Elaboration of trapping conditions on zirconia for the online SPE-LC-MS/MS analysis of glyphosate and other polar organophosphonate and -phosphinate pesticide residues in plant-based food extracts.

BACKGROUND: Previous studies involving cleanup via conventional solid-phase extraction (SPE) materials to overcome matrix effects for the polar organophosphonate and -phosphinate pesticides glyphosate, glufosinate, ethephon, fosetyl, and their various metabolites often showed limitations due to the existence of various matrix compounds in plant commodities with similar polarity. To overcome existing drawbacks, we utilized the unique selectivity provided by metal oxides as SPE materials. These were exploited in a novel automated online SPE-LC-MS/MS method which allowed analyte-specific trapping in the presence of excessive amounts of matrix compounds as typically contained in extracts of the Quick Polar Pesticides (QuPPe) method.

RESULTS: For the purpose of this study, we combined the analytes with high levels of ten food-relevant matrix compounds based on the highest levels encountered in various food commodities. Initial comparisons indicated a quantitative trapping of all the considered analytes under these quasi worst-case scenarios on zirconia (ZrO2) but not on titania (TiO2). The impact of different eluent additives (formic acid and acetic acid) and organic solvents (acetonitrile and methanol) were studied in terms of efficiency, selectivity and robustness. Finally, 50 mmol/L formic acid in water/methanol (50/50, v/v) was employed during the analyte trapping on the zirconia SPE column. Sugars and certain anions such as chloride and nitrate could be effectively removed, while matrix compounds such as organic acids with an affinity towards zirconia, similar to the analytes, were also trapped.

SIGNIFICANCE: The insights of the developed online SPE-LC-MS/MS method provided a viable strategy when developing online SPE approaches, as the presented setup enabled a flexible monitoring of all SPE steps within one run during method development without changes in the configuration. The ZrO2 SPE material offered a robust tool for future implementation in a fully developed and automated online-SPE-LC-MS/MS method for the routine analysis of polar organophosphonate and -phosphinate pesticide residues.