A procedure for the determination and confirmation of acidic herbicides In water Is described. This method is applicable to 13 commonly used herbicides, including the monochlorinated ones, at μg/L and sub-μg/L levels. The water sample is acidified to pH < 2 and extracted by dichloromethane. The herbicides are converted into their pentafluorobenzyl (PFB) derivatives and the products are cleaned up on a silica gel column. A gel permeation cleanup using a Bio-Beads S-X3 column is included to remove the PFB esters of fatty acids, which are the major Interferences in the final analysis using electron capture detection (ECD). Confirmation of herbicides employing electron Impact and negative ion chemical lonlzatlon/ mass spectrometry (NICI/MS) is discussed and applied to river water samples. The mean recoveries of herbicides for water samples fortified at 1 and 0.1 μg/L range from 45 to over 90%. The detection limit of herbicides in natural water samples is 0.05 μg/L with ECD and 0.02 μg/L with NICI/MS.
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