Covalent organic framework-based monolithic column with hydrophilic and π-π stacking interaction for efficient in-tube solid-phase microextraction of synthetic phenolic antioxidants

Currently, covalent organic framework-based (COF-based) monolithic columns show excellent application potential for high-efficient sorbent in sample preparation. Hydrophobic and π-π stacking interaction were their primary adsorption mechanisms for extraction. Hydrophilic interaction has not been involved yet. Herein, a novel COF-based monolithic column with hydrophilic interaction and π-π stacking interaction has been fabricated by the embedment of COFTAPB-TPA microspheres into urea–formaldehyde resin (UF) monolith. Due to the excellent adhesion performance of UF, the COFTAPB-TPA microspheres could be steadily embedded into the UF monolith. Taking the advantages of the hydrophilic interaction and the π-π stacking interaction between the COFTAPB-TPA@UF monolith and synthetic phenolic antioxidants (SPAs), the COFTAPB-TPA@UF monolith was adopted as efficient sorbent for in-tube SPME of trace SPAs in edible oils. Several SPME parameters, including the percentage of ACN in the sampling solution and eluent, the collection time span, and the pH value of the sampling solution, were optimized for satisfactory SPME performance. Under the optimized conditions, the LODs of the analytes varied from 0.2 to 1.2 ng/mL, and the recoveries ranged from 78.1 % to 98.4 % for sunflower oil samples at three spiked levels, with the RSDs lower than 7.2 %, indicating the superior extraction capacity of the COFTAPB-TPA@UF monolith as well as the promising feasibility of the proposed in-tube SPME-HPLC method. This work lighted a facile way for COF-based monoliths with hydrophilic interaction, and further expanded their applications for sample preparation.