Establishing Geochemical Standards and Methods for CHNS Abundances and CNS Isotopes

Importance of the Topic

Elemental abundances and stable isotope ratios of carbon, hydrogen, nitrogen and sulfur are essential for reconstructing Earth and biological evolution. A combined analysis platform streamlines workflows, lowers costs and increases throughput while maintaining high data quality and reproducibility.

Objectives and Study Overview

This study evaluates a single analytical system for simultaneous determination of CHNS abundances and C, N, S stable isotope ratios. Rock samples of varied geological age and thermal maturity, including USGS reference materials, were analyzed to assess accuracy, precision and comparability with separate EA and IRMS measurements.

Methodology and Instrumentation

• Instrument configuration combines a dynamic flash combustion elemental analyzer with a MAT253 isotope ratio mass spectrometer
• CHNS abundances measured by combustion in tin capsules, GC separation, thermal conductivity detection and data capture via dedicated software
• Isotope measurements use oxygen pulses in the combustion reactor, copper reduction, water traps, GC separation and IRMS detection processed by isotope software
• Calibration employs BBOT standards and K factor for abundances and international isotope references USGS-41, USGS-40, IAEA-S2 and IAEA-S3
• Fifteen rock samples, including shales and basalts, were run in replicates to evaluate repeatability

Main Results and Discussion

• Relative standard deviations below 1% for carbon, nitrogen and hydrogen; around 1–3% for sulfur at trace levels
• Isotope precision of 0.14–0.88 per mil for δ13C, 0.02–0.79 per mil for δ15N and 0.22–0.78 per mil for δ34S
• Excellent linear agreement (R² ≈ 0.98–1.00) with independent EA and university data
• No memory effects observed across diverse sample matrices and concentration ranges

Benefits and Practical Applications

• Single-system analysis reduces sample preparation steps and total runtime
• Lower cost per sample by avoiding separate EA and IRMS analyses
• High throughput suitable for large geochemical surveys and quality control
• Robust performance across a wide range of element levels and sample types

Future Trends and Potential Applications

Advances may include further automation, deeper integration with chromatographic separation for speciation, and expansion into emerging fields such as environmental forensics, metabolic studies and isotopic tracer research.

Conclusion

The integrated Flash IRMS elemental analyzer delivers reliable CHNS abundances and stable isotope ratios with precision and throughput comparable to separate systems, offering a cost-effective solution for geochemical and environmental studies.

Used Instrumentation

• Thermo Scientific Flash IRMS Elemental Analyzer
• MAS Plus Autosampler
• Thermo Scientific MAT253 Isotope Ratio MS
• EagerSmart and Isodat software suites

References

• Stueken et al 2014 Earth Science Reviews
• Canfield and Farquhar 2009 Proceedings of the National Academy of Sciences
• Claire et al 2014 Geochimica et Cosmochimica Acta
• Krissansen-Totton et al 2015 American Journal of Science