Magnetic cationic covalent organic framework for selective enrichment of phenoxy carboxylic acid herbicides prior to...

A magnetic ionic covalent organic framework (iCOF) was prepared with dimidium bromide (DB) as the ionic building blocks and named as Fe₃O₄@DB-iCOF. The Fe₃O₄@DB-iCOF was applied as magnetic solid-phase extraction (MSPE) adsorbent for the enrichment of phenoxy carboxylic acid herbicides (PCAs). Various MSPE parameters including pH, ionic strength, adsorbent dosage, extraction time, eluent type, and eluent volume were optimized. The coexistence interference and recycle experiments confirmed the Fe₃O₄@DB-iCOF possesses the selectivity characteristics of mixed-mode ion-exchange adsorbent and good reusability towards PCAs. The density function theory (DFT) computational adsorption energy verified the adsorption process is exothermic and spontaneous. The molecular dynamics (MD) simulation confirmed the crucial role of electrostatic interaction in driving adsorption process. A novel method for analyzing trace PCAs residues in water samples has been established by combining the Fe₃O₄@DB-iCOF based MSPE with liquid chromatography tandem mass spectrometry (LC-MS/MS). The proposed method exhibits wide linear range (10-2000 ng L^-1) and high sensitivity with limits of detection in the range 0.8-1.9 ng L^-1. The proposed method was utilized to determine PCAs in river and lake water, with spiked recoveries ranging from 90.8 to 103.1%, confirming its good accuracy.