Amino-modified covalent organic framework as solid phase extraction absorbent for determination of carboxylic acid pesticides in environmental water samples.

The amino-modified covalent organic framework (NH@COF) was synthesized via the thiol-ene click reaction of vinyl covalent organic framework (COF) with 4-aminobenzenethiol. The introduction of amino groups can interact with the anionic headgroup of carboxylic acid pesticides. Moreover, ample hydrophilic surface area can boost absorption in the water media. The NH@COF was fully characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Compared with vinyl COF and four commercial absorbents, the NH@COF shows higher extraction efficiency for carboxylic acid pesticides. The solid phase extraction (SPE) conditions, involving flow rate, ionic strength, sample pH, desorption solvent, and desorption solvent volume, were optimized in details. Under the optimized conditions, the NH@COF was successfully applied for the enrichment and determination of six carboxylic acid pesticides in environmental water samples combined with high performance liquid chromatography. The method features wide linearity (0.2-100 ng mL, r > 0.999), low limits of quantification (0.04-0.20 ng mL), and excellent precision (RSDs ≤ 8.7%). The recoveries range from 89.6% to 102.4% with RSDs ≤ 7.1%. Therefore, the NH@COF-SPE method is an efficient pretreatment procedure and can be utilized for the selective extraction of carboxylic acid pesticides from environmental water samples.