Analysis of perfluorooctane sulfonate and perfluorooctanoic acid with a mixed-mode coating-based solid-phase microextraction fiber

A novel mixed-mode coating-based solid-phase microextraction (SPME) fiber was prepared by chemical bonding dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride and 3-(trimethoxysilyl)-1-propanamine, the sol–gel precursors, on an anodized Ti wire, aiming to effectively adsorb perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). The anodized Ti wire with uniform TiO2 nanotube arrays provides high mechanical strength and strong adhesion to the mixed-mode coating. The prepared fiber shows excellent organic solvent stability due to the covalent bonding between the coating and the fiber, and significantly higher extraction efficiency than the commercial fibers, 100 μm polydimethylsiloxane and 85 μm polyacrylate fiber, due to the synergistic extraction effects of the coating functional groups. Good linearity (R2=0.9994 for PFOS, R2=0.9992 for PFOA) was obtained with detection limits of 2.5 and 7.5 pg mL−1 for PFOS and PFOA, respectively. Recoveries were in the range of 88%–102%. The proposed method was successfully applied in the analysis of PFOS and PFOA in a local river with the results of 0.05 and 0.06 ng mL−1, respectively.