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PW07 Pesticides and Pharmaceuticals
(PW115) Determination of Fipronil and Degradates in Environmental-Water Samples by SPE and GC/MS.
Sandstrom, M1, Madsen, J1, 1 U.S. Geological Survey (USGS), National Water Quality Laboratory, Denver, CO, USA
ABSTRACT- Fipronil is a broad-spectrum insecticide effective against a wide range of crop and veterinary pests. One of its main degradation products, desulfinylfipronil, is generally more toxic than the parent compound, and there is a need for increased environmental monitoring of the fipronil and its degradation products because risk assessment predictions have shown that some fipronil formulations present a risk to endangered bird, fish, and aquatic and marine invertebrates. We developed a method for the determination of the fipronil and four fipronil degradates in water samples at nanogram-per-liter (ng/L) concentrations using solid-phase extraction (SPE) and gas chromatography mass spectrometry. The degradates include desulfinylfipronil, desulfinylfipronil amide, fipronil sulfone and fipronil sulfide. The analytes are extracted from a 1-liter filtered surface- or ground-water sample onto a 0.5-gram octadecyl bonded silica SPE column and eluted with 3 milliliters of ethyl acetate. Following solvent evaporation and exchange to toluene, the extract is analyzed by gas chromatography with detection by electron-impact mass spectrometry operated in the selected-ion monitoring mode (GC/MS/SIM). Average recoveries for these five compounds in reagent-water samples fortified at 0.1 microgram per liter (g/L) were 85 to 115 percent with relative standard deviations of 6-14 percent. Initial method detection limits averaged 0.003 g/L. Fipronil and the amide degradate exhibited a matrix-induced chromatographic enhancement in some surface water samples.
Key words: insecticides, fipronil, degradates, analysis
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