Zeolitic Imidazolate Framework-based Magnetic Stir Bar for Micro-Solid Phase Extraction of Persistent Organic Pollutants in Water Samples

The data uploaded herein correspond to the optimization experimental data for establishing the proposed method. Three ZIF materials widely used in adsorption and extraction, namely ZIF-8, ZIF-67, and ZIF-71, were selected to prepare Fe₃O₄@ZIF composites via an in-situ growth method. Fe₃O₄ nanoparticles were first synthesized by dissolving 2.0 g FeSO₄·7H₂O and 2.0 g FeCl₃·6H₂O in 200 mL deionized water, followed by stirring for 5 min. A 5 mol/L NaOH solution was added, and the mixture was stirred for 1 h before drying. The obtained Fe₃O₄ nanoparticles were ground and set aside.
For Fe₃O₄@ZIF-8 preparation, 0.3 g Fe₃O₄ was mixed with 4.1 mL methanol, ultrasonicated for 5 min, then 0.6 g Zn(OAc)₂·2H₂O was added and stirred for 0.5 h to form Solution 1. Meanwhile, 2.24 g 2-methylimidazole was dissolved in 2.76 mL methanol as the ligand solution. After stirring Solution 1, the ligand solution was added, and the mixture was stirred for 4 h, then centrifuged at 3350 r/min. The product was washed three times with deionized water and methanol under an external magnetic field to remove non-magnetic impurities, dried at 70 °C, and ground to obtain Fe₃O₄@ZIF-8.
The preparation of Fe₃O₄@ZIF-67 and Fe₃O₄@ZIF-71 was similar, except that the metal solution was replaced with Co(NO₃)₂·H₂O, and the ligand with 4,5-dichloro-1H-imidazole, respectively.
A 4 mm-diameter magnetic sphere was used as the stir bar matrix. Multiple spheres were self-assembled into a multi-sphere elongated stir bar, whose length could be adjusted according to the actual instrument’s bottom diameter. A required amount of Fe₃O₄@ZIF was accurately weighed and uniformly distributed on the stir bar surface.
The stir bar was placed in a conical flask containing 30 mL aqueous solution (with target analytes) and magnetically stirred at 650 r/min for 10 min. The aqueous solution was removed, and 1 mL elution solvent was added for 2 min vortex-assisted elution (repeated twice). The stir bar was immobilized at the flask bottom with a magnet, and the eluate was withdrawn with a disposable syringe, filtered through a 0.22 μm membrane, and transferred into a sample vial for subsequent GC-μECD analysis.