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Hoffman DW, Rasmussen C. Position-specific carbon stable isotope analysis of glyphosate: isotope fingerprinting of molecules within a mixture. Anal Bioanal Chem 2024; 416:3847-3856. [PMID: 38740591 DOI: 10.1007/s00216-024-05326-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Revised: 04/27/2024] [Accepted: 04/30/2024] [Indexed: 05/16/2024]
Abstract
Glyphosate [N-(phosphonomethyl) glycine] is a widely used herbicide and a molecule of interest in the environmental sciences, due to its global use in agriculture and its potential impact on ecosystems. This study presents the first position-specific carbon isotope (13C/12C) analyses of glyphosates from multiple sources. In contrast to traditional isotope ratio mass spectrometry (IRMS), position-specific analysis provides 13C/12C ratios at individual carbon atom positions within a molecule, rather than an average carbon isotope ratio across a mixture or a specific compound. In this work, glyphosate in commercial herbicides was analyzed with only minimal purification, using a nuclear magnetic resonance (NMR) spectroscopy method that detects 1H nuclei with bonds to either 13C or 12C, and isolates the signals of interest from other signals in the mixture. Results demonstrate that glyphosate from different sources can have significantly different intramolecular 13C/12C distributions, which were found to be spread over a wide range, with δ13C Vienna Peedee Belemnite (VPDB) values of -28.7 to -57.9‰. In each glyphosate, the carbon with a bond to the phosphorus atom was found to be depleted in 13C compared to the carbon at the C2 position, by 4 to 10‰. Aminomethylphosphonic acid (AMPA) was analyzed for method validation; AMPA contains only a single carbon position, so the 13C/12C results provided by the NMR method could be directly compared with traditional isotope ratio mass spectrometry. The glyphosate mixtures were also analyzed by IRMS to obtain their average 13C/12C ratios, for comparison with our position-specific results. This comparison revealed that the IRMS results significantly disguise the intramolecular isotope distribution. Finally, we introduce a 31P NMR method that can provide a position-specific 13C/12C ratio for carbon positions with a C-P chemical bond, and the results obtained by 1H and 31P for C3 carbon agree with one another within their analytical uncertainty. These analytical tools for position-specific carbon isotope analysis permit the isotopic fingerprinting of target molecules within a mixture, with potential applications in a range of fields, including the environmental sciences and chemical forensics.
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Affiliation(s)
- David W Hoffman
- Department of Molecular Biosciences, The University of Texas at Austin, 100 East 24th St., Austin, TX, 78712, USA.
| | - Cornelia Rasmussen
- Institute for Geophysics, The University of Texas at Austin, J. J. Pickle Research Campus, 10601 Exploration Way, Austin, TX, 78758, USA
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Rasmussen C, Hoffman DW. Intramolecular distribution of 13C/ 12C isotopes in amino acids of diverse origins. Amino Acids 2020; 52:955-964. [PMID: 32594254 DOI: 10.1007/s00726-020-02863-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Accepted: 06/17/2020] [Indexed: 11/26/2022]
Abstract
Carbon stable isotope analysis can provide information about the origin and synthetic pathways that produce organic molecules, with applications in chemical, medical and (bio)geochemical sciences. The 13C/12C isotope ratios of organics such as amino acids are most commonly obtained as whole molecule averages. In this study, we apply proton nuclear magnetic resonance spectroscopy to conduct position-specific carbon isotope analyses of L-/D-alanine, L-threonine and L-histidine from different sources, in addition to molecule average stable isotope analyses obtained via mass spectrometry. Our results demonstrate that carbon isotope ratios can vary significantly between the individual carbon positions within an amino acid. For example, the β- and γ- carbons of L-threonine can differ in 13C/12C ratio by > 20 ‰. Comparisons of the position-specific and whole molecule average stable isotope abundances show that whole molecule analyses can mask the intramolecular isotope variation. These results provide the first experimentally measured position-specific isotope ratios for alpha and side chain carbons of alanine, threonine and histidine. Comparison with previous ab initio calculations of intramolecular equilibrium fractionation shows that the carbon isotope distributions are not at equilibrium, thus kinetic isotope effects play a significant role in amino acid synthesis. We hypothesize that position-specific 13C/12C isotope ratios provide an "isotopic fingerprint" that can give insight into the origin or synthesis pathway that formed an amino acid, and that this emerging analytical field will be a valuable addition to traditional stable isotope analysis.
