Concentration of Hydrophobic Organic Compounds by Polymer-Mediated Extraction

A water-soluble polymer, poly( N -isopropylacrylamide), becomes water-insoluble above a lower critical solution temperature (∼32 °C) and forms gumlike precipitates (polymer phase) having a very small volume fraction. The features in the polymer precipitation were dependent on the molecular weight of the polymer and/or the concentration of salts or buffer components. Accompanying the formation of the polymer phase, hydrophobic organic compounds including polycyclic aromatic hydrocarbons, alkylphenols, chlorobenzenes, chlorophenols, phthalic esters, pesticides, and steroid hormones in water were efficiently incorporated into the polymer phase. On the other hand, hydrophilic components such as inorganic ions or polysaccharides remained in the bulk aqueous solution. The extractabilities of the compounds increased with increasing hydrophobic properties. The distribution coefficients, based on the volume fractions of their aqueous and polymer phases, between the bulk aqueous and polymer phases were correlated with the water−octanol distribution coefficients. The linear relationship between the two equilibrium coefficients indicated that the hydrophobic interaction is the predominating force for incorporating solutes. The introduction of the concentrated polymer solution into the hygroorganic mobile phase of the reversed-phase HPLC rarely interfered with the chromatographic operation. The application of the polymer-mediated extraction to HPLC significantly enhanced the peak intensities of the hydrophobic analyte varieties by reducing the interferences of the hydrophobic matrix components.