Purification electrochemical separations

It should be noted, that the Lacc-GDH recycling electrode does not distinguish between epinephrine, norepinephrine or dopamine. Nevertheless, the selectivity is sufficient for discriminating the catecholamine signal from other components of the stimulating buffer without any purification or separation step. If the ratio between epinephrine and norepinephrine shall be determined, on the basis of the bioelectrocatalytic substrate regeneration by GDH immobilized on a carbon electrode (15) norepinephrine can be detected 40 times more sensitive than epinephrine while 1 4 selectivity is observed for the Lacc-GDH electrode. The conventional HPLC procedure for determination of catecholamines requires complex and expensive devices since the electrochemical detector has only low selectivity. 

Slater, S.A., Raraz, A.G., Willit, J.L., and Gay, E.C. (1999) Electrochemical separation of aluminum from uranium for research reactor spent nuclear fuel applications. Sep. Purif. Technol, 15(3), 197-205. 

Other Metals. AH the sodium metal produced comes from electrolysis of sodium chloride melts in Downs ceUs. The ceU consists of a cylindrical steel cathode separated from the graphite anode by a perforated steel diaphragm. Lithium is also produced by electrolysis of the chloride in a process similar to that used for sodium. The other alkaH and alkaHne-earth metals can be electrowon from molten chlorides, but thermochemical reduction is preferred commercially. The rare earths can also be electrowon but only the mixture known as mischmetal is prepared in tonnage quantity by electrochemical means. In addition, beryIHum and boron are produced by electrolysis on a commercial scale in the order of a few hundred t/yr. Processes have been developed for electrowinning titanium, tantalum, and niobium from molten salts. These metals, however, are obtained as a powdery deposit which is not easily separated from the electrolyte so that further purification is required. 

Among electrochemical methods of water purification, one can also list the various electromembrane technologies, electrodialysis in particular. The simplest elec-trodialyzer consists of three compartments separated by semipermeable membranes (usually, cation- and anion-exchange membranes). The water to be purified is supplied to the central (desalination) compartment. In the outer (concentration) compartments, electrodes are set up between which a certain potential difference is applied. Under the effect of the electric field, ions pass througfi the membranes so that the concentration of ionic contaminants in the central compartment decreases. 

Chen, G.H., Electrochemical technologies in wastewater treatment, Separation and Purification Technology, 38 (1), 11-41, 2004. 

Drogui, P., Asselin, M., Brar, S.K., Benmoussa, H., and Blais, J.F., Electrochemical removal of pollutants from agro-industry wastewaters, Separation and Purification Technology, 61, 301-310, 2008. 

Apart from the promising electrochemical properties that will be exhaustively discussed through this chapter, carbon nanotubes have become a hot research topic due to their outstanding electronic, mechanical, thermal, optical and chemical properties and their biocompatibility. Near- and long-term innovative applications can be foreseen including nanoelectronic and nanoelectromechanical devices, held emitters, probes, sensors and actuators as well as novel materials for mechanical reinforcement, fuel cells, batteries, energy storage, (bio)chemical separation, purification and catalysis [20]. 

However, behind the promising electrochemical devices, there are stUl many fundamental issues that affect the electrochemical response and that are poorly controlled. Such issues can be found right from the first steps of CNT growth, purification, separation, and so on. For instance, there are many unsettled issues in the fundamental CNTgrowth mechanism, hence CNT growth with controlled length, diameter and chirality is still not possible. Other difficulties comprise the removal of metal impurities from the tubes, the lack of practical techniques for CNT separation according to their chiralities and hence electronic properties, the control of defects /... 

Much of the early literature of polonium describes methods for separating it from these mixtures many of these have subsequently been adapted to the separation of milligram amounts of polonium from irradiated bismuth and to its purification. The methods range from a simple chemical separation of the element with a tellurium carrier to its electrodeposition on to a more noble metal or its spontaneous electrochemical replacement on the surface of a less noble metal. 

When complete electrolysis of ( )-74 is achieved at —1.8 V v. Ag, followed by reoxidation at 0 V, the three addends are removed and pure C2l, -C78 can be isolated in a 31 % yield, after purification. The other isomer, D3-C78, was obtained by HPLC separation of a mixture of C2v- and D3-C1S, as previously described [81]. Having these pure isomers allowed us to examine their electrochemical behavior independently [70],... 

Chlor-alkali production Electrochemical synthesis Water-organic liquid separation Organic liquid mixture separaion Fermentation products recovery and purification Cell harvesting, virus and antibody concentration Protein desalting, concentration and fractionation Blood processing, including artificial kidney Isolation, concentration, and identification of solutes and particulates... 

Huang, K.L., Holsen, T.M., Chou, T.C., and Selman, ).R. (2003) Comparing nafion and ceramic separators used in electrochemical purification of spent... 

Chen, G. (2004) Electrochemical technologies in wastewater treatment Separ. Purif. Technol. 38, 11-41. 

Quan, X., S. Chen, J. Su, J.W. Chen and G.H. Chen (2004). Synergetic degradation of 2,4-D by integrated photo- and electrochemical catalysis on a Pt doped Ti02/Ti electrode. Separation and Purification Technology, 34(1-3), 73-79. 

Preliminary extraction of 5-HIAA may be used as an initial purification step before HPLC analysis. Organic solvents, anion-exchange resins, and other solid phase extraction procedures have aU been used. For many systems, direct injection of urine onto the analytical column is a common practice,and samples are often merely diluted with a buffer to protect the HPLC system from contamination. Methods that analyze 5-HIAA without prior sample cleanup rely on the selectivity of the HPLC separation combined with fluorescence or electrochemical detection to provide the requisite specificity. 

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