Facile synthesis of magnetic covalent organic framework nanobeads and application to magnetic solid-phase extraction of trace estrogens from human urine

A rapid and facile approach was developed for the synthesis of core-shell structured magnetic covalent organic framework nanobeads by using the monodisperse Fe3O4 nanoparticles (NPs) as magnetic core, and 1,3,5-triformylbenzene (Tb) and benzidine (Bd) as two building blocks (denoted as Fe3O4@TbBd), which were explored as an adsorbent for magnetic solid-phase extraction (MSPE) of estrogens from human urine sample. The core-shell structured Fe3O4@TbBd nanobeads showed some attractive features involving high specific surface area (202.18 m2/g), uniform pore size distribution (2.8 nm), high magnetic responsivity (41.4 emu/g), as well as excellent thermal and chemical stability, which made it an ideal adsorbent for selective isolation and enrichment of estrogens. Some parameters influencing extraction efficiency, including adsorbent dosage, extraction time, pH, ion strength, desorption solvent and desorption time were investigated systematically. Combined with HPLC-MS, a simple, fast, and sensitive method was developed for the enrichment and sensitive determination of seven estrogens, which showed good linearity (r > 0.9978) in the range of 0.005-10 μg/L, low limits of detection (0.2-7.7 ng/L, S/N = 3), low limits of quantification (0.6-25.6 ng/L, S/N = 10), high enrichment factors (75-197 fold), and good precision with relative standard deviations (RSD) lower than 4.8% for intra-day and 6.7% for inter-day. The proposed method was successfully applied to the analysis of trace estrogens in urine sample of pregnant woman with good recoveries (80.6-111.6%), demonstrating the promising potential of the Fe3O4@TbBd nanobeads as adsorbent in sample pretreatment.