The separation and purification of quercetin and other components in sophora japonica extract is a crucial step in modern research on traditional Chinese medicine. Its core lies in achieving efficient enrichment and high-purity preparation of target components through advanced technologies. This process must balance selectivity, yield, and purity while avoiding degradation or structural damage to active ingredients. The following systematically elaborates on the key technical system for the separation and purification of sophora japonica extract from the perspectives of technical principles and applications.
Column chromatography is a classic method for quercetin separation. Its principle is based on the difference in partition coefficients between the stationary and mobile phases of different components. For sophora japonica extract, silica gel, alumina, or polyamide are commonly used as the stationary phase, with gradient elution using mixed solvents such as chloroform-methanol or ethyl acetate-methanol as the mobile phase. Because quercetin contains multiple phenolic hydroxyl groups, it interacts strongly with polar stationary phases. Separation from other flavonoids (such as rutin) can be achieved by adjusting the solvent polarity. In recent years, high-speed countercurrent chromatography (HSCCC) has been widely used for the separation of sophora japonica flavonoids because it eliminates the need for a solid stationary phase and avoids sample adsorption loss. This technology utilizes the density difference of a two-phase solvent system to achieve continuous separation. By optimizing the solvent ratio (e.g., a hexane-ethyl acetate-ethanol-water system), high-purity quercetin can be prepared from crude extract in one step.
Preparative high-performance liquid chromatography (Prep-HPLC) is the core technology for obtaining high-purity quercetin monomers. It uses high pressure to deliver the mobile phase, enabling rapid separation of samples in a column packed with a micron-sized stationary phase. For sophora japonica extract, a C18 reversed-phase column is commonly used, with methanol-water or acetonitrile-water as the mobile phase. A UV detector monitors the target peak in real time, achieving precise separation of quercetin from other impurities. This technology offers advantages such as high separation efficiency, good repeatability, and high automation, making it particularly suitable for laboratory-scale high-purity preparation.
Macroporous adsorption resin methods, due to their good selectivity, large adsorption capacity, and easy regeneration, have become a commonly used method for enriching total flavonoids from Sophora japonica flowers. This technology selectively adsorbs flavonoids through physical adsorption via resin pore size and surface functional groups, while excluding large molecular impurities such as sugars and proteins. For quercetin, resins with suitable affinity for phenolic hydroxyl groups (such as D101 and AB-8 types) must be selected, and efficient enrichment is achieved by optimizing the loading concentration, pH value, and elution solvent (such as 70% ethanol). This method can significantly increase the relative content of flavonoids in the extract, laying the foundation for subsequent purification steps.
Membrane separation technology achieves the separation of components with different molecular weights through the selective retention of membrane pore size. In the treatment of sophora japonica extract, ultrafiltration membranes (molecular weight cutoff 10,000-30,000 Da) can remove large molecular impurities (such as polysaccharides and proteins), while nanofiltration membranes (molecular weight cutoff 200-1,000 Da) can concentrate small flavonoid components. This technology has the advantages of mild operation, low energy consumption, and no phase change, and is particularly suitable for the separation of heat-sensitive components, effectively preserving the biological activity of quercetin. Crystallization and recrystallization are key steps in quercetin purification. By controlling the type, temperature, and concentration of solvent, quercetin is precipitated from solution in crystalline form. For example, crude quercetin is dissolved in hot ethanol, and after slow cooling, quercetin crystallizes due to decreased solubility, while impurities remain in the mother liquor. Repeating this process can further improve purity. Furthermore, adding seed crystals or adjusting solvent polarity (e.g., adding a small amount of water) can optimize crystal morphology, reduce impurity encapsulation, and improve product quality.
Ionic liquids, as novel green solvents, exhibit unique advantages in the separation of flavonoids from Sophora japonica. They achieve selective extraction by forming hydrogen bonds or ionic interactions with the target component. For example, ionic liquids containing imidazole rings can efficiently dissolve quercetin, while adjusting the hydrophobicity of the ionic liquid or adding an antisolvent (such as water) can achieve precipitation separation of quercetin. This method features solvent recovery and simple operation, providing a new approach for the green preparation of quercetin.
Enzymatic hydrolysis-assisted extraction technology utilizes specific enzymes to disrupt cell wall structures, promoting the release of quercetin. For example, cellulase can degrade cellulose in the cell walls of Sophora japonica flowers, increasing the dissolution of intracellular components; while pectinase can break down pectin in the intercellular matrix, improving extraction efficiency. Furthermore, using β-glucosidase to hydrolyze rutin (quercetin-3-O-rutin glycoside) to quercetin can significantly increase the quercetin content in the extract. Enzymatic hydrolysis offers advantages such as mild conditions and high selectivity, making it particularly suitable for scenarios where traditional solvent extraction is inefficient.