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Affiliation(s)
- Cornelia Rasmussen
- Institute for Geophysics and Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA.
- University of Texas Center for Planetary Systems Habitability, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA.
| | - David W Hoffman
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, USA
- University of Texas Center for Planetary Systems Habitability, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA
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3
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Jabeen S, Zeng Z, Altarawneh M, Gao X, Saeed A, Dlugogorski BZ. Thermal decomposition of model compound of algal biomass. INT J CHEM KINET 2019. [DOI: 10.1002/kin.21301] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Sidra Jabeen
- Discipline of Chemistry and PhysicsCollege of ScienceHealthEngineering and EducationMurdoch University Murdoch Australia
| | - Zhe Zeng
- Discipline of Chemistry and PhysicsCollege of ScienceHealthEngineering and EducationMurdoch University Murdoch Australia
| | - Mohammednoor Altarawneh
- Discipline of Chemistry and PhysicsCollege of ScienceHealthEngineering and EducationMurdoch University Murdoch Australia
- Department of Chemical EngineeringAl‐Hussein Bin Talal University Ma'an Jordan
| | - Xiangpeng Gao
- Discipline of Chemistry and PhysicsCollege of ScienceHealthEngineering and EducationMurdoch University Murdoch Australia
| | - Anam Saeed
- Discipline of Chemistry and PhysicsCollege of ScienceHealthEngineering and EducationMurdoch University Murdoch Australia
| | - Bogdan Z. Dlugogorski
- Discipline of Chemistry and PhysicsCollege of ScienceHealthEngineering and EducationMurdoch University Murdoch Australia
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Gauchotte-Lindsay C, Turnbull SM. On-line high-precision carbon position-specific stable isotope analysis: A review. Trends Analyt Chem 2016. [DOI: 10.1016/j.trac.2015.07.010] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Cowie BR, Greenberg BM, Slater GF. Determination of microbial carbon sources and cycling during remediation of petroleum hydrocarbon impacted soil using natural abundance (14)C analysis of PLFA. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2010; 44:2322-2327. [PMID: 20196610 DOI: 10.1021/es9029717] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
In a petroleum impacted land-farm soil in Sarnia, Ontario, compound-specific natural abundance radiocarbon analysis identified biodegradation by the soil microbial community as a major pathway for hydrocarbon removal in a novel remediation system. During remediation of contaminated soils by a plant growth promoting rhizobacteria enhanced phytoremediation system (PEPS), the measured Delta(14)C of phospholipid fatty acid (PLFA) biomarkers ranged from -793 per thousand to -897 per thousand, directly demonstrating microbial uptake and utilization of petroleum hydrocarbons (Delta(14)C(PHC) = -1000 per thousand). Isotopic mass balance indicated that more than 80% of microbial PLFA carbon was derived from petroleum hydrocarbons (PHC) and a maximum of 20% was obtained from metabolism of more modern carbon sources. These PLFA from the contaminated soils were the most (14)C-depleted biomarkers ever measured for an in situ environmental system, and this study demonstrated that the microbial community in this soil was subsisting primarily on petroleum hydrocarbons. In contrast, the microbial community in a nearby uncontaminated control soil maintained a more modern Delta(14)C signature than total organic carbon (Delta(14)C(PLFA) = +36 per thousand to -147 per thousand, Delta(14)C(TOC) = -148 per thousand), indicating preferential consumption of the most modern plant-derived fraction of soil organic carbon. Measurements of delta(13)C and Delta(14)C of soil CO(2) additionally demonstrated that mineralization of PHC contributed to soil CO(2) at the contaminated site. The CO(2) in the uncontaminated control soil exhibited substantially more modern Delta(14)C values, and lower soil CO(2) concentrations than the contaminated soils, suggesting increased rates of soil respiration in the contaminated soils. In combination, these results demonstrated that biodegradation in the soil microbial community was a primary pathway of petroleum hydrocarbon removal in the PEPS system. This study highlights the power of natural abundance radiocarbon for determining microbial carbon sources and identifying biodegradation pathways in complex remediation systems.
