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Electrochemical characterization of p-hydroxybenzoic acid

The aim of this master thesis was to examine the electrochemical properties of phydroxybenzoic acid in buffers of certain pH values and properties of real samples using differential pulse and cyclic voltammetry. The impact of pH on the oxidation peak potential was examined as well as the effect of concentration and scan rate on the oxido-reduction properties of p-hydroxybenzoic acid. Measurements were performed by using the PalmSens potentiostat/galvanostat. The three-electrode voltammetric system consists of a working glassy carbon electrode (GC), reference (Ag/AgCl) electrode, and counter electrode platinum wire. Before each measurement, the system was purged with high purity argon (ΦAr = 99.999 %). Cyclic voltammetry showed one oxidation and one reduction peak which corresponds to oxidation of the hydroxyl group and reduction of an oxidation product of p-hydroxybenzoic acid. Both peaks have increased with the increase of scan rate. It was also determined that the oxidation process was diffusion-controlled. The adsorption of p-hydroxybenzoic acid on the working electrode surface was determined by differential pulse voltammetry. The solution stability with time and the effect of pH on the oxidation peak current was determined. The optimal pH value for oxidation of p-hydroxybenzoic acid was pH = 6 for the glassy carbon electrode. It was determined that with an increase of concentraction of p-hydroxybenzoic acid the oxidation peak current also increased. Concentration of p-hydroxybenozic acid was determined in real samples (grapes, white wine, coconut milk, and dry coconut) and it varied from 1.4 μM to 7.6 μM.

p-hidroxybenzoic acid, cyclic voltammetry, differential pulse voltammetry

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