High precision iron isotope ratio measurements

Importance of the Topic

High‐precision measurement of iron isotope ratios is a cornerstone in geosciences, environmental monitoring and industrial quality control. Variations in Fe isotopic composition can reveal processes such as redox reactions, mineral formation and pollution sources. Reliable, accurate and sensitive analytical platforms are essential for routine isotope ratio determinations, especially when sample amounts are limited or natural abundances are close to instrumental detection limits.

Study Objectives and Overview

This application brief evaluates the performance of the Thermo Scientific Neoma MC-ICP-MS for iron isotope ratio analysis. The primary goals were to assess sensitivity, isotope ratio precision and accuracy at low sample concentrations, and to benchmark these results against both instrument specifications and prior-generation MC-ICP-MS systems.

Methodology and Instrumentation

Fe solutions at 100 ppb were prepared in 3 % HNO₃ and introduced via a self-aspirating 100 µL/min nebulizer coupled to an ESI Apex Omega Q desolvating system. The Neoma MC-ICP-MS was operated in medium resolution mode with automated alignment of its 11 Faraday cups. A five‐minute measurement consisted of 75 cycles of 4 s integration. Iron isotopic standard IRMM-014 was used for bracketing, and all measurements were blank‐corrected.

Main Results and Discussion

• Sensitivity: 2.1 Gcps/ppm (336 V/ppm on a 10¹¹ Ω scale), about three times higher than the nominal specification.
• Resolving power: ~7 600, sufficient to separate ⁵⁶Fe from ⁴⁰Ar¹⁶O without additional gas dilution.
• Precision (1 SD external reproducibility, five replicates at 100 ppb): 9 ppm for δ⁵⁶/⁵⁴Fe, 37 ppm for δ⁵⁷/⁵⁴Fe and 103 ppm for δ⁵⁸/⁵⁴Fe.
• Comparison: Previous-generation MC-ICP-MS yielded 40–45 ppm precision for δ⁵⁶/⁵⁴Fe and δ⁵⁷/⁵⁴Fe at 200 ppb; Neoma achieves superior performance at half the concentration.

Benefits and Practical Applications

The enhanced sensitivity and stability of the Neoma MC-ICP-MS enable analysis of smaller sample sizes without compromising precision. High throughput bracketed measurements facilitate routine monitoring in geochemical surveys, biogeochemical research and metallurgical quality control. Automated cup alignment and robust blank correction improve reproducibility and reduce operator intervention.

Future Trends and Potential Applications

Future developments may include coupling the Neoma system with laser ablation for spatially resolved Fe isotope mapping, on‐line chromatography for speciation studies, and integration into field‐deployable platforms. Advances in detector technology and software automation will further drive sensitivity and throughput, expanding applications in environmental forensics, planetary sciences and metallurgical process control.

Conclusion

The Thermo Scientific Neoma MC-ICP-MS delivers threefold higher sensitivity than its specifications, with excellent resolving power and isotope ratio precision at low sample concentrations. Its performance supports reliable, high‐precision Fe isotope analysis, reducing sample requirements and enhancing analytical throughput.

References

• Weyer, S. & Schwieters, J. (2003) International Journal of Mass Spectrometry, 226, 355–368.