Sample Types & Considerations

Carbon and Nitrogen stable isotopes (δ13C and δ15N) are measured by Elemental Analysis – Isotope Ratio Mass Spectrometry (EA-IRMS) using a Thermo Delta V Advantage IRMS machine and accompanying Flash 112 elemental analyser.

Analyses on bone collagen are routinely undertaken on samples submitted for carbon dating provided there is adequate material remaining following 14C processing.

The EA-IRMS is also used to produce a %Nitrogen content value on raw bone samples at the initial stages of bone processing. This value helps to decide if pre-treatment is viable by indicating how likely the sample is to yield sufficient collagen suitable for 14C dating.

Analyses on other sample types (e.g. flesh, hair, feathers, blood, food residues, charcoal, plants, insects) can be carried out by prior arrangement. Currently we are unable to provide stable isotope analysis as a routine stand-alone service. However, collaboration or specific projects can be discussed with Centre Director, Prof. P. Reimer (p.j.reimer@qub.ac.uk).

Protocol and Standards

Three blank (empty) capsules are measured at the start of the sequence and any C or N contribution from the tin is automatically deducted from the results.

The sample gas is compared against a relevant reference gas of known isotopic composition and the relative differences computed by the software to calculate an isotopic number for the sample gas. Samples are measured in duplicate with standards of certified isotopic composition typically bracketing every 10-12 samples. These standards are selected to encompass the result range normally observed for the material type being measured.

They are used to monitor machine performance, reproducibility and to correct sample data using a two-point regression line based on the offset between observed (measured) v expected results of the standards.

Standards of known isotopic composition currently in use in the laboratory

For NITROGEN isotopes
For CARBON isotopes
IAEA-N-2 Ammonium Sulphate  δ15N +20.30 ± 0.2 IA-R041 L-Alanine  δ13C -23.33 ± 0.10
IA-R041 L-Alanine  δ15N -5.56 ± 0.14 IAEA-CH-6 Sucrose  δ13C -10.45 ± 0.03
IA-R001 Wheat flour  δ15N +2.55 ± 0.22 IAEA-CH-7 Polyethylene  δ13C -32.15 ± 0.05
IA-R068 Soy Protein  δ15N +0.99 ± 0.07 IA-R006 Cane Sugar  δ13C -11.64 ± 0.03
IA-R069 Tuna Protein  δ15N +11.60 ± 0.09 IA-R001 Wheat flour  δ13C -26.43 ± 0.08
Sorghum Flour Standard OAS  155N +1.58 ± 0.15 IA-R068 Soy Protein  δ13C -25.22 ± 0.02
  IA-R069 Tuna Protein  δ13C -18.88 ± 0.05
  Sorghum Flour Standard OAS  δ13C -13.78 ± 0.17

Note: IAEA=International Atomic Energy Agency; IA=Iso-Analytical; OAS=Organic Analytical Standard by Elemental Microanalysis

An in-house fish standard (δ15N +17.78; δ13C -31.65) is also routinely measured as a mass spectrometry quality control sample and has currently been measured more than 2000 times.

Furthermore, collagen extraction is repeatedly performed on whale bone standard (UB 8968) and mammoth bone standard (UB 33333) and these are measured routinely both for C14 and stable isotopes for quality control purposes.

As the weight of the sample is known, the %C and %N can also be determined if a specific weight of a standard of known %C and %N is also combusted and measured. The standard currently in use to ascertain %element values is Nicotinamide (59.01% carbon and 22.94% nitrogen). The values are then used to calculate C:N ratios which are one of the primary indicators of the degree of preservation of bone collagen and/or contamination by soil organic substances.

The machine uncertainty is reported for δ13C and δ15N. This has been validated by the observed reproducibility of measurements on 10 replicate aliquots of seven different bone samples, which show no additional variability.

Other Stable Isotopes

14CHRONO Centre is also linked to the Stable Isotope Facility in the School of Natural and Built Environment, which offers stable isotope analysis of liquid, solid and gas samples for the following elements: carbon, hydrogen, oxygen, sulphur and nitrogen. The facility is one of the most comprehensive, centralised facilities for stable isotope analysis in the island of Ireland and UK.

Contact: Dr Neil Ogle

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email: n.ogle@qub.ac.uk
phone: +44 28 9097 4908

The facility has:
  • Thermo Delta V (IRMS) for 34S/32S (δ34S) ,18O/16O (δ18O) and 2H/1H (δ2H) Solids & GC-PAL Autosampler for (δ18O) and (δ2H) fluids
  • Analytical Precision 2003 with Acid Digester for the 13C/12C (δ13C) and δ18O analysis of carbonates.
  • Thermo Finnigan Delta Plus Advantage IRMS & Trace DSQ coupled Trace GC for compound specific isotope analysis (δ13C).
  • Isoprime Mass Spectrometer with EA for measurement of 13C/12C and 15N/14N in organic matter.

Background