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UC Davis Plant Sciences



Carbon (13C) and Nitrogen (15N) Analysis of Solids by EA-IRMS


The SIF provides 13C and 15N isotope analyses of solid materials, such as soils, sediments, plant and animal tissues, etc., using an elemental analyzer interfaced to a continuous flow isotope ratio mass spectrometer (IRMS). We analyze both 13C and 15N in the same sample, or we can use a CO2 trap and measure 15N only in the case of very low N materials like wood.

Analysis
Most solid materials (excluding glass fiber filters, soils, and sediments – see below) are analyzed for 13C and 15N isotopes using a PDZ Europa ANCA-GSL elemental analyzer interfaced to a PDZ Europa 20-20 isotope ratio mass spectrometer (Sercon Ltd., Cheshire, UK). Samples are combusted at 1000°C in a reactor packed with chromium oxide and silvered copper oxide. Following combustion, oxides are removed in a reduction reactor (reduced copper at 650°C). The helium carrier then flows through a water trap (magnesium perchlorate) and an optional CO2 trap (for N-only analyses). N2 and CO2 are separated on a Carbosieve GC column (65°C, 65 mL/min) before entering the IRMS.


Glass fiber filters, soils, and sediments are analyzed for 13C and 15N isotopes using an Elementar Vario EL Cube or Micro Cube elemental analyzer (Elementar Analysensysteme GmbH, Hanau, Germany) interfaced to a PDZ Europa 20-20 isotope ratio mass spectrometer (Sercon Ltd., Cheshire, UK). Samples are combusted at 1000°C in a reactor packed with copper oxide and lead chromate. Following combustion, oxides are removed in a reduction reactor (reduced copper at 650°C). The helium carrier then flows through a water trap (magnesium perchlorate). N2 and CO2 are separated using a molecular sieve adsorption trap before entering the IRMS.


During analysis, samples are interspersed with several replicates of at least two different laboratory standards. These laboratory standards, which are selected to be compositionally similar to the samples being analyzed, have been previously calibrated against NIST Standard Reference Materials (IAEA-N1, IAEA-N2, IAEA-N3, USGS-40, and USGS-41). A sample’s preliminary isotope ratio is measured relative to reference gases analyzed with each sample. These preliminary values are finalized by correcting the values for the entire batch based on the known values of the included
laboratory standards. The long term standard deviation is 0.2 permil for 13C and 0.3 permil for 15N.

The final delta values, delivered to the customer, are expressed relative to international standards V-PDB (Vienna PeeDee Belemnite) and Air for carbon and nitrogen, respectively. For information on delta notation and the international references, please refer to a stable isotope reference such as Sharp, Z. (2005) Principles of Stable Isotope Geochemistry (Prentice Hall).






 
e-mail: sif@ucdavis.edu | phone: 530-752-8100 | fax: 530-752-4361
UC Davis Stable Isotope Facility | Department of Plant Sciences
One Shields Avenue, Mail Stop #1 | Davis, California, 95616 | USA