Shell thickness controlled hydrophilic magnetic molecularly imprinted resins for high-efficient extraction of benzoic acids in aqueous samples.

Hydrophilic magnetic molecular imprinted resins (MMIRs) were firstly fabricated by one-pot copolycondensation of resorcinol, melamine, and formaldehyde in the pores of Fe3O4 @mSiO2. The porous structure of mSiO2 limited copolycondensation. After the removal of mSiO2, controllable imprinting shell thickness (about 5 nm) was formed, reducing the probability of embedded sites, favoring the efficient adsorption. Moreover, the reaction time (3 h) was just 1/5-1/8 of those synthesized by conventional heating method. The transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), vibrating sample magnetometer (VSM), thermo-gravimetric analysis (TGA), water contact angle analysis, and Brunauer‒Emmett‒Teller (BET) analysis indicated the successful preparation of MMIRs with excellent hydrophilic property, and magnetic separation characteristics. Steady-state adsorption studies showed that the resultant MMIRs had specific recognition for benzoic acids, GA, protocatechuic acid (PCA), vanillic acid (VA), 4-hydroxybenzoic acid (4-HBA), salicylic acid (SA), and benzoic acid (BA). MMIRs combination with high-performance liquid chromatography-ultraviolet (HPLC-UV) were then directly used for selective extraction and determination of benzoic acids in river water, fruit juices, and human serum. Obtained limits of detection (LOD) and recoveries were in the range of 0.02-1.0 μg/mL, and 81.8-108.7%, respectively, and the batch-to-batch relative standard deviation (RSD) was 5.9%. The proposed strategy showed excellent hydrophilicity and specificity, which was promising for detection of benzoic acids in real aqueous samples.