Laser Ablation Split Stream (“LASS”) between High Sensitivity SC- and MC-ICP-MS Instruments

Importance of the Topic

Laser ablation split stream (LASS) enables simultaneous high-precision measurements of U-Pb ages and Hf isotopic compositions from exactly the same ablation volume. This integration avoids bias from chemical zoning, increases sample throughput, and allows analysis of smaller mineral grains in geochronology and isotope geochemistry.

Study Objectives and Overview

The primary aim was to demonstrate that 30 µm laser spots can yield precise 176Hf/177Hf ratios and 206Pb/238U ages using LASS with high-sensitivity ICP-MS instruments. A Photon Machines Analyte.G2 laser ablation system was split between a Thermo Scientific Neptune Plus MC-ICP-MS and an Element XR SC-SF-ICP-MS to acquire complementary data in a single run.

Methodology and Instrumentation

• Laser Ablation System: Photon Machines Analyte.G2 (193 nm) with a 30 µm spot, 10 Hz repetition, ~7 J/cm² fluence, 60 s ablation.
• Carrier Gases: Helium (1.5 L/min) in HelEx cell; Nitrogen (11 mL/min) for sensitivity enhancement and oxide reduction; Argon make-up gas split equally to each MS.
• Split Configuration: Simple Y-piece connector providing a reproducible 50:50 split to both instruments.
• Mass Spectrometers:
  • Neptune Plus MC-ICP-MS: Faraday cups, high-performance interface pump, X-type skimmer cones, optional Jet sample cone.
  • Element XR SC-SF-ICP-MS: Sector-field analyzer with triple-mode detector, high-sensitivity interface.
• Data Reduction: Iolite v2.5 for isotope ratio calculations; U-Pb_Redux for age determination and concordia plotting.

Main Results and Discussion

• 176Hf/177Hf precision better than 1.4 ε units (2σ RSD) at 30 µm ablation spots.
• 206Pb/238U age precision within 1.2 % (2σ RSD), accurate within analytical uncertainties.
• Reference zircons (Plešovice, MUNZirc 4) confirmed reliable Yb corrections (~35 % contribution to mass 176) and reproducible results.
• Extension to monazite demonstrated simultaneous Nd isotopic and U-Pb age analyses, highlighting versatility.

Benefits and Practical Applications

• Eliminates assumptions of homogeneity by sampling identical volumes for multiple isotopic systems.
• Enables analysis of smaller mineral grains, increasing representativity and sample population.
• Combines two analytical sessions into one, reducing laboratory time and cost.
• Applicable to earth sciences, mineral exploration, environmental tracing, and industrial QA/QC.

Future Trends and Potential Applications

• Further sensitivity gains using Jet sample cones and refined gas tuning.
• Adapting LASS to additional isotopic systems (Lu-Hf, Sm-Nd, Pb-Pb) and diverse mineral matrices.
• Integration with automated data reduction pipelines and machine learning for real-time interpretation.
• Broader adoption in provenance studies, forensic geochemistry, and environmental monitoring.

Conclusion

LASS with high-sensitivity MC-ICP-MS and SC-SF-ICP-MS successfully achieves precise, simultaneous U-Pb age and Hf isotope determinations using 30 µm laser spots. This approach streamlines geochronological workflows, improves analytical accuracy, and can be extended to other isotopic systems and minerals.

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