Compound Specific 13C & 15N analysis of Amino Acids by GC-IRMS
GC-C-IRMS analysis of 13C and 15N in amino acids
We provide CSIA for both δ13C and δ15N of amino acids in organic samples (e.g. animal and plant tissues) by GC-C-IRMS. Sample preparation involves acid hydrolysis for the liberation of amino acids from proteins and derivatization by methyl chloroformate to produce compounds amenable to GC analysis.
Methoxy-carbonyl amino acid methyl esters (AA-MCF) are injected in split (13C) or splitless (15N) mode and separated on an Agilent DB-23 column (30m X 0.25mm ID, 0.25 micron film thickness). Once separated, AA-MCF are quantitatively converted to CO2 and N2 in a combustion reactor at 1000°C. Water is subsequently removed through a nafion dryer and, during N2 analysis only, CO2 is retained in a trapping loop using LN2. During the final step of the analysis, N2 or CO2 enters the IRMS.
A pure reference gas (CO2 or N2) is used to calculate provisional δ-values of each sample peak. Next, isotopic values are adjusted to an internal reference material (e.g. norleucine) of known isotopic composition. Final δ-values are obtained after adjusting the provisional values for changes in linearity and instrumental drift such that correct δ-values for laboratory reference materials (RMs) are obtained. Laboratory RMs are custom mixtures of commercially available amino acids that have been calibrated against IAEA-N1, IAEA-N2, IAEA-N3, USGS-40, and USGS-41. Additional quality assurance RMs are co-measured with all samples to verify data quality and are included with all data reports.
Precision estimates from the co-measured standard mixtures are provided with data reports. In general, average measurement error is approx. ± 1‰ from acid-hydrolyzed samples (1σ, n>100), but varies by amino acid. Additional information can be found on our Sample Preparation Page.
R.G. Walsh, S. He, and C.T. Yarnes. 2014.Compound-specific δ13C and δ15N analysis of amino acids: a rapid, chloroformate-based method for ecological studies. Rapid Commun. Mass Spectrom. 28, 96–108 DOI: 10.1002/rcm.6761
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