Overcoming the Challenges of Analysing Ionic Polar Pesticides in Food

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RAFA 2017
Benjamin Wuyts, Euan Ross, Simon Hird, Dimple Shah, and Gareth Cleland
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Other Symposium
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Glyphosate is a non-selective broad spectrum herbicide, which accounts for more than half of global herbicide sales.  While discussions on the toxicological concerns of glyphosate and associated compounds continue, maximum residue limits (MRLs) are enforced globally, requiring continued analytical testing to ensure consumer safety. The chromatographic analysis of glyphosate, its metabolites and similar compounds can prove challenging due to the lack of retention by reverse phase techniques.  Common alternatives include derivatization and ion chromatography. However, due to time-consuming sample preparation, MS incompatible solvents and the need for specialized equipment and/or reagents, the underivatized LC-MS/MS approach is still preferred. Due to the physicochemical characteristics of these compounds, repeatable peak shape and robust methodologies can be challenging to run routinely.

In the poster, a simple UPLC-MS/MS method will be presented for the direct analysis of highly polar pesticides, which gives sufficient retention and provides excellent sensitivity, robustly, to exceed enforced MRLs.  A panel of representative anionic polar pesticides, including aminomethylphosphonic acid (AMPA), glufosinate and glyphosate have been targeted in a selection of relevant foodstuffs prepared using a modified version of the Quick Polar Pesticides (QuPPe) extraction method. Chromatographic separation was achieved on a novel weak ion exchange/ hydrophilic interaction liquid chromatography (HILIC) column, applying an ammonium formate mobile phase gradient.

Method performance was evaluated, in the absence of isotopically labeled internal standard, by assessing chromatographic repeatability, linearity, accuracy and sensitivity.  Satisfactory linearity was found for all pesticides over a range of 0.0001 to 0.250 mg/kg in all matrices (R² > 0.995, residuals < 20%).  The repeatability (%RSD) of the method was determined using spiked matrices, prepared in replicates.  Incurred residues detected in certain samples were quantified using standard addition calibration curves and identified in accordance with the SANTE guidelines 11945/2015.


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