Hg film electrode

The aliquot of digested sample placed in the electrochemical vessel is purged for 15-20 minutes with N2, then it is rapidly transferred and screwed under the cell head of the electrochemical device where the Hg film electrode has already been prepared, tested and rinsed. The electrolytic pre-concentration step during the analytical measurement is carried out by constant potential electrolysis. The deposition potential is set at -0.95 V for Cd and Pb and at -0.85 V for Cu. The deposition time depends on the metal concentration, a time of 20 min normally being sufficient to determine Cd and Pb concentration in samples collected in... 

Preparation of Hg film electrode. The Hg film electrode, although possessing superior sensitivity characteristics, is more subject to irreproducible behavior than is the hanging Hg drop electrode. The following plating procedure is satisfactory. 

Figure 5.8. Cyclic voltammogram of a Hg-film electrode in contact with 100 mM NaC104 (pH 4) equilibrated with 20% CO2 (A, C) or N2 (B). B and C were recorded with the electrolyte solution also containing 0.2 mM Ni(cyclam) +. (1) Reductive adsorption of Ni(cyclam) + (2) Electrocatalytic reduction of CO2 (3) H2-evolution (4) electrocatalytic reduction of H+ (5) anodic dissolution of precipitated Ni(cyclam)-CO. Hg-film on rotating Au-disk electrode (diameter 1.5 mm), / = 3000 min , v = 100 mV s Reprinted from Figure 1 R Jacquinot and RC. Hauser, Ni(II) cyclam Catalyzed Reduction of CO2 Towards a Voltammetric Sensor for in Gas Rhase, Electronalysis 15(8), 1437-1444 (2003). With permission of Wiley-VCH, Germany.

Aleutian disease (Mink autoimmune disease) Ho,E,C,l Cholinesterase/butyryl thiocholine Hg-film electrode 1 -7 nM, specific Ab 95... 

In common with other compounds containing an aromatic nitro moiety, chloramphenicol (Figure 6.31) can be assayed in blood by EC reduction using an Hg film electrode.Abou-Khalil et used both reductive and oxidative ED in series with UV detection in the HPLC of chloramphenicol and four analogues. 

Hg film electrodes and, much more frequently, to bare or to modified electrodes. Hg thin film electrodes can be differently prepared. Typically, either by reduction of Hg salts onto a bare electrode, or simply by dipping a Au electrode in Hg, so that a layer of Hg-Au amalgam forms, on which pure Hg adheres. On the other hand, other elements are proposed to substitute Hg, such as in the bismuth film electrodes, as well as other modified electrodes where stripping techniques can be successfully applied. Similar electrode materials will be discussed in Chap. 16. Different stripping techniques have been formulated for determination of species of various natures. 

Similarly to ASV, the analysis by CSV consists of two stages, the preconcentratimi and stripping steps, respectively. For example, for the analysis of the anion A" at a Hg film electrode, these steps can be schematically written as ... 

Several portable, low-cost electrochemical sensors for detection of nitrated explosives were developed. " These include Hg-film electrodes, " glassy carbon... 

Capillary zone electrophoresis coupled with fast cyclic voltammetric detection was developed by Zhou et al. [27] for the separation and determination of OTC, TC, and CTC antibiotics. All compounds were well separated by optimization of pH and complexation with a boric acid sodium tetraborate buffer. The detection limit using fast on-line cyclic voltammetric detection with Hg-film-microm electrode was 1.5 x 10-6 mol/L for OTC (signal to noise ratio > 2). A continuous flow manifold coupled on-line to a capillary electrophoresis system was developed by Nozal et al. [28] for determining the trace levels of OTC, TC, and DC in surface water samples. 

Electrocatalytic hydrogenation has the advantage of milder reaction conditions compared to catalytic hydrogenation. The development of various electrode materials (e.g., massive electrodes, powder cathodes, polymer film electrodes) and the optimization of reaction conditions have led to highly selective electrocatalytic hydrogenations. These are very suitable for the conversion of aliphatic and aromatic nitro compounds to amines and a, fi-unsaturated ketones to saturated ketones. The field is reviewed with 173 references in [158]. While the reduction of conjugated enones does not always proceed chemoselectively at a Hg cathode, the use of a carbon felt electrode coated with polyviologen/Pd particles provided saturated ketones exclusively (Fig. 34) [159]. 

One of the subjects that is still quite intensively developed (using electrochemical methods frequently combined with nonelectrochemical techniques) concerns reduction of Hg compounds at various surfaces (e.g. Pt or Au), with the emphasis laid on underpotential deposition (UPD) of mercury. Deposition of mercury on other metals is generally important for better understanding of the mechanism of the formation of amalgams. Moreover, underpotential Hg deposition characteristics constitute a significant source of information on Hg-metal interactions. In turn, mercury film electrodes obtained by such deposition have a significant appKcation in electrochemical analysis ofvarious species. 

Film Electrodes and Related Hg Electrodes Mercury films were prepared on reticulated vitreous carbon flowthrough electrodes by Hg deposition from Hg + solutions in acetic buffer [31]. Such an electrode was designed for the purposes of trace metal analysis. Mercury film de-position/oxidation on reticulated vitreous carbon and glassy carbon electrodes were compared. 

Due to the possible toxic effects of Hg, alternative electrodes have been sought, such as bismuth, which has recently been used by Kadara and Tothill [155,156] for the determination of Pb2+ and Cd2+ at an SPCE. In this investigation, stripping chronopotentiometric measurements were carried out by depositing a metallic film of bismuth in situ with the target metal ions (lead and cadmium). A deposition potential was applied to preconcentrate the analytes, after which, a constant current was applied to strip the preconcentrated analytes until a limit of —0.2 V. The concentrations for Pb2+ and Cd2+ in the wastewater samples and acetic acid extracts of soils were quantified by the use of a multiple standard addition method. 

Instead of drops, liquid mercury can be used as thin films electrodepo-sited on some solid electrodes in order to increase the useable negative potential range of these electrodes. For example, on glassy carbon substrates the deposition can be done from a solution of 10-5 m Hg(II) in 0.1mHNO3, applying a convenient potential (—1.0 V vs. SCE) during a few minutes, and stirring the solution. Alternatively a mercury film can be formed on other substrates, such as copper, by simple immersion in liquid mercury. The special properties of these thin film electrodes are described in Section 9.10. 

If the voltammogram obtained does not show any peak and the base current is sufficiently low (300 00 nA), then it is possible to continue with the analysis of the samples, otherwise the Hg film is destroyed and prepared again. To avoid alteration of the complexation equilibria due to residual ionic Hg and to clean the electrode assembly, the latter is rinsed with a purged aliquot of the sample before transferring the cell cup containing the sample in the measurement position. 

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