Separators, bulk electrolysis methods

Tsujimura S, Kuriyama A, Fujieda N, Kano K, Ikeda T. Mediated spectroelectrochemical titration of proteins for redox potential measurements by a separator-less one-compartment bulk electrolysis method. Anal Biochem 2005 337 325-331. 

The methods can be classified by the controlled parameter (E or i) and by the quantities actually measured or the process carried out. Thus in controlled-potential techniques the potential of the working electrode is maintained constant with respect to a reference electrode. Since the potential of the working electrode controls the degree of completion of an electrolytic process in most cases, controlled-potential techniques are usually the most desirable for bulk electrolysis. However, these methods require potentiostats with large output current and voltage capabilities and they need stable reference electrodes, carefully placed to minimize uncompensated resistance effects. Placement of the auxiliary electrode to provide a fairly uniform current distribution across the surface of the working electrode is usually desirable, and the auxiliary electrode is often placed in a separate... 

An alternative method of bulk electrolysis involves flowing the solution to be electrolyzed continuously through a porous working electrode (38) of large surface area. Flow electrolytic methods can result in high efficiencies and rapid conversions and are especially convenient where large amounts of solution are to be treated. Flow methods are of use in industrial situations (e.g., removal of metals such as copper from waste streams) and have been broadly applied to electrosynthesis, separations, and analysis. 

It is the preconcentration period that enhances the sensitivity of this technique. In the preconcentration phase precise potential control permits the selection of species whose decomposition potentials are exceeded. The products should form an insoluble solid deposit or an alloy with the substrate. At Hg electrodes the electroreduced metal ions form an amalgam. Usually the potential is set 100-200 mV in excess of the decomposition potential of the analyte of interest. Moreover, electrolysis may be carried out at a sufficiently negative potential to reduce aU of the metal ions possible below hydrogen ion reduction at Hg, for example. Concurrent H" " ion reduction is not a problem, because the objective is to separate the reactants from the bulk electrolyte. In fact, methods have been devised to determine the group I metals and NEC " ion at Hg in neutral or alkaline solutions of the tetraalkylammonium salts. Exhaustive electrolysis is not mandatory and 2-3% removal suffices. Additionally, the processes of interest need not be 100% faradaically efficient, provided that the preconcentration stage is reproducible for calibration purposes, which is usually ensured by standard addition. 

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