2.2 Sample preparation
Fifteen grams of rhubarb were immersed in 150 mL distilled water for 1 h and refluxed for 40 min at 100 ºC. The aqueous extract was filtered, and the residue was refluxed for 20 min with another 150 mL distilled water under the same conditions. The two water extracts were combined and condensed to 100 mL and stored at 4 ºC until use.