Solid-Phase Microextraction Using Fused-Silica Fibers Coated with Sol−Gel-Derived Hydroxy-Crown Ether

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Abstract
A novel solid-phase microextraction (SPME) fiber containing hydroxydibenzo-14-crown-4 (OH-DB14C4)/hydroxy-terminated silicone oil (OH-TSO) was first prepared by a sol−gel method and investigated for the determination of phenols. The possible mechanism is discussed and confirmed by IR spectra. The coating has stable performance in high temperature (to 350 °C) and solvents (organic and inorganic) due to the chemical binding between the coating and the fiber surface. The addition of crown ether enhances the polarity of the coating compared with that of the sol−gel OH-terminated silicone oil fiber and, accordingly, provides higher extraction efficiency for polar phenolic compounds. On the other hand, OH-terminated silicone oil in the coating can not only increase the length of network but also help to spread the stationary phase on the silica surface uniformly. The fluorescence microscopy experiment suggests the benefit the more uniform surface of the sol−gel-derived OH-DB14C4/OH-TSO fiber in comparison with sol−gel-derived OH-DB14C4 fiber. Some parameters of the SPME fiber for the determination of phenols were investigated. Limits of detection of the phenols are below 1.0 ng/mL, and the precisions are from 2.9 to 4.6% (n = 6). Linear ranges were found to be 0.1−10 μg/mL. The sensitivity of the method is enhanced at a low-pH level (pH ∼1) and with the addition of salt. The method was applied to the analysis of wastewater sample from a paper mill.

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