Aqueous two-phase systems based on hexafluoroisopropanol and hydrophilic organic solvents: phase diagrams and extraction studies

This study explores a novel type of the aqueous two-phase system (ATPS) consisting of hexafluoroisopropanol (HFIP) and hydrophilic organic solvent as a phase separation inducing agent. Six solvents (acetone, acetonitrile, dimethyl sulfoxide, ethanol, methanol and tetrahydrofuran) were tested as HFIP-based ATPS inducing agents. Only aprotic solvents induced the formation of ATPS. The results suggest that the hydrogen bonding interaction between HFIP and aprotic solvent is the main driving force of phase separation. The phase separation ability of solvents increased with their log P values: less hydrophilic solvents induced phase separation at lower concentrations. HFIP/acetonitrile ATPS was evaluated as an extractant for organic compounds from various classes in aqueous solutions. Obtained extraction efficiencies can be ordered according to the following sequence: amines > esters ≈ aromatic hydrocarbons > hydroxy esters ≈ phenols > carboxylic acids. Interestingly, the proposed system shows an exceptionally good extractability of relatively hydrophilic neutral and positively charged basic compounds. The water immiscible phase possesses a high volatility, a higher than water density and a low viscosity. These properties make ATPS very promising as an extractant for conventional liquid–liquid extraction and particularly well-suited for liquid–liquid microextraction techniques.