Supporting electrolyte elimination

The shift of the half-wave potentials of metal ions by complexation is of value in polarographic analysis to eliminate the interfering effect of one metal upon another, and to promote sufficient separation of the waves of metals in mixtures to make possible their simultaneous determination. Thus, in the analysis of copper-base alloys for nickel, lead, etc., the reduction wave of copper(II) ions in most supporting electrolytes precedes that of the other metals and swamps those of the other metals present by using a cyanide supporting electrolyte, the copper is converted into the difficultly reducible cyanocuprate(I) ion and, in such a medium, nickel, lead, etc., can be determined. 

Foreign salts may frequently be present without interference and are, indeed, usually added as the supporting electrolyte in order to eliminate the migration current. 

Supporting electrolytes are required in controlled-potential experiments to decrease the resistance of the solution, to eliminate electromigration effects, and to maintain a constant ionic strength (i.e., swamping out the effect of variable... 

The reduction wave of peroxydisulphate at dme starts at the potential of the anodic dissolution of mercury. The current-potential curve exhibits certain anomalous characteristics under various conditions. At potentials more negative than the electrocapillary maximum, a current minimum can be observed this is due to the electrostatic repulsion of the peroxydisulphate ion by the negatively charged electrode surface. The current minimum depends on the concentration and nature of the supporting electrolyte, and can be eliminated by the adsorption of capillary active cations of the type NR4. ... 

If both liquid junction potentials are eliminated and supporting electrolytes MX are not adsorbed at the free surfaces of solvents, the compensating voltage is... 

The surface concentration Cq Ajc in general depends on the electrode potential, and this can affect significantly the form of the i E) curves. In some situations this dependence can be eliminated and the potential dependence of the probability of the elementary reaction act can be studied (called corrected Tafel plots). This is, for example, in the presence of excess concentration of supporting electrolyte when the /i potential is very small and the surface concentration is practically independent of E. However, the current is then rather high and the measurements in a broad potential range are impossible due to diffusion limitations. One of the possibilities to overcome this difficulty consists of the attachment of the reactants to a spacer film adsorbed at the electrode surface. The measurements in a broad potential range give dependences of the type shown in Fig. 34.4. 

Assuming that the migration current (Im) is virtually eliminated by the addition of a reasonably enough supporting electrolyte then the only cardinal factor which would affect the limiting current would be the rate of diffusion of the electro-active substance from the main body of the solution to the surface of the electrode. 

Interesting results have been obtained from polarographic studies in various donor solvents. Measurements have been made of various metal perchlorates in solutions of donor solvents containing tetraalkylammonium perchlorate as supporting electrolyte against an aqueous saturated calomel electrode 113. In order to eliminate differences in liquid-liquid junction potentials bisbiphenylchromium (I) has been used as a reference ion 114 118). 

Formation of allylic alcohols is favored by supporting electrolytes with tosylate anions. Scheme 7, [11], Under these conditions, only small amounts of ketone were produced. It has been suggested that the role of the tosylate is as a nucleophile that traps the carbocation. Elimination from this intermediate then leads to the allylic alcohol. This explanation is supported by isolation of the... 

Anodic oxidation of 2-oxazolidinones 81 in methanol using Et4N" OTs as a supporting electrolyte yields the 4-methoxylated derivatives 82 that undergo a facile elimination of methanol to give 2(3//)-oxazolones such as 83 and 84. ... 

The advantages of this preparation of dimethyl octadecane-dioate over that described earlier6 are purity of product, no foaming of the electrolyte, higher yields, and elimination of the use of large quantities of the salt of the acid ester as supporting electrolyte. The procedure is regarded as near the optimum for a Kolbe electrolysis. 

Supporting Electrolyte The electrolyte that is added to the electrolytic solution to make it electrically conductive as well as to control the reaction conditions. The supporting electrolyte also works to eliminate the migration current that flows in its absence. It may be a salt, an acid, a base or a pH buffer, which is difficult to oxidize or to reduce. It is used in concentrations between 0.05 and 1 M, which is much higher than that of electroactive species (usually 10-5 to 10 2 M). The supporting electrolyte sometimes has a great influence on the electrode reaction, changing the potential window of the solution, the double layer structure, or react-... 

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