ORIGINAL ABSTRACT

Here, we developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous determination of residual glyphosate, glufosinate, and their metabolites N-acetylglyphosate (Gly-A), 3-methylphosphinicopropionic acid (MPPA) and N-acetylglufosinate (Glu-A) in honey using a mixed mode column of reversed-phase and anion exchange without derivatization. The target analytes were extracted from honey samples using water, cleaned up on a reverse phase C18 cartridge column and an anion exchange NH2 cartridge column, and quantified using LC-MS/MS. Glyphosate, Glu-A, Gly-A, and MPPA were detected in negative ion mode based on deprotonation, whereas glufosinate was detected in positive ion mode. The coefficients of determination (R2) of the calibration curve, calculated in the range of 1-20 µg/kg for glufosinate, Glu-A, and MPPA, and 5-100 µg/kg for glyphosate and Gly-A, were higher than 0.993. The developed method was evaluated using honey samples spiked with glyphosate and Gly-A at 25 µg/kg and glufosinate, and MPPA and Glu-A at 5 µg/kg, based on the maximum residue levels. The validation results show good recoveries (86-106%) and precision (< 10%) for all target compounds. The limit of quantification of the developed method is 5 µg/kg for glyphosate, 2 µg/kg for Gly-A, and 1 µg/kg for glufosinate, MPPA and Glu-A. These results suggest that the developed method is applicable for quantifying residual glyphosate, glufosinate, and their metabolites in honey in compliance with Japanese maximum residue levels. Moreover, the proposed method was applied to the analysis of honey samples and glyphosate, glufosinate, and Glu-A were detected in some samples. The proposed method will be a useful tool for the regulatory monitoring of residual glyphosate, glufosinate, and their metabolites in honey.