Octadecyltrimethoxysilane functionalized ZnO nanorods as a novel coating for solid-phase microextraction with strong hydrophobic surface

In this paper, we have, for the first time, proposed an approach by combining self-assembled monolayers (SAMs) and nanomaterials (NMs) for the preparation of novel solid-phase microextraction (SPME) coatings. The self-assembly of octadecyltrimethoxysilane (OTMS) on the surface of ZnO nanorods (ZNRs) was selected as a model system to demonstrate the feasibility of this approach. The functionalization of OTMS on the surface of ZNRs was characterized and confirmed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The OTMS-ZNRs coated fiber exhibited stronger hydrophobicity after functionalization, and its extraction efficiency for non-polar benzene homologues was increased by a factor of 1.5-3.6 when compared to a ZNRs fiber with almost identical thickness and facade. In contrast, the extraction efficiency of the OTMS-ZNRs coated fiber for polar aldehydes was 1.6-4.0-fold lower than that of the ZNRs coated fiber, further indicating its enhanced surface hydrophobicity. The OTMS-ZNRs coated fiber revealed a much higher capacity upon increasing the OTMS layer thickness to 5 mm, leading to a factor of 12.0-13.4 and 1.8-2.5 increase in extraction efficiency for the benzene homologues relative to a ZNRs coated fiber and a commercial PDMS fiber, respectively. The developed HS-SPME-GC method using the OTMS-ZNRs coated fiber was successfully applied to the determination of the benzene homologues in limnetic water samples with recovery ranging from 83 to 113% and relative standard deviations (RSDs) of less than 8%.