Carbon isotope ratio measurements of glyphosate and AMPA by liquid chromatography coupled to isotope ratio mass spectrometry

Abstract

The interest in compound-specific isotope analysis for product authenticity control and source differentiation in environmental sciences has grown rapidly during the last decade. However, the isotopic analysis of very polar analytes is a challenging task due to the lack of suitable chromatographic separation techniques which can be used coupled to isotope ratio mass spectrometry. In this work, we present the first method to measure carbon isotope compositions of the widely applied herbicide glyphosate and its metabolite aminomethylphosphonic acid (AMPA) by liquid chromatography coupled to isotope ratio mass spectrometry. We demonstrate that this analysis can be carried out either in cation exchange or in reversed-phase separation modes. The reversed-phase separation yields a better performance in terms of resolution compared with the cation exchange method. The measurement of commercial glyphosate herbicide samples show its principal applicability and reveals a wide range of δ(13)C values between -24 and -34 ‰ for different manufacturers. The absolute minimum amounts required to perform a precise and accurate determination of carbon isotope compositions of glyphosate and AMPA were in the sub-microgram range. The method proposed is sensitive enough to further perform the experiments that are necessary to better understand the carbon isotope fractionation associated to the natural degradation of glyphosate into AMPA. Furthermore, it can be used for contaminant source allocation and product authenticity as well.

13C- and 15N-Isotope Analysis of Desphenylchloridazon by Liquid Chromatography–Isotope-Ratio Mass Spectrometry and Derivatization Gas Chromatography–Isotope-Ratio Mass Spectrometry

“…Like most polar organic compounds, however, DPC is not amenable to GC as it decomposes before reaching a boiling point (see Table S1). To analyze the isotopic composition of such polar organic compounds, derivatization-GC-IRMS has been brought forward as alternative strategy 24,25,31,32 . This approach is chosen as the methylation of DPC enhances its GC suitability.…”

Determination of carbon isotope ratios for honey samples by means of a liquid chromatography/isotope ratio mass spectrometry system coupled with a post‐column pump

“…Despite these problems, LC/IRMS has been used to analyze compounds in various sample media, including caffeine in beverages; organic acids, glucose, and fructose in lime and lemon juices; glycerol and ethanol in wine; vanillin in chocolate bars and snack foods; glyphosate and aminomethylphosphonic acid; sulfonamides in pharmaceuticals; glucose in blood plasma; amino acids; steroids; and sugars (glucose, fructose, disaccharides, trisaccharides, and oligosaccharides) in honey …”

Online wet oxidation/isotope ratio mass spectrometry method for determination of stable carbon isotope ratios of water‐soluble organic carbon in particulate matter

“…All the organic compounds are oxidized to CO 2 by thermally activated peroxodisulfate, as shown in Equation for ethanol: The generated CO 2 is separated from the liquid by means of a membrane and is transported by a carrier gas to the IRMS inlet. Recently, this LC/IRMS method has been used to determine δ 13 C values for various compounds, including sugars, amino acids, alcohols, pesticides, and black carbon . However, LC/IRMS has not been widely used to determine δ 13 C values for environmental field samples.…”

“…Recently, this LC/IRMS method has been used to determine δ 13 C values for various compounds, including sugars, [24][25][26] amino acids, 27,28 alcohols, [29][30][31] pesticides, 32 and black carbon. 33 However, LC/IRMS has not been widely used to determine δ 13 C values for environmental field samples.…”