Electroanalytical techniques polarography

Polarography, a well known electroanalytical technique, is currently being used to detn the purity of Tetracene as well as other compds contg nitrate and nitroso groups (Ref 38). 

The main electroanalytical techniques are electrogravimetry, potentiometry (including potentiometric titrations), conductometry, voltammetry/polarography, coulometry and electrochemical detection. Some electroanalytical techniques have become very widely accepted others, such as polarography/voltammetry, less so. Table 8.74 compares the main electroanalytical methods. 

A thorough discussion of electroanalytical techniques, including polarography, voltammetry, and amper-ometry, is given in Chapter 14. An understanding of these would be useful for understanding the amperometric HPLC detector. 

Most of the techniques employed can be traced back to polarography, which was already in use in 1925, to determine the concentrations of organic molecules [3]. Technical developments in instrumentation (potentiostats) [4], the use of nonaque-ous electrolytes [5], and the digital control of experiments [6] led to the spread of electroanalytical techniques. For example, cyclic voltammograms are frequently and routinely used today to define the redox... 

Voltammetry and polarography are dynamic electroanalytical techniques, that is, current flows. A three-electrode cell is needed to allow accurate and simultaneous determination of current and potential. The electrode of interest is the working electrode, with the other two being the reference and counter electrodes. 

In the previous chapter, we discussed dynamic electroanalytical techniques such as polarography and voltammetry. Each technique in that chapter was similar insofar as the principal mode of mass transport was diffusion. Mass transport by migration was minimized by adding an inert ionic salt to the electroanalysis sample and convection was wholly eliminated by keeping the solution still ( quiescent ). ... 

In principle, E° can be determined by the widely used electroanalytical techniques (e.g. polarography, cyclic voltammetry [25]). The combination of the techniques is also useful. It has been demonstrated recently where potentiom-etry, coulometry, and spectrophotometry have been applied [26]. The case of the cyclic voltammetry is examined below. 

Nevertheless, the mid-peak potentials determined by cyclic voltammetry and other characteristic potentials obtained by different electroanalytical techniques (such as pulse, alternating current, or square wave voltammetries) supply valuable information on the behavior of the redox systems. In fact, for the majority of redox reactions, especially for the novel systems, we have only these values. (The cyclic voltammetry almost entirely replaced the polarography which has been used for six decades from 1920. However, the abundant data, especially the half-wave potentials, 1/2, are still very useful sources for providing information on the redox properties of different systems.)... 

Other electroanalytical methods The use of h.v.t. in conjunction with electroanalytical techniques of the potentiometry-polarography type has been described in detail (Kesztelyi, 1984), so that it need not be discussed here. That author, however, ignores a very useful cell for electrosynthesis under vacuum (Schmulbach and Oommen, 1973) and the electrochemical techniques developed by Szwarc and his co-workers and others in the context of anionic polymerisation, which we have mentioned above. 

Detection of impurities and their estimation without separation, e.g. by their effect on colligative properties, or by some kind of spectroscopy, or an electroanalytical technique such as polarography. 

Several types of electroanalytical techniques may be used to gain knowledge concerning the reaction mechanism of an electrolytic reaction and to determine the optimal conditions for an electrosynthesis. The use of classical polarography was illustrated in part I.1 The different electroanalytical techniques have been treated comprehensively in a monograph,9 and the use of... 

G. J. Patriarche, M. Chateau-Gosselin, J. L. Vandenbalck, and P. Zuman, "Polarography and Related Electroanalytical Techniques in Pharmacy... 

Refs. [i] Kolthoff IM, Lingane JJ (1952) 2nd edn. Polarography. Polarographic analysis and voltammetry. Amperometic titrations. Interscience, New York, vol. 2, pp 887 [ii] Heyrovsky J, Kuta J (1966) Principles of polarography. Academic Press, New York, pp 267 [Hi] Classification and nomenclature of electroanalytical techniques (1976) Pure Appl Chem 45 81 [iv] Bard AJ, Faulkner LR (2001) Electrochemical methods, 2nd edn. Wiley, New York, pp 437... 

