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A carbon-paste electrode modified with the polymer poly(vinylpyrrolidone) was evaluated through electrochemical studies and the electroanalytical determination of quercetin. For this electrode, cyclic voltammograms of quercetin showed three oxidation peaks at +0.32, +0.78 and +1.04 V. The electro-oxidation associated with the first peak leads to the formation of the corresponding ortho-quinone, which can be reduced under favorable experimental conditions. Under such conditions, the reaction is quasi-reversible and the process is diffusion-controlled. This behavior was exploited for the electroanalytical determination of quercetin by square-wave voltammetry. The calibration curve was linear in the concentration range of 0.5 to 5.5 µmol L-1 (R2 = 0.998). The limits of detection and quantification obtained were 0.17 µmol L-1 and 0.52 µmol L-1, respectively. The sensor was successfully used for the determination of quercetin in a pharmaceutical sample. The accuracy of the results achieved with the sensor was evaluated through comparison with the results provided by the UV-Vis technique.

Determination of Quercetin in a Pharmaceutical Sample by Square-Wave Voltammetry Using a Poly(vinylpyrrolidone)-Modified Carbon-Paste Electrode