Chronopotentiometry instrumentation

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]. 

Integration of equation (1.48) with initial and boundary conditions appropriate to the particular experiment is the basis of the theory of instrumental methods such as chronopotentiometry, chronoamperometry and cyclic voltammetry. The first law applied at the electrode surface, x = 0, is used to relate the current to the chemical... 

Various electrochemical methods have been appfied for the analysis of NAs, including DPP [5, 11] and DPV[13, 269, 270], linear sweep and CV [13, 271] square wave [138] and a.c. voltammetry [272-274], and recently constant current chronopotentiometry [249, 255-257, 275, 276] and elimination voltammetry [139, 277-279]. DPP was applied for the analysis of DNA in 1966 [280], and in a short time, it replaced OP and d.c. po-larography used in the early NA studies [4, 5]. The main advantage of DPP is its better sensitivity and resolution of peaks. Calf thymus ssDNA produced a well-developed DPP peak III (Fig. 6d) at concentrations of about 10 to 20 igml while dsDNA was inactive at the same concentration. At higher concentrations (hundreds of pgml ), dsDNA produced peak II at potentials by about 70 mV more positive than peak III (Fig. 6c). For years, DPP was the most sensitive instrumental method of determination of traces of ssDNA in dsDNA samples [5]. 

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... 

The instrument should be capable of performing all the classic electrochemical methods such as cyclic voltammetry, potentiometry, chronoamperometry, chronopotentiometry, etc., and additionally modem thermoelectrochemical methods such as temperature pulse voltammetry. 

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