Simultaneous enrichment and speciation of lead and mercury by magnetic solid-phase extraction coupled to HPLC-ICP-MS based on magnetic hydrazine-linked covalent organic frameworks

Background Trace levels of organic and inorganic lead and mercury species in the environment, including divalent lead (Pb 2+ ), trimethyllead (TML), divalent mercury (Hg 2+ ), monomethylmercury (MeHg), and ethylmercury (EtHg), are highly toxic to humans and ecology. It is of great importance for speciation of lead and mercury to evaluate the toxicity of lead and mercury and their biogeochemistry in the environment. However, simultaneous multi-elemental enrichment and speciation at trace level remains a challenge. There are few reports of simultaneous magnetic solid-phase extraction (MSPE) of organic and inorganic lead and mercury species at trace level in the real water. Results In this work, a novel core-shell magnetic hydrazine-linked covalent organic frameworks (Fe 3 O 4 @COF-TCH) was prepared for the first time by grafting hydrazine-linked COFs on the Fe 3 O 4 nanoparticles. Fe 3 O 4 @COF-TCH with abundant thione and imino groups has strong adsorption for lead and mercury species. Based on it, a simple and practical magnetic solid-phase extraction high-performance liquid chromatography-inductively coupled plasma mass spectrometry (MSPE-HPLC-ICP-MS) method was developed for extraction and determination of trace lead and mercury species, including Hg 2+ , MeHg, EtHg, Pb 2+ and TML. The limits of detection (3δ) of the developed method were 0.08, 0.81, 0.90, 0.56 and 0.88 ng L −1 with the enrichment factors (EFs) of 384, 376, 379, 389 and 360-fold for Pb 2+ , TML, Hg 2+ , MeHg and EtHg, respectively. The high accuracy and reproducibility have been proved by the spiked recoveries (94.4–103 %) in real samples. Significance The proposed method with simple operation and high sensitivity has been successfully applied to simultaneous speciation of lead and mercury at trace levels in the water samples with complicated matrices, including underground water, surface water, sea water. Meanwhile, it has the advantages of cost-saving, labor-saving and time-saving and is suitable for the investigation and risk assessment in water. The development of MSPE-HPLC-ICP-MS method provides ideas and guidance for the simultaneous multi-elemental enrichment and speciation.