Electrodes hanging drop

Mercury electrodes (a) hanging mercury drop electrode (b) dropping mercury electrode (c) static mercury drop electrode. 

In contrast, the coupling of electrochemical and spectroscopic techniques, e.g., electrodeposition of a metal followed by detection by atomic absorption spectrometry, has received limited attention. Wire filaments, graphite rods, pyrolytic graphite tubes, and hanging drop mercury electrodes have been tested [383-394] for electrochemical preconcentration of the analyte to be determined by atomic absorption spectroscopy. However, these ex situ preconcentration methods are often characterised by unavoidable irreproducibility, contaminations arising from handling of the support, and detection limits unsuitable for lead detection at sub-ppb levels. 

Batley [780] examined the techniques available for the in situ electrodeposition of lead and cadmium in seawater. These included anodic scanning 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. 

Bond et al. [791 ] studied strategies for trace metal determination in seawater by ASV using a computerised multi-time domain measurement method. A microcomputer-based system allowed the reliability of the determination of trace amounts of metals to be estimated. Peak height, width, and potential were measured as a function of time and concentration to construct the database. Measurements were made with a potentiostat polarographic analyser connected to the microcomputer and a hanging drop mercury electrode. The presence of surfactants, which presented a matrix problem, was detected via time domain dependent results and nonlinearity of the calibration. A decision to pretreat the samples could then be made. In the presence of surfactants, neither a direct calibration mode nor a linear standard addition method yielded precise data. Alternative ways to eliminate the interferences based either on theoretical considerations or destruction of the matrix needed to be considered. 

The hanging drop mercury electrode can usually be applied down to trace levels of 0.1 - 0.05 xg/l. 

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. 

Spherical Diffusion. If, as it might happen, the electrode is spherical rather than planar (e.g. using a hanging drop mercury electrode), See Figure 19, Fick s second law should be integrated by corrective terms accounting for the sphericity, or the radius r, of the electrode ... 

Electrochemical impedance measurements of the physical adsorption of ssDNA and dsDNA yields useful information about the kinetics and mobihty of the adsorption process. Physical adsorption of DNA is a simple and inexpensive method of immobilization. The ability to detect differences between ssDNA and dsDNA by impedance could be applicable to DNA biosensor technology. EIS measurements were made of the electrical double layer of a hanging drop mercury electrode for both ssDNA and dsDNA [34]. The impedance profiles were modeled by the Debye equivalent circuit for the adsorption and desorption of both ssDNA and dsDNA. Desorption of denatured ssDNA demonstrated greater dielectric loss than desorption of dsDNA. The greater flexibility of the ssDNA compared to dsDNA was proposed to account for this difference. 

Recently, Darowicki [29, 30] has presented a new mode of electrochemical impedance measurements. This method employed a short time Fourier transformation to impedance evaluation. The digital harmonic analysis of cadmium-ion reduction on mercury electrode was presented [31]. A modern concept in nonstationary electrochemical impedance spectroscopy theory and experimental approach was described [32]. The new investigation method allows determination of the dependence of complex impedance versus potential [32] and time [33]. The reduction of cadmium on DM E was chosen to present the possibility of these techniques. Figure 2 illustrates the change of impedance for the Cd(II) reduction on the hanging drop mercury electrode obtained for the scan rate 10 mV s k... 

Nangniot and Martens [3] determined triphenyltin acetate fungicide in vegetable matter by a method based on the hanging drop mercury electrode. 

Kemula electrode - hanging mercury drop electrode... 

The voltammetry of [OsioC(CO)24] at a hanging drop mercury electrode is a complex process whose nature is not fully understood. Controlled electrolysis at a mercury pool of 0.8 V leads to a product that upon standing reacts slowly to yield [Os2oHg(C)2(CO)4g] . This compound has also been generated chemically by reaction of [Os,oC(CO)24] with mercuric salts or AgBp4 and mercury (338) (see Section II,B,2,a). 

Majda and co-workers provided an elegant demonstration of through-bond and chain-chain hopping processes as parallel mechanisms for electron transfer across SAMs [46, 133]. In n-alkanethiol monolayers formed on hanging drop mercury electrodes, the adsorbate coverage T is measured by chronocoulometry of the mercuric thiolate formed upon adsorption. For the as-adsorbed films, geometric con-... 

A basic voltametric instrument consists of a cell, a potentiostat, and a recorder. Chemical reactions are caused by applying a potential to an electrode in a cell. The current, which flows under the experimental conditions, is monitored with the recorder. The cell generally consists of three electrodes placed in seawater (1) the working electrode, usually a hanging drop of Hg or a Hg-plated graphite or glassy-carbon surface (2) the reference electrode, made of either calomel or Ag wire anodized to form AgCl and (3) a counterelectrode made of pure Pt wire. 

Both metallic and membrane electrodes have been used to detect end points in potentiometric titrations involving complex formation. Mercury electrodes are useful for EDTA titrations of cations that form complexes that are less stable than HgY- . See Section 21D-1 for the half-reactions involved and Equation 21-5 for the Nernst expression describing the behavior of the electrode. Hanging mercury drop and thin mercury film electrodes appropriate for EDTA titrations are available from a number of manufacturers. As always, whenever mercury is used in experiments like these, we must take every precaution to avoid spilling it, and it must be stored in a well-ventilated hood or a special cabinet to remove the toxic vapors of the liquid metal. Before working with mercury, be sure to read its Materials Safety Data Sheet (MSDS), and follow all appropriate safety procedures. 

---