The cartridge was washed first with 0.1 mol/L
HCl (5 mL) and the phenolic compounds were then eluted with
2.0 mL of aqueous methanol (1:9 v/v). The solution was evaporated
to dryness. The dry residue was dissolved in 2.00 mL
methanol. The obtained solution was divided for further analyses.
For HPLC analysis, internal standard (IS) 150 mL was added and the
volume was made up to 2.00 mL with methanol and was then
analyzed by HPLC after filtering through a 0.2 mm nylon filter. For
the determination of total phenolic compounds, total flavonoid
and antioxidant activity, the solution was diluted with methanol
to the final volume of 10.00 mL before analysis. All analyses were
performed in triplicate