Development of a Novel Sensitive and Fast Semi-Covalent Molecularly Imprinted Polymer-Based Magnetic Dispersive Solid-Phase Extraction Method (MIP-MDSPE) for Cholesterol Determination in Milk Samples

In the present study, a novel magnetic dispersive solid-phase extraction method using molecularly imprinted polymer synthesized through semi-covalent imprinting approach was developed for cholesterol (CHO) determination in milk samples by high-performance liquid chromatography with diode array detector (HPLC-DAD). The adsorbent named Fe3O4/SiO2/MIP (MIP: molecularly imprinted polymers) was prepared through sol-gel polymerization of 3-(triethoxysilyl)propyl isocyanate (ICPTES) covalently bonded to CHO with tetraethoxysilane (TEOS), in the presence of Fe3O4/SiO2 particles. The adsorbent was characterized by attenuated total reflection Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), dynamic light scattering (DLS) and scanning electron microscopy (SEM). The proposed molecularly imprinted polymer-based magnetic dispersive solid-phase extraction method (MIP-MDSPE) was based on vortex-assisted preconcentration of 10.0 mL of CHO solution in chloroform as donor phase using 10.0 mg of Fe3O4/SiO2/MIP during 60 s. After this step, the magnetic particles were collected using a permanent magnet and the vortex-assisted elution was carried with 500 µL of ethanol during 180 s. A wide analytical curve ranging from 38.5 to 25000 µg L-1 (determination coefficient (R2 ) = 0.998) and low limits of detection (LOD) and quantification (LOQ) 11.5 and 38.5 µg L-1, respectively, were obtained. Milk samples (whole and reduced-fat milk) were subjected to MIP-MDSPE method after saponification reaction followed by CHO extraction with chloroform. Using external calibration, the CHO concentration ranged from 99.2 (reduced-fat milk) to 397.6 mg kg-1 (whole milk) and the accuracy was attested by addition and recovery tests (92 to 97%).