The carbon stable isotope compositions of glyphosate and aminomethylphosphonic acid (AMPA): Improved analytical sensitivity and first application to environmental water matrices

Rationale The presence of glyphosate and its degradation product aminomethylphosphonic acid (AMPA) in the environment has adverse effects on environmental quality, raising the need to better constrain their fates, in particular the processes that control their production and degradation. Our aim was to improve the sensitivity of their delta C-13 analysis and demonstrate the feasibility of measuring them in natural surface water. Methods The delta C-13 values of dissolved glyphosate and AMPA were determined using isotope ratio mass spectrometry (IRMS) (Delta V Plus instrument) coupled to a high-performance liquid chromatography (HPLC) unit, where glyphosate and AMPA were separated on a Hypercarb column. Results We demonstrated an improved sensitivity of the delta C-13 analysis for glyphosate and AMPA by LC/IRMS compared with previous studies. For waters from the carbonate and silicate hydrofacies, while no pretreatment was required for the isotope analysis of glyphosate, removal by H3PO4 acidification of dissolved inorganic carbon, that co-elutes with AMPA, was required prior to its analysis. We successfully tested a freeze-drying pre-concentration method showing no associated isotope fractionation up to concentration factors of 500 and 50 for glyphosate and AMPA, respectively. Conclusions We demonstrated, for the first time, the feasibility of measuring the delta C-13 values of glyphosate and AMPA in natural surface waters with contrasted hydrofacies (calcium carbonate and silicate types). This opens new fields in pesticide research, especially on the characterization of processes that control their degradation and the production of their secondary byproducts.

Automated summary

The study aimed to improve the sensitivity of delta C-13 analysis of glyphosate and AMPA, and demonstrate their measurability in natural surface water. LC/IRMS technology showed improved analysis results, and a freeze-drying pre-concentration method was successfully tested. Differentiation was needed in water samples, highlighting the feasibility of measuring these compounds in various hydrofacies.