δ13C and/or δ15N Analysis of Organics

Sample Material: Sediment and rocks, various biological materials (e.g., feathers, plant material), and some liquids (e.g., blood, honey) that can dried down.

Sample Preparation: All solid samples submitted for isotopic analysis MUST be homogeneous, fine-grained powders. Liquids must be pipetted into tin cups and then air-dried (or freeze-dried).

Sample weight: Dependent on the carbon and/or nitrogen content of the sample material. To aid in sample collection, Table 1 provides a rough idea of the amount of sample that maybe required. To determine the actual required weight, contact the lab manager BEFORE weighing your samples.

Table 1.

Sample Type Approximate Weight
Sediments, soils 10 to 50 mg*
Wood, seeds, peat (C only) 1 ± 0.2 mg
Wood, seeds, peat (N only) 5 to 20 mg
Animal, fish, insect tissue 1 ± 0.2 mg
GFF filters Highly variable
* In general, materials with <0.5 %C and <0.2 %N cannot be analyzed.

Additional Information: Concentration data MUST be provided when samples are submitted. At this time we do NOT analyze isotopically enriched samples. For samples with high C/N ratios (>20) it is not possible to obtain C and N isotopic data on the same aliquot of material.Thus, two separate analyses, one for δ13C and one for δ15N, will be necessary and you will be billed accordingly (i.e., for two analyses). Contact lab manager for further information.

Precision: ±0.10 permil for δ13C and ±0.20 permil for δ15N

Method: The samples are weighed into tin cups (5x9 mm, Costech #041077) that are then folded into “tiny balls” (Fig. 1a and 1b), and placed in a 96-well sample tray (Costech #080016). The sample name, weight and sample tray hole ID (e.g., A1 to H12) are recorded. You can weight your samples using the labs ultra-microbalance. If you are unable to weigh your samples we can weigh them for you; however you will be billed for our time ($60/hour).

Figure 2.

Figure 1.

Prepared samples are loaded into the Costech Zero Blank Autosampler along with the isotopic lab standards that have been calibrated against various international standards (e.g., USGS40, USGS41, IAEA-600, USGS25, IAEA-N1, IAEA-N2, IAEA-CH-6, USGS24). Samples are then flashed combusted at >1000°C using a Carlo Erba NA1500 elemental analyzer (aka EA). A detailed description of how the EA works can be found in Verardo et al. (1990). The resulting CO2 and N2 are then analyzed by continuous-flow mass spectrometry using a DeltaPlus isotope ratio mass spectrometer.

Typically, to obtain both δ13C and δ15N data for the same aliquot of material it is necessary to dilute the C peak using helium. For materials with a C/N ratio >20 (e.g., wood) He-dilution is not enough and the C peak will saturate the collector. For these samples it is necessary to analyze C and N isotopes separately, and when analyzing N a CO2-scrubber must be used in the EA.

Suggested Reading:

Barrie, A., Davies, J.E., Park, A.J., and Workman, C.T. (1989) Continuous-flow stable isotope analysis for biologists. Spectroscopy, 4(7), 42–52.

Verardo, D.J., Froelich, P.N., and McIntyre, A. (1990) Determination of organic carbon and nitrogen in marine sediments using the Carlo Erba NA-1500 Analyzer. Deep-Sea Research, 37(1), 157-165.