Materials
Standards of andrographolide, AP1 (purity = 100.00%); 14-deoxy-11, 12-didehydroandrographolide, AP3 (purity = 99.80%); neoandrographolide, AP4 (purity = 99.67%); and 14-deoxyandrographolide, AP6 (purity = 100.00%) were supplied by Phytolab GmbH & Co.KG (Vestenbergsgreuth, Germany). The internal standard (IS) of digoxin (purity = 96.6%) was purchased from Sigma-Aldrich (St. Louis, MO, USA). The tested product, For enzymatic digestion, 