Electrochemical analysis methods electroanalysis

For the purposes of this book, the term electroanalysis will be taken to mean the analysis of an analyte by using electrochemical methods. The analyte will be termed the electroactive species (or material). Sometimes, however, we will also call it the electroanalyte. At heart, analysts working with electrochemical techniques monitor the behaviour of an electroactive species by performing two types of experiment they will either measure a potential (or occasionally variations in potential), or they will measure the charges, Q, and changes in the charge, AQ. 

This review has attempted to put hydrodynamic modulation methods for electroanalysis and for the study of electrochemical reactions into context with other electrochemical techniques. HM is particularly useful for the extension of detection limits in analysis and for the detection of heterogeneity on electrode surfaces. The timescale addressable using HM methodology is limited by the time taken for diffusion across the concentration boundary layer, typically >0.1 s for conventional RDE and channel electrode geometries. This has meant a restriction on the application of HM to deduce fast reaction mechanisms. New methodologies, employing smaller electrodes and thin layer geometries look to lift this restraint. 

Potentiometric methods of electroanalysis (see Chapter 7 of this handbook) depend on the ability of a membrane material to transport either cations or anions selectively. This selective behaviour results in an imbalance of concentrations on either side of the membrane which, in turn, leads to the estabhshment of a measurable potential difference across the membrane. In the simplest possible analysis, if we consider our membrane to be infinitely thin, or alternatively to have some kind of electrolyte boundary that is infinitely thin, then the equality of electrochemical potential, /I, in either of the solution phases, a and P, implies that... 

Mannino, S. and Wang, 1.(1992) Electrochemical methods for food and drink analysis. Electroanalysis, 4, 835-840. 

Electrochemical methods of analysis (electroanalysis) have made progress by laser-assisted techniques [44, 92-94]. They were useful to detect ascorbic acid at a carbon electrode in flow injection [44]. Capabilities of pulsed laser beam illumination of gold and platinum disk electrodes were tested with the well-known redox couples toluidine blue, iodide, ferricyanide, ruthenium hexammine and ferrocene (see Fig. 4.10) [92]. Laser-activated voltammetry proved useful for selective removal of impurities from glassy carbon- and boron-doped diamond surfaces [93]. 

With respect to analytes it can be stated that electrochemical sensors hardly wiU be designed for elemental analysis as batch laboratory techniques here, electromagnetic and mass spectrometric methods offer so many advantages over electroanalysis that their performance is hardly reached by the latter one. Nevertheless, sensors which can be applied in the field may be advantageous in this respect because they may help in an early stage of the entire sampling and analytical protocol to decide, if it is necessary to analyze a sample in more details in the laboratory or not. 

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