Electrodes, bismuth reference

The three electrodes GECE as working electrode, the Ag/AgCl as reference electrode and the platinum as auxiliary electrode, are immersed in a 25 ml electrochemical cell containing 0.1 M acetate buffer (pH 4.5) and 400 pg/1 of bismuth. During the stripping step, the current is recorded in quiescent solution. 

Fig. 18. SEM image of a 70-nm bismuth nanowire with four electrodes attached to the nanowire. The circle on the large left electrode is a reference point used to find the nanowire and to attach electrodes to it by a lithographic process (Cronin et al., 1999).

Lead perchlorate and bismuth nitrate were added to the electrolytic solution at 5 x 10-5 and 10 5 M, respectively, to modify a platinum electrode, which has a real surface area of 40 cm2. The electrolysis cell has two identical compartments separated by an ion-exchange membrane (Nation 423). A Ptgolrio sheet and the Hg/Hg2S04, SOf s i, electrode served as counter and reference electrodes, respectively. 

Anodic stripping voltammetry was in use already in 1972 to determine Bi in plasma [120]. Bismuth is one of the elements most easily determined with this method. It can be deposited on electrodes at potentials at which most other elements ate in solution. Glassy carbon electrodes coated with films of mercury [100,121-124], but also of gold [101,125], are used. As reference served calomel or silver/silver chloride electrodes [121]. Platinum foils or wires were used as counterelectrodes. At -0.7 V carbon electrodes are precoated with mercury from acid Hg(II) or gold from acid Au(III) solutions. To deposit Bi on the electrode -0.2 to -0.3 V is a sufficient potential for preelectrolysis, but mostly higher voltages are chosen to determine other metals as well. Bi is stripped fiom the electrode at potentials of about -0.10 to -0.16 V. Only some elements interfere with Bi, such as arsenic, mercury, copper, and antimony. Copper interferes at high concentrations and is separated by extraction [101]. Arsenic or antimony in urine are oxidized to their pentavalent states [125]. 

Fig. 16.1 Stripping voltammograms of zinc, cadmium, and lead recorded at glassy carbon and carbon fiber electrodes coated with (a) bismuth or (b) mercury films. Reprinted with permission from reference (20) Copyright (2000) American Chemical Society...

A miniaturized sensor for heavy-metal ions consisting of a nontoxic bismuth working electrode, an integrated Ag/AgCl reference electrode, and a gold counter electrode, has been proposed by Zou et al." Pb(II) and Cd(II) are positioned in a microchamber of 4.5 pL in which a planar array of multiple sensors can be located for multiple measurements using different sensor son one chip (Fig. 21.7). 

Last but not least, it should also be mentirmed that the fundamental configuration of bismuth film electrodes, BiFEs, has a number of derived varieties and modifications (see references (50-52) and references therein), as well as some related counterparts. Craiceming the former, there are the bismuth bulk electrode (BiBE), heterogeneous carbon-based electrodes modified with bismuth powder, bismuth nanoparticles, bismuth alloys or various bismuth(in) compounds, such as Bi203, BiOCl, (Bi0)2C03, specially encapsulated Bi(N03)3, Bip3 and NFi,BiF4. 

Normally, when using stripping techniques for non-metallic species, there is no deposition comparable to the amalgamation at mercury electrodes or alloying for bismuth alternatives nevertheless, a possible accumulatirai step cannot be simplified to a pure oxidation and/or reduction. As documented in the table, such a case is only seldom (e.g. in references 16,18), whereas the prevailing accumulations utilise... 

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