Electroanalytical techniques chronopotentiometry

Many of the electroanalytical techniques that are routinely employed in conventional solvents, such as, chronoamperometry, chronocoulometry, chronopotentiometry, coulometry, cyclic (stationary electrode) voltammetry, rotating electrode voltammetry, and pulse voltammetry, have also been applied to molten salts. Some of these techniques are discussed next with special attention to their employment in molten salts. References to noteworthy examples appearing in the literature are included. Background information about these techniques is available elsewhere in this book. 

Viscosity. In many applications a low viscosity is desirable so that mass transport by diffusion or convection will extend the time range for mass transport by pure diffusional control to periods as long as 40-50 s, which can be advantageous to electroanalytical techniques such as chronopotentiometry.34 At low temperatures the solvent may not appear to crystallize, but may form a rigid glass whose viscosity is so high that mass transport practically ceases the experimentalist must be alert to this possibility. 

This would suggest that chronopotentiometry could be a sensitive electroanalytical technique. It is rarely used in this context, however, since it is often difficult to determine the transition time accurately, because of double-layer charging at short times and competing reactions at long times. The same limitations apply when one attempts to use Eq. 49K to measure the diffusion coefficient. On the other hand this equation can be used as a quick method of obtaining n,... 

The first group consists of conventional electroanalytical techniques such as cyclic voltammetry (CV), chronoamperometry, chronopotentiometry, coulometry, and electrochemical impedance spectroscopy (EIS), all of which provide general information about the doping process (see also Chapters 4 and 5). Below are listed some typical questions that can be answered using the above group of techniques ... 

Electrochemical biosensors have some advantages over other analytical transducing systems, such as the possibility to operate in turbid media, comparable instrumental sensitivity, and possibility of miniaturization. As a consequence of miniaturization, small sample volume can be required. Modern electroanalytical techniques (i.e., square wave voltammetry, chronopotentiometry, chronoamperometry, differential pulse voltammetry) have very low detection limit (1(T7-10 9 M). In-situ or on-line measurements are both allowed. Furthermore, the equipments required for electrochemical analysis are simple and cheap when compared with most other analytical techniques (2). Basically electrochemical biosensor can be based on amperometric and potentiometric transducers, even if some examples of conductimetric as well as impedimetric biosensor are reported in literature (3-5). 

Electrochemistry involves the study of the relationship between electrical signals and chemical systems that are incorporated into an electrochemical cell. It plays a very important role in many areas of chemistry, including analysis, thermodynamic studies, synthesis, kinetic measurements, energy conversion, and biological electron transport [1]. Electroanalytical techniques such as conductivity, potentiometry, voltammetry, amperometric detection, co-ulometry, measurements of impedance, and chronopotentiometry have been developed for chemical analysis [2], Nowadays, most of the electroanalytical methods are computerized, not only in their instrumental and experimental aspects, but also in the use of powerful methods for data analysis. Chemo-metrics has become a routine method for data analysis in many fields of analytical chemistry that include electroanalytical chemistry [3,4]. 

Oscillographic chronopotentiometry is a new type of electroanalytical technique, developed in the P. R. China [35]. This technique is based on the change of oscillographic signal on the cathode ray oscilloscope. Harr and Daubechies wavelet functions were employed by another group in the P. R. China to de-noise the oscillographic signals of Pb(II) ions in NaOH solution and multi-components systems such as Cu(II) and Al(III) ions in LiCl solution and Cd(II) and In(III) in NaOH solution [34,35]. They found that this... 

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... 

Notwithstanding, the experimental simplicity of chronopotentiometry may still make it a first-choice electroanalytical technique for higher-temperature molten systems. Furthermore, in the current-reversal mode, it is one of only a few diagnostic techniques for assessing the classical reversibility of an electrode process. A recent review has surveyed many of its applications in this context, and so, bearing in mind the authors own interests, it seems appropriate to use examples of chronopotentiometric studies to illustrate some of the present aspects of current interest. 

Stan Van Den Berg is a Professor of Chemical Oceanography at the University of Liverpool. His research interests focus on the chemical specia-tion of trace elements and organic compounds in natural waters and the redox chemistry of metals and sulfides. His research group has pioneered advances in analytical techniques using electroanalytical methods (cathodic stripping voltammetry and chronopotentiometry). Dr. Van Den Berg is a broad-based analytical chemist. 

Current step— The excitation signal used in controlled current techniques in which the potential is measured at a designated time [i]. See also - chronopotentiometry, -> cyclic chronopotentiometry, - staircase voltammetry. Ref. [i] Heineman WR, Kissinger PT (1984) In Kissinger PT, Heine-man WR (eds) Laboratory techniques in electroanalytical chemistry. Marcel Dekker, New York, pp 129-142... 

Basically, experimental approaches to ion transfer kinetics rely on classical galvanostatic [152] or potentiostatic [146] techniques, such as chronopotentiometry [118, 138], chronocoulometry [124], cyclic voltammetry [146], convolution potential sweep voltammetry [147], phase selective ac voltammetry [142], or equilibrium impedance measurements [148]. These techniques were applied mostly to liquid-liquid interfaces with a macroscopic area (typically around 0.1 cm ). However, microelectrode methodology has been successfully introduced into liquid-liquid electrochemistry as a novel electroanalytical tool by Senda and coworkers [153] and... 

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