Magnetic solid-phase extraction of trace cobalt(II) on iron oxide-hexagonal boron nitride in water and food samples

Determination of trace cobalt(II) (Co(II)) in real samples remains challenging because of its very low concentration and strong matrix interferences. In this study, a simple and green magnetic solid-phase extraction (mSPE) method was developed for the selective separation and preconcentration of Co(II) ions using a newly designed iron oxide/hexagonal boron nitride (IOhBN) nanocomposite. The material was synthesized through a one-step, surfactant-free coprecipitation process, combining the high surface area, stability, and layered structure of hBN with the magnetic and reactive features of Fe₃O₂ nanoparticles. This hybrid structure provided abundant active sites and rapid magnetic separability, enabling efficient extraction within 5 min using only 15 mg of sorbent. The optimized conditions were pH 7.0, eluent type and volume (3.0 mol L^-1 of HNO₃, 0.5 mL), and total extraction time of 5 min. The method exhibited reliable and environmentally efficient analytical performance with a limit of detection of 0.67 μg L^-1, a relative standard deviation of 4.2%, and an enrichment factor of 20. Validation with certified reference materials (water, BCR 505; onion NCS ZC 73033; spinach leaves, NIST1570a) and successful applications to water and food samples confirmed its reliability. The results demonstrate that the proposed IOhBN-based mSPE method is a novel, rapid, and environmentally sustainable approach for ultra-trace Co determination in complex matrices.