Coupling Solid-Phase Extraction and Enzyme-Linked Immunosorbent Assay for Ulratrace Determination of Herbicides in Pristine WaterBy D.S. Aga and E.M. Thurman AbstractSolid-phase extraction (SPE) and enzyme-linked immunosorbent assay (ELISA) were coupled for automated trace analysis of pristine water samples containing 2-chloro-4-ethylamino-6-isopropylamine-s-triazine (atrazine) and 2-chloro-2',6'-diethyl-N-(methoxymethyl) acetanilide (alachlor). The isolation of the two herbicides on a C18-resin invloved the selection of an elution solvent that both removes interfering substances and is compatible with ELISA. Ethyl acetate was selected as the elution solvent followed by a solvent exchange with methanol/water (20/80, % v/v). The SPE-ELISA method has a detection limit of 5.0 ng/L (5 ppt), >90% recovery, and a relative standard deviation of �%. The performance of a microtiter plate-based ELISA and a magnetic particle-based ELISA coupled to SPE was also evaluated. Although the sensitivity of the two ELISA methods was comparable, the precision using magnetic particles was improved considerably (�% versus �%) because of the faster reaction kinetics provided by the magnetic particles. Finally, SPE-ELISA and isotope dilution gas chromatography/mass spectrometry correlated well (correlation coefficient of 0.96) for lake-water samples. The SPE-ELISA method is simple and may have broader applications for the inexpensive automated analysis of other contaminants in water at trace levels. Additional information about the Organic Geochemistry Research Laboratory can be found at: http://ks.water.usgs.gov/studies/reslab/Aga, D.S., and Thurman, E.M., 1993, Coupling solid-phase extraction and enzyme-linked immunosorbent assay for ulratrace determination of herbicides in pristine water [abst.]: Analytical Chemistry, v. 65, no. 20, p. 2894-2898. To request a paper copy of this journal article, email: scribner@.usgs.gov |