An in-situ extraction–preconcentration method using ionic liquid-based surfactants for the determination of organic contaminants contained in marine sediments

The determination of a group of organic contaminants from marine sediments samples including three polycyclic aromatic hydrocarbons, five alkylphenols (i.e., bisphenol-A or nonylphenol) and one paraben has been carried out using an extraction/preconcentration strategy with ionic liquid-based surfactants and high-performance liquid chromatography (HPLC) with diode array detection (DAD). Sediments are first extracted using two IL-based surfactants, specifically 1-hexadecyl-3-methyl imidazolium bromide (C16MIm–Br) and 1-hexadecyl-3-butyl imidazolium bromide (C16C4Im–Br), as the extraction media in a microwave-assisted extraction (MAE) procedure, followed by a novel in situ preconcentration method. The optimized MAE method requires 0.1 g of sediment and 5 mL of 40 mM C16MIm–Br IL solution. The extracts are then centrifuged and filtered. The subsequent preconcentration in situ approach consists of the insolubilization of an IL-based surfactant formed by a metathesis reaction using the anion-exchange reagent lithium bis[(trifluoromethane)sulfonyl]imide (LiNTf2), which produces an analyte enriched IL microdroplet. The optimized in situ approach utilizes 4 mL of the filtered extract, which are mixed with acetonitrile and 92 μL of LiNTf2 solution (0.5 g mL−1), heated, vortexed and centrifuged. The formed IL microdroplet is then simply diluted with acetonitrile (∼100 μL) and injected in the chromatograph without any further clean-up steps. The overall extraction/preconcentration method requires approximately 25 min in spite of dealing with complex solid samples, is nearly free of organic solvent (requires ∼900 μL of acetonitrile per sample), and produces high preconcentration factors and quantification limits down to 0.04 mg kg−1 using HPLC–DAD.