U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Measurement of Concentrations of Alachlor and Its Ethanesulfonic Acid Metabolite in Water by Solid-Phase Extraction and Enzyme-Linked Immunosorbent Assay

Abstract

Solid-phase extraction (SPE) and enzyme-linked immunosorbent assay (ELISA) were combined for the trace analysis of 2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide (alachlor) and 2-[(2,6-diethylphenyl)(methoxymethyl)amino-]-2-oxoethanesulfonic acid (ESA, a major soil metabolite of alachlor). The anti-alachlor antibody reacted not only with alachlor but also with ESA, which produced false-positive immunoassay detections of alachlor in natural water samples. The combination of SPE with ELISA effectively separates and determines both parent and metabolite compounds; thus, the same antibody may be used for two ELISA methods. Alachlor and ESA were isolated from water by SPE on C18 resin and were eluted sequentially with ethyl acetate and methanol. The separation involves the difference in solubility of the ionic sulfonic acid in ethyl acetate and methanol. The SPE-ELISA method has a detection limit of 0.01 µg/L (micrograms per liter) for alachlor and 0.05 µg/L for ESA with a precision of ±10 percent. Analyses of surface-water and ground-water samples were confirmed by high-performance liquid chromatography with photodiode-array detection and gas chromatography/mass spectrometry. Results showed widespread presence of ESA in surface water and ground water of the midwestern United States in concentrations of 0.10 to greater than 10 µg/L.