Nanostructured octadecylsilica chemically coated stainless-steel fiber for vacuum-assisted HS-SPME sampling of PAHs in soil

An efficient and robust solid-phase microextraction (SPME) fiber was developed for vacuum-assisted sampling of polycyclic aromatic hydrocarbons (PAHs) in solid samples. The surface of a stainless-steel fiber was first oxidized and then coated with nanostructured n-octadecylsilica using the Stöber method, by hydrolysis and condensation of tetraethylorthosilicate in the presence of octadecyltrichlorosilane through a sol–gel strategy. The synthesized sorbent was characterized using scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX) and Fourier transform infrared spectroscopy (FT-IR). The developed vacuum-assisted headspace SPME (VA-HS-SPME) procedure was coupled with GC-FID and optimized for the analysis of PAHs in soil, using multivariate statistical analysis, based on Box-Behnken design. The calibration graphs for seven PAHs were linear (R² > 0.995) over 0.001-4000 ng g^-1. The limits of detection were found to be 0.1-0.9 pg g^-1. The relative standard deviations for six repeated analyses of 100 ng g^-1 of the PAHs (using a single fiber) were calculated 3.2-8.7% and fiber-to-fiber reproducibility (n = 6) obtained 5.2-12.34%. The nanostructured octadecylsilica was shown to be substantially robust and durable. It was utilized for ultrasensitive VA-HS-SPME/GC analysis of the PAHs in different polluted soil samples and satisfactory results were obtained, with low matrix effects.