A novel method was developed for the analysis of the herbicide glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) based on lyophilization. Sample preparation steps are limited to fortification with aspartic acid as internal standard and water removal by lyophilization (3-4 days for 72 samples), followed by suspension of dry residues in borate buffer (pH=9.0) and addition of ethylenediaminetetraacetic acid (EDTA) and 9-fluorenylmethylchloroformate (FMOC-Cl) for pre-column derivatization. The obtained derivatization mixture was injected on a highly endcapped C18 column where a basic pH gradient separation of the anionic analytes from neutral derivatization byproducts was achieved, with simultaneous quantitation by fluorescence and compound confirmation by tandem mass spectrometry. Method detection limits (for 20 mL samples) were 0.058 μg/L and 0.108 μg/L for glyphosate and AMPA, respectively. The method had a high dynamic range (0.1-50.0 μg/L) which allowed quantitation at both background and high levels of the herbicide. As a case study, the methodology was successfully applied to detect the occurrence of these compounds in water canals managed by the South Florida Water Management District. These canals will be used as freshwater source to hydrate estuarine wetlands of Biscayne National Park under the Comprehensive Everglades Restoration Project, in order to decrease ecosystem stress from hypersaline conditions caused by anthropogenic reduction of historical freshwater flow towards the Biscayne Bay. Method development, validation, advantages, limitations and measured environmental concentrations are discussed. This methodology has minimal requirements in terms of materials, instruments and analyst training, which could represent a desirable tool for laboratories interested in the monitoring of glyphosate in surface waters.
Keywords: AMPA; Fluorescence; Glyphosate; Lyophilization; MS/MS; Surface waters.
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