Capillary electrophoresis-mass spectrometry for the direct analysis of glyphosate: method development and application to beer beverages and environmental studies

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, Nacetyl 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.

Phosphate addition enhances alkaline extraction of glyphosate from highly sorptive soils and aquatic sediments

“…Glyphosate and AMPA quantification was conducted using a matrix‐tolerant and derivatization‐free CE‐MS method previously published, 42 but using bare fused silica capillaries (length 68 cm, inner diameter 50 μm). In brief, separation was achieved using a background electrolyte of 175 mmol L −1 formic acid titrated to pH 2.8 using ammonia and a separation voltage of −30 kV with additional 30 mbar of pressure applied to the CE‐inlet.…”

“…1(C). Clearly, the use of derivatization‐free methods ideally with a high matrix tolerance would greatly facilitate glyphosate and AMPA analysis 34, 42 …”

Advancements in capacitance‐to‐digital converter‐based C4D technology for detection in capillary electrophoresis using amplified excitation voltages and comparison to classical and open‐source C4Ds

“…For the determination of glyphosate, the capillary was preconditioned prior to the first run with 1 M NaOH for 20 min at 1.5 bar and filled with a 3 mM glyphosate solution and immersed for approximately 60 h at room temperature to achieve a surface coating with glyphosate as the binding to bare fused silica is very strong and more or less irreversible at pH 6.1. No leaching was observed, which is demonstrated by the high migration time precision of <1.5% RSD ( n = 15) [31]. After immersion, the capillary was immediately used for CE separation.…”

Capillary electrophoresis applied for the determination of acidity constants and limiting electrophoretic mobilities of ionizable herbicides including glyphosate and its metabolites and for their simultaneous separation

“…Further, it is beneficial, if all analytes have a mobility high enough to ensure separation from neutral matrix compounds. The simplest way to estimate suitable pH values is by plotting the effective electrophoretic mobility of the analytes as well as potentially interfering components (here: phosphate [32]) against the pH as done in Figure 1. To achieve stable separation conditions and high migration time repeatability a pH should be chosen where the slopes of the curves in the µ(pH)-plot are low (ideally zero) to avoid a significant 1 mobility change by minimal pH changes in the BGE.…”