Residue Level Determination of the Aquatic Herbicide Fluridone and a Potential Photoproduct (N-Methylformamide) in Water

Abstract

Methods are presented for the determination of the aquatic herbicide fluridone and N-methylformamide (NMF), a potential photoproduct of fluridone which has thus far been observed only in a laboratory aqueous photolysis study. Water samples are passed through a Sep-Pak C18 cartridge to extract fluridone while NMF passes unretained through the cartridge with the water. Fluridone is eluted from the cartridge with methanol, which is then concentrated for analysis by liquid chromatography with UV detection at 313 nm. The water eluate containing NMF is concentrated for analysis by rotary vacuum evaporation at 40-46 degrees C. Methanol is added to help evaporate the water, and glycerol is added as a keeper solvent to retain NMF during the evaporation. The residual NMF is dissolved in methanol for analysis by gas chromatography with a Hall electrolytic conductivity detector operated in the nitrogen mode. The assay limits of detection are 1 and 2 ppb for fluridone and NMF, respectively. Recoveries averaged 98% for fluridone at 1-400 ppb and 87% for NMF at 2-50 ppb.