Synthesis of polydopamine coated magnetic halloysite nanotubes for fast enrichment and extraction of anthraquinones in brewed slimming tea

In this work, a magnetic halloysite nanotubes composite material modified with polydopamine (MHNTs@PDA) was synthesized through a facile and green synthesis strategy, and employed as an efficient adsorbent for magnetic solid-phase extraction (MSPE) of three anthraquinones. The material showed very fast adsorption ability (adsorption time of 3 min), good reusability and strong magnetic response. The main parameters affecting the extraction efficiency of MSPE, including adsorption time, amounts of adsorbent, sample pH, salt concentration and desorption conditions, were investigated and optimized. By coupling MHNTs@PDA-based MSPE with HPLC-UV, the method exhibited good linearity (R 2  ≥ 0.9944) in the concentration range of 5–1000 μg L -1 and low limits of detection (1.0–1.5 μg L -1 ) for anthraquinones. Finally, the developed method was successfully applied to determine anthraquinones in brewed slimming tea, and the obtained recoveries were in the range of 73.5–119.1%, with RSD less than 9.7%.