A novel preconcentration strategy for extraction methods based on common cationic surfactants: an alternative to classical coacervative extraction.
A novel and simple preconcentration step for aqueous micellar solutions of the common cationic surfactant cetyltrimethylammonium bromide (CTAB) has been developed. The procedure is based on the formation of another phase (a micro-droplet), not soluble in water, in which analytes (originally present in the aqueous solution) experience preconcentration. The method resembles to that of classical coacervation, but it does not require high ionic strengths neither acidic pH values. The optimum method implies mixing aqueous micellar solutions of CTAB with lithium bis[(trifluoromethane)sulfonyl]imide (Li-NTf₂) in a 1:1 molar ratio with a 16.5% (v/v) of acetonitrile content, followed by vortex, heating at 65 °C during 2 min, and centrifugation. The obtained microdroplet containing analytes is then subjected to high-performance liquid chromatography (HPLC) with diode-array detection (DAD). The method has been applied to the determination of a group of organic contaminants including alkylphenols, polycyclic aromatic hydrocarbons and parabens, present in aqueous samples (including seawater) or solid samples (such as sediment samples, which are subjected to a previous microwave-assisted extraction). Average preconcentration factors of roughly 14 and 12 are obtained for aqueous and sediment samples, respectively; being the limits of quantification down to 0.5 μg L⁻¹ and 0.02 mg kg⁻¹, respectively.