Bromine-Functionalized Covalent Organic Frameworks Enhancing the Desorption Efficiency and Enabling Preconcentration of Brominated Pollutants for Mass Spectrometry Detection

Abstract

Covalent organic frameworks (COFs) exhibit exceptional adsorption capacity but suffer from challenging desorption. In this study, a bromine-functionalized magnetic COF composite (Fe₃O₄@COF-Br) was synthesized via bromodimethylsulfonium bromide-mediated bromination of imine-linked COF on Fe₃O₄ nanospheres (Fe₃O₄@COF), where the COF framework was constructed by 1,3,5-tris(4-formylphenyl)benzene and 2,6-diamino-3,5-diethynylpyridine. Compared with pristine Fe₃O₄@COF, Fe₃O₄@COF-Br enhanced desorption efficiencies for brominated contaminants by about 30% while maintaining adsorption capacity. Systematic characterization and DFT simulations revealed reduced host-guest binding strengths in the brominated composite with interaction energies lowered by about 30 kcal mol^-1. Employing Fe₃O₄@COF-Br as the magnetic solid-phase extraction (MSPE) adsorbent coupled with ESI-MS detection, the method achieved detection limits of 1.4-9.5 ng L^-1 for tetrabromobisphenol A (TBBPA) and its derivatives (TBBPA-BHEE, TBBPA-BGE, TBBPA-BME, TBBPA-BAE, TBBPA-BDBPE), with coefficients of determination (R²) > 0.99 and precision (relative standard deviations) ≤ 8.4%. Validated in landfill leachate, soil, lake water, tap water, juice, soy sauce, and urine matrices, the method delivered 75-125% recoveries, demonstrating practicability and accuracy for complex environmental analysis.