Derivative methods: chronopotentiometr

A chronopotentiometric method for determination of amino derivatives of PAH is based on the high affinity of DNA for such compounds. In a cell consisting of a DNA-modified CPE, a reference SSCE and a Pt wire auxiliary electrode, an aqueous solution of the PAA is submitted to an accumulation period, during which the analytes are transferred to the working electrode by an intercalation mechanism, after which the solution is changed... 

Consider a chronopotentiometric experiment dealing with two components that are reversibly reduced in waves separated by 500 mV. Derive an expression for the second transition time in an experiment carried out in a thin-layer cell. Compare and contrast the properties of multicomponent systems in thin-layer chronopotentiometry with those of the semi-infinite method. 

This case for the chronopotentiometric method was treated in Section 12.2.2, and the zones for pure diffusion behavior (DP) and pure kinetic behavior (KP) were derived in terms of the dimensionless kinetic parameter A (Table 12.3.1) DP, A < O.T, KP, A > 5 (Figure 12.2.1). These zones generally apply with the other techniques as well. 

Laviron55 has recently noted that linear potential sweep or cyclic voltammetry does not appear to be the best method to determine the diffusion coefficient D of species migrating through a layer of finite thickness since measurements are based on the shape of the curves, which in turn depend on the rate of electron exchange with the electrode and on the uncompensated ohmic drop in the film. It has been established that chronopotentiometric transition times or current-time curves obtained when the potential is stepped well beyond the reduction or oxidation potential are not influenced by these factors.55 An expression for the chronopotentiometric transition has been derived for thin layer cells.66 Laviron55 has shown that for a space distributed redox electrode of thickness L, the transition time (r) is given implicitly by an expression of the form... 

Several precautions and limitations should be mentioned upon the application of chronopotentiometry as an electrochemical method to analyze interface properties of layered-modified-electrodes, and, specifically, monolayer-function-alized-electrodes (1) The chronopotentiometric pulse results in a potential shift on the electrode after the transition-time, x, resulting in the discharge of the electrolyte. This potential shift often ruins the chemically functionalized layer on the electrode (e.g., thiolated monolayers on Au-electrodes). Thus, it is essential to terminate the chronopotentiometric pulse at shorter time-intervals than the transition time, X, in order to eliminate the destruction of the functionalized electrode. (2) The electrode resistance, R, values derived from the chronopotentiometric exper-... 

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