Trace determination of nitrotoluenes in water by hollow fiber protected stir bar liquid phase microextraction based on magnetic ionic liquids

In this work, a novel hybrid approach called hollow fiber protected stir bar liquid phase microextraction (HF-SBLPME) that combines the advantages of stir bar sorptive extraction (SBSE) [1] and hollow fiber protected liquid phase microextraction (HF-LPME) [2] has been employed for the accurate and sensitive determination of ten nitrotoluenes (NTs) in complex water samples. The extraction is carried out using a 2cm hollow fiber which was also filled with a magnetic ionic liquid (MIL) as extraction phase, in such a way that the MIL inside the hollow fiber is stirred in the solution at high stirring rates. Five magnetic ionic liquids ([aliquat+]2[MnCl4 2−],[P6,6,6,14 +]2[MnCl42−], [P6,6,6,14 +][Ni(II)(hfacac)3-], [P6,6,6,14+][Dy(hfacac)4−] and[P6,6,6,14+][Mn(hfacac)3−]) were evaluated as extraction solvents. Once the stirring is ceased, the hollow fiber was magnetically stirred into the sample solution, and subsequently the MIL along with concentrated analytes were subjected to a gas chromatography-mass spectrometry (GC-MS) system. The main parameters that affecting the extraction efficiency (i.e., MIL amount or hollow fiber size, pH of solution, extraction time and ionic strength) were evaluated by Response Surface Methodology (RSM) and a multivariate optimization was done using Box-Behnken Design (BBD) [3]. Under the optimized conditions, the method was successfully validated showing good linearity (R2  0.986), dynamic linear range (30 ng.L-1-0.05 mg.L-1), limits of detection and quantification in the low ng.L−1 levels (less than 10 ng.L-1), good intra- and inter-day repeatability and reproducibility (RSD<7%) and good enrichment factors (1950-2785). This sensitive analytical method was applied to the determination of trace amounts of NTs in two natural water samples (industrial and rainwater) with satisfactory relative recovery values (91–106%), highlighting that the matrices under consideration do not affect the extraction process.