METHOD FOR THE DETERMINATION OF GLYPHOSATE AND (AMINOMETHYL)PHOSPHONIC ACID IN SOIL USING ELECTRON-CAPTURE GAS-CHROMATOGRAPHY

A procedure for extraction of the phosphonic acid herbicide glyphosate and its metabolite (aminomethyl)-phosphonic acid from soils and for analysis of these two compounds by electron capture gas chromatography is described. Both compounds were extracted from the soil with aqueous triethylamine, cleaned up with anion- and cation-exchange resins, and derivatized in a single-step procedure with trifluoroacetic anhydride and trifluoroethanol. Where extraction of soil immediately followed fortification, recovery of glyphosate ranged from 88% to 104%. However, where extraction was delayed 13 h after fortification, the recovery of glyphosate varied from 48% to 67%. This low recovery of glyphosate was thought to be due to adsorption of some of the herbicide to soil particles during the period prior to extraction. This suggested that triethylamine was able to extract soluble glyphosate and weakly adsorbed glyphosate but not glyphosate that was strongly adsorbed during a pre-extraction period.