Selective enrichment of licorice triterpenoid saponins from complicated samples by magnetic poly(ionic liquid)-functionalized metal-organic framework

Licorice is a frequently-used natural sweetener and herbal medicine, and triterpenoid saponins are the main sweet constituents. This study provided a novel method for selective enrichment of licorice triterpenoid saponins by Fe3O4@UiO-66-(SH)2@p[VBAI]Cl, a new magnetic poly(ionic liquid)-functionalized metal-organic framework composite. Triterpenoid saponins had strong electrostatic interactions with p[VBAI]Cl, namely poly[1-(4-vinyl)benzyl-3-alkylimidazolium chloride], and UiO-66-(SH)2 further increased the adsorption ability. Fe3O4@UiO-66-(SH)2@p[VBAI]Cl could selectively enrich triterpenoid saponins from licorice-containing commercial products and plasma/tissue samples after oral consumption, and enrichment conditions were optimized with the representative compound glycyrrhizic acid. Based on this, two quantitative analysis methods were established combined with HPLC and LC-MS analysis, respectively, which were used to efficiently determine triterpenoid saponin content in in vitro and in vivo samples. The achieved LC-MS detection sensitivity was higher than previous studies. This is the first study for selective enrichment of natural products by poly(ionic liquid)-based magnetic solid phase extraction, and the method can contribute to quality assessment and mechanistic study of licorice.