Sensitive analysis of six phthalate esters in water using magnetic covalent organic framework-based solid-phase extraction and LC–MS/MS

Phthalates (PAEs), including dimethyl phthalate (DMP), diethyl phthalate (DEP), benzyl butyl phthalate (BBP), dibutyl phthalate (DBP), di-n-octyl phthalate (DNOP), and di(2-ethylhexyl) phthalate (DEHP), are well-documented endocrine-disrupting chemicals posing significant environmental and health risks. To address the limitations of conventional detection methods, we developed a novel core-shell magnetic covalent organic framework (Fe₃O₄@TAPOB-COF) via a multi-step synthesis protocol involving solvothermal reactions, silica coating, amino functionalization, and Schiff-base condensation. Comprehensive characterization using FTIR, XRD, SEM/TEM, and VSM confirmed the successful formation of a 25 nm crystalline COF shell with preserved superparamagnetism (12.7 emu/g), exceptional thermal stability (<10 % capacity loss at 300 °C), and broad pH tolerance (pH 2.0–11). When employed for magnetic solid-phase extraction (MSPE) of the six target PAEs, the material exhibited outstanding performance with detection limits of 0.14–22 ng/L and quantification limits of 0.46–73 ng/L, demonstrating wide linear ranges (1.0–1000 μg/L, R  > 0.999) and excellent precision (intra-day RSD 4.9–9.1 %; inter-day RSD 7.3–13.5 %). The extraction mechanism, driven by synergistic π–π interactions and hydrophobic effects, achieved adsorption capacities of 312–1110 μg/g. In real water samples, consistent recoveries of 66.5–113.1 % were obtained with >75.0 % efficiency retention after six regeneration cycles, while complete extraction of BBP/DBP and 91.8 % removal of high-concentration DNOP (4600 μg/L) were achieved in industrial wastewater applications. Compared to conventional methods (SPE-GC–MS, LLE-LC–MS), this approach reduced solvent consumption by 80.0 %, improved throughput fivefold, and achieved detection limits 2–4 orders of magnitude lower than EPA Method 8061. The developed method establishes a robust, sensitive, and environmentally friendly analytical platform for trace-level PAE monitoring, offering significant advancements in environmental pollution control through enhanced sensitivity, cost-effectiveness, and operational efficiency.