Mercury film electrode , stripping

Stripping voltammetry involves the pre-concentration of the analyte species at the electrode surface prior to the voltannnetric scan. The pre-concentration step is carried out under fixed potential control for a predetennined time, where the species of interest is accumulated at the surface of the working electrode at a rate dependent on the applied potential. The detemiination step leads to a current peak, the height and area of which is proportional to the concentration of the accumulated species and hence to the concentration in the bulk solution. The stripping step can involve a variety of potential wavefomis, from linear-potential scan to differential pulse or square-wave scan. Different types of stripping voltaimnetries exist, all of which coimnonly use mercury electrodes (dropping mercury electrodes (DMEs) or mercury film electrodes) [7, 17]. 

Anodic stripping voltammetry at a mercury film electrode can be used to determine whether an individual has recently fired a gun by looking for traces of antimony in residue collected from the individual s hands, fn a typical analysis a sample is collected with a cotton-tipped swab that had been wetted with 5% v/v HNO3. When returned to the lab, the swab is placed in a vial containing 5.00 mb of 4 M HCl that is 0.02 M in hydrazine sulfate. After allowing the swab to soak overnight,... 

Stripping voltammetry procedure has been developed for determination of thallium(I) traces in aqueous medium on a mercury film electrode with application of thallium preconcentration by coprecipitation with manganese (IV) hydroxide. More than 90% of thallium present in water sample is uptaken by a deposit depending on conditions of prepai ation of precipitant. Direct determination of thallium was carried out by stripping voltammetry in AC mode with anodic polarization of potential in 0,06 M ascorbic acid in presence of 5T0 M of mercury(II) on PU-1 polarograph. 

Voltaic cells 64. 504 Voltammetry 7, 591 anodic stripping, 621 concentration step, 621 mercury drop electrode, 623 mercury film electrode, 623 peak breadth, 622 peak current, 622 peak potential, 622 purity of reagents, 624 voltammogram, 622 D. of lead in tap water, 625 Volume distribution coefficient 196 Volume of 1 g of water at various temperatures, (T) 87... 

FIGURE 3-13 Concentration gradient of the metal in the mercury film electrode and nearby solution dining the stripping step. 

Example 4-2 A rotating mercury film electrode (2 mm diameter) yielded a stripping peak current of 2.2 pA for a 1 x 10 8 M lead(II) solution following a 3 min deposition at —1.0 V with a 1600 rpm rotation. Calculate the peak current for a 2.5 x 10 8M lead(II) solution following a 2 min deposition with a 2500 rpm rotation. 

Fig. 6.5 Schematic representation of a bioelectronic protocol for detection of DNA hybridization (A) binding of the target to magnetic beads (B) hybridization with CdS-labeled probe (C) dissolution of CdS tag (D) potentiometric stripping detection at a mercury-film electrode. (Reprinted from [136], Copyright 2009, with permission from Elsevier)...

Scarponi et al. [781] studied the influence of an unwashed membrane filter (Millpore type HA, 47 mm diameter) on the cadmium, lead, and copper concentrations of filtered seawater. Direct simultaneous determination of the metals was achieved at natural pH by linear-sweep anodic stripping voltammetry at a mercury film electrode. These workers recommended that at least 1 litre of seawater be passed through uncleaned filters before aliquots for analysis are taken the same filter can be reused several times, and only the first 50-100 ml of filtrate need be discarded. Samples could be stored in polyethylene containers at 4 °C for three months without contamination, but losses of lead and copper occurred after five months of storage. 

The conditions for reliable cyclic voltametry determination of trace Sn concentrations in sea water were investigated. All organotin compounds should be converted to Sn(II) by UV-photolysis adsorption on mercury drop in the presence of 40 pM of tropolone (1) cyclic voltametry stripping shows two cathodic peaks, corresponding to the two-step process Sn(IV) — Sn(II) -> Sn(0)29. A complex of Sn ions with catechol can be accumulated in a glassy carbon mercury film electrode, followed by stripping voltametry measurement in the cathodic direction, at pH 4.2-4.7. Interference occurs when Cu, Cd and Cr are present LOD 0.5 pg/L for 300 s accumulation30. 

After tq is passed, the second step starts by scanning the potential from Ed to a potential when all the deposited metals are re-oxidized (the reverse of reaction 25). The oxidation current recorded as a function of potential is the anodic stripping voltammogram (ASV). A typical ASY of three metals (Cd, Pb, and Cu) deposited on a mercury film electrode is shown in Fig. 18b.12b. The sensitivity of ASY can be improved by increasing the deposition time and by using the pulse technique to record the oxidation current. ASV in Fig. 18b. 12b was obtained by using the square wave voltammetry. In most cases a simple linear or step ramp is sufficient to measure sub-ppm level of metals in aqueous solution. The peak current of a linear scan ASV performed on a thin mercury film electrode is given by... 

