CN-EA-iRMS instrument method

Compilation of 148 replicate CN-EA-iRMS measurements of bone collagen from 20 stable isotope laboratories by Pestle et al. (2014). UCSC SiL measured 8 replicates shown in blue on this plot (two points are equivalent).

Carbon and nitrogen isotope ratios (δ¹⁵N and δ¹³C) and C and N amount analysis are performed with an elemental analyzer coupled to an isotope ratio mass spectrometer (CN-EA-iRMS). A single weighed and pelleted sample produces simultaneous measurements of δ¹⁵N, δ¹³C, μg C, μg N, C:N, and (if the sample is weighed) wt%C and wt%N.

In the EA, tin-encapsulated samples are converted to N₂ and CO₂ via Dumas combustion/reduction in a continuous stream of He and separated into discrete peaks by gas chromatography. These N₂ and CO₂ peaks are carried to the isotope ratio mass spectrometer (iRMS) using a continuous flow of He carrier gas, where stable isotope ratios and amounts of C and N are measured.

The instrumentation used for most CN-EA-iRMS measurements at UCSC SiL is a CE Instruments NC2500 EA coupled to a Thermo Scientific Delta Plus XP iRMS via a Thermo Scientific Conflo III. An image of this instrument and an example chromatogram are shown here.

Typical isotope ratio precision (1σ) is <0.1 ‰ VPDB for δ¹³C and <0.2 ‰ AIR for δ¹⁵N. Typical amount precision (1σ) is 2.5 μg C and 0.5 μg N. UCSC SiL carbon and notrogen isotope ratio measurements have excellent external accuracy in the measurement of real world materials as demonstrated by the yellow plot of data from Pestle et al. (2014) shown on this page.

Are you preparing a Methods section for a manuscript? Here is an appropriately detailed instrument methods description that you may use for this purpose:

Samples were weighed, encapsulated in tin, and analyzed for carbon (C) and nitrogen (N) stable isotope ratios and C and N amounts by the University of California Santa Cruz Stable Isotope Laboratory using a CE Instruments NC2500 elemental analyzer coupled to a Thermo Scientific DELTAplus XP isotope ratio mass spectrometer via a Thermo-Scientific Conflo III. For high C content samples, automated in line CO2 trapping is used to remove interference with N₂. Measurements are corrected to VPDB (Vienna PeeDee Belemnite) for δ¹³C and AIR for δ¹⁵N against an in-house gelatin standard reference material (PUGel) which is extensively calibrated against international standard reference materials. Measurements are corrected for size effects, blank-mixing effects, and drift effects. An externally-calibrated Acetanilide standard reference material purchased from Dr. Arndt Schimmelmann of Indiana University is measured as a sample for independent quality control. For high C:N samples, an additional matrix matched in-house standard reference material (Oak) is measured for QC. Typical reproducibility is significantly better than 0.1 permil for δ¹³C and significantly better than 0.2 permil for δ¹⁵N.