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Affiliation(s)
- Benjamin R Cowie
- School of Geography and Earth Sciences, McMaster University, Hamilton, ON, Canada
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Gauchotte C, O'Sullivan G, Davis S, Kalin RM. Development of an advanced on-line position-specific stable carbon isotope system and application to methyl tert-butyl ether. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2009; 23:3183-3193. [PMID: 19725079 DOI: 10.1002/rcm.4222] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We present an advanced system for on-line position-specific carbon isotope analysis. The main limitation of on-line intramolecular isotope ratio measurements has been that optimal pyrolytic fragments are obtained mostly at temperatures where the analyte has not completely reacted. As a result of undetermined isotopic fractionation, the isotopic signatures of the pyrolysis products are not strictly equal to these of the equivalent moieties in the parent molecule. We designed a pyrolytic unit in which both temperature and reaction time are variable parameters, enabling determination of the enrichment factor of the pyrolysis at optimal temperature by construction of a Rayleigh plot. In the case of methyl tert-butyl ether (MTBE) presented here, a 'pre-pyrolysis' fractionation of MTBE leading to a depletion of 0.9 per thousand was discovered and the enrichment factor of the optimal pyrolysis reaction was determined at -1.7 per thousand. Absolute delta(13)C values of two functional groups of MTBE - the methoxy group and the 2-methylpropane group - could be determined with 95% confidence intervals of 0.4 per thousand and 0.5 per thousand, respectively.
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Affiliation(s)
- Caroline Gauchotte
- Department of Civil Engineering, University of Strathclyde, John Anderson Building, Glasgow G4 0NG, UK.
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Wolyniak CJ, Sacks GL, Metzger SK, Brenna JT. Determination of Intramolecular δ13C from Incomplete Pyrolysis Fragments. Evaluation of Pyrolysis-Induced Isotopic Fractionation in Fragments from the Lactic Acid Analogue Propylene Glycol. Anal Chem 2006; 78:2752-7. [PMID: 16615789 DOI: 10.1021/ac0522198] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Intramolecular carbon isotope ratios reflect the source of a compound and the reaction conditions prevailing during synthesis and degradation. We report here a method for determination of relative (Deltadelta13C) and absolute (delta13C) intramolecular isotope ratios using the volatile lactic acid analogue propylene glycol as a model compound, measured by on-line gas chromatography-pyrolysis coupled to GC-combustion-isotope ratio mass spectrometry. Pyrolytic fragmentation of about one-third of the analyte mass produces optimal fragments for isotopic analysis, from which relative isotope ratios (Deltadelta13C) are calculated according to guidelines presented previously. Calibration to obtain absolute isotope ratios is achieved by quantifying isotope fractionation during pyrolysis with an average fractionation factor, alpha, and evaluated by considering extremes in isotopic fractionation behavior. The method is demonstrated by calculating ranges of absolute intramolecular isotope ratios in four samples of propylene glycol. Relative and absolute isotope ratios were calculated with average precisions of SD(Deltadelta13C) <0.84 per thousand and SD(delta13C) <3.0 per thousand, respectively. The various fractionation scenarios produce an average delta(13)C range of 2 per thousand for each position in each sample. Relative isotope ratios revealed all four samples originated from unique sources, with samples A, B, and D only distinguishable at the position-specific level. Regardless of pyrolysis fractionation distribution, absolute isotope ratios showed a consistent pattern for all samples, with delta13C(3) > delta13C(2) > delta13C(1). The validity of the method was determined by examining the difference in relative isotope ratios calculated through two independent methods: Deltadelta13C calculated directly using previous methods and Deltadelta13C extracted from absolute isotope ratios. Deviation between the two Deltadelta13C values for all positions averaged 0.1-0.2 per thousand, with the smallest deviation obtained assuming equal fractionation across all fragment positions. This approach applies generally to all compounds analyzed by pyrolytic PSIA.
