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Greule M, Le PM, Meija J, Mester Z, Keppler F. Comparison of Carbon Isotope Ratio Measurement of the Vanillin Methoxy Group by GC-IRMS and 13C-qNMR. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2024; 35:100-105. [PMID: 38015023 PMCID: PMC10767744 DOI: 10.1021/jasms.3c00327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Revised: 11/07/2023] [Accepted: 11/09/2023] [Indexed: 11/29/2023]
Abstract
Site-specific carbon isotope ratio measurements by quantitative 13C NMR (13C-qNMR), Orbitrap-MS, and GC-IRMS offer a new dimension to conventional bulk carbon isotope ratio measurements used in food provenance, forensics, and a number of other applications. While the site-specific measurements of carbon isotope ratios in vanillin by 13C-qNMR or Orbitrap-MS are powerful new tools in food analysis, there are a limited number of studies regarding the validity of these measurement results. Here we present carbon site-specific measurements of vanillin by GC-IRMS and 13C-qNMR for methoxy carbon. Carbon isotope delta (δ13C) values obtained by these different measurement approaches demonstrate remarkable agreement; in five vanillin samples whose bulk δ13C values ranged from -31‰ to -26‰, their δ13C values of the methoxy carbon ranged from -62.4‰ to -30.6‰, yet the difference between the results of the two analytical approaches was within ±0.6‰. While the GC-IRMS approach afforded up to 9-fold lower uncertainties and required 100-fold less sample compared to the 13C-qNMR, the 13C-qNMR is able to assign δ13C values to all carbon atoms in the molecule, not just the cleavable methoxy group.
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Affiliation(s)
- Markus Greule
- Institute
of Earth Sciences, Heidelberg University, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany
| | - Phuong Mai Le
- Metrology, National
Research Council Canada, 1200 Montreal Road, Ottawa, ON K1A
0R6, Canada
| | - Juris Meija
- Metrology, National
Research Council Canada, 1200 Montreal Road, Ottawa, ON K1A
0R6, Canada
| | - Zoltán Mester
- Metrology, National
Research Council Canada, 1200 Montreal Road, Ottawa, ON K1A
0R6, Canada
| | - Frank Keppler
- Institute
of Earth Sciences, Heidelberg University, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany
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A precise and rapid isotopomic analysis of small quantities of cholesterol at natural abundance by optimized 1H- 13C 2D NMR. Anal Bioanal Chem 2021; 413:1521-1532. [PMID: 33506339 DOI: 10.1007/s00216-020-03135-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 12/15/2020] [Accepted: 12/16/2020] [Indexed: 10/22/2022]
Abstract
Cholesterol, the principal zoosterol, is a key metabolite linked to several health complications. Studies have shown its potential as a metabolic biomarker for predicting various diseases and determining food origin. However, the existing INEPT (insensitive nuclei enhanced by polarization transfer) 13C position-specific isotope analysis method of cholesterol by NMR was not suitable for very precise analysis of small quantities due to its long acquisition time and therefore is restricted to products rich in cholesterol. In this work, a symmetric and adiabatic heteronuclear single quantum coherence (HSQC) 2D NMR sequence was developed for the high-precision (few permil) analysis of small quantities of cholesterol. Adiabatic pulses were incremented for improving precision and sensitivity. Moreover, several strategies such as the use of non-uniform sampling, linear prediction, and variable recycling time were optimized to reduce the acquisition time. The number of increments and spectral range were also adjusted. The method was developed on a system with a cryogenically cooled probe and was not tested on a room-temperature system. Our new approach allowed analyzing as low as 5 mg of cholesterol in 31 min with a long-term repeatability lower than 2‰ on the 24 non-quaternary carbon atoms of the molecule comparing to 16.2 h for the same quantity using the existing INEPT method. This result makes conceivable the isotope analysis of matrices low in cholesterol. Graphical abstract.
