In this research, solid phase extraction based on a new monolithic column named reduced graphene oxide@deep eutectic solvent-halloysite nanotube/Co0.5·ZnO0.5(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.
