Stripping process, voltammetry

Xanthine and xanthosine were investigated on HMDE, applying out-of-phase ac and dc voltammetries [74]. It has been shown that both compounds are strongly adsorbed and interact chemically. In the cathodic stripping process, one could determine both compounds at trace level. Naidu et al. [146] have performed polaro-graphic studies to show that the product of anodic reaction (prewave) of potassium isobutyl xanthate is strongly adsorbed at the mercury electrode. 

Morrison, G.M., Florence, T.M. and Stauber,J.L. (1990) The effects of complexing agents and surfactants on the deposition and stripping processes in differential pulse anodic stripping voltammetry of metals at the hanging mercury drop electrode. Electroanalysis (NY), 2, 9-14. 

Potentiometric stripping analysis, as stated in one review,92 "is not as general an analytical technique for the determination of metal traces as is graphite-furnace atomic absorption spectroscopy." It is used as a complementary technique for assay of some toxic metals in water (zinc, cadmium, lead, and copper in potable water and wastewater,93 94 and lead and thallium in seawater.95 The advantage of anodic stripping voltammetry (ASV) is summarized in two steps, which include electrolytic preconcentration and the stripping process. There are a number of interfering ions that can affect the... 

Figure 6.20 shows the repetitive cyclic voltammetry of the lithium deposition and stripping process on a nickel substrate from a cell using a (PE0)8LiCF3S03 polymer electrolyte, i.e. one of the first generation electrolytic membrane commonly used for the development of LPBs. The trend of the voltammetric curves indicates that the process at the lithium interface ... 

Figure 6.20 Cyclic voltammetry of the lithium plating-stripping process from a (PE0)9LiCp3S03 cell at 80°C. Electrode surface 1.75 cm. The number of consecutive cycles is indicated in the figure. From [15] by permission of the Electrochemical Society, Inc.

Stripping process, for example, by sweep voltammetry or differential pulse... 

Square-wave voltammetry (SWV) is one of the four major voltammetric techniques provided by modern computer-controlled electroanalytical instruments, such as Autolab and pAutolab (both EcoChemie, Utrecht), BAS 100 A (Bioana-lytical Systems) and PAR Model 384 B (Princeton Applied Research) [1], The other three important techniques are single scan and cyclic staircase, pulse and differential pulse voltammetry (see Chap. II.2). All four are either directly applied or after a preconcentration to record the stripping process. The application of SWV boomed in the last decade, firstly because of the widespread use of the instruments mentioned above, secondly because of a well-developed theory, and finally, and most importantly, because of its high sensitivity to surface-confined electrode reactions. Adsorptive stripping SWV is the best electroanalytical method for the determination of electroactive organic molecules that are adsorbed on the electrode surface [2]. 

From the nature of the process described above it has been referred to as stripping polarography , but the term anodic stripping voltammetry is preferred. It is also possible to reverse the polarity of the two electrodes of the cell, thus leading to the technique of cathodic stripping voltammetry. 

Anodic stripping voltammetry (ASV) has been used extensively for the determination of heavy metals in samples of biological origin, such as lead in blood. ASV has the lowest detection limit of the commonly used electroanalytical techniques. Analyte concentrations as low as 10 M have been determined. Figure 16 illustrates ASV for the determination of Pb at a mercury electrode. The technique consists of two steps. The potential of the electrode is first held at a negative value for several minutes to concentrate some of the Pb " from the solution into the mercury electrode as Pb. The electrode process is... 

To date, a few methods have been proposed for direct determination of trace iodide in seawater. The first involved the use of neutron activation analysis (NAA) [86], where iodide in seawater was concentrated by strongly basic anion-exchange column, eluted by sodium nitrate, and precipitated as palladium iodide. The second involved the use of automated electrochemical procedures [90] iodide was electrochemically oxidised to iodine and was concentrated on a carbon wool electrode. After removal of interference ions, the iodine was eluted with ascorbic acid and was determined by a polished Ag3SI electrode. The third method involved the use of cathodic stripping square wave voltammetry [92] (See Sect. 2.16.3). Iodine reacts with mercury in a one-electron process, and the sensitivity is increased remarkably by the addition of Triton X. The three methods have detection limits of 0.7 (250 ml seawater), 0.1 (50 ml), and 0.02 pg/l (10 ml), respectively, and could be applied to almost all the samples. However, NAA is not generally employed. The second electrochemical method uses an automated system but is a special apparatus just for determination of iodide. The first and third methods are time-consuming. 

Stripping voltammetry or stripping analysis has a special place in electrochemistry because of its extensive application in trace metal analysis. Stripping voltammetry (SV) is a two-step process as shown schematically in Fig. 18b. 12. In the first step, the metal ion is reduced to metal on a mercury electrode (thin mercury film on glassy carbon or a HMDE) as amalgam. 

The Pb(II)/Pb(Hg) electrode process has been analyzed using digital simulation and the results have been compared with experiments carried out in aqueous sodium nitrate solutions applying convolution/deconvolution voltammetry to determine charge-transferrate constants and transfer coefficients [41]. Principles of thin-layer anodic stripping voltammetry have been discussed and a model for the stripping step has been proposed. 

Analytical Applications In addition to the above-mentioned analytical aspects of the processes at Hg electrodes, in this section, we briefly review the papers focused on the subject of the affinity of various compounds to the mercury electrode surface, which allowed one to elaborate stripping techniques for the analysis of inorganic ions. Complexes of some metal ions with surface-active ligands were adsorptively accumulated at the mercury surface. After accumulation, the ions were determined, usually applying cathodic stripping voltammetry (CSV). Representative examples of such an analytical approach are summarized as follows. 

Ivanov and Kaplun [76] used catechol in the determination of vanadium by adsorptive stripping voltammetry. It has been shown that the studied electrode process comprised one-electron reversible reduction of vanadium (IV) triscatecholate, previously accumulated at the electrode. It has also been found that the reduced... 

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