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

Abstract

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 0.1g of sediment and 5mL of 40mM 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 4mL of the filtered extract, which are mixed with acetonitrile and 92μL of LiNTf2 solution (0.5gmL−1), heated, vortexed and centrifuged. The formed IL microdroplet is then simply diluted with acetonitrile (∼100μL) and injected in the chromatograph without any further clean-up steps. The overall extraction/preconcentration method requires approximately 25min in spite of dealing with complex solid samples, is nearly free of organic solvent (requires ∼900μL of acetonitrile per sample), and produces high preconcentration factors and quantification limits down to 0.04mgkg−1 using HPLC–DAD.