

Xie, Y., and Huber, C.O. 1991. Electrocatalysis and amperometric detection using an electrode made of copper oxide and carbon paste. Analytical Chemistry 63, 1714-1719. 

Determination of carbohydrates by CZE with amperometric detection at a copper microelectrode... 

The various tunable properties of zeolites have inspired a great variety of concepts in electrochemistry with zeolite-modified electrodes. For example, silver ions inside the zeolite pore system arc not electrochemically active in amperometric detection. Flowever, indirect analyte detection can occur when the analyte causes the removal of silver ions into the solution where they are electrochemically detected.[94] This indirect approach was extended to different copper-exchanged zeolites and demonstrated for the detection of several non-elcctroactive ions including alkali metal, ammonium and calcium.[95] A zeolite-modified electrode (ZME) with high selectivity towards Pb over Cd in cyclic voltammetry was prepared via electrophoretic deposition of zeolite Y, coated with Nafion.[96]... 

The detection of the current generated by reaction at the surface of (usually) carbon fiber or copper microelectrodes at a fixed voltage is capable of low detection limits for electroactive compounds using amperometry, Table 8.14. Several approaches that allow the full possibilities of multiple electrode and pulsed amperometric detection (established techniques in liquid chromatography (section 5.7.4)) have been proven for capillary electrophoresis [508,511]. These methods are not widely used, possibly due to a lack of commercial products and support. Potentiometric detection with polymer-coated wire microelectrodes containing relatively non-specific ion exchange ionophores was used for the detection of low-mass anions or cations [510,511]. 

Several research groups implemented carbohydrate analysis on-chip with direct detection of underivatized sugar molecules. Electrochemical detection is the most attractive approach, as it offers reasonable sensitivity and selectivity, and it is ideally suited for microchip format. Schwarz et al. [203] developed amperometric detection of sugars using microfabricated copper electrode. They separated fructose, sucrose, and galactose in 70 s on a glass chip with 50-p,m wide and 20-p,m deep microchannel and double tee injection geometry. The detection was based on Teflon-coated platinum wire plated with copper and inserted in the end of the separation channel etched in a conical shape. The detection limit down to 1 JtM was achieved. Hebert and coworkers [204] reported an... 

Colon, L. A., Dadoo, R. and Zare, R. N. Determination of carbohydrates by capillary zone electrophoresis with amperometric detection at a copper microelectrode. Anal Chem, 65, 476, 1993. 

Reducing-sugars, separated on amine-bonded silica, have been determined by post-column reaction with copper bis(phenanthroline) and amperometric detection (in which the reduced copper complex is re-oxidized). The method was compatible with organic eluants, could detect down to 1 ng of glucose, and was applied without... 

Amino acids can also be determined by amperometric detection with a copper electrode under neutral or alkaline conditions. This method is very selective, with the working electrode potential set at only -1-0.10 mV versus Ag/AgCl. In this detection method, amino acids complex with Cu " " ions present on the electrode surface, producing a response that is proportional to the concentration of the amino acid. Detection limits are between 10 and 100 pmol and can be improved if microbore chromatography is employed. The slower flow rates utilized with microbore chromatography columns allow more time for complexation to take place, thus improving the detection limits. 

HPLC methods are extremely sensitive toward sugars and sugar derivatives, an important advance over detection by means of refractive index measurement lying in the use of ion chromatography with pulsed amperometric detection at copper, platinum, or gold electrodes. Analytical processes may be fully automated using various postcolumn derivatization procedures as required. 

W.Th., Kok, H.B. Hanekamp, P. Bos and R.W. Frei, Amperometric detection of amino acids with a passivated copper electrode. Anal Chim. Acta, 1983, 142, 31- 5. 

Detection Methods. — A nickel-titanium alloy electrode for stable and sensitive electrochemical detection of carbohydrates has been reported." Similarly, several copper(II) oxide modified electrodes were highly sensitive for constant-potential amperometric detection of picomole levels of carbohydrates (Glc, Xyl, xylitol) in alkaline solution in flow through systems (anion-exchange h.p.l.c. and flow injection analysis), although problems with day-to lay reproducibility remained to be solved."... 

Colon, L.A. Dadoo, R. Zare, R.N. Determination of Carbohydrates by Capillary Electrophoresis with Amperometric Detection at a Copper Microelectrode. Anal. 

Luo, J.P., Zhang, F. and Baldwin, R.P. (1991) Constant-potential amperometric detection of underivatized amino acids and peptides at a copper electrode. Anal. Chem., 63,1702-1707. 

Detection methods. - Various metallic wires were investigated for use in constant-potential amperometric detection of carbohydrates in HPAEC eluates. Copper proved best, and when conditions were optimized, picomole amounts of various sugars could be detected. Conditions fcH-post-column generation of fluorescence by reaction of mono- to tri-saccharides with an ethanolamine-boric acid reagent were optimized, and applied to the h.p.Lc. analysis (anion-exchanger, alkaline aq. borate eluant) of mono- and di-saccharides in wine. The detection of disaccharides was markedly improved if a post-column acid-catalysed hydrolysis reactor was added prior to detection. ... 

A copper electrode in an alkaline medium with amperometric detection has been used for sulfite determination in beverages (Corbo and Bertotti, 2002). Other systems have been reported such as a potentiometric sensor with a hydrated titanium oxide anion exchanger and an epoxy resin matrix membrane (Hassan et al., 2001) enzymes (sulfite... 

Alamo LS, Tangkuaram T, Satienperakul S (2010) Determination of sulfite by pervaporation-flow injection with amperometric detection using copper hexacyanoferrate-carbon nanotube modified carbon paste electrode. Talanta 81 1793-1799... 

Casella, I.G., Gatta, M. and Desimoni, E. (1998) Applications of a copper-modified gold electrode for amperometric detection of polar aliphatic compounds by anion-exchange chromatography. Journal of Chromatography A, 814, 63-70. 

Before considering the special requirements for automated on-line determination of metals from industrial effluents, it is worthwhile examining the features of standard laboratory procedures associated with the off-line determination of copper as a dithiocarbamate complex by liquid chromatography with electrochemical detection. The off-line determination of copper as its diethyldithiocarbamate complex in aqueous samples, zinc plant electrol3d e, and urine have been described [3, 7, 10] using reverse phase liquid chromatography with amperometric detection. A standard instrumental configuration for the conventional laboratory off-line method as used in these studies is depicted in Fig. 7.2. 

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