A new residue method for the analysis of glyphosate and (aminomethyl)phosphonic acid has been validated with an interlaboratory study. Five different analysts from Monsanto Co. and other laboratories participated in testing of five different matrixes: alfalfa forage, cabbage, grapes, soybean grain, environmental water. These were chosen to represent the wide variety of matrixes analyzed for glyphosate-related residues. The cornerstone of the method is concentration and isolation via chelation ion exchange, with subsequent quantitation by HPLC with postcolumn reaction detection. The method was validated over the concentration range from 0.05 to 5.00 ppm with overall analytical recoveries of 80.9 ± 13.8% for glyphosate and 79.2 ± 13.8% for (aminomethyl)phosphonic acid. The coefficient of variation for both analytes was 17%, which fits well with that predicted for the analysis of compounds in this concentration range.

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