High-performance liquid chromatography (HPLC) analysis

The concentration of quercetin was determined by an HPLC apparatus (DIONEX Ultimate 3000, Germering, Germany). A Symmetry C18 column (4.6 mm × 250 mm, 5 mm; Agilent Technologies, San Deigo, IL) was used for chromatographic separation at 30 °C. The mobile phase was composed of acetonitrile and 0.1% formic acid (40:60, v/v). The flow rate was 0.8 mL/min. The UV detection wavelength was 366 nm (UV detector, DIONEX, Sunnyvale, CA).

The methods provided good linearity (R² = 0.9996) over a concentration range of 2–200 µg/mL with the intra-day and inter-day precision of less than 2.0% and 1.0%, respectively, and LOQ of 200 ng/mL.