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
by
Diana S. Aga (U.S. Geological Survey, Lawrence, KS), E. Michael
Thurman (U.S. Geological Survey, Lawrence, KS), and Michael L. Pomes (U.S.
Geological Survey, Lawrence, KS)
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.
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