A more informative electroanalytical technique for investigation of adsorption processes is -> AC polarography, which among other information enables distinguishing between adsorption of the oxidized, the reduced form, or of both. 

Lingane was a leader in the field of - electro analytical chemistry and wrote, with Kolthoff, the definitive, two volume monograph, Polarography [i] that remains a useful reference work. He also helped develop other electroanalytical techniques, like controlled potential electrolysis, -> coulometry, -> coulometric titrations, and developed an early electromechanical (Lingane-Jones) potentiostat, He wrote the widely-used monograph in this field, Electroanalytical Chemistry (1st edn., 1953 2nd edn., 1958). Lingane received a number of awards, including the Analytical Chemistry (Fisher) Award of the American Chemical Society in 1958. Many of his Ph.D. students, e.g., -> Meites, Fred Anson, Allen Bard, Dennis Peters, and Dennis Evans, went on to academic careers in electrochemistry. 

Before embarking on an electrosynthesis it is desirable to know the potential at which the desired reaction is expected to occur. That information can be obtained from electroanalytical techniques, such as polarography and cyclic voltammetry. ... 

The results were summarized by Fichter in his useful book Organische Elektrochemie in 1942. This development took place along with the invention of new electroanalytical techniques for the study of electrode processes, for instance, polarography at the dropping mercury electrode introduced by Heyrovsky in the early 1920s. Other important contributions were made by Lingane, Kolthoff, Laitinen, and Delahay. 

Metallothioneins (MT), low molar mass proteins, have been studied electrochemically alone and in the presence of Cd(II) and Zn(II) ions [110-115]. The electrochemical behavior of zinc MTs from rabbit liver, with respect to solution pH, as well as the influence of the addition of zinc [116] and also zinc MT from rat liver, was investigated [117] using electroanalytical techniques. Studies of complexing properties of the alpha-MT with Zn(II) were carried out using differential pulse polarography [118]. 

Electrochemical methods of analysis have grown greatly in application and importance over the last 40 years, and this has been largely due to the development and improvement of electronic systems permitting refinements in the measurement of the critical characteristics mentioned in the foregoing. In addition to this, the measurement systems and the advanced electronics now permit much of the work in electroanalytical chemistry to be automated and controlled by microprocessors or computers. Some electroanalytical techniques have become very widely accepted others, such as polarography/voltammetry, less so. This has been due to early problems with equipment. Despite the fact... 

This broad spectrum of analytical problems can be solved by electroanalytical techniques as will be shown with the following results. The use of electroanalytical methods in polymer research is often restricted to direct current polarography and this paper lays emphasis on the demonstration of the application of other methods. Showing the applicability of electroanalytical methods in polymer research might initiate further work in this field to get a widespread use of these methods in polymer science. 

Each electroanalytical technique has certain characteristic potentials, which can be derived from the measured curves. These are the half-wave potential in direct current polarography (DCP), the peak potentials in cyclic voltammetry (CV), the mid-peak potential in cyclic voltammetry, and the peak potential in differential pulse voltammetry (DPV) and square-wave voltammetry. In the case of electrochemical reversibility (see Chap. 1.3) all these characteristic potentials are interrelated and it is important to know their relationship to the standard and formal potential of the redox system. Here follows a brief summary of the most important characteristic potentials. 

Anodic stripping voltammetry, potentiometric stripping voltametry, and differential pulse polarography are used for the simultaneous determination of up to 10 analytes at extremely low concentrations (detection limits <0.01 pgl ). Electroanalytical techniques are applicable for 30 elements. Stripping analysis allows differentiation between chemical forms but is subject to interference from adsorption... 

Quite a variety of electroanalytical techniques have been used in chloroaluminate melts, dating back to 1942, when Yntema et al. (38) determined deposition potentials for a number of metal ions. Polarography with the dropping mercury electrode was described by Saito et al. in 1962 (39), and numerous papers on steady state... 

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