Highly sensitive detection of okadaic acid in seawater by magnetic solid-phase extraction based on low-cost metal/nitrogen-doped carbon nanotubes

Algae toxins pose a severe threat to human health all over the world. In this study, magnetic metal/nitrogen-doped carbon nanotubes (M-NCNTs) were facilely synthesized based on one-step carbonization and applied for magnetic solid-phase extraction of okadaic acid (OA) from seawater followed by high performance liquid chromatographic tandem mass spectrometry (HPLC-MS/MS) analyses. Differences in the physicochemical properties of the three prepared materials (Fe/Co/Ni-NCNTs) were investigated to confirm the best extraction material. Among them, Ni-NCNTs demonstrated a faster extraction rate (10 min) and higher adsorption capacity (223.5 mg g −1 ), mainly due to the higher specific surface area, suitable pore structure and more abundant pyridine nitrogen ring. Under the optimal conditions, the calibration curve was linear over the range (1.0–800.0 pg mL −1 ) with good determination coefficients (R) of 0.9992. The limit of detection (LOD) obtained in multiple replicates was 0.4 pg mL −1 . Three seawater samples were measured by the developed method, 12.3 pg mL −1 of OA was detected with a satisfying recovery (88.6%-106.7%) and acceptable repeatability (RSD ≤ 4.8%, n  = 6). The results demonstrate that M-NCNTs materials are a promising candidate for magnetic solid-phase extraction. Benefiting from its high extraction and interference resistance, the established analytical method is expected to be extended to detect other marine environmental pollutions.