Amino bearing core-shell structured magnetic covalent organic framework nanospheres: Preparation, postsynthetic modification with phenylboronic acid and enrichment of monoamine neurotransmitters in human urine

Covalent organic frameworks (COFs) have been increasingly employed in separation science, including sample preparation. Herein we fabricated the amino bearing core-shell structured COFs nanospheres [Fe3O4@TpBD(NH2)2], and a novel magnetic boronate affinity adsorbent was synthesized by postsynthetic modification of the Fe3O4@TpBD(NH2)2 with 2-formylphenylboronic acid. The magnetic boronate affinity adsorbent possesses fast magnetic response and high binding capacity up to 1037 μmol g−1 for dopamine. Besides, it was used as an adsorbent for extraction of urinary monoamine neurotransmitters at neutral pH. A method for detection of the monoamine neurotransmitters was developed by coupling the magnetic solid phase extraction with high-performance liquid chromatography-fluorescence detection. Under the optimized conditions, a good analytical method was obtained in the linear dynamic range of 2–200 ng mL−1 with R2 between 0.9917 and 0.9966, with low limit of detection (0.31–0.54 ng mL−1) and limit of quantification (1.04–1.80 ng mL−1). The recoveries of the monoamine neurotransmitters were in the range of 86.3–115%, with relative standard deviations of 2.34–10.5% (intra-day) and 2.84–14.4% (inter-day). The method was successfully applied to the determination of the monoamine neurotransmitters in human urine samples. This work is of great importance for preparing functionalized core-shell structured magnetic covalent organic framework nanospheres, it also demonstrates the feasibility of the functionalized magnetic COFs as adsorbents in sample pretreatment.