Study on purification of 2,3,5,4′-tetrahydroxy-stilbene-2-O-β-Dglycoside from Polygonum multiflori Determination of 2,3,5,4-tetrahydroxystilbene-2-O-β-D-glucopyranoside and anthraquinon simultaneously in Polygonum multifloriof different growing stage and gathering periods by HPLC