An acid-induced phase cloud point separation approach using anionic surfactants for the extraction and preconcentration of organic compounds

The acid-induced liquid-liquid phase separation of anionic surfactants in a queous solutions, and its applicability to cloud point extraction methodolo gy, were examined. The phase diagrams obtained (e.g., [HCl] vs [surfactant] ) consisted of three regions: a homogeneous liquid region, two coexisting i sotropic phases, and a solid region. The breadth of each region was found t o depend on the surfactant structure. The behavior of each phase was also e xamined in relation to temperature and added salts. The anionic surfactants investigated were sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfo nic acid (SDB-SA), sodium dodecanesulfonic acid (SDSA), and sodium dioctyls ulfosuccinate (Aerosol OT). The use of anionic surfactant-mediated phase se parations provided very high extraction efficiencies (80-100%) for pyrene i n aqueous samples and various PAHs in a certified reference material (dried sewage sludge). The preconcentration factor achieved was found to be a fun ction of both surfactant and acid concentrations. Theoretical preconcentrat ion factors as high as 230 can be reached with Aerosol OT. Allyl surfactant s were used to preconcentrate polar PAHs and progesterone prior to their de termination 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 su rfactants to extract thermally labile compounds was confirmed by extracting vitamin E at 10 degrees C with recoveries of about 80-85%.