Process electroanalytical instruments

Let us dwell on Figure 6.4 for a moment. The standards and sample solutions are introduced to the instrument in a variety of ways. In the case of a pH meter and other electroanalytical instruments, the tips of one or two probes are immersed in the solution. In the case of an automatic digital Abbe refractometer (Chapter 15), a small quantity of the solution is placed on a prism at the bottom of a sample well inside the instrument. In an ordinary spectrophotometer (Chapters 7 and 8), the solution is held in a round (like a test tube) or square container called a cuvette, which fits in a holder inside the instrument. In an atomic absorption spectrophotometer (Chapter 9), or in instruments utilizing an autosampler, the solution is sucked or aspirated into the instrument from an external container. In a chromatograph (Chapters 12 and 13), the solution is injected into the instrument with the use of a small-volume syringe. Once inside, or otherwise in contact with the instrument, the instrument is designed to act on the solution. We now address the processes that occur inside the instrument in order to produce the electrical signal that is seen at the readout. 

Square-wave voltammetry (SWV) is one of the four major voltammetric techniques provided by modern computer-controlled electroanalytical instruments, such as Autolab and pAutolab (both EcoChemie, Utrecht), BAS 100 A (Bioana-lytical Systems) and PAR Model 384 B (Princeton Applied Research) [1], The other three important techniques are single scan and cyclic staircase, pulse and differential pulse voltammetry (see Chap. II.2). All four are either directly applied or after a preconcentration to record the stripping process. The application of SWV boomed in the last decade, firstly because of the widespread use of the instruments mentioned above, secondly because of a well-developed theory, and finally, and most importantly, because of its high sensitivity to surface-confined electrode reactions. Adsorptive stripping SWV is the best electroanalytical method for the determination of electroactive organic molecules that are adsorbed on the electrode surface [2]. 

Refs. [i] Sluyters-Rehbach M, Sluyters JH (1970) Sine wave methods in the study of electrode processes. In Bard AJ (ed) Electroanalytical chemistry, vol. 4. Marcel Dekker, New York, p 1 [ii] Southampton electrochem-istry group (1985) Instrumental methods in electrochemistry. Ellis Norwood, Chichester, p 251... 

Gary wrote the first edition of this book in 1971. He is the author of over 300 research papers and has authored five other books, including Instrumental Analysis. His research interests include electroanalytical chemistry, atomic spectroscopy, process analysis, and flow injection analysis. 

As discussed in more detail in Sect. 1.1.5, this volume of the Encyclopedia is divided into three broad sections. The first section, of which this chapter is an element, is concerned with introducing some of the basic concepts of electroanalytical chemistry, instrumentation - particularly electronic circuits for control and measurements with electrochemical cells - and an overview of numerical methods. Computational techniques are of considerable importance in treating electrochemical systems quantitatively, so that experimental data can be analyzed appropriately under realistic conditions [8]. Although analytical solutions are available for many common electrochemical techniques and processes, extensions to more complex chemical systems and experimental configurations requires the availability of computational methods to treat coupled reaction-mass transport problems. 

Volume 3 of this series may be consulted for a survey of electrochemical instrumentation and electroanalytical chemistry. In addition, several chapters in this volume contain detailed information on methods of importance to bioanalysis. In particular. Chapter 17 (mediated electron transfer). Chapter 7 (electrochemistry of nitric oxide). Chapter 12 (electrochemistry of nucleic acids). Chapter 13 (enzyme electrodes). Chapter 14 (in vivo electrochemistry), Chapter 5 (electrochemical immunoassays), Chapter 2 (single cell electrochemistry), and Chapter 9 (ion-selective electrodes) provide more details on the fundamental processes underlying the applications to bioanalysis that are described in this chapter. 

Electroanalytical techniques, essentially similar to those employed in aqueous solutions, can be adapted for use in melts to provide data on solution equilibria by way of stability constant determinations, ion transport through diffusion coefficient measurements, as well as mechanistic analysis and product identification from mathematical data treatment. Indeed, techniques such as linear sweep voltammetry and chronopotentiometry may often be applied rapidly to assess or confirm general characteristics or overall stoichiometry of electrode processes in melts, prior to more detailed kinetic or mechanistic investigations requiring more elaborate instrumentation and equipment, e.g., as demanded by impedance studies. Thus, answers to such preliminary questions as... 

All these characteristics have placed electroanalytical methods in the forefront of chemical analysis. The equivalence between the amount of electricity, which can be measured by electrical and electronic instrumentation and the results processed by most sophisticated computer-systems, and the amount of chemical substance demonstrated by Michael Faraday as long ago as in 1838, has resulted in a proposal that the unit of electricity, the Coulomb, be taken as the basic standard in in chemical analysis. 

Figure 5.25(a). Further, Figure 5.25(b)—(d) show the block diagram of the virtual electrochemical NO analyzer, front panel with block diagram of the potential sweep, and front panel with block diagram of the process of the virtual electrochemical NO analyzer. The overall electroanalytical performance of the virtual electrochemical NO analyzer was compared with the standard cyclic voltammetry instrument as shown in Table 5.1. 

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