Abstract
In this study, we developed and validated a CE-TOF-MS method for the quantification of glyphosate (N-(phosphonomethyl)glycine) and its major degradation product aminomethylphosphonic acid (AMPA) in different samples including beer, media from toxicological analysis with Daphnia magna, and sorption experiments. Using a background electrolyte (BGE) of very low pH, where glyphosate is still negatively charged but many matrix components become neutral or protonated, a very high separation selectivity was reached. The presence of inorganic salts in the sample was advantageous with regard to preconcentration via transient isotachophoresis. The advantages of our new method are the following: no derivatization is needed, high separation selectivity and thus matrix tolerance, speed of analysis, limits of detection suitable for many applications in food and environmental science, negligible disturbance by metal chelation. LODs for glyphosate were < 5 μg/L for both aqueous and beer samples, the linear range in aqueous samples was 5–3000 μg/L, for beer samples 10–3000 μg/L. For AMPA, LODs were 3.3 and 30.6 μg/L, and the linear range 10–3000 μg/L and 50–3000 μg/L, for aqueous and beer samples, respectively. Recoveries in beer samples for glyphosate were 94.3–110.7% and for AMPA 80.2–100.4%. We analyzed 12 German and 2 Danish beer samples. Quantification of glyphosate and AMPA was possible using isotopically labeled standards without enrichment, purification, or dilution, only degassing and filtration were required for sample preparation. Finally, we demonstrate the applicability of the method for other strong acids, relevant in food and environmental sciences such as N-acetyl glyphosate, N-acetyl AMPA (present in some glyphosate resistant crop), trifluoroacetic acid, 2-methyl-4-chlorophenoxyacetic acid, glufosinate and its degradation product 3-(methylphosphinico)propionic acid, oxamic acid, and others.
Highlights
Glyphosate (GLP) is a widely used broadband herbicide with an annual production of more than one million tons [1]
Twenty-five percent aqueous ammonia solution (p.a. grade), aluminum chloride, iron(III) chloride hexahydrate, manganese(II) chloride tetrahydrate, magnesium chloride hexahydrate (99.6%), zinc acetate dihydrate (> 99%), aminomethylphosphonic acid (> 99%), 2-methyl-4-chlorophenoxyacetic acid (99.2%), oxamic acid (> 98%), difluoroacetic acid (98%), 3-(methylphosphinico)propionic acid (98%), and iminodiacetic acid were obtained from Sigma (Steinheim, Germany)
Labeled 13C2-15N-glyphosate, N-nitroso glyphosate, N-acetyl glyphosate, and N-acetyl aminomethylphosphonic acid (AMPA) were bought from TRC/BIOZOL (Echingen, Germany), 13C-15N-D2AMPA from LGC Standards (Wesel, Germany), phosphonic acid from HPC Standard (Cunnersdorf, Germany), and trifluoroacetic acid (99%) from VWR (Darmstadt, Germany)
Summary
Glyphosate (GLP) is a widely used broadband herbicide with an annual production of more than one million tons [1]. Despite the fact that GLP is the most widely applied herbicide worldwide [3, 4], a thorough understanding of its fate in the environment including mobility, bioavailability, and microbial degradation is still lacking. GLP can sorb to soil minerals which may limit bioavailability and prevent quantitative mineralization. An overview on findings of GLP in water samples was summarized in the reviews by Vereecken [7] and Saunders and Pezeshki [6], and for AMPA by Grandcoin et al [8]. Human dietary exposure to GLP was discussed by Stephenson and Harris [9], who presented a large overview on GLP findings in foodstuff
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