ELUTION OF ORGANIC SOLUTES FROM DIFFERENT POLARITY SORBENTS USING SUBCRITICAL WATER

The intermolecular interactions between organic solutes and sorbent ma trices under subcritical water conditions have been investigated at a pressure of 50 bar and temperatures ranging from 50 to 250 degrees C. Both polar and nonpolar organics (chlorophenols, amines, n-alkanes, an d polycyclic aromatic hydrocarbons) and five different sorbent matrice s (glass beads, alumina, Florisil, silica-bonded C-18, and polymeric X AD-4 resins) were used. From the same matrix, the polar solutes always eluted at lower temperatures, while the moderately polar and nonpolar solutes only eluted at higher temperatures. Similar to matrix effects previously observed using supercritical carbon dioxide, the sorbent t ype greatly influenced the elution efficiency under subcritical water conditions. Lower temperatures are sufficient to elute a particular so lute from glass beads, alumina, and Florisil, but higher temperatures (less polar water) are needed to elute the same solute from silica-bon ded C-18. The highest temperatures were required to elute aromatic org anics from XAD-4. These matrix effects demonstrate that, while low tem perature water can break inert or dipole interactions between solutes and glass beads, alumina, and Florisil, higher temperature water is re quired to interrupt the van der Waals attractions between solutes and silica-bonded C-18, and even higher temperatures needed to overcome th e pi-electron interactions between aromatic solutes and XAD-4. (C) 199 8 Elsevier Science B.V. All rights reserved.