Efficient protocol for purification of diosgenin and two fatty acids from Rhizoma dioscoreae by SFE coupled with high-speed counter-current chromatography and evaporative light scattering detection.

Supercritical fluid extraction (SFE) was used to extract diosgenin, linoleic acid, and linolenic acid following acid hydrolysis from Rhizoma dioscoreae, a famous traditional Chinese medicine. The process was performed using a preparative SFE system under 35 MPa of pressure, 65 degrees C of temperature, and modified CO(2) with 95% ethanol for 180 min dynamic extraction. Then, the crude extract was successfully isolated and separated by high-speed counter-current chromatography (HSCCC) with evaporative light scattering detection (ELSD). A two-phase solvent system composed of n-hexane/ethyl acetate/methanol/water was used for HSCCC separation in a stepwise elution mode. The upper phase of the solvent system at the volume ratio of 1:1:1.4:0.6 by volume was used as the stationary phase, and the mobile phase after 200 min was changed into the lower phase of the solvent system at the volume ratio of 1:1.2:1.4:0.6 by volume. The separation produced a total of 20.8 mg diosgenin, 12.1 mg linoleic acid, and 18.4 mg linolenic acid from 300 mg crude extract in one-step purification. The purities of the products were 98.9, 99.0, and 99.4%, respectively, as determined by HPLC. Their chemical structures were identified by MS, UV, and the standards.