Dropping electrode

It should be noted that the capacity as given by C, = a/E, where a is obtained from the current flow at the dropping electrode or from Eq. V-49, is an integral capacity (E is the potential relative to the electrocapillary maximum (ecm), and an assumption is involved here in identifying this with the potential difference across the interface). The differential capacity C given by Eq. V-50 is also then given by... 

Mercury electrodes (a) hanging mercury drop electrode (b) dropping mercury electrode (c) static mercury drop electrode. 

A form of voltammetry using a dropping mercury electrode or a static mercury drop electrode. 

Potential-excitation signal and voltammogram for anodic stripping voltammetry at a hanging mercury drop electrode. 

Faraday s law (p. 496) galvanostat (p. 464) glass electrode (p. 477) hanging mercury drop electrode (p. 509) hydrodynamic voltammetry (p. 513) indicator electrode (p. 462) ionophore (p. 482) ion-selective electrode (p. 475) liquid-based ion-selective electrode (p. 482) liquid junction potential (p. 470) mass transport (p. 511) mediator (p. 500) membrane potential (p. 475) migration (p. 512) nonfaradaic current (p. 512)... 

Here Ee is the standard potential of the reaction against the reference electrode used to measure the potential of the dropping electrode, and the potential E refers to the average value during the life of a mercury drop. Before the commencement of the polarographic wave only a small residual current flows, and the concentration of any electro-active substance must be the same at the electrode interface as in the bulk of the solution. As soon as the decomposition potential is exceeded, some of the reducible substance (oxidant) at the interface is reduced, and must be replenished from the body of the solution by means of diffusion. The reduction product (reductant) does not accumulate at the interface, but diffuses away from it into the solution or into the electrode material. If the applied potential is increased to a value at which all the oxidant reaching the interface is reduced, only the newly formed reductant will be present the current then flowing will be the diffusion current. The current / at any point... 

Reactions of organic substances at the dropping electrode usually involve hydrogen ions a typical reaction can be represented by the equation... 

The following functional groups can be expected to react at the dropping electrode. 

Various tests can be applied, including the influence of the height of the mercury column of the dropping electrode on the diffusion current to decide if any of the above non-diffusion processes are operative.49... 

If a commercial polarograph which includes a potentiostat is employed, then the three-electrode procedure (Sections 16.7 and 16.8) is conveniently used with the controlled potential supplied by the potentiostat applied between the dropping electrode and the calomel reference electrode, while the electrolysis current flows between the working (mercury) electrode and the auxiliary... 

Electrodes. The Hanging Mercury Drop Electrode is traditionally associated with the technique of stripping voltammetry and its capabilities were investigated by Kemula and Kublik.51 In view of the importance of drop size it is essential to be able to set up exactly reproducible drops, and this can be done as explained in Section 16.8 for the S.M.D.E. 

Voltaic cells 64. 504 Voltammetry 7, 591 anodic stripping, 621 concentration step, 621 mercury drop electrode, 623 mercury film electrode, 623 peak breadth, 622 peak current, 622 peak potential, 622 purity of reagents, 624 voltammogram, 622 D. of lead in tap water, 625 Volume distribution coefficient 196 Volume of 1 g of water at various temperatures, (T) 87... 

DME = dropping mercury electrode HMDE = hanging mercury drop electrode MFE = mercury film... 

FIGURE 1-13 Double-layer capacitance of a mercury drop electrode in NaF solutions of different concentrations. (Reproduced with permission from reference 5.)... 

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