Mercury electrodes heavy metals

Since the past decade, different types of sensors and biosensors based on SPE have been prepared in our laboratory, such as a choline sensor with choline oxidase immobilized on the surface of a ruthenized-carbon screen-printed electrode as part of a system for pesticide detection [25], a screen-printed ruthenium dioxide electrode for pFI measurements [26], carbon-modified electrodes with mercury for heavy metals analysis [27], and two kinds of disposable electrochemical DNA biosensors for environmental screening [8-10,15,28,29]. 

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... 

Stripping analysis with inherent pre-concentration seems attractive to CFA, but until recently such a procedure appeared rather exceptional. It has been used in the automatic determination of heavy metals in water by anodic stripping voltammetry (ASV12S) in a continuous flow cell with a mercury-covered graphite electrode, having the advantage that one can distinguish... 

Although anodic stripping voltammetry is one of the few techniques suitable for the direct determination of heavy metals in natural waters [310,756-764], it is not readily adaptable to in situ measurements. Lieberman and Zirino [623] examined a continuous flow system for the anodic stripping voltammetry determination of zinc in seawater, using a tubular graphite electrode predeposited with mercury. A limitation of the approach was the need to pump seawater to the measurement cell, while the method required the removal of oxygen with nitrogen before measurements. 

ISOTRON Corporation s electrokinetic decontamination process is a patented, in situ process for the removal of contaminants from soil, groundwater, and porous concrete. The technology applies a low-intensity direct current (DC) across electrode pairs to facilitate electromigration and electro-osmosis of contaminants. The process works primarily on highly soluble ionized inorganics including alkah metals, chlorides, nitrates, and phosphates. Heavy metals such as lead, mercury, cadmium, and chromium have also responded favorably. 

Mercury is quickly limited at positive potentials (+0.25 V with respect to SCE). Beyond this potential, anodic dissolution of mercury occurs. However, mercury can be used at up to —1.8 or —2.3 V depending on whether the supporting electrolyte is acidic or alkaline. This range offers several possibilities, especially for the determination of heavy metals. The mercury used must be extremely pure (six-time distilled, under nitrogen). Unfortunately, the use of mercury as an electrode is a disadvantage because of its toxicity the mercury must be recycled after each use. 

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... 

The development of the reductive mode LCEC technique has been slow because of difficulties in preparing convenient and reliable working electrodes for use with a high efficiency chromatographic separation. In addition, problems are encountered with dissolved oxygen and heavy metals. Solid electrodes have been used with limited success for reductive LCEC. Mercury pool electrodes (44-47), the DME (48-53), and platinum wire electrodes coated with mercury (49) are generally not satis-... 

The aim of this work is to demonstrate how the screen printed electrodes (SPEs) can be used for on site heavy metals monitoring in surface waters in the frame of the WFD. The sensors used consist of mercury-coated screen-printed electrodes coupled with square wave anodic stripping voltammetry (SWASV) (Palchetti et al., 1999). Three metals Cu, Cd, and Pb which are classically analysed in water matrices have been considered. Moreover, Cd and Pb belong to the priority substances list of the WFD. Performance criteria of the device are first established to evaluate the level of confidence of the method. The potential use of the device and its main advantages are then highlighted through two illustrative field applications. 

Electrokinetic remediation involves passing a low level (mA cm ) DC electric current having potential difference a few volts through the soil, either in situ with electrodes placed into the soils, or in an external reactor. It has been shown that heavy metals such as zinc, copper, cadmium, chromium, lead, arsenic, mercury, nickel and iron can be efficiently removed from soils by electrokinetics. 

Probably the most commonly used instruments for cation impurity analysis of silicates are flame atomic absorption spectrophotometers and ion selective electrodes. In most cases, separation of silica is required to reduce interferences. The sample may also have to be diluted to bring the analyte concentration within the linear operating range. For cations, the atomic absorption spectrophotometer is more versatile than ion specific electrodes. If the analyst is concerned with the presence of heavy metals, then accessories such as a hydride system for the elements that form high vapor pressure compounds, e.g., Sb, and a mercury vapor cold trap are useful. If a large number of elements are to be determined, a substantial investment in hollow cathode and electrode discharge lamps must be made. Several gas mixtures will also be required. 

Heyrovsky worked out the theory for the mercury electrode In polarography, an electrochemical analysis method which, after a few improvements, meant that ultra-traces could be analysed In heavy metals for instance. He was awarded the Nobel prize for his work In 1959. 

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