An Acid-Induced Phase Cloud Point Separation Approach Using Anionic Surfactants for the Extraction and Preconcentration of Organic Compounds

Abstract

The acid-induced liquid−liquid phase separation of anionic surfactants in aqueous solutions, and its applicability to cloud point extraction methodology, were examined. The phase diagrams obtained (e.g., [HCl] vs [surfactant]) consisted of three regions: a homogeneous liquid region, two coexisting isotropic phases, and a solid region. The breadth of each region was found to depend on the surfactant structure. The behavior of each phase was also examined in relation to temperature and added salts. The anionic surfactants investigated were sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonic acid (SDBSA), sodium dodecanesulfonic acid (SDSA), and sodium dioctylsulfosuccinate (Aerosol OT). The use of anionic surfactant-mediated phase separations provided very high extraction efficiencies (80−100%) for pyrene in aqueous samples and various PAHs in a certified reference material (dried sewage sludge). The preconcentration factor achieved was found to be a function of both surfactant and acid concentrations. Theoretical preconcentration factors as high as 230 can be reached with Aerosol OT. Alkyl surfactants were used to preconcentrate polar PAHs and progesterone prior to their determination by HPLC. The lack of an aromatic moiety in the structure of the surfactants and their ionic character enables complete resolution of their chromatographic peak from those of the analytes. The ability of anionic surfactants to extract thermally labile compounds was confirmed by extracting vitamin E at 10 °C with recoveries of about 80−85%.