The effects of mercury film electrode morphology in the anodic stripping SWV of electrochemically reversible and quasi-reversible processes were investigated experimentally [47-51], Mercury electroplated onto solid electrodes can take the form of either a uniform thin film or an assembly of microdroplets, which depends on the substrate [51 ]. At low sqtrare-wave frequencies the relationship between the net peak crrrrent and the frequency can be described by the theory developed for the thin-film electrode because the diffusion layers at the snrface of microdroplets are overlapped and the mass transfer can be approximated by the planar diffusion model [47,48],... 

Wang et al. [34] have introduced a new heated mercury film electrode based on a screen printed carbon substrate. It was used in anodic stripping and exhibited a significantly improved signal-to-noise ratio. A directly heated mercury film electrode for anodic stripping voltammetry has been described by Jasinski [35]. Different factors influencing the quality of analytical determination have been investigated. Renewed mercury electrodes and examples of their various applications have been reviewed in Ref. 36. Lovric and Scholz [37] have discussed the conditions... 

Various voltammetric waveforms can be employed during the stripping step, including linear scan, differential pulse, square-wave, staircase, or alternating-current operations. The differential pulse and square-wave modes are usually performed at the hanging mercury drop electrode, while linear scan stripping is usually performed in connection with the mercury film electrode. 

For reversible stripping reactions, the applied potential controls the concentration at the mercury-solution interface (according to the Nernst equation). Because of the rapid depletion of all the metal from thin mercury films, the stripping behavior at these electrodes follows a thin-layer behavior. The peak current for the linear scan operation at thin mercury film electrodes is thus given by... 

Figure 24.3 (A) Differential pulse and (B) square-wave stripping voltammograms for a nondeaerated solution containing 50 pg/L (ppb) Cd, Pb, and Cu ions. Two-minute deposition at a mercury film electrode held at -1.1 V. Acetate buffer solutions (0.1 M, pH 4.5).

On one hand, mercury-film electrodes give increased resolution when compared to the hanging mercury drop electrode (HMDE). On the other hand, BCFMEs have the inherent characteristics of an ERD. Hence, it would be extremely desirable to combine all properties. Furthermore, this combination may provide additional advantages such as easy handling, low cost, and other well-known analytical advantages associated with the use of UMEs itself, for example, the elimination of convective hydrodynamics along the accumulation step in stripping voltammetric techniques. 

Capelo, S., Mota, A.M. and Gongalves, M.L.S. (1995) Complexation of lead with humic matter by stripping voltammetry. Prevention of adsorption with Nafion-coated mercury film electrode. Electroanalysis, 7, 563-568. 

EDTA was determined in waste water by Fayyad et al, who used potentiometric stripping analysis after adding Bi(III) and K C O to the test solution. Uncomplexed Bi(III) was electrodeposited on a mercury film electrode (at -0.4 V vs. SCE) for 50 seconds. The working range was 4.5-95 ppb of EDTA [20]. 

Taking advantage of the ability to detect multiple group II and group III metals at mercury film electrodes using stripping analysis, a multianalyte DNA sensor was developed using different semiconductor nanocrystals (ZnS, CdS, and PbS) for the... 

The voltammetric peak reflects the time-dependent concentration gradient of the metal in the mercury electrode during the potential scan. Peak potentials serve to identify the metals in the sample. The peak current depends on various parameters of the deposition and stripping steps, as well as on the characteristics of the metal ion and the electrode geometry. For example, for a mercury film electrode, the peak current is given by... 

The mercury film electrode (MFE), used for stripping analysis or flow amperometry, consists of a very thin (10-100-pm) layer of mercury covering a conducting and inert support. Because of the adherent oxide films on metal surfaces, and the interaction of metals with mercury, glassy carbon is most often used as a substrate for the MFE. The mercury film formed on a glassy carbon support is actually composed of many droplets. Because they do not... 

Wang, J., Thongngamdee, S. and Lu, D. L. (2006b), Adsorptive stripping voltammetric measurements of trace beryllium at the mercury film electrode. Anal. Chim. Acta, 564(2) 248-252. 

Zaitsev, N. K., Osipova, E. A., Fedulov, D. M., Eremenko, E. A. and Dedov, A. G. (2006), Determination of selenium(IV) by cathodic stripping voltammetry using a copper-modified mercury-film electrode modified with copper. J. Anal. Chem., 61(1) 77-83. 

Mercury film electrode An electrode that has been coated with a thin layer of mercury used in place of a hanging mercury drop electrode in anodic stripping analysis. 

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