The dropping mercury electrode dme

Two types of electrodes with convection are common the dropping mercury electrode (dme) and the rotating disk electrode (rde). Both are usually idealised to one-dimensional systems for convenience. 

For good references on the dme, see Koutecky (1953), Markowitz and Elving (1958), Koutecky and von Stackelberg (1962), Newman (1967), Duda and Vrentas (1968). Feldberg (1980) and Pons et al (1982B) simulated it. 

The diffusion equation for the simple expanding-plane model of the dme is 

Note that is negative that is, flow is towards the electrode. 

Introducing a sphericity factor similar to that of Feldberg (1980), in this case being the ratio of the diffusion layer to drop radius at time 

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There are several types of mercury electrodes. Of these, the dropping mercury electrode (DME), the hanging mercury drop electrode (HMDE), and mercury film electrode (MFE) are the most frequently used. 

Copper(II) ions in the presence of chloride ions are reduced at the dropping mercury electrode (dme) in two steps, Cu(II) -> Cu(I) and Cu(I) -> Cu(0) producing a double wave at -1-0.04 and 0.22 V versus sce half-wave potentials. In the presence of peroxydisulphate , when the chloride concentration is large enough, two waves are also observed the first limiting current corresponds to the reduction of the Cu(II) to Cu(I) plus reduction of a fraction of peroxydisulphate and the total diffusion current at a more negative potential is equal to the sum of the diffusion currents of reduction of Cu(II) to Cu(0) and of the peroxydisulphate. There is evidence that peroxydisulphate is not reduced at the potential of the first wave because of the adsorption of the copper(I) chloride complex at... 

In voltammetry as an analytical method based on measurement of the voltage-current curve we can distinguish between techniques with non-stationary and with stationary electrodes. Within the first group the technique at the dropping mercury electrode (dme), the so-called polarography, is by far the most important within the second group it is of particular significance to state whether and when the analyte is stirred. 

For many years, the study of the electrode—electrolyte interface and electrode kinetics was confined to the very reproducible mercury-aqueous system because of the availability of the dropping mercury electrode (DME) and development of polarography. Extensive leading work in this field was carried out by Heyrovsky, Frumkin, Grahame, and Randles. 

Moreover, it is difficult to find one s way in the overwhelming amount of literature on this subject because the major part of it is focussed on d.c. polarography and thus to the mass transfer problem at the dropping mercury electrode (DME). Neglecting the sphericity, the expansion of the drop has still to be accounted for in the diffusion equation for a species i. Equation (19b), which we have adopted thus far, should therefore be replaced by [11, 147]... 

The dropping-mercury electrode. The usefulness of the dropping-mercury electrode (DME) for analytical voltammetry was discovered by Heyrovsky, and the history of this discovery has been recounted.102 The DME usually is prepared from a 10-20-cm length of glass-capillary tubing with an approxi-... 

High-pressure cells mainly are used to contain low-boiling solvents such as liquid NH3 or liquid S02 at ambient temperature or to study solvents with moderate boiling points at elevated temperature.53 The dropping-mercury electrode (DME) can be readily operated at several thousand atmospheres, and one interesting result is that the hydrogen overpotential on mercury declines about 1 V over a range of 200°C. 

Figure 6. Cyclic voltammetry (CV) on platinum and polarography at the dropping mercury electrode (DME) of [Zn(l)2] + in 0.1 M CHjCb- n-C4Hg)4 NCl04 (0.1 M) (scan rate for CV, 40 mV s E versus Ag/AgsU ).

Polarography measurement at the dropping mercury electrode (DME) in CH2CI2. 

Polarography is the term used for voltammetry with the dropping mercury electrode (DME). The technique has been discussed extensively in several textbooks and reviews [1-, 237-242] to which the reader is referred for details concerning both theoretical problems and practical applications. The electrode (Fig. 31) was developed early in the century by Heyrovsky and was the dominating tool in electroanalytical chemistry for several decades. Because of the low oxidation potential of mercury (0.3-0.4 V versus SCE), the DME has been used almost exclusively for the study of reduction processes. Compared with mercury film electrodes, the DME offers the advantage that the electrode surface is continuously renewed. This property reduces undesirable surface effects caused by adsorption. 

Polarographic data show that below pH 1 the doubly protonated phenylhydroxylamine is the species reduced at the dropping mercury electrode (DME) between pH 5 and 7 the monoprotonated molecule is reduced. The unprotonated molecule is not reducible [176]. Phenylhydroxylamine is for the main part reduced to aniline, but according to the polarographic data a certain degree of dimerization of an intermediate radical takes place. As discussed, phenylhydroxylamines may react chemically in several ways. 

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