Electrodes, bismuth mercury

Electrodes BDDE boron-doped diamond electrode, BiFE bismuth film electrode, CFiE carbon fibre electrode, CPE carbon paste electrode, GCE glassy carbon electrode, HMDE hanging mercury drop electrode, Hg(Ag)FE silver-amalgam film electrode, (M)CPE (modified) carbon paste electrode, MFE mercury film electrode, MWCNTs-Na/Bi multiwall carbon nanotubes dispersed in Nafion used in combination with Bi, SCE saturated calomel electrode, SMDE static mercury drop electrode, SP-BiFE screen-printed... 

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]. 

Florence [98] carried out anodic stripping voltammetry of bismuth in a weakly acidic medium, with a polished vitreous carbon electrode mercury-... 

The magnesium will be liberated quantitatively and may then be titrated with a standard EDTA solution. Where mixtures of metal ions are analysed, the masking procedures already discussed can be utilized or the pH effect exploited. A mixture containing bismuth, cadmium and calcium might be analysed by first titrating the bismuth at pH = 1-2 followed by the titration of cadmium at an adjusted pH = 4 and finally calcium at pH = 8. Titrations of this complexity would be most conveniently carried out potentiometrically using the mercury pool electrode. 

Owing to the toxicity of mercury and its disposal problem, solid electrodes are now very popular. In particular, electrodes made of carbon such as glassy carbon, graphite, carbon paste, and carbon fibers have gained popularity. Mercury, gold, bismuth, and other metals can be deposited as thin metal films on carbon and serves as thin metal film electrodes (TMFE) with excellent analytical advantages in trace metal analysis. The choice of working electrode is determined by the redox... 

The enhancement of SWV net peak current caused by the reactant adsorption on the working electrode surface was utilized for detection of chloride, bromide and iodide induced adsorption of bismuth(III), cadmium(II) and lead(II) ions on mercury electrodes [236-243]. An example is shown in Fig. 3.13. The SWV net peak currents of lead(II) ions in bromide media are enhanced in the range of bromide concentrations in which the nentral complex PbBr2 is formed in the solntion [239]. If the simple electrode reaction is electrochemically reversible, the net peak cnnent is independent of the composition of supporting electrolyte. So, its enhancement is an indication that one of the complex species is adsorbed at the electrode snrface. 

Anastopoulos et al. [47] have analyzed interfacial rearrangements of triphenyl-bismuth and triphenylantimony at mercury electrode in nonaqueous solvents of high dielectric constant. These phenomena were detected as the peaks in the capacitance-potential curves at intermediate negative potentials for triphenyl-bismuth and triphenylantimony in N-methylformamide, A,A-dimethylforma-mide, dimethyl sulfoxide, propylene carbonate, and methanol solutions. 

Fig. 6.3. Stripping voltammograms for 50ppb Zn, Cd and Pb at glassy-carbon electrodes coated with bismuth (a) and mercury (b) films. Two-min deposition at -1.4 V. (Based on Ref. [12], with permission obtained from The American Chemical Society).

Bismuth-film electrodes (BiFEs), consisting of a thin bismuth-film deposited on a suitable substrate, have been shown to offer comparable performance to MFEs in ASY heavy metals determination [17]. The remarkable stripping performance of BiFE can be due to the binary and multi-component fusing alloys formation of bismuth with metals like lead and cadmium [18]. Besides the attractive characteristics of BiFE, the low toxicity of bismuth makes it an alternative material to mercury in terms of trace-metal determination. Various substrates for bismuth-film formation are reported. Bismuth film was prepared by electrodeposition onto the micro disc by applying an in situ electroplating procedure [19]. Bismuth deposition onto gold [20], carbon paste [21], or glassy carbon [22-24] electrodes have been reported to display an... 

Other metals, such as copper, nickel, or silver, have been used as electrode materials in connection with specific applications, such as the detection of amino acids or carbohydrates in alkaline media (copper and nickel) and cyanide or sulfur compounds (silver). Unlike platinum or gold electrodes, these electrodes offer a stable response for carbohydrates at constant potentials, through the formation of high-valence oxyhydroxide species formed in situ on the surface and believed to act as redox mediators (40,41). Bismuth film electrodes (preplated or in situ plated ones) have been shown to be an attractive alternative to mercury films used for stripping voltammetry of trace metals (42,43). Alloy electrodes (e.g., platinum-ruthenium, nickel-titanium) are also being used for addressing adsorption or corrosion effects of one of their components. The bifunctional catalytic mechanism of alloy electrodes (such as Pt-Ru or Pt-Sn ones) has been particularly useful for fuel cell applications (44). 

The mercury electrode has been used by researches in melts up to about 250°C, especially for nitrate and chloroaluminate melts [82,83], Liquid lead (m.p. 327.5°C) is another liquid metal [84] used for molten halides. Liquid electrodes of bismuth (m.p. 271°C), indium (m.p. 157°C) and thallium (m.p. 303°C) have also been, used but to a limited extent [85],... 

Coulometric determinations of metals with a mercury cathode have been described by Lingane. From a tartrate solution, copper, bismuth, lead, and cadmium were successively removed by applying the appropriate cathode potential, which was selected to correspond to a region of diffusion-controlled current determined from current-voltage curves with a dropping mercury electrode. With a silver anode, iodide, bromide, and chloride can be deposited quantitatively as the silver salt. By controlling the anode potential, Lingane and Small determined iodide in the presence of bromide or chloride. The separation of bromide and chloride, however, was not successful because solid solutions were formed (Section 9-4). 

Liquid amalgams For the liquid amalgams of zinc, cadmium, lead, and bismuth, the potentials do not differ widely from those of solid metals, for the following reasons. ° ° If solid metal is added to mercury, a solid phase eventually is formed, and at equilibrium both phases of the saturated, two-phase amalgam must have the same electrode potential. The emf of the cell... 

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