An easy-prepared adsorbent with high stable and good dispersibility is especially valuable for the development of magnetic solid-phase extraction (MSPE) techniques. In this study, magnetic nitrogen-doped carbon nanotube cages (N-CNTCs) were synthesized via direct carbonization of cobalt (II)-containing metal-organic frameworks. During carbonization, cobalt ions inside the MOFs were converted into magnetic functional nanoparticles of N-CNTCs. Simultaneously, large amounts of nitrogen, originating from the organic ligands, were doped into the carbon framework. This unique structure gave the N-CNTCs excellent chemical stability, high affinity, and good dispersibility. The synthesized magnetic N-CNTCs were then used for MSPE of okadaic acid (OA) from aquatic samples. A simple, efficient, and sensitive method for detecting and quantitating OA was developed by combining the above sample pretreatment technique with high-performance liquid chromatography -tandem mass spectrometry (HPLC-MS/MS). The resulting method boasts a linear dynamic range of 3.0–1000.0 pg mL −1 with good linearity (R 2 ≥ 0.9994). The limit of detection (LOD) and limit of quantification (LOQ) were 1.3 pg mL −1 and 3.0 pg mL −1 , respectively. Several shellfish and seafood samples were analyzed using the developed method, showing satisfactory recoveries (82.0–107.0%) and relative standard deviations (<4.5%). The developed method was also used to investigate the OA distribution in crab tissues. Our results demonstrate that magnetic N-CNTCs are promising adsorbents for providing reliable support for the early warning and tracing to the source of algae toxins.
A novel three-dimensional covalent organic framework (3D-COF) with content-tunable and active hydroxyl groups (OH) on the pore walls was developed and adopted for the high-performance capture of okadaic acid (OA) marine toxins. Using pore-surface engineering, the integration of linear building blocks (4,4′-diamino-3,3′-biphenyldiol, BD(OH) 2 and benzidine, BD) with the 3D structural building block backbone (4,4′,4′',4′''-methane-tetrayltetrabenzaldehyde, TFPM) was achieved. By adjusting the ratio of BD(OH) 2 , functional multicomponent-COFs [OH] x -BD-TFPM COFs ( X = 25%) were synthesized, which offered ideal access to convert a conventional COF into a functional platform with multiple-mode interactions of hydrophobic and hydrophilic groups for OA capture. [OH] x -BD-TFPM was characterized using SEM, XRD, FT-IR, and BET. The adsorption features and analytical performance of OA were screened and evaluated. Optimization of dispersive solid-phase extraction using [OH] 25 -BD-TFPM was accomplished, and the method was verified for sensitive quantitative detection of OA in clam and mussel samples. Coupled with LC-MS/MS, the resultant [OH] 25 -BD-TFPM COF demonstrated the ability to analyze OA, and the limit of detection for OA in shellfish was determined to be 0.005 μg/kg. A significant improvement in trace OA detection was observed compared to previously reported SPE materials without adjustable hydrophilic interactions. The recoveries of OA in the fortified clam and mussel samples were in the ranges of 93.9‒105.1% and 96.7‒110.2%, respectively. This study highlights that OH-group surface engineering in channel walls is a facile and powerful strategy for developing functional 3D-COFs with multiple interactions for high-performance target capture.
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