title: A reliable compound-specific nitrogen isotope analysis of amino acids by GC-C-IRMS following derivatisation into N-pivaloyl-iso-propyl (NPIP)esters for high-resolution food webs estimation.
abstract: The signatures of natural stable nitrogen isotopic composition (δ(15)N) of individual amino acid (AA) have been confirmed to be a potentially effective tool for elucidating nitrogen cycling and trophic position of various organisms in food webs. In the present study, a two-stage derivatisation approach of esterification followed by acylation was evaluated. The biological samples underwent acid hydrolysis and the released individual AA was derivatived into corresponding N-pivaloyl-isopropyl (NPIP) esters for nitrogen isotopic analysis in gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Usually, 13 individual AA derivatives were separated with fine baseline resolution based on a nonpolar gas chromatography column (DB-5ms). The minimum sample amount required under the presented conditions is larger than 20ngN on column in order to accurately determine the δ(15)N values. The δ(15)N values determined by GC-C-IRMS with a precision of better than 1‰, were within 1‰ after empirical correction compared to the corresponding measured by element analysis (EA)-IRMS. Bland-Altman plot showed highly consistency of the δ(15)N values determined by the two measurement techniques. Cation-exchange chromatography was applied to remove interfering fraction from the extracts of plant and animal samples and without nitrogen isotope fractionation during the treatment procedure. Moreover, this approach was carried out to estimate the trophic level of various natural organisms in a natural lake environment. Results highly proved that the trophic level estimated via the presented AA method well reflected the actual food web structure in natural environments.
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; University of Chinese Academy of Sciences, Beijing 100039, China.
authors.forename: Zhongyi
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; University of Chinese Academy of Sciences, Beijing 100039, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Tian
authors.affiliation: Laboratory of Atmospheric Environment, Key Laboratory of Nuclear Resource and Environment (Ministry of Education), East China University of Technology, Nanchang330013, China.
authors.forename: Hongwei
authors.initials: H
authors.lastname: Xiao
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; University of Chinese Academy of Sciences, Beijing 100039, China.
authors.forename: Nengjian
authors.initials: N
authors.lastname: Zheng
authors.affiliation: University of Chinese Academy of Sciences, Beijing 100039, China; Aquatic Ecohealth Group, Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China.
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Gao
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; Laboratory of Atmospheric Environment, Key Laboratory of Nuclear Resource and Environment (Ministry of Education), East China University of Technology, Nanchang330013, China.
authors.forename: Renguo
authors.initials: R
authors.lastname: Zhu
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China. Electronic address: huayunxiao@outlook.com.
authors.forename: Huayun
authors.initials: H
authors.lastname: Xiao
mesh_terms: D000596:Amino Acids / Q000032:analysis*; D002412:Cations; D002852:Chromatography, Ion Exchange; D004952:Esters / Q000737:chemistry*; D020387:Food Chain; D005618:Fresh Water; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D007553:Isotope Labeling / Q000379:methods*; D009587:Nitrogen Isotopes; D012015:Reference Standards
chemical_list: D000596:Amino Acids; D002412:Cations; D004952:Esters; D009587:Nitrogen Isotopes
keywords: Amino acid; GC-C-IRMS; NPIP ester; Trophic level