In-situ synthesis of fluorinated magnetic covalent organic frameworks for fluorinated magnetic solid-phase extraction of ultratrace perfluorinated compounds from milk

Perfluorinated compounds (PFCs) are new types of persistent organic pollutants known to bioaccumulate in organism, which have come under increased scrutiny due to the close relation with various health problems. Sensitive detection of PFCs remains a significant challenge because of their ultratrace levels in complex samples. Herein, fluorinated magnetic covalent organic frameworks (Fe3O4@TpPa-F4) were first synthesized via a monomer-mediated in situ growth strategy and served as fluorinated magnetic adsorbent. Accordingly, a novel pretreatment method based on fluorinated magnetic solid-phase extraction (FM-SPE) combined with HPLC-MS/MS was developed to detect ultratrace PFCs from milk samples. The as-prepared Fe3O4@TpPa-F4 possessed regular porosity (0.81 nm) with large surface areas (188.04 m2/g), high fluorine content (4.85%), strong magnetic responsiveness (50 emu/g), and good chemical and thermal stability, which rendered it an ideal adsorbent material for highly efficient extraction of PFCs. Under the optimized parameters, the developed method displayed good linearity for six PFCs in the range of 0.1–250 ng/L with high correlation coefficients (r ≥ 0.9952), and the corresponding limits of detection (LODs) were 0.005–0.05 ng/L (S/N ≥ 3). Furthermore, high enrichment factors (EFs, 21.91–100.6 folds) and acceptable relative standard deviations (RSDs) of inter-day (0.5–11.8%) and batch-to-batch (2.3–11.7%) for the six PFCs were achieved. Moreover, this method was further employed to milk samples with different brands and packages, in which ultratrace PFCs were found with diverse concentrations from 10.36 to 729.34 ng/L, confirming the promising applicability of the Fe3O4@TpPa-F4 as an alternative adsorbent for sample pretreatment.