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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

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Isocratic Separation of Alachlor Ethanesulfonic Acid, Alachlor Oxoacetic Acid, and Hydroxyatrazine by Reversed-Phase Liquid Chromatography

by

Michael L. Pomes (U.S. Geological Survey, Lawrence, Ks.), Douglas F. Holub (U.S. Geological Survey, Lawrence, Ks.), Diana S. Aga (U.S. Geological Survey, Lawrence, Ks.), and E.M. Thurman (U.S. Geological Survey, Lawrence, Ks.)

Abstract

The polar nature of two alachlor metabolites, alachlor ethanesulfonic acid and alachlor oxoacetic acid, makes their detection by gas chromatography/mass spectrometry impossible without derivatization. Enzyme-linked immunosorbent-assay techniques cannot distinguish alachlor metabolites from alachlor; thus, reversed-phase high-performance liquid chromatography with photodiode-array detection is required for the separation and spectral detection of these analytes. Use of an isocratic, methanol/10 millimolar sodium phosphate dibasic buffer mixture as the mobile phase with reversed-phase (C-18) high-performance liquid chromatography allows for the separation and quantification of alachlor ethanesulfonic acid, alachlor oxoacetic acid, and hydroxyatrazine at concentrations greater than or equal to 0.10 micrograms per liter in 100-milliliter water samples. The buffer in the methanol mixture provides cations that ion pair with the alachlor metabolite anions to decrease polarity and promote nonpolar interactions between the analytes and the reversed-phase column. Enhanced chromatographic resolution results from injecting samples in a matrix that contains less methanol than the mobile phase. The disparity between the methanol content of the sample matrix and the mobile phase focuses the analytes at the head of the chromatographic column to produce sharper peaks because the analytes are less soluble in the sample matrix than in the mobile phase. Results by reversed-phase high-performance liquid chromatography show that one can detect alachlor ethanesulfonic acid in surface-water, along with lesser concentrations of alachlor oxoacetic acid and hydroxyatrazine.

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