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Queipo-Abad S, Lagane C, Point D. Sensitive determination of methylmercury δ 13C compound specific stable isotopic analysis by purge and trap gas chromatography combustion isotope ratio mass spectrometry. J Chromatogr A 2020; 1617:460821. [PMID: 31932087 DOI: 10.1016/j.chroma.2019.460821] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2019] [Revised: 12/17/2019] [Accepted: 12/19/2019] [Indexed: 11/17/2022]
Abstract
Despite several decades of mercury research, answering fundamental questions on where and how methylmercury (CH3Hg) toxin is naturally produced in aquatic ecosystems, is still highly challenging. Investigating complex and/or coupled processes in the context of global changes requires new high-resolution analytical tools. The purpose of the compound specific carbon stable isotopic analysis (δ13C-CSIA) of the methyl group of methylmercury (CH3Hg), is to explore how the carbon cycle contributes to CH3Hg sources and formation pathways. The main problem associated with recent CH3Hg δ13C-CSIA methods is the limited sensitivity when using Liquid Injection (LI)-GC-C-IRMS techniques, requiring several micrograms of CH3Hg (as Hg). In this work, we present the development and application of an original Purge-&-Trap system (PT) coupled to a GC-C-IRMS with the purpose of transferring and analyzing the total amount of CH3Hg available in a sample vial in the low nanogram range. The new PT-GC-C-IRMS system enhance the sensitivity by a factor better than 200, relative to LI-GC-C-IRMS, by minimizing the sample mass requirements. The δ13CCH3Hg values obtained, following the same sample derivatization approach coupled to PT-GC-C-IRMS (-53.5 ± 1.9 ‰), were in good agreement with the ones obtained in a previous study (-53.8 ± 1.1 ‰). The standard solution was prepared from the same salt, requesting only 25-200 ng of CH3Hg (as Hg). This new methodology represents a milestone towards the analysis of large array of biological samples displaying CH3Hg concentrations in the low-mid ng g-1 range, in order to explore the meaning of the carbon stable isotopic signature of CH3Hg in the environment.
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Affiliation(s)
- Silvia Queipo-Abad
- Department of Physical and Analytical Chemistry, University of Oviedo, Julián Clavería, 8, 33006 Oviedo Spain
| | - Christelle Lagane
- Observatoire Midi-Pyrénées, Géosciences Environnement Toulouse, UMR CNRS 5563/IRD 234/Université Paul Sabatier Toulouse 3, 14 avenue Edouard Belin, 31400 Toulouse, France
| | - David Point
- Observatoire Midi-Pyrénées, Géosciences Environnement Toulouse, UMR CNRS 5563/IRD 234/Université Paul Sabatier Toulouse 3, 14 avenue Edouard Belin, 31400 Toulouse, France.
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Dunn PJH, Bilsel M, Şimşek A, Gören AC, Tunç M, Ogrinc N, Horvat M, Goenaga-Infante H. Practical and theoretical considerations for the determination of δ 13 C VPDB values of methylmercury in the environment. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2019; 33:1122-1136. [PMID: 30968483 DOI: 10.1002/rcm.8453] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2019] [Revised: 04/01/2019] [Accepted: 04/04/2019] [Indexed: 06/09/2023]
Abstract
RATIONALE Analytical methods that can identify the source and fate of mercury and organomercury compounds are likely to be useful tools to investigate mercury in the environment. Carbon isotope ratio analysis of methylmercury (MeHg) together with mercury isotope ratios may offer a robust tool to study environmental cycling of organomercury compounds within fish tissues and other matrices. METHODS MeHg carbon isotope ratios were determined by gas chromatography/combustion-isotope ratio mass spectrometry (GC/C-IRMS) either directly or following derivatization using sodium tetraethylborate. The effects of a normalization protocol and of derivatization on the measurement uncertainty of the methylmercury δ13 CVPDB values were investigated. RESULTS GC/C-IRMS analysis resulted in a δ13 CVPDB value for an in-house MeHg reference material of δ13 CVPDB = -68.3 ± 7.7‰ (combined standard uncertainty, k = 1). This agreed very well with the value obtained by offline flow-injection analysis/chemical oxidation/isotope ratio mass spectrometry of δ13 CVPDB = -68.85 ± 0.17‰ (combined standard uncertainty, k = 1) although the uncertainty was substantially larger. The minimum amount of MeHg required for analysis was determined to be 20 μg. CONCLUSIONS While the δ13 CVPDB values of MeHg can be obtained by GC/C-IRMS methods with or without derivatization, the low abundance of MeHg precludes such analyses in fish tissues unless there is substantial MeHg contamination. Environmental samples with sufficient MeHg pollution can be studied using these methods provided that the MeHg can be quantitatively extracted. The more general findings from this study regarding derivatization protocol implementation within an autosampler vial as well as measurement uncertainty associated with derivatization, normalization to reporting scales and integration are applicable to other GC/C-IRMS-based measurements.
