Magnetic solid-phase extraction and HPLC-UV determination of fat-soluble vitamins based on a multifunctional monomer covalent organic frameworks

The effective separation of fat-soluble vitamins from complex matrices prior to instrumental analysis remains a significant challenge. Herein, a novel magnetic covalent organic framework (Fe₃O₄@tetrakis(4-aminophenyl)methane (TAM)-2,6-dihydroxynaphthalene-1,5-dicarbaldehyde (DHNDA), Fe₃O₄@TAM-DHNDA) was successfully designed and prepared for the efficient separation and enrichment of three fat-soluble vitamins in dairy products. The maximal adsorption efficiency of Fe₃O₄@TAM-DHNDA to fat-soluble vitamin was as high as 26.94 mg/g. Moreover, the adsorption mechanism of Fe₃O₄@TAM-DHNDA for V_A, V_D, and V_E was revealed by molecular simulation techniques. van der Waals forces and hydrogen bonds were the main interactions between Fe₃O₄@TAM-DHNDA and fat-soluble vitamins. Importantly, the magnetic solid phase extraction (MSPE) method based on Fe₃O₄@TAM-DHNDA could be used as an effective sample pretreatment technology for separation and enrichment of fat-soluble vitamins from complex matrices prior to instrumental analysis. When coupled with high-performance liquid chromatography-ultraviolet detector (HPLC-UV), the proposed method enabled the efficient detection of fat-soluble vitamins in dairy products. The limit of detection (S/N = 3) and limit of quantification (S/N = 10) were achieved at 20–50 ng/mL and 55–150 ng/mL, respectively. Good linearity (R² > 0.9998) was obtained within the range of 2–100 μg/mL. The average recoveries of spiked milk samples were determined to be 83 %–101 % and the relative standard deviation (RSD) was 0.83 %–3.46 % (n = 3). This work provided novel insights for the development of novel magnetic adsorbents and the separation and enrichment of fat-soluble vitamins in complex matrices.