Ionic liquid-functionalized poly-N-phenylpyrrole coated on a NiTi alloy substrate for highly efficient solid-phase microextraction

Abstract

A novel ionic liquid (i.e. 1-butyl-3-methylimidazolium hexafluorophosphate [C₄MIM]PF₆) doped poly-N-phenylpyrrole (PPPy) composite coating ([C₄MIM]PF₆@PPPy) was successfully fabricated by direct electrochemical polymerization on the surface of a NiTi substrate as a solid phase microextraction fiber. To obtain a uniform and stable fiber, the NiTi substrate was initially hydrothermally treated in sodium hydroxide solution for the in situ growth of titanium–nickel oxide composite nanoflakes (TiO₂–NiOCNFs). After electrochemical deposition, dense [C₄MIM]PF₆@PPPy composite nanoparticles were coated on the surface of the TiO₂–NiOCNF coating and porous nanostructures were obtained. Due to the embedding of an ionic liquid in the PPPy coating, the resulting [C₄MIM]PF₆@PPPy@TiO₂–NiOCNFs@NiTi fiber shows higher extraction selectivity for polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) with aromatic compounds as model analytes. The new fiber was used to extract PCBs and PAHs in water samples, which were quantified by HPLC with UV detection. Moreover the fabricated [C₄MIM]PF₆@PPPy@TiO₂–NiOCNFs@NiTi fiber exhibits the best extraction capability for PCBs and PAHs in the presence of 0.05% (V/V) [C₄MIM]PF₆. Under the optimized conditions, the calibration curves were linear in the range of 0.05–350 μg L⁻¹ for PCBs and 0.1–350 μg L⁻¹ for PAHs with correlation coefficients (r) above 0.9984. The limits of detection (LODs) and limits of quantitation (LOQs) varied from 0.015 to 0.095 μg L⁻¹ and from 0.049 to 0.316 μg L⁻¹, respectively. Furthermore, the enrichment factors (EFs) ranged from 67 to 237. Relative standard deviations (RSDs) for single fiber repeatability were less than 6.0% and 6.9% for intra-day and inter-day measurements, respectively. The developed SPME-HPLC method was successfully applied to the extraction and detection of trace PCBs and PAHs in different real water samples. Recoveries from 83.0% to 103% were obtained with RSDs below 8.5%. In addition, the novel [C₄MIM]PF₆@PPPy@TiO₂–NiOCNFs@NiTi fiber exhibits high stability and long lifespan.