Simultaneous determination of two anthraquinone-O-glucosides in five processed pieces from Rheum palamatum Simultaneous determination of two anthraquinone-O-glucosides in five processed pieces from Rheum palamatum Separation and purification of emodin-8-O-β-D-glucopyranoside from Polygoni Cuspidati Rhizoma et Radix by column and high-speed counter-current chromatography Variety regulation of aloe-emodin-3-CH2-O-β-D-glucopyranoside and emodin-8-O-β-D-glucopyranoside in five processed pieces from Rheum palmatum