Novel octahedral structured Fe3O4@SiO2@polydimethylsiloxane magnetic nanoparticles (Fe3O4@SiO2@PDMS MNPs) have been successfully synthesized for the first time. The magnetic nanoparticles (MNPs) were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectrometry and vibrating sample magnetometry. The Fe3O4@SiO2@PDMS MNPs were used as the sorbent for magnetic solid phase extraction (MSPE) to determine benzene, toluene, ethylbenzene and xylenes (BTEX) in water samples. Extraction parameters, the amount of sorbent, the extraction time, the stirring rate, the salt effect, the type of desorption solvent, the volume of desorption solvent and the desorption time were optimized. The optimal extraction conditions were amount of sorbent, 100 mg; extraction time, 15 min; stirring rate, 200 rpm; no salt; desorption solvent, dichloromethane; volume of desorption solvent, 0.5 mL; and desorption time, 1.0 min. Good linearity was observed in the calibration range from 0.05 to 20 μg L−1, and the coefficient of determination (r2) was more than 0.9980. The limits of detection (LODs) and limits of quantitation (LOQs) for BTEX were observed to be 0.002–0.005 μg L−1 and 0.008–0.017 μg L−1, respectively. The intra- and inter-batch relative standard deviations (RSDs) were less than 11.6% and 15.0%, respectively.
