LA-ICP-MS for U-(Th)-Pb geochronology: Which analytical capability is right for my laboratory?

Importance of the Topic

LA-ICP-MS U-(Th)-Pb geochronology is a cornerstone method in earth sciences for determining the age of zircon and other uranium and thorium bearing minerals. The technique leverages the decay of U and Th isotopes to stable Pb isotopes and couples laser ablation sampling with ICP-MS detection to deliver rapid, spatially resolved age data. Its widespread adoption reflects a balance of sensitivity, precision, and cost that suits many research and industrial laboratories.

Goals and Study Overview

This work compares three ICP-MS platforms for LA U-(Th)-Pb dating and guides laboratories in selecting the most suitable configuration. The study focuses on quadrupole single-collector with collision reaction cell (LA-Q-ICP-MS), high-resolution single‐collector (LA-HR-ICP-MS), and multicollector (LA-MC-ICP-MS) instruments. Key criteria include detection sensitivity, age precision, ease of operation, footprint, and overall cost.

Methodology and Instrumentation

All instruments were coupled to a 193 nm excimer laser ablation system operating at 3 J/cm2 energy and 7 Hz repetition rate with a 35 µm spot and 30 second ablation duration. The quadrupole ICP-MS (iCAP TQ) used an ammonia reaction gas in a collision reaction cell to remove 204Hg interference on 204Pb. The double‐focusing Element XR HR-ICP-MS provided an order of magnitude higher sensitivity than the Q-ICP-MS. The Neptune XT MC-ICP-MS employed a Jet Interface for maximal sensitivity and a suite of Faraday cups and ion counters for simultaneous detection of U-Pb isotopes.

Used Instrumentation

• Laser ablation system Teledyne Photon Machines Analyte G2 with HelEx ablation cell
• Thermo Scientific iCAP TQ ICP-MS with Qtegra ISDS software and ammonia CRC
• Thermo Scientific Element XR HR-ICP-MS with Jet Interface
• Thermo Scientific Neptune XT MC-ICP-MS with Multicollector detector array

Main Results and Discussion

• LA-Q-ICP-MS achieved baseline age determinations but showed higher uncertainty due to lower sensitivity and reliance on off‐line 204Hg correction.
• LA-HR-ICP-MS delivered ~20× greater 238U signal compared to Q-ICP-MS, reducing external error on 207Pb/206Pb ages and enabling smaller ablation pits for improved spatial resolution.
• Multicollector MC-ICP-MS provided the highest precision through simultaneous isotope detection and allowed coupling U-Pb dating with high-precision Hf isotope measurements.
• Laser-induced fractionation effects were effectively mitigated at lower fluence and shorter durations on HR and MC platforms, reducing systematic biases in age results.

Benefits and Practical Applications

• LA-Q-ICP-MS offers a cost-effective entry point with straightforward setup and CRC interference removal.
• LA-HR-ICP-MS improves age precision and spatial resolution for detailed zonal studies of mineral growth.
• LA-MC-ICP-MS sets the benchmark for ultimate precision and multi‐isotope workflows in advanced geochemical research.

Future Trends and Opportunities

• Further development of reaction cell gases and laser technologies to enhance sensitivity on quadrupole platforms.
• Integration of AI‐driven data processing for real-time corrections of fractionation and interferences.
• Expansion of combined isotope systems, such as simultaneous U-Pb and non-traditional stable isotopes, to unravel complex geological histories.
• Miniaturization of multicollector technology for broader accessibility in smaller laboratories.

Conclusion

The choice of ICP-MS platform for LA U-(Th)-Pb geochronology depends on laboratory priorities. Quadrupole systems deliver ease of use and lower cost, high-resolution instruments strike a balance of sensitivity and resolution, and multicollector systems offer unparalleled precision for cutting-edge research. Understanding these trade-offs ensures optimal investment and analytical outcomes.

References

1. Asogan D 2018 Using triple quadrupole interference removal to improve data quality in laser ablation ICP-MS for geochemical applications Thermo Sci Appl Note 44387
2. Triple Quadrupole ICP-MS or High Resolution ICP-MS Which Instrument is Right for Me Thermo Sci Smart Note 43402
3. Schaltegger U Schmidt A Horstwood MSA 2015 U-Th-Pb zircon geochronology by ID-TIMS SIMS and laser ablation ICP-MS Chemical Geology 402 89-110
4. Craig G Managh AJ Stremtan C Lloyd NS Horstwood MSA 2018 Doubling Sensitivity in Multicollector ICPMS Using High-Efficiency Rapid Response Laser Ablation Technology Analytical Chemistry 90 11564-11571
5. Pullen A Ibáñez-Mejia M Gehrels GE Giesler D Pecha M 2018 Optimization of a laser ablation-single collector-inductively coupled plasma-mass spectrometer for zircon U-Th-Pb geochronology Geochem Geophys Geosyst 19