Abstract: An analytical method for the determination of glyphosate and its metabolite aminomethylphosphonic acid in tea was established by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The samples were extracted and preliminarily purified using a water dichloromethane system and the sample matrix was further purified by mixed-mode cation exchanger column filled with polystyrene bonded benzenesulfonic acid in an automatic solid phase extractor. The optimal derivation conditions obtained by orthogonal test and variance analysis were 5% sodium borate buffer solution and 10 mg·mL^-1 FMOC-Cl derivatizing agent for derivatization at room temperature for 2 h. The derived sample solution was subjected to gradient elution separation on HSS T₃ column and 5 mmol·L^-1 ammonium acetate solution (containing 0.1% formic acid)-acetonitrile mobile phase system. The targets were analyzed by UPLC-MS/MS and quantified by internal standard method. The linearity of glyphosate and aminomethylphosphonic acid was good in the concentration range of 0.2-50 ng·mL^-1 and the correlation coefficient (R²) was greater than 0.999. The detection limit of the method was 2 μg·kg^-1, and the quantitation limit was 5 μg·kg^-1. The recoveries of 5, 50 and 250 μg·kg^-1 were in range of 94.2%-106.7% with relative standard deviations of 3.8%-4.9%, at low, medium and high spiked levels. The method is suitable for the determination of glyphosate and aminomethylphosphonic acid residues in daily large quantities of tea samples in the laboratory with the advantages of high efficiency, high accuracy, high throughput, low matrix interference and high degree of automation.

Key words: glyphosate, aminomethylphosphonic acid, automatic solid phase extractor, UPLC-MS/MS