Facile in situ fabrication of oriented titania submicrorods embedded into a superelastic nickel–titanium alloy fiber substrate and their application in solid-phase microextraction

Abstract

A nickel–titanium oxide (NiO/TiO₂) coating was in situ grown on a nickel–titanium (NiTi) alloy fiber substrate by anodic oxidation. After annealing, a uniform and dense Ni-free coating of rutile phase TiO₂ submicrorods (TiO₂SRs) was obtained. In particular, the TiO₂SRs were embedded into the NiTi fiber substrate and oriented outwards, leading to high mechanical stability, a large contact surface area and an open access structure. In solid-phase microextraction (SPME), the TiO₂SR coating showed high extraction capacity and excellent extraction selectivity for polycyclic aromatic hydrocarbons (PAHs) among the studied aromatic compounds. The key factors affecting the SPME coupled to high-performance liquid chromatography with ultraviolet detection (HPLC-UV) of PAHs were further investigated and optimized. Under the optimized conditions, the proposed method presented linear ranges from 0.05 to 250 μg L⁻¹ with correlation coefficients more than 0.998 and limits of detection from 0.002 to 0.120 μg L⁻¹. The intra-day and inter-day repeatability for the single fiber varied from 2.05% to 5.01% and from 3.57% to 5.45% for five replicates of PAHs, respectively. The fiber-to-fiber reproducibility for five fibers fabricated in different batches ranged from 4.23% to 6.15% at a spiking level of 20 μg L⁻¹, respectively. This SPME-HPLC-UV method was successfully applied to the selective concentration and sensitive determination of PAHs in different environmental water samples. Furthermore, the NiTi@TiO₂SR fiber can be fabricated in a precisely controllable manner, and has high stability and long service time.