Rapid separation and enrichment of emodin and rhein in Sanhuang Xiexin Decoction by molecularly imprinted nanoparticles and evaluation of DPP-4 inhibitory activity

To achieve efficient separation of emodin and rhein, a double-template Fe₃O₄-imprinted polymer (DT-MIP@Fe₃O₄) was successfully synthesized. The characterization (FT-IR, XRD, TGA, SEM, TEM, VSM) demonstrated that the synthesized DT-MIP@Fe₃O₄ exhibited a core-shell architecture, exhibiting thermal stability up to 270 °C and superparamagnetic characteristics, facilitating separation in 8 s. This material exhibited significant adsorption capacities (31.7823 mg/g and 15.8942 mg/g) and quick adsorption kinetics (equilibrium achieved within 35 min), coupled with the benefits of facile separation, high selectivity, and exceptional reusability. DT-MIP@Fe₃O₄ was utilized as an adsorbent for magnetic solid-phase extraction (MSPE) in conjunction with high-performance liquid chromatography (HPLC) for the simultaneous separation and detection of emodin and rhein in the Chinese herbal medicine SXD. The optimization of parameters influencing MSPE-HPLC was conducted, such as adsorbent dosage, type and volume of desorbent, desorption time, and salt effect. The established method demonstrated exceptional linearity (R² > 0.9999) across the 0.1–100 mg/L, exhibiting high sensitivity and stability. The limits of detection (LOD) and the limits of quantification (LOQ) were established at 0.0092–0.02 mg/L and 0.0307–0.0668 mg/L, respectively. Moreover, the separated fractions demonstrated remarkable hypoglycemic efficacy by DPP-4 inhibition. These findings confirmed the effectiveness of the strategy and indicated that it has considerable prospects in the rapid separation of rhein and emodin from complex Chinese herbal compound, providing a method for the search of natural DPP-4 inhibitors.