Separation of Hf and Lu for high-precision isotope analysis of rock samples by magnetic sector-multiple collector ICP-MS |
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Authors: | J Blichert-Toft Catherine Chauvel F Albarède |
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Institution: | (1) Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, 69364 Lyon Cedex 07, France, FR;(2) Geosciences Rennes, Université de Rennes, Campus de Beaulieu, 35042 Rennes Cedex, France, FR |
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Abstract: | Potential applications of the Lu-Hf isotope system have long been impeded by the analytical difficulties of obtaining data
on a wide variety of geological materials. Many of these limitations will now be eliminated because Hf isotopes can be readily
measured with high precision and accuracy on small and/or Hf-poor samples using the newly developed magnetic sector-multiple
collector ICP-MS, also known as MC-ICP-MS or the `Plasma 54'. We present here a new method to separate and determine isotopic
compositions of both Hf and Lu from various types of geological materials using MC-ICP-MS. The chemical separation of Hf and
Lu has been designed to take advantage of the characteristics of this unique instrument. The separation of Hf can be achieved
with a straightforward two-step ion-exchange column chemistry, which has a high efficiency (better than 85% recovery) and
low blanks (typical total blanks less than 150 pg for the largest samples of 1 g bulk rock). The isolation of Lu is achieved
with a single-stage ion-exchange column procedure with near 100% yields and blanks below 20 pg. Hf isotopic compositions can
be routinely measured on 50 ng Hf with an internal precision better than 20 ppm in less than 15 min and with an external precision
better than 40 ppm. Our value for the 176Hf/177Hf ratio of the JMC 475 Hf standard currently is 0.282163 ± 9 (2s). The Lu isotopic ratio is measured rapidly and precisely
without isolating Lu from the bulk of Yb, and a mass fractionation correction increases the accuracy of the results compared
with TIMS data. Our current reproducibility of the Lu/Hf ratio is ≈1%. Selected Lu-Hf isotope analyses of some modern and
ancient geological samples validate the technique we have described here and illustrate the new opportunities for Lu-Hf isotope
geochemistry that have opened up with the advent of magnetic-sector ICP mass spectrometry.
Received: 12 September 1996 / Accepted: 13 January 1997 |
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