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Affiliation(s)
- Christopher J Wolyniak
- Division of Nutritional Sciences, Savage Hall, Cornell University, Ithaca, New York 14853, USA
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Oba Y, Naraoka H. Site-specific carbon isotope analysis of aromatic carboxylic acids by elemental analysis/pyrolysis/isotope ratio mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2006; 20:3649-53. [PMID: 17094169 DOI: 10.1002/rcm.2777] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Site-specific carbon isotope composition of organic compounds can provide useful information on their origin and history in natural environments. Site-specific isotope analyses of small amounts of organic compounds (sub-nanomolar level), such as short-chain carboxylic acids and amino acid analogues, have been performed using gas chromatography/pyrolysis/isotope ratio mass spectrometry (GC/pyrolysis/IRMS). These analyses were previously limited to volatile compounds. In this study, site-specific carbon isotope analysis has been developed for non-volatile aromatic carboxylic acids at sub-micromolar level by decarboxylation using a continuous flow elemental analysis (EA)/pyrolysis/IRMS technique. Benzoic acid, 2-naphthylacetic acid and 1-pyrenecarboxylic acid were pyrolyzed at 500-1000 degrees C by EA/pyrolysis/IRMS to produce CO2 for delta13C measurement of the carboxyl group. These three aromatic acids were most efficiently pyrolyzed at 750 degrees C. Conventional sealed-tube pyrolysis was also conducted for comparison. The delta13C values of CO2 generated by the continuous flow technique were within 1.0 per thousand of those performed by the conventional technique, indicating that the new continuous flow technique can accurately analyze the carbon isotopic composition of the carboxyl group in aromatic carboxylic acids. The new continuous flow technique is simple, rapid and uses small sample sizes, so this technique will be useful for characterizing the isotopic signature of carboxyl groups in organic compounds.
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Affiliation(s)
- Yasuhiro Oba
- Graduate School of Natural Science and Technology, Okayama University, 1-1, Naka 3-chome, Tsushima, Okayama 700-8530, Japan.
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Wolyniak CJ, Sacks GL, Pan BS, Brenna JT. Carbon Position-Specific Isotope Analysis of Alanine and Phenylalanine Analogues Exhibiting Nonideal Pyrolytic Fragmentation. Anal Chem 2005; 77:1746-52. [PMID: 15762581 DOI: 10.1021/ac048524v] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Recent advances in gas chromatography combustion-isotope ratio mass spectrometry (GCC-IRMS) has made compound-specific isotope analysis routine, but reports on position-specific isotopic analysis are still scarce. On-line GC-pyrolysis (Py) coupled to GCC-IRMS is reported here for isolation and isotopic characterization of alaninol and phenethylamine, analogues of alanine and phenylalanine, respectively. Ideally, pyrolytic fragments will originate from unique sites within the parent molecule, and isotope ratios for each position within the parent can either be measured directly or calculated from fragment isotope ratios without substantially degrading the analytical precision. Alaninol pyrolysis yielded several fragments, of which CO and CH4 were used for isotope ratio calculations. Isotope labeling experiments showed that CO derived entirely from the C(1) position, while all three positions of alaninol contributed to CH4 (29.0 +/- 0.3% from C(1), 3.6 +/- 0.2% from C(2), and 66.9 +/- 1.1% from C(3)). We demonstrate iterative use of mass balance to calculate isotope ratios from all positions despite the nonideal positional fidelity of CH4. Pyrolysis of phenethylamine generated benzene and toluene fragments. Benzene derived entirely from C(ring), and toluene was proportionately formed from C(3) and C(ring). Relative intramolecular isotope ratios (Deltadelta13C) were calculated directly from delta13C of fragments or indirectly by mass balance. Though the C(3) isotope ratio was calculated from the benzene and toluene fragments, propagation of errors showed that the final precision of the determination was degraded due to the small contribution that C(3) makes to toluene. Samples of each amino acid from four different vendors showed natural variability between sources, especially at the C(1) position of alaninol (range of Deltadelta13C approximately 50 per thousand). The average precision was SD(Deltadelta13C) < 0.20 per thousand for directly measured positions of alaninol and phenethylamine. The precision of indirectly measured positions was poorer (SD(Deltadelta13C) = 0.94 per thousand for alaninol, 6.54 per thousand for phenethylamine) due to propagation of errors. These data demonstrate that GC-Py-GCC-IRMS data can be used to extract high-precision isotope ratios from amino acids despite nonideal positional fidelity in fragments and that natural intramolecular variability in delta13C can be used to distinguish different sources of amino acids.
