TIMS: Long Term Reproducibility of Nd Isotopic Data Acquired on TRITON Plus

Significance of the Topic

Precise measurement of neodymium (Nd) isotopic ratios at parts-per-million (ppm) level underpins advances in geochronology, geochemistry, cosmochemistry and environmental studies. High reproducibility over extended periods enables robust comparison of datasets across laboratories and supports investigation of fundamental processes in Earth and planetary sciences.

Objectives and Study Overview

This application note evaluates the long-term precision and reproducibility of Nd isotopic analyses on the Thermo Scientific TRITON Plus TIMS. Using static acquisition with a virtual amplifier and 1011 Ω amplifiers, the study monitors one year of measurements on a Merck Nd ICP standard (170335) over sample loads of 100 ng to 500 ng, with typical run times of 1 to 1.5 hours.

Methodology and Instrumentation

Sample Preparation and Loading:

• Standard: Merck Nd ICP standard 170335 (143Nd/144Nd = 0.512399 ± 3, 2SD).
• Filaments: Zone-refined rhenium double-filament assemblies with Nd in 6 M HCl and 1 µL 0.3 M H3PO4 as activator.
• Outgassing: 40 min at 3.2 A, 10 min at 4.5 A.

Acquisition Parameters:

• Ion Beam: Nd+ signals of 2–9 V on 142Nd.
• Mode: Static multi-collection with virtual amplifier rotation over 2–3 cycles (320–480 ratio measurements).
• Temperature: Filament at ~1650 °C.
• Baseline: 105 s before each data block.
• Mass Bias Correction: Normalized to 146Nd/144Nd = 0.7219 using exponential law.

Instrumentation:

• Thermo Scientific TRITON Plus TIMS.
• Virtual Amplifier Technique: Sequentially connects all Faraday cups to each amplifier to average out gain calibration bias.
• 1011 Ω Amplifiers in static mode.

Main Results and Discussion

Over 73 analyses spanning one year, external reproducibility (2RSD) ranged from 2 to 6 ppm/amu for both 100 ng and 500 ng Nd loads. Data show no significant difference between higher and lower sample loads, demonstrating reliable performance down to 100 ng. Faster runs using higher ion beam intensities (10 V on 142Nd) reduced analysis time to one hour without compromising precision. Comparison with literature values confirms that the TRITON Plus with virtual amplifier achieves reproducibility equivalent to or better than previously reported 2–5 ppm/amu.

Benefits and Practical Applications

Use of the virtual amplifier on TRITON Plus offers:

• Enhanced long-term reproducibility at the ppm level for Nd isotopic ratios.
• Reduced analysis time, enabling higher sample throughput.
• Capability to handle low sample loads (100 ng) for scarce or precious materials.
• Routine applicability in geochronology, geochemistry and environmental monitoring.

Future Trends and Applications

Continued improvements in amplifier design and automation will further decrease measurement time and sample requirements. Integration with automated sample loading systems and development of advanced data processing algorithms will extend applications to isotopic studies of other rare earth elements and facilitate large-scale environmental and extraterrestrial sample analyses.

Conclusion

The TRITON Plus TIMS combined with a virtual amplifier and 1011 Ω amplifiers delivers robust, long-term reproducibility of 2–6 ppm/amu for Nd isotopic analyses in just one hour. This performance matches or exceeds established benchmarks while supporting lower sample loads and higher throughput, validating its use for routine high-precision isotopic measurements.

Reference

1. Caro et al. 2003 Nature 423, 428–432.
2. Boyet and Carlson 2005 Science 309, 576–581.
3. Delmonte et al. 2008 Geophys. Res. Lett. 35, L07703.
4. Harvey and Baxter 2009 Chem. Geol. 258, 251–257.
5. Application Note 30015, Thermo Fisher Scientific.