National Water Quality Laboratory

Thursday August 11, 2022

USGS Open-File Report 95-181

Methods of Analysis by the U.S. Geological Survey National Water Quality Laboratory — Determination of Pesticides in Water by C-18 Solid-Phase Extraction and Capillary-Column Gas Chromatography/Mass Spectrometry with Selected-Ion Monitoring

Steven D. Zaugg, Mark W. Sandstrom, Steven G. Smith, and Kevin M. Fehlberg


A method for the isolation and analysis of 41 pesticides and pesticide metabolites in natural-water samples is described. The pesticides are isolated by C-18 solid-phase extraction and determined by capillary-column gas chromatography/mass spectrometry with selected-ion monitoring. Water samples are filtered to remove suspended particulate matter and then are pumped through disposable solid-phase extraction columns containing octadecyl-bonded porous silica to extract the pesticides. The columns are dried using carbon dioxide or nitrogen gas, and adsorbed pesticides are removed from the columns by elution with hexane-isopropanol (3:1). Extracted pesticides are determined by capillary-column gas chromatography/mass spectrometry with selected-ion monitoring of three characteristic ions. The upper concentration limit is 4 micrograms per liter (µg/L) for most pesticides, with the exception of widely used corn herbicides — atrazine, alachlor, cyanazine, and metolachlor — which have upper concentration limits of 20 µg/L. Single operator method detection limits in reagent-water samples range from 0.001 to 0.018 µg/L. Recoveries in reagent-water samples ranged from 37 to 126 percent for most pesticides. The estimated holding time for pesticides after extraction on the solid-phase extraction columns was 7 days. An optional on-site extraction procedure allows for samples to be collected and processed at remote sites where it is difficult to ship samples to the laboratory within the recommended pre-extraction holding time.

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