Kinetic-fluorimetric determination of flavonoids at the nanomole level

Abstract

A kinetic-fluorimetric method is proposed for the determination of flavonoids. The method is based on the activating effect of flavonoids on the aerobic oxidation of 2-hydroxynaphthaldehyde thiosemicarbazone in the presence of manganese(II), which acts as a catalyst. The reaction is monitored spectrofluorimetrically by measuring the initial rate at the excitation and emission wavelengths of the oxidation product. The concentration ranges for the determination of different flavonoids are some of the lowest achieved so far (e.g., a linear calibration graph is obtained for quercetin from 0.25 to 12.5 µM). The reactivities of 14 flavonoids have been studied, showing a relationship between the structure and reactivity of the flavonoids. This relationship is similar to that obtained in mutagenesis tests. The kinetic-fluorimetric method has also been applied to the determination of flavonoids in tea and red wine by using fecalase and hesperidinase.