Facile fabrication of magnetic covalent organic frameworks and their application in selective enrichment of polychlorinated naphthalenes from fine particulate matter

Magnetic covalent organic frameworks (Fe₃O₄@TPPCl₄) were synthesized via a one-pot process in which magnetic nanoparticles (Fe₃O₄@MNP) served as a magnetic core and 2,4,6-trihydroxy-1,3,5-benzenetricarbaldehyde (TP) and 2,2′,5,5′-tetrachlorobenzidine (PCl₄) as two building blocks to form a shell. The as-prepared Fe₃O₄@TPPCl₄ nanoparticles have superior features, including large surface area (186.5 m² g⁻¹), high porosity, strong magnetic responsiveness (42.6 emu g⁻¹), high chlorine content, and outstanding thermal stability, which make them an ideal adsorbent for highly selective enrichment of polychlorinated naphthalenes (PCNs). Combining with atmospheric pressure gas chromatography tandem mass spectrometry (APGC-MS/MS), a simple analytical method of Fe₃O₄@TPPCl₄-based magnetic solid-phase extraction (MSPE)-APGC-MS/MS was developed, which exhibited good linearity (r ≥ 0.9991) for eight PCNs in the concentration range 0.1–100 ng L⁻¹. Moreover, low detection limits (0.005–0.325 ng L⁻¹), high enrichment factors (46.62–81.97-fold), and good relative standard deviations (RSDs) of inter-day (n = 3, 1.64 to 7.44%) and day-to-day (n = 3, 2.62 to 8.23%) were achieved. This method was successfully applied to the selective enrichment of PCNs in fine particulate matter (PM)_2.5 samples, and ultra-trace PCNs were found in the range 1.56–3.75 ng kg⁻¹ with satisfactory recoveries (93.11–105.81%). The successful application demonstrated the great potential of Fe₃O₄@TPPCl₄ nanoparticles as an adsorbent for enrichment of halogenated compounds. Graphical abstract: [Figure not available: see fulltext.]