Application of elimination voltammetry to adsorptive stripping of DNA
Adsorptive stripping voltammetry has been extended by elimination voltammetry with linear scan rate (EVLS). EVLS offers the elimination of selected currents from the linear scan voltammetry results. It can be achieved by an elimination function formed by a linear combination of total currents measured at different scan rates, because the basic idea of elimination of chosen currents (for example the charging current, I-c, the reversible current for substances transported only by linear diffusion, I-r, and the purely kinetic current, I-k) consists of the different dependence of voltammetric current on the scan rare. In this article, the problem of substance adsorption influence on the elimination voltammetry results has been studied. Theoretical curves of an irreversible current with adsorbed substance being electroactive were calculated for three elimination functions. A: the function eliminating I-k and I-c and conserving I-r B: the function eliminating I-c and I-r. conserving I-k; and C: the function eliminating I-r and I-k and conserving I-c, where I-c, I-r, and I-k are the charging current, the reversible diffusion current, and the kinetic current, respectively. A larger difference between diffusion and adsorption was exhibited by the elimination function A. It provides a substantial increase in resolution and sensitivity as compared to the linear scan voltammetry current peak and clearly marks the adsorption. In case of the adsorption of electroactive substances this elimination function A can be useful for analytical applications, particularly for the adsorptive stripping voltammetry with electrochemical irreversible systems. As a practical application, the adsorptive stripping voltammetry of thermally denatured DNA on a hanging mercury electrode has been developed. While the LSV signal of single-stranded DNA at low concentrations gives a slight hint of the cathodic peak (due to the reduction of adenine and cytosine residues), the elimination A provides quite a clear signal in the form of the peak-counterpeak. It is possible to determinate DNA at concentrations below micrograms per milliliter by using this elimination function. The results received by the adsorptive stripping voltammetry in the mode of linear scan (LSV), square-wave (SWV) and elimination with linear scan (EVLS) are discussed.