Preparative separation of four triterpene saponins from radix astragali by high-speed counter-current chromatography coupled with evaporative light scattering detection

Four triterpene saponins, including astragaloside IV, astragaloside II, astragaloside I and acetylastragaloside I, were successfully isolated and separated by high-speed counter-current chromatography coupled with evaporative light scattering detection from Radix Astragali using stepwise elution with a pair of solvent systems composed of n-hexane:ethyl acetate:ethanol:water in volume ratios of 1:0.6:0.6:1 and 1:1:1:1 (by volume). The isolation produced 26.5 mg astragaloside IV, 28.2 mg astragaloside II, 48.7 mg astragaloside I and 17.6 mg acetylastragaloside I with purities of 97.6, 96.4, 98.8 and 96.8%, respectively, determined by high-performance liquid chromatography from 250 mg crude extract. The chemical structures of the isolated compounds were identified by UV, NMR and MS, and confirmed by authentic standards.