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Chemically assisted laser ablation ICP mass spectrometry
1Laboratory for Planetary Sciences, Tokyo Institute of Technology, O-okayama 2-12-1, Meguro, Tokyo 152-8551, Japan. hrt1@geo.titech.ac.jp
Analytical Chemistry
|January 30, 2003
Summary
A new chemically assisted laser ablation (CALA) technique improves elemental ratio analysis by reducing fractionation. This method enhances precision for lead/uranium (Pb/U) isotopic ratio measurements in zircon, crucial for geological dating.
Area of Science:
- Geochemistry
- Analytical Chemistry
- Mass Spectrometry
Background:
- Elemental ratio analysis of solid samples using inductively coupled plasma mass spectrometry (ICPMS) often suffers from elemental fractionation.
- Conventional laser ablation techniques exhibit significant Pb/U elemental fractionation due to differences in volatility, impacting isotopic ratio accuracy.
- Accurate Pb/U isotopic ratios are critical for reliable U-Pb geochronology.
Purpose of the Study:
- To develop and evaluate a novel chemically assisted laser ablation (CALA) technique for improved elemental ratio analysis.
- To enhance the analytical repeatability and accuracy of Pb/U isotopic ratio measurements.
- To validate the CALA-ICPMS technique by comparing U-Pb age data with previously reported values.
Main Methods:
- A new chemically assisted laser ablation (CALA) technique was developed, integrating laser ablation with a chemical evaporation reaction.
- Freon R-134a (1,1,1,2-tetrafluoroethane) gas was introduced into the laser cell as a fluorination reactant during Pb/U ratio measurement.
- The Freon gas reacted with ablated uranium (U) to form volatile uranium fluoride compounds (UF6), preventing redeposition and improving U transmission.
Main Results:
- The CALA technique significantly improved the analytical repeatability of elemental ratio measurements.
- Typical precision of 3-5% (2sigma) for 206Pb/238U ratio measurements was achieved for zircon standards.
- U-Pb age data obtained using CALA-ICPMS showed good agreement with previously reported values within analytical uncertainties.
Conclusions:
- The developed CALA-ICPMS technique effectively overcomes elemental fractionation issues in Pb/U ratio measurements.
- This method offers improved precision and reliability for isotopic ratio analysis and U-Pb geochronology.
- The technique's insensitivity to laser power and ablation time simplifies optimization, making it more robust for routine analysis.