A method for the isolation of organonitrogen herbicides from natural
water samples using solid-phase extraction and analysis by capillary-column
gas chromatography/mass spectrometry with selected-ion monitoring is
described. Water samples are filtered to remove suspended particulate matter
and then are pumped through disposable solid-phase extraction cartridges
containing octadecyl-bonded porous silica to remove the herbicides. The
cartridges are dried using carbon dioxide, and adsorbed herbicides are
removed from the cartridges by elution with 1.8 milliliters of hexaneisopropanol
(3:1). Extracts of the eluants are analyzed by capillary-column gas
chromatography/mass spectrometry with selected-ion monitoring of at least
three characteristic ions. The method detection limits are dependent on
sample matrix and each particular herbicide. The method detection limits,
based on a 100-milliliter sample size, range from 0.02 to 0.25 microgram per
liter. Recoveries averaged 80 to 115 percent for the 23 herbicides and 2
metabolites in 1 reagent-water and 2 natural-water samples fortified at levels
of 0.2 and 2.0 micrograms per liter.
