Determination of New Sulfonic Acid Metabolites of Chloroacetanilide Herbicides in Ground Water by Ion Trap MS/MS

Abstract

The analysis of several groundwater samples containing acetochlor, alachlor, and metolachlor by ion trap tandem mass spectrometry (MS/MS) showed the presence of several sulfonated metabolites of these parent herbicides. Previous analysis of the samples by high-performance liquid chromatography/mass spectrometry (HPLC/MS) by using a single quadruple mass spectrometer indicated the presence of acetochlor, alachlor, and metolachlor ethane sulfonic acids (ESAs). Ion trap MS/MS was used to confirm the presence of the acetochlor and alachlor ESAs which have the same exact mass of 314 amu. Acetochlor and alachlor ESAs were differentiated by isolating the 314 amu parent ion by ion trap and the subsequent fragmentation in the trap to the 162 and 121 ions for acetochlor and 176 and 121 ions for alachlor. Although the characteristic 80 amu ion, corresponding to SO₃¯ ¯, was detected in scan mode, it did not appear in the trap under isolation conditions, which is a shortcoming of the trap compared to triple quad MS/MS. However, the signature ions of the ESA metabolites were found for two new compounds, which are secondary amides of acetochlor, alachlor, and metolachlor ESAs. The approximate concentrations of the ESA amides were about 10 percent of the level of the primary ESAs and these compounds represent the first identification of secondary metabolites of the ubiquitous ESA metabolites of acetochlor, alachlor, and metolachlor in groundwater samples of the Midwestern United States.

Additional information about the Organic Geochemistry Research Laboratory can be found at: http://ks.water.usgs.gov/studies/reslab/

Thurman, E.M., Lindsey, M.T. Lindsey, Ferrer, Imma, and Furlong, E.T., 2001, Determination of new sulfonic acid metabolites of chloroacetanilide herbicides in ground water by ion trap MS/MS [abst.], in Abstracts of the Eighth Symposium on the Chemistry and Fate of Modern Pesticides, August 21-24, 2001, Copenhagen, Denmark: International Association of Environmental Analytical Chemistry, p. 72.