Fabrication of Integrated Monolithic Columns Based on Reduced Graphene Oxide-Deep Eutectic Solvents/Bimetallic Metal–Organic Framework@ Molecular Imprinted Polymer for Selective Solid-Phase Extraction of Vitamins D2 and D3 from Milk and Dairy Products

Abstract

In this research, solid phase extraction based on a new monolithic column named reduced graphene oxide@deep eutectic solvent-halloysite nanotube/Co_0.5·ZnO_0.5(MeIm)₂@molecular imprinted polymer (rGO@DES-HNT/Co0.5·ZnO0.5(MeIm)₂@MIP) is reported for the simultaneous extraction of vitamins D₃ and D₂ from milk and yogurt samples and their measurement by HPLC–UV. The synthesis of the adsorbent was explained step by step, and the final product was identified by Fourier-transform infrared (FT-IR), scanning electronic microscope (SEM), and X-ray powder diffraction (XRD). To find optimum extraction conditions, the influences of effective variables were investigated using one factor at a time. The method had a suitable linear range (0.1–60 µg/L), a high coefficient of determination (R²; 0.9991 and 0.9987), and a low detection limit (0.05 and 0.03 µg/L) for vitamins D2 and D3, respectively. The applicability of the method was evaluated by estimating the recovery of analytes from milk and yogurt samples. Recovery of more than 91.95% and RSDs of less than 3.4% show the acceptable accuracy and precision of the proposed method.