Double-Disk Solid-Phase Extraction:
Simultaneous Cleanup and Trace Enrichment of Herbicides and Metabolites from Environmental Samples

By Imma Ferrer, Damiæ Barcelš, and E.M. Thurman
Department of Environmental Chemistry, CID-CSIC c/Jordi Girona, 18-26, 08034 Barcelona, Spain, and
U.S. Geological Survey, 4821 Quail Crest Place, Lawrence, Kansas 66049

Abstract

Phenylurea and triazine herbicides, including some metabolites, were isolated from water and soil extracts by solid-phase extraction using a layered system of two extraction disks, a method called double-disk solid-phase extraction. The first disk consisted of strong anion exchange (SAX) of 10-Îm stryene divinylbenzene (SDB) particles embedded in Teflon, and the second disk was a C18; disk of 10-Îm particles also embedded in Teflon. A volume of 500 mL of water or aqueous soil extract is passed through the layered system with the SAX disk first. The purpose of the SAX disk is to remove the humic and fulvic acids from the water or aqueous soil extract by ion exchange through their carboxyl groups. Even during methanol elution of herbicides, the humic substances remain bound to the SAX dish with <85% retention. Elution with methanol results in more than 90% recovery of the herbicides from the layered extraction disks. Removal of the humic and fulvic acids results in greater sensitivity for diode array detection quantitation (0.05 Îg/L for herbicides) by substantially reducing the absorbance of the humic peak on the LC chromatogram. The herbicides adsorb to the SAX disk either through hydrogen bonding to the anion-exchange sites or by hydrophobic interaction with the SDB surface of the anion-exchange disk. The method was tested for the analysis of natural water samples from the Mississippi Embayment, a cotton growning area of the southeastern United States.

Additional information about the Organic Geochemistry Research Laboratory can be found at: http://ks.water.usgs.gov/Kansas/studies/reslab/

Ferrer, Imma, Barcelš, Damiæ, and Thurman, E.M., 1999, Double-Disk Solid-Phase Extraction [abst.]: Simultaneous Cleanup and Trace Enrichment of Herbicides and Metabolites from Environmental Samples: Analytical Chemistry, v. 71, n. 5, p. 1009-1015.

To request a paper copy of this journal article, email: scribner@usgs.gov