ABSTRACT
Two different approaches were evaluated and used to estimate the aqueous pK(a) values of some flavonols sparingly soluble in water (morin, fisetin and quercetin) from their pK(a) values in methanol/water mixtures obtained by potentiometry. Both approaches lead to similar results, although one of them requires only one pK(a) value at one unique methanol/water mixture, whereas the other (the classical Yasuda-Shedlovsky plot) requires several pK(a) data at different methanol/water mixtures. Thus, the first approach is recommended because it is faster and simpler. The automated potentiometric method is strongly recommended for pK(a) determination of these types of compounds because of its simplicity and speed of operation.
ABSTRACT
A fast RP-HPLC method for the simultaneous separation of eleven main flavonoid aglycones in food samples was developed. Flavonoids were divided in three groups according to their hydrophobicity and were resolved by a ternary gradient elution and diode array detection within analysis times less than 15 min. The detection limits of the flavonoids studied were in the range between 0.04 and 0.31 microg/mL, with repeatabilities values between 0.4 and 5%. The method was successfully applied to the analysis of these compounds in complex natural samples, like propolis and Ginkgo biloba.
