2.8. Determination of flavonoids
The percentage of flavonoids was measured using rutin as a reference (State Pharmacopoeia of USSR., 1989). One millilitre of plant
extract solution in 95% ethanol (10 g/l) and 1 ml of aluminium trichloride solution in 95% ethanol (20 g/l) were pipetted into a
25 ml volumetric flask and made up to volume with 95% ethanol.
The absorbance was read at 415 nm after 40 min at 20C. Blank
samples were prepared from the mixture of 1 ml of plant extract
and one drop of diluted acetic acid. The absorbance of a reference
solution, which was prepared by using 1 ml of rutin solution instead
of plant extract, was read simultaneously. Rutin solution was prepared from 0.05 g of dried at 130–150C for 3 h rutin, which was diluted in 100 ml of 95% ethanol. All determinations were performed
in triplicate. The percentage of flavonoids in plant extracts was calculated by formula:X=(Amo10010)/(Aom100), where
Ais the absorbance of extract;Aois the absorbance of rutin;mis the
weight of pure extract (g);mois the weight of rutin (g).