Application of accelerated solvent extraction coupled with counter-current chromatography to extraction and online isolation of saponins with a broad range of polarity from Panax notoginseng

Abstract

Accelerated solvent extraction (ASE) coupled with high-performance counter-current chromatography (HPCCC) was successfully used for the structural modification, extraction and online isolation of the saponins with a wide range of polarity from Panax notoginseng by one extraction–separation operation with three stages. At the first stage, the upper phase of the solvent system of ethyl acetate–n-butanol–water (1:1:2 or 1.2:1:2, v:v:v) or ethyl acetate–n-butanol–methanol–water (3:5:1.5:6, v:v:v:v) was used as both the ASE solvent and HPCCC stationary phase (extracted at 60°C), and the polar target compounds which pumped in the CCC column were eluted with the corresponding lower phase of the solvent system mentioned above. At the second stage, the upper phases of the solvent system of ethyl acetate–n-butanol–methanol–water (6:3:2:6 or 7:3:2:7, v:v:v:v) was used as both the ASE solvent and HPCCC stationary phase (extracted at 115°C), and the target moderate polar compounds were eluted with the corresponding lower phase of the solvent system. Finally, the upper phase of the solvent system of n-hexane–n-butanol–methanol–water (8:2:2:8, v:v:v:v) or n-hexane–ethyl acetate–n-butanol–methanol–water (0.2:10:0.5:1.5:8, v:v:v:v:v) was used as both the ASE solvent and HPCCC stationary phase (extracted at 135°C), and the target low polar compounds were eluted with the corresponding lower phase of the solvent system. More than nine pure compounds including notoginsenosides R6, R1, Spt1 and ginsenosides Rb1, F4, Rh3, Rg3, Rs3 and Rk1 with a wide range of polarity were successfully separated via the seven sets of solvent systems in one extraction–separation operation within 400min. The compounds separated by ASE/HPCCC were identified by HPLC/MS/MS and NMR.