Solid-phase extraction of polycyclic aromatic hydrocarbons in surface water - Negative effect of humic acid

The effect of humic acid on solid-phase extraction of polycyclic aromatic h ydrocarbons (PAHs) from surface water was studied. The hydrophobic PAHs sho w significant association with humic acid, and this was confirmed to be the cause of negative effect when conventional reversed-phase solid-phase extr action (RP-SPE) was employed to extract the analytes from aqueous samples. As an alternative, dynamic ion-exchange (DIE) SPE could simultaneously extr act both the fraction of the analytes which was associated with humic acid, and that which was freely dissolved. Using the 16 US Environmental Protect ion Agency priority PAHs as model compounds, the recoveries of the highly h ydrophobic components by DIE-SPE were 10-30% higher than those by RP-SPE fo r a 1000-ml water sample dissolved with Aldrich humic acid (of 4.1 mg/l dis solved organic carbon content). A similar result was also obtained for 500 mi of natural surface water although the difference in recoveries between t he two methods for this sample was smaller than that for the simulated samp le. For validation of the method, the artifacts in connection with DIE-SPE in extracting the fraction of analytes which was freely dissolved and that which was associated with humic acid were investigated. (C) 2001 Elsevier S cience BN. All rights reserved.