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The electrochemistry of quercetin on a carbon paste electrode in non aqueous and aqueous media has been investigated. Cyclic voltammetric experiments were carried out and the basic electrochemical parameters such as diffusion coefficient, exchange current density and the anodic Tafel slopes were determined. A differential pulse voltammetric procedure was proposed for the determination of quercetin in aqueous solution using a carbon paste electrode, and the detection limit was obtained as 38.5 nM L−1. The electrochemical properties of quercetin were studied using a DNA-modified carbon paste electrode using electrochemical impedance measurements. From spectroelectrochemical measurements it was evident that the hydroxyl groups at the 3′ and 4′ positions were oxidized in the presence of Cu(II) and are responsible for DNA damage. Impedance measurements supported the intercalation of quercetin into the DNA strands.

Bi-film was deposited on the carbon paste electrode and used as the modified electrode in stripping voltammetry. Bi deposition was carried out ex-situ in acetate buffer solution of pH 4.5 under mild stirring conditions. The deposition potential, deposition time and the Bi-concentration in the deposition solution were optimized and the corresponding values are −0.8 V (SCE), 300 s and 0.3 mM Bi-nitrate solution respectively. A substantial enhancement of an order of magnitude in the sensitivity has been observed when carbon paste electrode was modified with nafion coated carbon nano tube on which Bi-film was deposited. This enhanced sensitivity was attributed to the increased active surface area and also the enhanced charge transfer processes which increased the deposition processes and so the stripping current. Effect of different surfactants on the stripping peak of the heavy metal ions is investigated with and without modification by nafion. Detection limits using Bi-film electrode was obtained for Zn, Cd and Pb as 17.3, 16.9, 11.9 μg L−1, respectively, using Bi-film electrode. Analysis result of two water samples and two ayurvedic medicines are reported.