Anodic stripping voltammetry, mercury film electrodes

Anodic stripping voltammetry consists of two steps (Figure 11.37). The first is a controlled potential electrolysis in which the working electrode, usually a hanging mercury drop or mercury film, is held at a cathodic potential sufficient to deposit the metal ion on the electrode. For example, with Cu + the deposition reaction is... 

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... 

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. 

Batley [28] examined the techniques available for the in situ electrodeposition of lead and cadmium in estuary water. These included anodic stripping voltammetry at a glass carbon thin film electrode and the hanging drop mercury electrode in the presence of oxygen and in situ electrodeposition on mercury coated graphite tubes. Batley [28] found that in situ deposition of lead and cadmium on a mercury coated tube was the more versatile technique. The mercury film, deposited in the laboratory, is stable on the dried tubes which are used later for field electrodeposition. The deposited metals were then determined by electrothermal atomic absorption spectrometry, Hasle and Abdullah [29] used differential pulse anodic stripping voltammetry in speciation studies on dissolved copper, lead, and cadmium in coastal sea water. 

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... 

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... 

The improvement in the preparation of renewable and reproducible mercury film-covered carbon paste electrode for use in anodic stripping voltammetry has been reported in Ref. 39. Mercury salts (mercuric oxalate) distributed in the electrode bulk served as a source of mercury. 

Wong DKY, Ewing AG (1990) Anodic stripping voltammetry at mercury films deposite on ultrasmaU carbon-ring electrodes. Anal Chem 62 2697-2702. 

Anodic stripping voltammetry (ASV) is the oldest, and still the most widely used version of stripping analysis [3]. The technique is applicable to metal ions that can be readily deposited at the working electrode, and particularly for those metals that dissolve in mercury. In this case, the metals are being preconcentrated by electrodeposition into a small-volume mercury electrode (a thin mercury film or a hanging mercury drop). The preconcentration is done by cathodic deposition at a controlled potential and time. The deposition potential is usually ca. 0.3 Y more negative than E° for the least easily reduced metal ion to be determined. The metal ions reach the mercury electrode by diffusion and convection, where they are reduced and concentrated as amalgams ... 

Mercuric and mercurous salts — Salts of Hg(II) and Hg(I), respectively. Soluble mercuric and mercurous salts such as acetates and nitrates are used for the deposition of mercury films on conducting substrates (see -> anodic stripping voltammetry). Insoluble salts, e.g., chloride and sulfate of Hg(I) in chloride and sulfate medium, respectively, can be used to prepare reference electrodes (see -> calomel electrode). The formation of insoluble salts of mercury on - mercury electrodes determines, among others, the positive limit of their voltam-metric potential window. 

Sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca), concentrations were measured by atomic absorption spectrophotometry (Perkin Elmer 2380 equipped with deuterium background corrector). Cd, Zr, and Cu concentrations were obtained in a quartz cell, by differential pulse anodic stripping voltammetry (DPASV) with a assy carbon thin-film mercury covered electrode (Tacussel polarographic equipment fitted with a Tacussel EDI type electrode). Pure water was produced by a Milli. Q water purification system (Millipore). Chlorate, sulfate and carbonate were measured using classical methods. 

Anodic stripping voltammetry (ASV) with the tubular mercury graphite electrode (TMGE) possesses adequate sensitivity and precision under repeated use to characterize zinc in San Diego Bay water. The TMGE, made by electrolysis of a mercuric nitrate solution to form a thin mercury film inside a graphite tube, is described elsewhere (I). 

Bismuth is one of the elements most easily determined with anodic stripping voltammetry (Florence 1972) as it can be deposited onto electrodes at potentials at which most other elements are in solution. Glassy carbon electrodes coated with films of mercury, but also of gold, have been used (Florence 1974). In biological materials with low concentrations of Bi, interference from other metals is not to be expected because of the low levels of most metals in these materials. Best results are reached with solutions containing 0.1 M hydrochloric acid, with detection limits in the range of 1 (IfQand 1993). 

Wang, J. and Hutchins-Kumar, L. (1986). Cellulose acetate coated mercury film electrodes for anodic stripping voltammetry. Anal. Chem., 58.402. 

At a very thin film (A < 0.1), the real peak current of the reversible reaction (II.3.1) is linearly proportional to the frequency because A p linearly depends on the parameter A [59, 60]. In reaction (II.3.1), it is assumed that only the species Red is initially present in the solution. This is the condition usually encountered in anodic stripping square-wave voltammetry [Red = M(Hg)]. In the range 0.1 < A < 5, Amonotonously increases with A from 0.03 to 0.74, without a maximum for A = 1. The peak width changes from 99/n mV (for A < 0.3) to 124/ mV, for A > 3 [60, 61]. Simulations of SWV in the restricted diffusion space were extended to a thin layer cell [62]. The influence of electrode kinetics on direct and anodic stripping SWV on thin mercury film electrodes was analyzed recently [63-65]. 

The accumulation of amalgams can be used in anodic stripping voltammetry if both the reduction of ions and the oxidation of metal atoms occur within the working window of the mercury electrode [22]. Ions that give the best responses are listed in Table n.7.4. In electroanalysis of traces, mercury film electrodes are used [23-25]. 

ASV anodic stripping voltammetry ATP adenosine triphosphate AuE gold electrode CV cyclic voltammetry DPV dififerential pulse voltammetry DPASV differential pulse adsorptive stripping voltammetry GCE assy carbon electrode MFE, mercury film electrode NPGE nanoporous gold electrode SPE screen-printed electrode. 

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