Construction of highly hydrophilic carbamide-linked covalent organic framework for efficient extraction of polar...

Covalent organic frameworks (COFs) have attracted much attention in the field of sample pretreatment due to their high specific surface area, designable pore structures, and excellent stability. However, their weak polarity and low electron cloud density characteristics limit their efficient enrichment of polar and hydrophilic pollutants.

This study focused on the trace detection requirements of polar aromatic amines (AAs), which are typical hydrophilic pollutants in foods, and proposed a new carbamide functionalization strategy to modify COFs, aiming to achieve efficient extraction of AAs. By carbamide functionalization, a large number of O-CO active sites were introduced into COF. Experimental studies indicated that the introduced O-CO sites can enhance the hydrophilicity of COF and enable hydrogen bonding and electrostatic interactions with AAs. Meanwhile, hydrophilicity and π-π interactions were also involved in the adsorption process. Moreover, carbamide functionalization enhances the stabilities of COF fiber, ensuring its application in solid-phase microextraction (SPME). Based on the modified COF, a SPME-gas chromatography-tandem mass spectrometry (GC-MS/MS) method was developed for AAs detection. The developed method possessed wide linearity (2.0-800.0 ng L^-1), good correlation coefficients (0.9988-0.9994) and low detection limits (0.5-1.0 ng L^-1). Additionally, this method was successfully applied to the detection of trace AAs in tea beverages, demonstrating favorable recovery rates (83.6-116.8 %) and good repeatability (RSD≤9.5 %).

This study provided a new idea for the polarity regulation of COFs and the efficient enrichment of hydrophilic pollutants. Meanwhile, it lays a technical foundation for the trace analysis of polar AAs in food and beverages.