Determination of glyphosate, AMPA, and glufosinate in honey by online solid-phase extraction-liquid chromatography-tandem mass spectrometry

Glyphosate is currently one of the most important herbicides worldwide. Its unique properties provide for a wide range of uses in agriculture but also in non-agricultural areas. At the same time, its zwitterionic nature prevents the inclusion in multi-residue analytical methods for environmental monitoring. Consequently, despite its extensive use, data on occurrence of glyphosate in the aquatic environment is still scarce. Based on existing methods, we developed a simplified procedure for the determination of glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) in water samples using derivatization with fluorenylmethyl chloroformate FMOC-Cl, combined with on-line solid phase extraction and liquid chromatography-tandem mass spectrometry (LC-MS/MS) detection. This method was extensively tested on over 1000 samples of surface water, groundwater, and treated wastewater and proved to be simple, sensitive, and reliable. Limits of quantification of 0.005 μg/L were routinely achieved. Glyphosate and AMPA were detected in the vast majority of stream water samples in the area of Zurich, Switzerland, with median concentrations of 0.11 and 0.20 μg/L and 95th percentile concentrations of 2.1 and 2.6 μg/L, respectively. Stream water data and data from treated wastewater indicated that non-agricultural uses may significantly contribute to the overall loads of glyphosate and AMPA in surface waters. In the investigated groundwater samples, selected specifically because they had shown presence of other herbicides in previous monitoring programs, glyphosate and AMPA were generally not detected, except for two monitoring sites in Karst aquifers, indicating that these compounds show much less tendency for leaching.

Despite having been the focus of much attention from the scientific community during recent years, glyphosate is still a challenging compound from an analytical point of view because of its physicochemical properties: relatively low molecular weight, high polarity, high water solubility, low organic solvent solubility, amphoteric behaviour and ease to form metal complexes. Large efforts have been directed towards developing suitable, sensitive and robust methods for the routine analysis of this widely used herbicide. In the present work, a magnetic particle immunoassay (IA) has been evaluated for fast, reliable and accurate part-per-trillion monitoring of glyphosate in water matrixes, in combination with a new analytical method based on solid-phase extraction (SPE), followed by liquid chromatography (LC) coupled to tandem mass spectrometry (MS/MS), for the confirmatory analysis of positive samples. The magnetic particle IA has been applied to the analysis of about 140 samples of groundwater from Catalonia (NE Spain) collected during four sampling campaigns. Glyphosate was present above limit of quantification levels in 41% of the samples with concentrations as high as 2.5 μg/L and a mean concentration of 200 ng/L. Good agreement was obtained when comparing the results from IA and on-line SPE-LC-MS/MS analyses. In addition, no false negatives were obtained by the use of the rapid IA. This is one of the few works related to the analysis of glyphosate in real groundwater samples and the presented data confirm that, although it has low mobility in soils, glyphosate is capable of reaching groundwater.