DETERMINATION OF DISSOLVED-PHASE PESTICIDES IN SURFACE-WATER FROM THEYAKIMA RIVER BASIN, WASHINGTON, USING THE GOULDEN LARGE-SAMPLE EXTRACTOR AND GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

Concentrations of pesticides in the dissolved phase of surface water s amples from the Yakima River basin, WA, were determined using preconce ntration in the Goulden large-sample extractor (GLSE) and gas chromato graphy/mass spectrometry (GC/MS) analysis. Sample volumes ranging from 10 to 120 L were processed with the GLSE, and the results from the la rge-sample analyses were compared to those derived from 1-L continuous liquid-liquid extractions. Few of the 40 target pesticides were detec ted in 1-L samples, whereas large-sample preconcentration in the GLSE provided detectable levels for many of the target pesticides. The numb er of pesticides detected in GLSE processed samples was usually direct ly proportional to sample volume, although the measured concentrations of the pesticides were generally lower at the larger sample volumes f or the same water source. The GLSE can be used to provide lower detect ion levels relative to conventional liquid-liquid extraction in GC/MS analysis of pesticides in samples of surface water.