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Affiliation(s)
- Philip J H Dunn
- National Measurement Laboratory, LGC Limited, Queens Road, Teddington, TW11 0LY, UK
| | - Mine Bilsel
- TUBITAK Ulusal Metroloji Enstitüsü (TÜBİTAK UME), PO Box 54, 41470, Gebze, Kocaeli, Turkey
| | - Adnan Şimşek
- TUBITAK Ulusal Metroloji Enstitüsü (TÜBİTAK UME), PO Box 54, 41470, Gebze, Kocaeli, Turkey
| | - Ahmet Ceyhan Gören
- TUBITAK Ulusal Metroloji Enstitüsü (TÜBİTAK UME), PO Box 54, 41470, Gebze, Kocaeli, Turkey
- Faculty of Pharmacy, Department of Analytical Chemistry, Bezmialem Vakıf University, 34093, Istanbul, Turkey
| | - Murat Tunç
- TUBITAK Ulusal Metroloji Enstitüsü (TÜBİTAK UME), PO Box 54, 41470, Gebze, Kocaeli, Turkey
| | - Nives Ogrinc
- Jožef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia
| | - Milena Horvat
- Jožef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia
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Greule M, Moossen H, Geilmann H, Brand WA, Keppler F. Methyl sulfates as methoxy isotopic reference materials for δ 13 C and δ 2 H measurements. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2019; 33:343-350. [PMID: 30452095 DOI: 10.1002/rcm.8355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Revised: 11/09/2018] [Accepted: 11/09/2018] [Indexed: 06/09/2023]
Abstract
RATIONALE Stable hydrogen and carbon isotope ratios of methoxy groups (OCH3 ) of plant organic matter have many potential applications in biogeochemical, atmospheric and food research. So far, most of the analyses of plant methoxy groups by isotope ratio mass spectrometry have employed liquid iodomethane (CH3 I) as the reference material to normalise stable isotope measurements of these moieties to isotope-δ scales. However, comparisons of measurements of stable hydrogen and carbon isotopes of plant methoxy groups are still hindered by the lack of suitable reference materials. METHODS We have investigated two methyl sulfate salts (HUBG1 and HUBG2), which exclusively contain carbon and hydrogen from one methoxy group, for their suitability as methoxy reference materials. Firstly, the stable hydrogen and carbon isotope values of the bulk compounds were calibrated against international reference substances by high-temperature conversion- and elemental analyser isotope ratio mass spectrometry (HTC- and EA-IRMS). In a second step these values were compared with values obtained by measurements using gas chromatography/isotope ratio mass spectrometry (GC/IRMS) where prior to analysis the methoxy groups were converted into gaseous iodomethane. RESULTS The 2 H- and 13 C isotopic abundances of HUBG1 measured by HTC- and EA-IRMS and expressed as δ-values on the usual international scales are -144.5 ± 1.2 mUr (n = 30) and -50.31 ± 0.16 mUr (n = 14), respectively. For HUBG2 we obtained -102.0 ± 1.3 mUr (n = 32) and +1.60 ± 0.12 mUr (n = 16). Furthermore, the values obtained by GC/IRMS were in good agreement with the HTC- and EA-IRMS values. CONCLUSIONS We suggest that both methyl sulfates are suitable reference materials for normalisation of isotope measurements of carbon of plant methoxy groups to isotope-δ scales and for inter-laboratory calibration. For stable hydrogen isotope measurements, we suggest that in addition to HUBG1 and HUBG2 additional reference materials are required to cover the full range of plant methoxy groups reported so far.
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Affiliation(s)
- Markus Greule
- Institute of Earth Sciences, Heidelberg University, Im Neuenheimer Feld 234-236, 69120, Heidelberg, Germany
| | - Heiko Moossen
- Max-Planck-Institute for Biogeochemistry, Hans-Knoell-Str. 10, 07749, Jena, Germany
| | - Heike Geilmann
- Max-Planck-Institute for Biogeochemistry, Hans-Knoell-Str. 10, 07749, Jena, Germany
| | - Willi A Brand
- Max-Planck-Institute for Biogeochemistry, Hans-Knoell-Str. 10, 07749, Jena, Germany
| | - Frank Keppler
- Institute of Earth Sciences, Heidelberg University, Im Neuenheimer Feld 234-236, 69120, Heidelberg, Germany
- Heidelberg Center for the Environment (HCE), Heidelberg University, 69120, Heidelberg, Germany
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Jin B, Rolle M. Joint interpretation of enantiomer and stable isotope fractionation for chiral pesticides degradation. WATER RESEARCH 2016; 105:178-186. [PMID: 27619494 DOI: 10.1016/j.watres.2016.08.057] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Revised: 08/22/2016] [Accepted: 08/27/2016] [Indexed: 06/06/2023]
Abstract
Chiral pesticides are important contaminants affecting the health and functioning of aquatic systems. The combination of stable isotope and enantiomer analysis techniques has been recently proposed to better characterize the fate of these contaminants in natural and engineered settings. We introduce a modeling approach with the aim of unifying and integrating the interpretation of isotopic and enantiomeric fractionation. The model is based on the definition of enantiomer-specific isotopologues and jointly predicts the evolution of concentration, enantiomer fractionation, as well as changes in stable isotope ratios of different elements. The method allows evaluating different transformation pathways and was applied to investigate enzymatic degradation of dichlorprop (DCPP), enzymatic degradation of mecoprop methyl ester (MCPPM), and microbial degradation of α-hexachlorocyclohexane (α-HCH) by different bacterial strains and under different redox conditions. The model accurately reproduces the isotopic and enantiomeric data observed in previous experimental studies and precisely captures the dual-dimensional trends characterizing different reaction pathways. Furthermore, the model allows testing possible combinations of enantiomer analysis (EA), compound specific isotope analysis (CSIA), and enantiomer specific isotope analysis (ESIA) to identify and assess isotope and enantiomer selective reaction mechanisms.
