In situ formation of hydrophobic magnetic ionic liquids for dispersive liquid-liquid microextraction

A new class of magnetic ionic liquid (MIL) containing paramagnetic cations has been applied for in situ dispersive liquid-liquid microextraction in the determination of both polar and non-polar pollutants, including ultraviolet filters, polycyclic aromatic hydrocarbons, alkylphenols, a plasticizer and a preservative in aqueous samples. The MILs were based on cations containing Ni(II) metal centers coordinated with four N-alkylimidazole ligands and chloride anions. The MILs were capable of undergoing in situ metathesis reaction with the bis[(trifluoromethyl)sulfonyl]imide ([NTf2-]) anion during the microextraction procedure, generating a water-immiscible extraction solvent containing the preconcentrated analytes. The MIL was then isolated by magnetic separation, followed by direct analysis using reversed-phase high performance liquid chromatography with diode array detection. Among all of the studied MILs, those containing the N-butylimidazole and N-benzylimidazole ligands ([Ni(C4IM)(4)(2+)]2[Cl-] and [Ni(BeIM)(4)(2+)](2)[Cl-], respectively) exhibited the best extraction performance. The method under optimum conditions required 5mL of sample at pH 3, 20 mg of [Ni(C4IM)(4)(2+)](2)[Cl-] or 30mg of [Ni(BeIM)(4)(2+)](2)[Cl-], 300 mu L of acetone or acetonitrile as dispersive solvent (depending on the MIL), a 1:2M ratio of MIL to [NTf2-], and 3 min of vortex. The developed method achieved higher extraction efficiency compared to the conventional MIL-dispersive liquid-liquid microextraction mode, with extraction efficiencies of 46.8-88.6% and 65.4-97.0% for the [Ni(C4IM)(4)(2+)](2)[Cl-] and the [Ni(BeIM)(4)(2+)](2)[Cl-] MILs (at a spiked level of 81 mu gL(-1)), respectively, limits of detection down to 5.2 mu gL(-1), and inter-day relative standard deviation lower than 16%. (C) 2018 Elsevier B.V. All rights reserved.