In situ anodic growth of rod-like TiO2 coating on a Ti wire as a selective solid-phase microextraction fiber

Abstract

A novel rod-like TiO₂ based solid-phase microextraction (SPME) coating was directly fabricated by in situ anodization of Ti wire substrates in ethylene glycol and aqueous solution with 5 wt% NH₄F (v/v = 1 : 1). The compact rod-like TiO₂ has much larger surface area with a diameter of about 150 nm and a length of about 1.2 µm. The SPME performance of the as-fabricated fiber was investigated for the concentration and determination of polycyclic aromatic hydrocarbons, phthalates and ultraviolet (UV) filters coupled to high performance liquid chromatography with UV detection (HPLC-UV). It was found that the rod-like TiO₂ coating exhibited high extraction capability, good selectivity and rapid mass transfer for some UV filters. The main parameters affecting extraction performance were investigated and optimized. Under the optimized conditions, the calibration graphs were linear in the range of 0.05–200 µg L⁻¹. The limits of detection of the method were 0.024–0.032 µg L⁻¹ (S/N = 3). The single fiber repeatability varied from 5.44% to 7.81% and the fiber-to-fiber reproducibility ranged from 7.41% to 8.63% for the extraction of spiked water with 50 µg L⁻¹ UV filters (n = 5). The SPME-HPLC-UV method was successfully applied to the selective concentration and determination of target UV filters from real environmental water samples with recoveries from 84.68% to 104.8% at the spiking level of 5 µg L⁻¹, 25 µg L⁻¹ and 50 µg L⁻¹. The relative standard deviations were below 9.82%. Furthermore, the in situ growth of the rod-like TiO₂ coating on a Ti wire by one-step anodization is simple, rapid and reproducible. The rod-like TiO₂ coating was cross-linked and embedded into the Ti wire substrate. As a result, the as-fabricated fiber is robust and has long service time.