Coupling Solid-Phase Extraction and Enzyme-Linked Immunosorbent Assay for Ulratrace Determination of Herbicides in Pristine Water

By D.S. Aga and E.M. Thurman

Abstract

Solid-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.

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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.

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