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Affiliation(s)
- Biao Jin
- Department of Environmental Engineering, Technical University of Denmark, Miljøvej Building 113, DK-2800 Kgs. Lyngby, Denmark
| | - Massimo Rolle
- Department of Environmental Engineering, Technical University of Denmark, Miljøvej Building 113, DK-2800 Kgs. Lyngby, Denmark.
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Jin B, Rolle M. Position-specific isotope modeling of organic micropollutants transformation through different reaction pathways. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2016; 210:94-103. [PMID: 26708763 DOI: 10.1016/j.envpol.2015.11.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Revised: 10/16/2015] [Accepted: 11/12/2015] [Indexed: 06/05/2023]
Abstract
The degradation of organic micropollutants occurs via different reaction pathways. Compound specific isotope analysis is a valuable tool to identify such degradation pathways in different environmental systems. We propose a mechanism-based modeling approach that provides a quantitative framework to simultaneously evaluate concentration as well as bulk and position-specific multi-element isotope evolution during the transformation of organic micropollutants. The model explicitly simulates position-specific isotopologues for those atoms that experience isotope effects and, thereby, provides a mechanistic description of isotope fractionation occurring at different molecular positions. To demonstrate specific features of the modeling approach, we simulated the degradation of three selected organic micropollutants: dichlorobenzamide (BAM), isoproturon (IPU) and diclofenac (DCF). The model accurately reproduces the multi-element isotope data observed in previous experimental studies. Furthermore, it precisely captures the dual element isotope trends characteristic of different reaction pathways as well as their range of variation consistent with observed bulk isotope fractionation. It was also possible to directly validate the model capability to predict the evolution of position-specific isotope ratios with available experimental data. Therefore, the approach is useful both for a mechanism-based evaluation of experimental results and as a tool to explore transformation pathways in scenarios for which position-specific isotope data are not yet available.
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Affiliation(s)
- Biao Jin
- Department of Environmental Engineering, Technical University of Denmark, Miljøvej Building 113, DK-2800, Kgs. Lyngby, Denmark.
| | - Massimo Rolle
- Department of Environmental Engineering, Technical University of Denmark, Miljøvej Building 113, DK-2800, Kgs. Lyngby, Denmark
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Jin B, Rolle M. Mechanistic approach to multi-element isotope modeling of organic contaminant degradation. CHEMOSPHERE 2014; 95:131-139. [PMID: 24034890 DOI: 10.1016/j.chemosphere.2013.08.050] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Revised: 08/06/2013] [Accepted: 08/15/2013] [Indexed: 06/02/2023]
Abstract
We propose a multi-element isotope modeling approach to simultaneously predict the evolution of different isotopes during the transformation of organic contaminants. The isotopic trends of different elements are explicitly simulated by tracking position-specific isotopologues that contain the isotopes located at fractionating positions. Our approach is self-consistent and provides a mechanistic description of different degradation pathways that accounts for the influence of both primary and secondary isotope effects during contaminant degradation. The method is particularly suited to quantitatively describe the isotopic evolution of relatively large organic contaminant molecules. For such compounds, an integrated approach, simultaneously considering all possible isotopologues, would be impractical due to the large number of isotopologues. We apply the proposed modeling approach to the degradation of toluene, methyl tert-butyl ether (MTBE) and nitrobenzene observed in previous experimental studies. Our model successfully predicts the multi-element isotope data (both 2D and 3D), and accurately captures the distinct trends observed for different reaction pathways. The proposed approach provides an improved and mechanistic methodology to interpret multi-element isotope data and to predict the extent of multi-element isotope fractionation that goes beyond commonly applied modeling descriptions and simplified methods based on the ratio between bulk enrichment factors or on linear regression in dual-isotope plots.
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Affiliation(s)
- Biao Jin
- Center for Applied Geosciences, University of Tübingen, Sigwartstrasse 10, D-72076 Tübingen, Germany
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