Mercury-plated electrodes

Elorence, T.M. Anodic stripping voltammetry with a glassy carbon electrode mercury-plated in situ. J. Electroanal. Chem. 1970, 27, 273-281. 

FIGURE 21. The Compton-Waller cell. A, PTFE annulus B, PTFE insulation C, electrode (mercury-plated copper) D, copper E, TEqh cylindrical cavity F, PTFE sheath G, precision-bore silica tubing. The numbers represent the dimensions in millimeters. 

If it is assumed that the interface between mercury (which is widely used as an electrode for studies of the e.d.l.) and an electrolyte solution forms the two plates of a capacitor, then at equilibrium the mercury plate will have an excess charge and the solution plate a charge of equal magnitude but opposite sign q, and the capacitance C is given by... 

Garcia-Monco Carra et al. [296] have described a hybrid mercury film electrode for the voltammetric analysis of copper (and lead) in acidified seawater. Mercury plating conditions for preparing a consistently reproducible mercury film electrode on a glassy carbon substrate in acid media are evaluated. It is found that a hybrid electrode , i.e., one preplated with mercury and then replated with mercury in situ with the sample, gives very reproducible results in the analysis of copper in seawater. Consistently reproducible electrode performance allows for the calculation of a cell constant and prediction of the slopes of standard addition plots, useful parameters in the study of copper speciation in seawater. 

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. 

Mercury-plated electrodes. Platinum can be plated with mercury to form an electrode with many of the properties of a mercury surface. This is done by cleaning a platinum electrode in nitric acid, connecting it as the cathode in perchloric acid solution over a pool of mercury, and then dipping it into the mercury while it is still connected in the circuit. The method works well for plating a planar platinum inlay electrode to give a flat mercury-coated surface, but it can be used for electrodes of any shape.112... 

Mercury-Plated Platinum Electrode. Anal. Chem. 25, 1351 (1953)-... 

DPASV equipped with the Thin Mercury Film Electrode (TMFE) plated onto a Rotating Glassy Carbon Disc Electrode (RGCDE), is one of the most sensitive and powerful techniques at present available for the determination of ultra-trace metals in real time samples (59, 60). Cadmium, Cu, Pb and Zn are the most frequently determined metals at subnanomolar or even picomolar concentration in sea water, without any preconcentration step (17, 61, 62), but other elements can also be determined (63-66). Detection limits lower than 0.5 ng/1 are normally reached (17, 60). 

Figure 11.8.5 Anodic stripping analysis of a solution containing 2 X 10 M Zn, Cd, Pb, and Cu at an MFE (mercury-plated, wax-impregnated graphite electrode). Stripping carried out by differential pulse voltammetry.

Recently Compton and Northing have described a method for the measurement of N2O in acetonitrile [51], They have shown that N2O reacts with the radical anion of the organic compound fluoranthene (Figure 10). Fluoranthene is reduced on mercury plated copper electrodes at potentials more negative than 1.5V (vs SCE). The reaction in the presence of N2O is a classical EC or catalytic mechanism, ie. 

Buffle and coworkers [117] have investigated iridium-based mercury-plated microelectrodes for the determination of trace metals including Pb " " and Cd + at nM levels. These electrodes give analytically reproducible results and have... 

The electrochemical reduction of 2-nitro-propane at mercury-plated copper electrodes was investigated in aqueous solution, using Triton-X as a stabilizer. Two waves were observed, the first corresponding to the [(CH3)2CHN02] radical anion, as evidenced by electrochemical EPR. Upon removing the applied potential from the electrode, EPR signal transients were obtained, analysis of which in terms... 

Using a mercury plated platinum electrode, Marple... 

A mercury-plated glassy carbon rotating disc electrode (which accelerates the accumulation process) was studied with various pulse methods during the stripping period [166]. The highest sensitivity was obtained... 

The combination of ASV with the flow injection analysis (FIA) improves the reproducibility and versatility of the anodic stripping procedure. For a conventional operation the detection limit is of 10" M. The disadvantage of the FIA, namely the short deposition time, can be compensated by repeated reversals of the flow direction [174]. The multiple passage of the same sample along the mercury-plated carbon fiber electrode increases the effective deposition time and thus the stripping current response. 

FIGURE 18.10 Differential-pulse anodic-stripping voltammogram of tap water at a mercury-plated, wax-impregnated graphite electrode showing detection of metals at subparts-per-billion levels. 

The one-electron reduction of 3mM fluoranthene, FI, to its radical anion was studied in acetonitrile solution containing 0.1 M tetrabutylammonium perchlorate as supporting electrolyte, using a mercury-plated rotating disc electrode of... 

Lead has also been determined using the hanging mercury drop technique involving electrolysis of the metal into the mercury followed by anodic stripping to measure the lead concentration (149). Marple and Rogers (150) preferred to use a mercury-plated platinum electrode for the coulometric determination of lead a moderate increase in sensitivity was claimed. 

In this way, it was shown that the anion radical of 2-nitropropane formed during the reduction of the parent compound in aqueous solution (pH 10.2) at a mercury-plated foil electrode undergoes a first-order decay with a rate constant of 0.36 s A combination of the in situ electrochemical ESR data and voltammetric measurements made simultaneously at the channel electrode produced the spectrum shown in Figure 7. They, additionally, permitted the deduction that the reduction of 2-nitropropane under the specified conditions proceeded via an ECE mechanism in which the chemical step was ratedetermining proton uptake by the radical anion. In the buffered media employed, this was seen as a pseudo-first-order step. The electrochemical reaction sequence can therefore be written ... 

Zakharchuk NF, Brainina KZ (1998) The surface morphology of mercury plated glassy carbon electrodes and stripping voltammetry of heavy metals. Electroanalysis 10 379-386... 

Mercury layers plated onto the surface of analytical electrodes serve as Hquid metal coatings. These function as analytical sensors (qv) because sodium and other metals can be electroplated into the amalgam, then deplated and measured (see Electro analytical techniques). This is one of the few ways that sodium, potassium, calcium, and other active metals can be electroplated from aqueous solution. In one modification of this technique, a Hquid sample can be purified of trace metals by extended electrolysis in the presence of a mercury coating (35). 

Another important primary battery is the mercury cell. It usually comes in very small sizes and is used in hearing aids, watches, cameras, and some calculators. The anode of this cell is a zinc-mercury amalgam the reacting species is zinc. The cathode is a plate made up of mercury(II) oxide, HgO. The electrolyte is a paste containing HgO and sodium or potassium hydroxide. The electrode reactions are... 

Compact, ready-prepared calomel electrodes are available commercially and find wide application especially in conjunction with pH meters and ion-selective meters. A typical electrode is shown in Fig. 15.1(h). With time, the porous contact disc at the base of the electrode may become clogged, thus giving rise to a very high resistance. In some forms of the electrode the sintered disc may be removed and a new porous plate inserted, and in some modern electrodes an ion exchange membrane is incorporated in the lower part of the electrode which prevents any migration of mercury(I) ions to the sintered disc and thus... 

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