Selective extraction of quinolizidine alkaloids from Sophora flavescens Aiton root using tailor-made deep eutectic solvents and magnetic molecularly imprinted polymers

In this study, an eco-friendly extraction method that used tailor-made deep eutectic solvents (DESs) for the extraction of oxymatrine and matrine from Sophora flavescens Aiton root was implemented for the first time. The extraction parameters, including the DES type, DES water content, solid-to-liquid ratio, extraction time, and extraction temperature, which affected the extraction efficiencies of oxymatrine and matrine were optimised. High-performance liquid chromatography with a diode-array detector and quantitative analysis of the DES components was conducted. The highest oxymatrine and matrine extraction yields (21.04 and 1.53 mg·g−1, respectively) were obtained using DES-2 (comprising choline chloride and malonic acid; molar ratio of 1:2) with 50% water and DES-8 (comprising choline chloride and ethylene glycol; molar ratio of 1:2) with 30% water as the extraction solvents, respectively. Furthermore, magnetic molecularly imprinted polymers (MMIPs) were successfully synthesised using oxymatrine, acrylic acid, ethylene glycol dimethylacrylate, azobisisobutyronitrile, and acetonitrile–methylbenzene (3:1, v/v) as the template, functional monomer, cross-linker, initiator, and porogen, respectively. The MMIPs were characterised using transmission electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analyses, and the results demonstrated the successful preparation of MMIPs. The adsorption properties of MMIPs were further analysed using static and dynamic adsorption experiments, and the results indicated that MMIPs presented good adsorption capacities for oxymatrine and matrine (110.8 and 63.4 mg·g−1, respectively). Lastly, MMIPs were used as sorbents for the extraction and enrichment of oxymatrine and matrine from DES extracts of S. flavescens roots. The extraction efficiencies of oxymatrine and matrine (80.21–89.15% and 85.33–95.28%, respectively) were satisfactory. The proposed DES-based extraction followed by MMIPs secondary enrichment appeared to be an effective method for the selective extraction of specific components from complex samples.