Environmental analysis, electroanalytical methods

R Kalvoda, Electroanalytical Methods in Chemical and Environmental Analysis, Plenum, New York, 1987... 

There may be circumstances in which an electroanalytical method, as a consequence of the additional chemicals required, has disadvantages in comparison with instrumental techniques of analysis however, the above-mentioned advantages often make electroanalysis the preferred approach for chemical control in industrial and environmental studies. Hence, in order to achieve a full understanding of what electroanalysis can do in these fields first, it will be treated more systematically in Part A second, some attention will be paid in Part B to electroanalysis in non-aqueous media in view of its growing importance and finally, the subject will be rounded off in Part C by some insight into and some examples of applications to automated chemical control. 

Vesely, J. andStulik, K. (1987) Potentiometry with ion-selective electrodes. In R. Kalveda (Ed.) Electroanalytical Methods in Chemical and Environmental Analysis. Plenum, Prague. 

Extraction can be used as an efficient and selective sample preparation method before analysis by chromatographic, spectroscopic, electroanalytical, or electrophoretic methods (see for example [5-10]). International norms from the International Standards Organization, US Food and Drug Administration, and US Environmental Protection Agency recommend application of extraction methods in analysis of food products and environmental and pharmaceutical samples. Novel ideas and new views concerning extraction have led to many controversies about terminology and to reallocation and softening of the boundaries between extraction and other analytical sample treatment techniques. 

Practically all commonly employed electroanalytical methods can be used in environmental analysis the choice of method depends on the character of the compound to be determined and of the matrix in which it occurs, as well as on sensitivity and selectivity requirements. The principal methods are voltammetry and polarography, potentiometry, coulo-metry and conductometry. 

J. Fexa, Semiconductor sensors, "Electroanalytical Methods in Chemical and Environmental Analysis," R. Kalvoda, ed.. Plenum Press, London (1985). 

Very good results have been obtained in all system provided with calibration and zeroing. If the passivation of the electrode is slow and predictable, it is possible to eliminate its influence on the accuracy of the measurement by frequent calibration and zeroing. The introduction of automatic calibration and zeroing and microprocessor adjustment of the sensor s signal to the correct value represents a real milestone in the development of electroanalytical methods. It has been Introduced in automatic laboratory measurement, industrial sensors and environmental monitors, allowing automatic analysis to be carried out for several weeks or even months with accuracy 3%. 

All analysts are familiar with the principles of potentiometry and potarography and indeed, most analytical laboratories will contain a pH meter and a polarograph. However, electrochemical methods arc, in general, not very important in modern analysis. In contrast, there arc spccifiG applications such as trace metal ion analysis in water and effluents and also some other aspects of environmental analysis for which electrochemical methods are particularly attractive. This is because (1) some methods, especially anodic stripping voltammetry, have a very high sensitivity for heavy-metal ions and the lowest detection limit of from 10 to mol dm is well below that of other available methods (2) electrochemical methods are well suited for modification to on-line and/or portable devices for analysis in the held. Whether the analysis is based on current, conductivity or the response of an ion-selective electrode, both the cell and the control electronics are readily miniaturized and operate on low power Hence, this chapter considers the principles of the electroanalytical methods important in environmental and on-line analysis, together with biochemical applications of electrochemical sensors. 

Recent reviews of analytical methods for thallium have been provided by either Esteban et al. (1998) (electroanalytical techniques) or Chou and Moffatt (1998) (species analysis in aquatic environmental samples). 

Specific chapters of this book give a detailed description of the wide range of electrochemical sensors available for many different environmental applications, so only a short discussion will be given in this subchapter about the present status of electrochemical sensing in environmental water analysis. We ll present an overview about the main features and applicability of the most relevant electroanalytical techniques, some outstanding trends about instrumental and technological aspects and a brief comment on standardised methods. 

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