Hierarchically Micro- and Mesoporous Metal-Organic Framework-Based Magnetic Nanospheres for Nontargeted Analysis of Chemical Hazards in Vegetables

Sample purification is vital for the non-targeted screening of chemical hazards in foods, which requires high removal efficiency for interferences and high recoveries for chemical hazards during sample preparation. Phytochromes are primary interferences for screening hazards in vegetables. Hierarchically porous materials with controlled porosity show great potential in the selective adsorption of size-matched molecules. For sample pretreatment, both complex matrix-processing capacity and mass transfer efficiency are important. Here we fabricate a hierarchical micro- and mesoporous metal–organic framework-based magnetic nanosphere by the self-assembly of framework-building blocks in the presence of surfactant micelles on the surface of Fe3O4 nanoparticles (H-MOF@Fe3O4). By controlling the layer of MOFs on the surface of Fe3O4 nanoparticles, the removal efficiency for phytochromes in vegetables and material consumption achieve the optimal, when the layer number is 6. It was proved that our nanospheres show preferable stabilities in both organic solvents and water with excellent reusability. Complete removal of phytochromes and satisfactory recoveries (70–120%, n = 5, RSDs <17%) of 227 (10 μg kg−1) and 246 (100 μg kg−1) out of 258 chemical hazards at two spiked levels were achieved. The limit of quantification (LOQs) for 258 chemical hazards was 10 μg kg−1. The porous filling effect is the main adsorption mechanism of phytochromes. Such versatile nanospheres may bring opportunities to the next generation of sample pretreatment materials for the nontargeted analysis of chemical hazards in many fields such as food safety and integrity, and environment monitoring.