Thiol-functionalized magnetic biochar as an efficient sorbent for magnetic dispersive micro-SPE coupled with ICP-MS determination of Pb(ii), Cd(ii), and Hg(ii) in environmental waters

A thiol-functionalized magnetic biochar (MB–SH) was synthesized and utilized as an efficient sorbent for magnetic dispersive micro-solid-phase extraction (MD-µSPE) coupled with inductively coupled plasma mass spectrometry (ICP-MS) for the simultaneous determination of trace Pb(II), Cd(II), and Hg(II) in environmental water samples. The MB–SH material was prepared by functionalizing magnetic biochar with thiol groups, resulting in high-density chelating sites for heavy metal ions. The optimized MD-µSPE process allowed for quick preconcentration of target analytes in 3–5 minutes, with preconcentration factors ranging from 100 to 250. Under ideal circumstances (pH 5.5, 20 mg of sorbent, 250 mL sample volume, and 2 mL of eluent), the method obtained limits of detection at the ng L⁻¹ level (0.5–1.2 ng L⁻¹), exceptional recoveries of 90–102%, and relative standard deviations of <5%. The approach was successfully applied to both natural and industrial water samples, displaying good accuracy when compared to certified reference material (SRM 1643e). The MB–SH sorbent demonstrated good reusability for at least five cycles with low performance loss, providing a green, cost-effective, and sustainable alternative to trace heavy metal monitoring in aquatic environments.