Mercury electrode voltammetric

FIGURE 10. Voltammetric curves of fully aliphatic allylic sulphones (c = 3 x 10-3 M) in DMF/TBAP 0.1 m electrolyte, stationary mercury electrode, sweep rate 10 mV s—1 (a) and (b) curves in aprotic DMF (c) response of the sulphone, (b) with phenol 10-2 m (after Reference 26). 

The properties of anodic layers of HgS formed on mercury in sulfide solutions have been investigated in comparison with anodic sulfide layers of cadmium and bismuth. Also, the electrochemistry of mercury electrodes in aqueous selenite solutions has been studied (see Sect. 3.2.1). The problem with the presence of several cathodic stripping peaks for HgSe in acidic Se(IV) solutions has been addressed using various voltammetric techniques at a hanging-mercury-drop electrode [119]. 

If a stationary electrode is used, such as platinum, gold, or glassy carbon, the technique is called voltammetry. One useful voltammetric technique is called stripping voltammetry, in which the product of a reduction is deposited on the surface on purpose and then stripped off by an oxidizing potential— a potential at which the oxidation of the previously deposited material occurs. This technique can also use a mercury electrode, but one that is held stationary. 

Wang and Tsai [40] have described voltammetric behavior of chlorhexidine at film mercury electrodes in the aqueous medium. 

Kamal etal. [188] have described adsorptive stripping voltammetric analysis of 2,3,6-tri(2 -pirydyl)-l,3,5-triazine at mercury electrode, based on preliminary adsorption and accumulation of the determined compound. 

Fig. 5.8 Schematic diagram of polarographic (or voltammetric) circuits for two-electrode (a) and three-electrode (b) systems. WE(DME) indicator or working electrode (dropping mercury electrode in the case of polarography) RE reference electrode CE counter electrode DC voltage (V) DC voltage source Current (/) current measuring device.

In earlier studies mercury has been plated onto electrodes to be used in voltammetric and spectrochemical analysis.2 DeAngelis (1976) developed thin film mercury electrodes by plating a solution of mercuric nitrate onto a variety of different electrodes in order to detect the presence of trace metals in small volumes. The results demonstrated that mercury plating occurred with tungsten, vanadium, chromium, and iron and there was little amalgamation. 

DeAngelis, T.P., "Mercury Film Electrodes Voltammetric and Optical Applicability", J. Electrochem Soc., Vol. 

Polarography has been largely replaced by voltammetry with electrode materials that do not present the toxicity hazard of mercury. Principles described for the mercury electrode apply to other electrodes. Mercury is still the electrode of choice for stripping analysis, which is the most sensitive voltammetric technique. For cleaning up mercury spills, see note 18. 

The working electrodes found to be useful at room temperature can also be used at low temperature. There are no special constraints. Platinum is probably the most widely used, simply because it is the most common electrode material for room-temperature work. A mercury electrode can also be employed, either as a hanging mercury drop electrode (HMDE) [23], a thin mercury film on a solid support, or an amalgam [26]. The HMDE was reported to extend the range of usable potentials to somewhat more negative values than found with platinum [23]. Of course, below -39°C, the HMDE is actually a solid electrode however, no detectable change in its voltammetric behavior is noted at the phase transition. 

The first voltammetric methods met are stationary voltammetries performed on a dropping mercury electrode (polarography) or on a solid rotating disk electrode. The limiting current measured is directly proportional to the concentration of the electroactive species in the solution. Experimental potential scan rate is lower than lOrnVs-1. 

---