Monolithic Column Prepared with UiO-66-2COOH MOF as Monomer for Enrichment and Purification of Ursolic Acid in Plants by Online Solid-Phase Extraction

Abstract

A method for preparing a metal–organic framework (MOF)–polymeric monolith was established by in situ radical polymerization with derivatized UiO-66-2COOH and N-isopropylacrylamide (NIPAAm) as co-monomers. It was worth noting that the obtained monolith possessed characteristics of relatively uniform porous structure and a high surface area (84.16 m2 g−1). The adsorption capacity of the monolith increased from 22.87 to 44.92 mg−1 due to the addition of MOF. The monolith was used as adsorbent and coupled with HPLC for the online purification and extraction of ursolic acid (UA) in medicinal plant. The limit of detection (LOD, S/N = 3) and the limit of quantification (LOQ, S/N = 10) were 0.17 μg mL−1 and 0.57 μg mL−1, respectively; the relative standard deviation (RSD) of intra-day and inter-day assays for five plant samples were 1.00–3.67% and 2.43–5.76%, respectively; a good accuracy was demonstrated by the recovery of 92.2–103.28%. The results indicated that the MOF–polymer monolith was feasible for the online enrichment and purification of UA in plant.