Determinação eletroanalítica de compostos fenólicos utilizando um eletrodo de pasta de carbono modificado com poli(vinilpirrolidona)

Abstract

Abstract : A carbon paste electrode modified with poly (vinylpyrrolidone) polymer was used to study the electrochemical quercetin and kaempferol and the electroanalytical determination of phenol compounds and in pharmaceutical vegetable matrices. About this electrode , cyclic voltammograms of quercetin presented three oxidation peaks located at +0.32 , +0.78 and +1.04 V. The electro-oxidation in the first peak leads to the formation of the corresponding ortho-quinone, which can be reduced in favorable experimental conditions. Under these favorable conditions, the reaction is quasi-reversible, and the process is controlled by diffusion. This behavior has been exploited for the electroanalytical determination of quercetin by square-wave voltammetry. The calibration curve obtained for quercetin was linear in the concentration range from 0.5 to 5.5 mmol L-1 (R2 = 0.998). The limits of detection and quantification were 0.17 ?mol L-1 and 0.52 ?mol L-1, respectively. The sensor was used for the determination of quercetin in pharmaceuticals. The accuracy of the results provided by the sensor was evaluated by comparison with the results obtained by UV-vis technique. The sensor was also applied to study the electrochemical behavior of kaempferol and quantification of phenolic compounds in plant samples. About this electrode, cyclic voltammograms for kaempferol showed only one oxidation peak at +0.58 V and a signal reduction in +0.46 V. Under favorable conditions, the reaction is quasi-reversible, and the process is controlled by diffusion. The calibration curve for the kaempferol showed two linear ranges in concentration ranges of 0.05 to 0.50 ?mol L-1 and 0.50 to 6.0 ?mol L-1 (R2 = 0.980). Using the most sensitive range, the limits of detection and quantification were 45.0 nmol L-1 and 138.0 nmol L-1, respectively. The sensor was applied to the electroanalytical determination of phenolics by square-wave voltammetry compounds in plant samples. The content of total phenolic compounds were expressed in terms of kaempferol (CE)/g of plant in nature mg. The plant that showed a higher content of phenolics was spinach (0.32 mg g-1), followed by the cauliflower (0.29 mg g-1), broccoli (0.21 mg g-1) and, finally, with lower concentrations, chicory (0.08 mg g-1). The accuracy of the results provided by the sensor was evaluated by comparison with the results obtained by Folin-Ciocalteau method.