*2.3. Preparation of Bee Pollen Extracts*

In brief, 25 mL of 80% methanol was added to accurately weighed 0.5 g samples of powdered bee pollen in a 50 mL vial. After supersonic extraction for 1.5 h at 4 ◦C, the mixture was kept still for 30 min, followed by 0.22 μm membrane filtration (Shimadzu, Shanghai, China). Tolbutamide and sulfacetamide, at final concentrations of 2 μg/mL and 4 μg/mL, respectively, were added as internal standards for retention time correction.
