Solvent-free synthesis of a magnetic covalent organic framework as a high-performance adsorbent for selective extraction and ultrasensitive determination of Bi(III), Hg(II), Ag(I), and Pb(II).

A novel urea-based magnetic covalent organic framework composite (Fe3O4@U-COF) was synthesized via a simple, solvent-free mechanochemical method and introduced as a high-performance adsorbent for sample preparation. Comprehensive characterization confirmed a synergistic enhancement in the material's properties. The resulting nanocomposite exhibited a specific surface area (76.05 m2 g-1) significantly greater than its individual components, which is crucial for achieving high adsorption efficiency. The material was successfully applied in a magnetic solid-phase microextraction (MSPME) method for the selective preconcentration of trace Bi(III), Hg(II), Ag(I), and Pb(II) ions. The quantitative determination of the analytes was performed by inductively coupled plasma optical emission spectrometry. Following a systematic optimization of all critical parameters, the optimal conditions were established: an adsorbent amount of 1 mg, a sample volume of 10 mL, and elution with 300 µL of 2 mol l-1 HCl. Notably, the method demonstrated exceptional robustness, operating effectively across a wide pH range (5-9), which advantageously eliminates the need for sample pH adjustment. Under optimal conditions, the method achieved very low limits of detection (0.03-300 ng l-1), wide linear dynamic ranges, satisfactory enhancement factors, and excellent precision, with intra-day relative standard deviations below 2.7%. The practical applicability and accuracy of the method were validated through the analysis of diverse real-world samples, including environmental waters and human plasma, yielding excellent relative recoveries (90-115%) and demonstrating its high tolerance to matrix interferences.