Chemical structures of studied molecules: a) Glyphosate; b) Aminomethylphosphonic acid (AMPA); c) Glufosinate. 

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... [N-(phosphonomethyl)glycine] is a non- selective, post-emergence herbicide world-wide used for weed and vegetation control. [1] In Switzerland, it rep- resented around 13% of all plant protection products sales in 2005, [2] whereas in the United States it was 26% in 2007. [3] When applied in the field, it shows a strong tendency to sorption and is rapidly transformed into AMPA [aminomethylphosphonic acid] in soils. Glyphosate is therefore often assumed to not reach water bodies. [4] However, due to their high water solubility, glyphosate and AMPA were found to be leached or washed out from soil surface layers and to reach ground and surface waters. [5][6][7] A large survey carried out in [2003][2004] in France showed that more than 50% of the analyzed surface water sam- ples contained AMPA and that more than 30% contained glyphosate. [8] The maximum concentrations reached 48 and 165 µg/l for AMPA and glyphosate respectively. In ground- water samples, only 2-3% contained these molecules with a maximum concentration of 6.8 µg/l for glyphosate. But due to its zwitterionic nature and its tendency to form stable complexes with metal ions, trace quantification of glyphosate remains an analytical challenge. [9][10][11] Indeed, glyphosate is an amino acid with several acid dissociation constant values (pKa = 2, 2.6, 5.6 and 10.6), due to the ionization of its functional groups: phosphonate, carboxyl and amine, [12] which renders the analytical method not Downloaded by [Université de Genève] at 01: 38 11 March 2014 trivial. Its main metabolite AMPA and the herbicide glufos- inate [2-amino-4-(hydroxy-methylphosphinyl)butyric acid] are also aminophosphonates, but with primary amine groups, whereas glyphosate has a secondary one (Fig. 1). In order to analyze these compounds, gas chromatogra- phy was used by several authors, [13][14][15] but this is time- consuming and needs a derivatization procedure, in order to confer volatility to these compounds. [16,17] According to Stalikas and Konidari, [16] liquid chromatography is con- sidered a more adequate technique to analyze chemi- cals with these kind of properties. Moreover, the recent use of tandem mass spectroscopy techniques, following liquid chromatography (LC-MS/MS), allows determin- ing low concentrations of ionizable pesticides, possess- ing, like glyphosate, either acidic and/or basic functional group(s). [17] Glyphosate detection at trace levels, i.e. below 100 ng/l, needs a concentration step of the water samples. Among available methods, solid phase extraction (SPE) was proposed by several authors, [17][18][19] but a derivatization step, in order to lower its polarity, is nonetheless required. [20] To do so, the pre-column derivatization with FMOC-Cl [9-fluorenymethylchloroformate] is considered the most simple and showed better results than other derivatization agents. [21] Moreover, the use of isotope-labeled standards as internal standards (IS) can minimize the so-called "matrix-effect", [22] as well as derivatization variations. [17] Glyphosate analysis was also improved with a pre- acidification step at pH 1, in order to break complexes that are formed with some metals or with natural organic matter, especially in groundwater samples. [23] Furthermore, Freuze et al. [9] proposed to add the complexing agent ethylenediamine tetraacetic acid (EDTA) to the sample, because some complexes may be reformed at the required pH of 9.2 for the derivatization with FMOC-Cl. These latter improvements are included in the "state of the art" analytical procedure proposed by Hanke et al. [24] and developed for surface-and groundwater samples. These authors reached limits of quantification at the ng/l level and obtained very good recoveries (91-107%). Considering the analytical challenges posed by glyphosate, AMPA and glufosinate, the objectives of this study were two-fold. First, it aimed at testing and validati- ng an analytical method that allows quantifying glyphosate, its main by-product AMPA and the less used herbicide glu- fosinate, by ultra performance liquid chromatography and tandem mass spectrometry (UPLC-MS/MS) in different typical environmental water samples (from surface water samples to soil solutions). The purpose was to test the reli- ability of the method and validate the matrix effect correc- tion with internal standards for further analysis in relevant natural samples. Indeed and as mentioned earlier, matrix effects can alter significantly the obtained signal. To do so, the significance of slope and intercept discrepancies be- tween different matrices, spiked at several concentrations, was tested. Second, the occurrence of the three compounds was determined in different kinds of aqueous media with different anthropogenic influences. To do so, a small river of western Switzerland situated in a vineyard catchment was chosen, as well as the Vidy Bay, part of Lake Geneva, which receives the effluents of the city of ...