Glyphosate is a commonly applied herbicide in coffee plantations. Because of its non-selective mode of action it can damage the crop exposed through spray drift. Therefore, it is of interest to study glyphosate fate in coffee plants. The aim of this study was to develop an analytical method for accurate and precise quantification of glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) at trace levels in coffee leaves using liquid chromatography with single-quadrupole mass spectrometry detection. The method is based on a two-step solid phase extraction (SPE) with an intermediate derivatization reaction using 9-fluorenylmethylchloroformate (FMOC). An isotope dilution method was used to account for matrix effects and to enhance the confidence in analyte identification. The limit of quantification (LOQ) for glyphosate and AMPA in coffee leaves was 41 and 111 μg kg(-1) dry weight, respectively. For the method optimization a design of experiments (DOE) approach was used. The sample clean-up procedure can be simplified for the analysis of less challenging matrices, for laboratories having a tandem mass spectrometry detector and for cases in which quantification limits above 0.1 mg kg(-1) are acceptable, which is often the case for glyphosate. The method is robust, possesses high identification confidence, while being suitable for most commercial and academic laboratories. All leaf samples from five coffee fields analyzed (n=21) contained glyphosate, while AMPA was absent. The simplified clean-up procedure was successfully validated for coffee leaves, rice, black beans and river water.
Keywords: Coffea arabica; Coffee; Glyphosate analysis; Liquid chromatography mass spectrometry; Single quadrupole.
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