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Affiliation(s)
- Christopher J Wolyniak
- Division of Nutritional Sciences, Savage Hall, Cornell University, Ithaca, New York 14853, USA
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Sacks GL, Brenna JT. 15N/14N Position-Specific Isotopic Analyses of Polynitrogenous Amino Acids. Anal Chem 2005; 77:1013-9. [PMID: 15858980 DOI: 10.1021/ac048903o] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
15N/14N isotope ratios are widely used to study processes and systems involving amino acids. Nitrogen isotope fractionation in biological processes occurs primarily at sites of bond-breaking and formation; the finest discrimination for "isotopic fingerprinting" and studies of isotopic fluxes is thus obtained at the position-specific level. While there are numerous reports of natural intramolecular carbon isotope variability, there are no literature reports of 15N/14N position-specific isotopic analysis (N-PSIA) of biologically relevant molecules. We report a methodology for high-precision N-PSIA of four polynitrogenous alpha-amino acids (asparagine, glutamine, lysine, histidine) and the first survey of natural intramolecular 15N/14N in these biomolecules. Selective liberation of N-atoms from multiple commercial standards of each parent amino acid was achieved by an appropriate enzymatic reaction or by acid hydrolysis. 15N/14N measurements were performed on N-ethoxycarbonyl ethyl ester derivatives of the parent amino acids and their analogues by gas chromatography combustion isotope ratio mass spectrometry, and the average precision for replicate injections was found to be SD(delta15N) = 0.3%. Position-specific delta15N values of the parent amino acid were directly observed or indirectly calculated using mass balance. The average precision obtained for directly measured positions was SD(delta15N) = 0.2-0.4%. The average precision for indirectly obtained positions was SD(delta15N) = 0.6-1.3% as a result of propagation of errors. Enrichment in the side chain-N with respect to the peptide-N was observed in nearly all of the amino acid sources, most notably in asparagine (average delta delta(side-peptide) = + 11%), which may be indicative of its method of production. In some cases, it was possible to distinguish commercial sources by N-PSIA that could not be distinguished at the compound-specific level.
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Affiliation(s)
- Gavin L Sacks
- Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853, USA
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Whitelegge JP, Katz JE, Pihakari KA, Hale R, Aguilera R, Gómez SM, Faull KF, Vavilin D, Vermaas W. Subtle modification of isotope ratio proteomics; an integrated strategy for expression proteomics. PHYTOCHEMISTRY 2004; 65:1507-1515. [PMID: 15276448 DOI: 10.1016/j.phytochem.2004.05.018] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2004] [Revised: 05/25/2004] [Indexed: 05/24/2023]
Abstract
Use of minor modification of isotope ratio to code samples for expression proteomics is being investigated. Alteration of (13)C abundance to approximately 2% yields a measurable effect on peptide isotopic distribution and inferred isotope ratio. Elevation of (13)C abundance to 4% leads to extension of isotopic distribution and background peaks across every unit of the mass range. Assessment of isotope ratio measurement variability suggests substantial contributions from natural measurement variability. A better understanding of this variable will allow assessment of the contribution of sequence dependence. Both variables must be understood before meaningful mixing experiments for relative expression proteomics are performed. Subtle modification of isotope ratio ( approximately 1-2% increase in (13)C) had no effect upon either the ability of data-dependent acquisition software or database searching software to trigger tandem mass spectrometry or match MSMS data to peptide sequences. More severe modification of isotope ratio caused a significant drop in performance of both functionalities. Development of software for deconvolution of isotope ratio concomitant with protein identification using LC-MSMS, or any other proteomics strategy, is underway (Isosolv). The identified peptide sequence is then be used to provide elemental composition for accurate isotope ratio decoding and the potential to control for specific amino acid biases should these prove significant. It is suggested that subtle modification of isotope ratio proteomics (SMIRP) offers a convenient approach to in vivo isotope coding of plants and might ultimately be extended to mammals including humans.
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Affiliation(s)
- Julian P Whitelegge
- The Pasarow Mass Spectrometry Laboratory, Department of Psychiatry, University of California, Los Angeles, CA 90095, USA.
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