Metals voltammetric techniques

With the introduction of modern electronics, inexpensive computers, and new materials there is a resurgence of voltammetric techniques in various branches of science as evident in hundreds of new publications. Now, voltammetry can be performed with a nano-electrode for the detection of single molecular events [1], similar electrodes can be used to monitor the activity of neurotransmitter in a single living cell in subnanoliter volume electrochemical cell [2], measurement of fast electron transfer kinetics, trace metal analysis, etc. Voltammetric sensors are now commonplace in gas sensors (home CO sensor), biomedical sensors (blood glucose meter), and detectors for liquid chromatography. Voltammetric sensors appear to be an ideal candidate for miniaturization and mass production. This is evident in the development of lab-on-chip... 

Electrochemical interconversion of homo- and heteronuclear gold cluster compounds remains an area that has received scant attention, despite the potential for changing the electron count and hence the metal cage geometries of these clusters by electrochemical methods. The electrochemical redox reactions of [Pt(AuPPh3)8]2+ have been studied, using pulse, differential pulse, and cyclic voltammetric techniques (124, 242) and two reversible, one-electron reduction steps have been... 

Esteban, M., Anno, C., Dfaz-Cruz, J.M., Dfaz-Cruz, M.S., and Tauler, R., Multivariate curve resolution with alternating least squares optimization a soft-modeling approach to metal complexation studies by voltammetric techniques, Trends Anal. Chem., 19, 49-61, 2000. 

For chemical monitoring, a list of priority substances has been established that includes metals such as cadmium, lead, and nickel. As far as metals are concerned, voltammetric techniques and more precisely electrochemical stripping analysis has long been recognized as a powerful technique in environmental samples. In particular, anodic stripping voltammetry (ASV) coupled with screen-printed electrodes (SPEs) is a great simplification in the design and operation of on site heavy metal determination in water, for reasons of cost, simplicity, speed, sensitivity, portability and simultaneous multi-analyte capabilities. The wide applications in the field for heavy metal detection were extensively reviewed (Honeychurch and Hart, 2003 Palchetti et al., 2005). 

Potentiometric probes are the oldest forms of electrochemical sensors. They can conveniently be used for studying many interesting chemical systems not accessible to voltammetric techniques. In particular, alkali and alkaline earth metal ion concentrations, of importance in biological systems,... 

Another electrochemical sensor for heavy metal detection in liquids has been fabricated by Miu et A three-electrode cell on silicon and voltammetric techniques for... 

Because of its remarkable sensitivity (down to 10-11 M) stripping analysis is the most widely used voltammetric technique for trace metal determination in clinical samples (Wang, 1982A). Stripping analysis can be considered as a two-step technique. In the first step, metals in solution are effectively preconcentrated onto the working electrode by electrodeposition ... 

Santamaria M del Campo, Vazquez Barbado MD, Tascon Garcia ML et al. Determination of hydrogen peroxide by voltammetric techniques at carbon paste electrodes modified with transition metal phthalocyanines. Quimica Analitica 1998 17 147-152. 

Perhaps the most important advantage of the voltammetric techniques over the atomic spectroscopic techniques is the ability of the voltammetric techniques to differentiate between the different oxidation states of the metal, and hence give environmentally more relevant information. As was briefly stated (5.1) this applies only to the final solution used in the instrumental determination step. However it does mean that a simpler separation step can be used prior to the voltammetric procedure and still allow quantitative specia-tion. In some cases, involving effluent or natural water samples, the separation step can even be eliminated. 

The development of routine and easy handling procedures for continuous and real-time speciation of trace metals in waters has led, in the last years, to the development of microsensors coupled to voltammetric techniques. Microelectrodes offer several advantages for speciation measurements in real-world samples, including their application in low ionic strength media (e.g., freshwaters), reproducibility, and sensitivity. Some Cd speciation studies carried out in river waters, heavily loaded with suspended material, using microelectrodes demonstrated that most of Cd was associated with colloidal material. In addition, this technique also enables the determination of the corresponding complexation stability constants for Cd and protons. 

Both ASV and CSV measure labile metal concentrations (assumed to approximate the concentration of inorganic metal species and weakly bound organic complexes) and have been used to elucidate the extent of complexation by dissolved organic matter for a range of metals. The value of voltammetric techniques in metal speciation studies lies in the fact that discrimination can be achieved on the basis of their reactivity at the electrode. This will include not only the free metal ion, but those in complexed forms (ML), provided the dissociation of the complex in the diffusion layer is very fast compared to diffusion, i.e., the thermodynamic equilibrium of the dissociation of ML is maintained despite consumption of M at the... 

Many applications of cationic clays are directed toward the detection of heavy metals [1]. hi this case, the analytical method followed is very similar to an anodic stripping voltammetric technique a step reducing pre-concentrated metal ions to the zero valence state is performed and the analytical signal is collected in the subsequent anodic re-oxidation step [61]. The selectivity of the clay toward a target metal ion can be improved by a functionalization of the material with suitable alkylsilane derivatives [64, 65, 80] or by intercalation of a specific organic ligand inside the clay interlayers [66, 67, 81]. 

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