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

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

Analytical and bioanalytical chemistry (2015-05-15)
Emmanuel O Mogusu, J Benjamin Wolbert, Dorothea M Kujawinski, Maik A Jochmann, Martin Elsner
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.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
N-(Phosphonomethyl)glycine, 96%
Sigma-Aldrich
Methanol, anhydrous, 99.8%
Sigma-Aldrich
Isopropyl chloroformate solution, 1.0 M in toluene
Sigma-Aldrich
Methanol, suitable for HPLC, gradient grade, 99.93%
Sigma-Aldrich
Diethyl ether, contains 1 ppm BHT as inhibitor, anhydrous, ≥99.7%
Sigma-Aldrich
N-(Phosphonomethyl)glycine, BioReagent, suitable for plant cell culture
Sigma-Aldrich
Methanol, HPLC Plus, ≥99.9%, poly-coated bottles
Sigma-Aldrich
Methanol, JIS 300, ≥99.8%, for residue analysis
Sigma-Aldrich
Diethyl ether, JIS 300, ≥99.5%, for residue analysis
Sigma-Aldrich
Diethyl ether, ≥99.5%
Sigma-Aldrich
Diethyl ether, JIS 1000, ≥99.5%, for residue analysis
Sigma-Aldrich
Diethyl ether, for residue analysis, JIS 5000
Sigma-Aldrich
Methanol, SAJ special grade
Sigma-Aldrich
Phosphoric acid solution, 85 wt. % in H2O, FCC, FG
Sigma-Aldrich
Diethyl ether, JIS special grade, ≥99.5%
Sigma-Aldrich
Phosphoric acid solution, NMR reference standard, 85% in D2O (99.9 atom % D), NMR tube size 3 mm × 8 in.
Sigma-Aldrich
Phosphoric acid solution, NMR reference standard, 85% in D2O (99.9 atom % D), NMR tube size 5 mm × 8 in.
Sigma-Aldrich
Diethyl ether, SAJ first grade, ≥99.0%
Sigma-Aldrich
Phosphoric acid solution, NMR reference standard, 85% in D2O (99.9 atom % D), NMR tube size 4.2 mm × 8 in. , WGS-5BL Coaxial NMR tube
Sigma-Aldrich
Methanol, suitable for HPLC
Sigma-Aldrich
Methanol, SAJ first grade, ≥99.5%
Sigma-Aldrich
Methanol, JIS special grade, ≥99.8%
Sigma-Aldrich
Methanol, NMR reference standard
Sigma-Aldrich
Hexane, HPLC Plus, for HPLC, GC, and residue analysis, ≥95%
Sigma-Aldrich
Hexane, for residue analysis, JIS 5000
Sigma-Aldrich
Ethyl acetate, suitable for HPLC
Sigma-Aldrich
Hexane, ≥96.0%, suitable for residual phthalate analysis
Sigma-Aldrich
Hexane, JIS 300, ≥96.0%, for residue analysis
Sigma-Aldrich
Potassium hydroxide solution, 1 M
Sigma-Aldrich
Potassium hydroxide solution, 0.1 M in isopropanol