Abstract: The effect of secondary gradient crystallizing pressure, temperature and time on the purity and the crystallization ratio of andrographolide was investigated via single factor experiments. The shape of crystal was observed with scanning electron microscopy (SEM). The purity of andrographolide was determined by high pressure liquid chromatography (HPLC). The result showed that the optimum parameters were pressure 14 MPa, temperature 55℃, time 60 min, and under these conditions the particle of andrographolide was much smaller, the crystal of andrographolide was distributed in floccule on crystal board, the purity of andrographolide was 92.5%, the crystallization ratio was 48.9%.

Key words: Supercritical carbon dioxide, Secondary gradient crystallization, Andrographolide, Scanning electron microscopy(SEM), High pressure liquid chromatography(HPLC)