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
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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