Molecularly imprinted polymer for solid-phase extraction of oleanolic acid from Ligustrum lucidum fruit

A molecularly imprinted polymer (MIP) was synthesized for the selective extraction of oleanolic acid (OA), employing OA as the template molecule, acrylamide as the functional monomer, ethylene glycol dimethacrylate as the cross-linking agent, azobisisobutyronitrile as the initiator, and chloroform as the porogenic solvent. The characterization of the obtained MIPs was evaluated by scanning electron microscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller (BET) analysis and X-ray photoelectron spectroscopy. The MIPs reached adsorption equilibrium within 2 hours to OA, with high adsorption capacity of 124.68 mg/g. Subsequently, these MIPs were packed in empty solid-phase extraction (SPE) cartridge to enrichment OA from Ligustrum lucidum fruit extract. The parameters of SPE were optimized as follows: loading 0.5 ml of a 1.0 mg/ml OA reference solution, washing with 0.5 ml of toluene, and eluting with 4 ml of methanol. Under these conditions, the enrichment rate of OA from L. lucidum extract reached 76.0%. Additionally, an high-performance liquid chromatography method for determining OA content was validated. This study provides an effective approach for the separation and enrichment of OA from complex matrices and also provides practical feasibility for the separation and enrichment of other triterpenoids.