Preconcentration of synthetic phenolic antioxidants by using magnetic zeolites derived with carboxylatocalix[4]arenes combined with high performance liquid chromatography.

Here, we synthesized a novel organic-inorganic hybrid material combining carboxylatocalix[4]arenes and magnetic zeolites by covalent bonding. The complex was characterized by scanning electron microscopy, transmission electron microscopy, Fourier-transformed infrared spectroscopy, X-ray diffraction spectrometry, thermogravimetric analysis/differential thermal gravity analysis, and by using an X-ray photoelectron spectrometer and a vibrating sample magnetometer. The resulting magnetic composite was employed as a solid phase adsorbent to separate and preconcentrate synthetic phenolic antioxidants. Various interactions between the targets and the adsorbent contributed to the adsorption efficiency including hydrophobic interaction, hydrogen-bond interaction, and π-π complexation. The superparamagnetic participation in the process of synthesizing zeolites made the separation process of adsorbent from solutions convenient by an external magnetic field. Taking advantage of this property, this adsorbent could be recycled more than 30 times. The concentrations of the preconcentrated SPAs were determined directly by high-performance liquid chromatography. Various experimental parameters were optimized, according to which the method was evaluated. Finally, the prepared magnetic zeolite@carboxylatocalix[4]arene was successfully applied to identify synthetic phenolic antioxidants from juice and infant milk powder samples with high enrichment factors in the range of 41.9-92.5. The magnetic materials allowed rapid and simple preconcentration, implying their potential in the field of adsorption.