A hybrid material composed of graphitic carbon nitride and magnetite (Fe3O4) for magnetic solid-phase extraction of trace levels of hydroxylated polycyclic aromatic hydrocarbons.

Magnetic carbon nitride composites were synthesized via a solvothermal reaction and developed as an effective adsorbent for magnetic solid-phase extraction of trace hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) from urine samples prior to their determination by HPLC. The sorbent was characterized by Fourier transform infrared spectrometry, X-ray diffractometry, scanning electron microscopy, vibrating sample magnetometry and solvent stability experiments. The adsorption of hydroxy-PAHs is better by a factor or 20 to 49 compared to bare Fe3O4 and comparable that of a commercial C18 sorbent. The adsorbent amount, adsorption time and eluting solvent and volume were optimized. The complete extraction for the OH-PAHs at a level of 40 ng·mL-1 and by using 4 mg sorbent is completed within 3 min. With an enzymatic hydrolyzed urine sample loading volume of 2 mL, enhancement factors in the range of 9-10, and a limit of detection (at S/N = 3) of 0.08 ng·mL-1 were achieved. The method showed a linear response in the 0.25-250 ng·mL-1 hydroxy-PAH concentration range, and intra-day and inter-day precisions are 1.5-7.7% and 2.2-8.7%, respectively. The recovery from spiked urine samples ranged from 90.1% to 102%. The sorbent was stable over 10 successive cycles of extraction/desorption of urine sample without significant loss of extraction efficiency. The method was successfully applied for the determination of OH-PAHs in urine samples of smoking volunteers. Graphical abstract Schematic presentation of the preparation of graphitic carbon nitride (g-C3N4)/magnetite (Fe3O4) using a solvothermal reaction, and application for magnetic solid-phase extraction of three trace hydroxy polycyclic aromatic hydrocarbons (OH-PAHs) in urine samples of smoking volunteers.