Spectrometric pK Determination of Daphnetin, Chlorogenic Acid and Quercetin

Abstract Daphnetin, Chlorogenic Acid, Quercetin Polyphenols play an important role in the ‘immune system’ of plants. Since their charge is important for their physiological effect it is important to know their pKj values. Therefore, the pKj values of some plant contents such as daphnetin (pK = 7.36), chlorogenic acid (pK ≈ 8.5), and quercetin (pK1 = 7.03, pfro = 9.15) were determined in the pH range 7 -10 using UV/VIS spectroscopy. The decomposition kinetics of quercetin in alkaline solutions was taken into consideration by extrapolating the absorbance time curves to time zero (t = 0). The graphic method of absorbance (A) diagrams was used to determine the pKi values. In the case of quercetin the method of linear regression was also used for the determination.