An Agilent 1260 HPLC Diamonsi IC18 (2.1 mm × 150 mm × 5 μm) was used in the analysis. The mobile phase consisted of methanol (solvent A) and pure water (solvent B), and the flow rate was set at 0.80 mL/min. The optimal gradient program started with 50 % methanol at the time of injection and increased linearly to 70 % methanol over 2 min, which was maintained for 5 min. Subsequently, the gradient was increased linearly to 90 % methanol over 2 min and held for 5 min, followed by a decrease back to 50 % acetonitrile over 0.1 min and held for another 5 min until the next injection. The temperature of the column oven was maintained at 30 °C, and the sample injection volume was 5 μL. The detection wavelengths used for catechin and quercetin were λ1 = 270 nm and λ2 = 368 nm, respectively.
The MS analysis was performed using the Agilent 1100 series ion trap mass spectrometer with an electrospray ionization source in the positive ion detection mode. The following parameters were used: spray voltage, 4,000 V; ionization temperature, 350 °C; atomizer pressure, 35 psi; nitrogen flow rate, 8 L/min; and mass scan range, 200 – 800 m/z.
The MS analysis was performed using the Agilent 1100 series ion trap mass spectrometer with an electrospray ionization source in the positive ion detection mode. The following parameters were used: spray voltage, 4,000 V; ionization temperature, 350 °C; atomizer pressure, 35 psi; nitrogen flow rate, 8 L/min; and mass scan range, 200 – 800 m/z.