EA-IRMS: Tracking human and animal dietary habits using isotope fingerprints recorded in bone collagen

Importance of the Topic

Bone collagen stable isotope analysis (δ13C, δ15N and δ34S) offers a window into past and present dietary and environmental conditions. Because collagen reflects the protein portion of the diet and can record geochemical signatures from food sources, multi-isotope studies contribute to archaeology, forensic investigations, palaeodietary research and provenance studies.

Goals and Overview of the Study

This study demonstrates the capability of the Thermo Scientific EA IsoLink IRMS System to perform simultaneous measurements of δ13C, δ15N and δ34S on bone collagen. By addressing the challenge of accurately quantifying low sulfur concentrations (~0.2-0.3%), the work aims to streamline multi-isotope analysis in a single run.

Methodology and Instrumentation

• Approximately 1 mg of dried and homogenized bone collagen was encapsulated in tin capsules.
• Combustion took place at 1020°C in a reactor containing an oxidizer (tungstic anhydride) and a reducer (copper wires).
• The resulting N2, CO2 and SO2 gases were separated in a temperature-ramped gas chromatograph.
• Separated gases were introduced to a Thermo Scientific DELTA V IRMS via a ConFlo IV interface.
• Calibration employed USGS 40 and USGS 42 for C and N, and IAEA S1-S3 for S; analysis time was under 10 minutes consuming less than 1.4 L He per sample.

Used Instrumentation

• Thermo Scientific EA IsoLink IRMS System
• MAS Plus Autosampler
• Thermo Scientific DELTA V IRMS
• Thermo Scientific ConFlo IV Universal Interface
• Combustion reactor with tungstic anhydride oxidizer and copper wire reducer

Main Results and Discussion

• High-precision isotope data (≤0.1‰) for cattle, human and mammoth bone collagen were obtained in triplicate.
• Cattle values clustered around δ13C = -16 to -20‰, δ15N = 3-9‰ and δ34S = 2-13‰, reflecting C3/C4 terrestrial diets.
• Human bones showed δ13C ≈ -17.9 to -18.9‰, δ15N = 8.5-10.7‰, δ34S = 2.9-4.7‰, indicating marine protein intake.
• Mammoth samples displayed δ34S as low as -25.4‰, suggesting distinct ecological or geographical signatures.
• Plotting δ15N vs. δ34S clearly separates species and dietary sources.

Benefits and Practical Applications

• Single-run analysis of C, N and S reduces sample size requirements and instrument reconfiguration.
• Lower material usage (1 mg vs. 10-15 mg for sulfur) cuts costs and maintenance.
• Enhanced throughput and rapid turnaround support high-volume archaeological, forensic and environmental studies.

Future Trends and Applications

• Integration with additional isotopes (e.g. O, Sr) for more comprehensive provenance studies.
• Automation and miniaturization of IRMS setups to further reduce sample needs.
• Expansion of multi-isotope databases for wildlife migration, climate reconstruction and food authenticity.

Conclusion

The demonstration of the EA IsoLink IRMS System for simultaneous δ13C, δ15N and δ34S analysis in bone collagen underscores its value in dietary reconstruction and provenance research. The method offers high precision, reduced sample requirements and efficient workflow, broadening the scope of multi-isotope applications.

References

1. Nehlich O., Oelze V.M., Jay M., Conrad M., Stäuble H., Teegen W.R., Richards M.P. Sulfur isotope ratios of multi-period archaeological skeletal remains from central Germany: A dietary study. Anthropologie. LII(1):15-33, 2014.