Analytical solution chronoamperometry

A. Molina, C. Serna, and J. Gonzalez. General analytical solution for a catalytic mechanism in potential step techniques at hemispherical microelectrodes Apphcations to chronoamperometry, cyclic staircase voltammetry and cyclic linear sweep voltammetry, J. Electroanal. Chem. 454, 15-31 (1998). 

The chronoamperometric technique illustrates the principle that analytically useful current responses depend critically on the efficiency of analyte mass transport within the solution. The analyte mass transport in turn depends on the efficiency with which an appHed voltage can maintain the surface concentrations of oxidized and reduced species at values specified by the Nemst equation. It is generally the case in chronoamperometry that the bulk concentration of one of the species is zero whereas the surface concentration of the other species is forced to zero by the appHed potential, but this is not always so. 

Electroanalytical techniques, such as conductometry [174], potentiometry [22], voltammetry [6], chronoamperometry [25] and EIS [175], have been used extensively for transduction of the detection signal in the MIP-based chemosensors. The chemosensor response may be due to different interfacial phenomena occurring at the electrode-electrolyte interface [16], which will be discussed below in the respective sections. The electrochemical transduction scheme can be devised for accurate measurements tailored to the analytes exhibiting either faradic or non-faradic electrode behaviour. In many instances, the detection medium is an inert buffer solution [24]. In order to enhance the chemosensor response, some of the... 

This procedure can be applied irrespectively of whether the analyte is electroactive or electroinactive (Case b in Scheme 4). Here, the template is removed from the MIP film with a suitable solvent solution. Next, the chemosensor with template-free MIP is immersed in the test solution for analyte preconcentration. Analyte determination can be carried out with the chemosensor in the same test solution. Alternately, the determination can be performed in another solution. For an electroactive analyte, the chemosensor is removed from the test solution (after preconcentration) and transferred to a blank electrolyte solution followed by the analyte determination. In the case of an electroinactive analyte, the chemosensor is transferred to solution of an electroactive competitor for displacement of this analyte from the MIP film. All the electrochemical transductions, i.e. conductometric, impedimetric, potentiometric, chronoamperometric and voltammetric, are operative under this scheme. In particular, voltammetry and chronoamperometry can be used for determination of both electroactive and electroinactive analytes. This approach as well as the relevant experimental design will be elaborately discussed below in the same section. 

Case a in Scheme 6. MIP particles are mixed with both the analyte and electroactive competitor, and allowed to reach equilibration. Subsequently, the mixture is centrifuged. The unbound electroactive competitor in the supernatant solution is detected using voltammetry or chronoamperometry with a template-free MIP chemosensor. 

The Cottrell equation is derived from Pick s second law of diffusion (Section 1.5) and predicts the variation of the current in time, when a potential step is applied under conditions of large overpotential. For this equation to be valid the current must be limited by diffusion of the analyte to the electrode surface, and thus the solution has to be unstirred. The overpotential at which the reaction is driven must be large enough to ensure the rapid depletion of the electroactive species (O) at the electrode surface, such that the process would be controlled by the diffusion to the electrode. This equation is most often applied to potential step methods (e.g., chronoamperometry see Chapter 11) ... 

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