Dual element (15N/14N, 13C/12C) isotope analysis of glyphosate and AMPA by derivatization-gas chromatography isotope ratio mass spectrometry (GC/IRMS) combined with LC/IRMS

Abstract

To assess sources and degradation of the herbicide glyphosate [N-(phosphonomethyl) glycine] and its metabolite AMPA (aminomethylphosphonic acid), concentration measurements are often inconclusive and even (13)C/(12)C analysis alone may give limited information. To advance isotope ratio analysis of an additional element, we present compound-specific (15)N/(14)N analysis of glyphosate and AMPA by a two step derivatization in combination with gas chromatography/isotope ratio mass spectrometry (GC/IRMS). The N-H group was derivatized with isopropyl chloroformate (iso-PCF), and remaining acidic groups were subsequently methylated with trimethylsilyldiazomethane (TMSD). Iso-PCF treatment at pH <10 gave too low (15)N/(14)N ratios indicating an incomplete derivatization; in contrast, too high (15)N/(14)N ratios at pH >10 indicated decomposition of the derivative. At pH 10, and with an excess of iso-PCF by 10-24, greatest yields and accurate (15)N/(14)N ratios were obtained (deviation from elemental analyzer-IRMS: -0.2 ± 0.9% for glyphosate; -0.4 ± 0.7% for AMPA). Limits for accurate δ(15)N analysis of glyphosate and AMPA were 150 and 250 ng injected, respectively. A combination of δ(15)N and δ(13)C analysis by liquid chromatography/isotope ratio mass spectrometry (LC/IRMS) (1) enabled an improved distinction of commercial glyphosate products and (2) showed that glyphosate isotope values during degradation by MnO2 clearly fell outside the commercial product range. This highlights the potential of combined carbon and nitrogen isotopes analysis to trace sources and degradation of glyphosate.

Solid-phase extraction method for stable isotope analysis of pesticides from large volume environmental water samples

“…16 Various analytical methods have been recently developed. [17][18][19][20][21][22][23][24][25][26][27][28][29] Nonetheless, application of CSIA of pesticides to field studies remain scarce 24,[30][31][32][33][34] because of two major challenges. First, isotope effect-free extraction and pre-concentration methods are required to allow CSIA at low environmentally relevant concentrations by gas chromatography-isotope ratio mass spectrometry (GC/IRMS) or -in the case of compounds like desphenylchloridazon for which GC/IRMS-based carbon isotope analysis does not work -by liquid chromatography-IRMS (LC/IRMS).…”

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.…”

Derivatization‐free method for compound‐specific isotope analysis of nonexchangeable hydrogen of 4‐bromophenol

“…The majority of CSIA work concerns the analysis of compounds readily amenable to gas chromatography (GC), i.e., compounds with low polarity and low reactivity during the passage through a GC column. CSIA of polar compounds is less common, but a significant number of studies of carbon and nitrogen isotope ratios have been conducted on certain classes of polar compounds, most notably, biological fatty acids, amino acids, and environmental micropollutants, derivatized to make them more GC‐amenable . Whereas derivatization facilitates GC of polar or reactive compounds, it can also lead to various undesirable effects in the measurement of isotope ratios .…”

“…CSIA of polar compounds is less common, but a significant number of studies of carbon and nitrogen isotope ratios have been conducted on certain classes of polar compounds, most notably, biological fatty acids, 2,5 amino acids, 6,7 and environmental micropollutants, [8][9][10] derivatized to make them more GC-amenable. [11][12][13] Whereas derivatization facilitates GC of polar or reactive compounds, it can also lead to various undesirable effects in the measurement of isotope ratios.…”