Research Express@NCKU - Articles Digest
Research Express@NCKU Volume 28 Issue 8 - March 13, 2015 [ http://research.ncku.edu.tw/re/articles/e/20150313/2.html ]
Micro-sublimation separation of boron in rock samples for isotopic measurement by MC-ICPMS
Ju-lien Pi1, Chen-Feng You1,2,* , Chuan-Hsiung Chung2
1 Department of Earth Sciences, National Cheng Kung University, Tainan 70101, Taiwan.
2 Earth Dynamic System Research Center, National Cheng Kung University, Tainan 70101, Taiwan [email protected]
J. Anal. At. Spectrom., 2014,29, 861-867
The material recycling and redistribution in subduction zones is of research interest because the subduction process, which includes slabs dehydration/metamorphism and arcs forming, is the major way that crusts back to the mantle. Boron was regarded as an excellent tracer for studying crust-mantle interaction in subduction zones, for its great discrepancy both in concentrations and isotopic ratios in these two reservoirs1,2. Besides boron is fluid-mobile3 in the slab dehydration/metamorphism process and incompatible1 during partial-melting of
arc magmas. The boron isotopes in rock were not easily measurable because it is rather volatile in acid digestion process and contamination may bias isotope values. Until latest two decades, the reliable acid digestion method has been developed4 and laboratory environment generally improved. But the conventional boron separation by using multi-steps ion-exchange is still of labor-consuming. For the analytical techniques, the MC-ICPMS measurement for boron isotopes was developed and is as precise as TIMS but much faster. In this study an efficient
microsublimation technique is developed to separation boron from rock solution for isotopes measurement by MC- ICPMS.
Microsublimation was reported capable of separating boron from organic-rich solution5 and from Na, Ca-rich solution6. This study evaluated it for rock samples. Our experiments show that proper NaCl doing into the rock solution makes boron separation successful by microsublimation. The experimental procure is shown in Fig 1.
Nine international rock standards were examined and the result shows consistency between our measurements and the literature values (Fig 2). The evaluation of our developed technique show that there was still minor quantity of Si in rock solution not separable by microsublimation and make possible error of <0.8‰ in the MC-ICPMS measurement. This technique is readily applicable on geochemistry studies for rocks > 5 ppm boron and potentially for low-boron rock and complex-matrices aqueous. This study developed an efficient low-blank microsublimation method of rock boron separation for MC-ICPMS isotopes measurement.
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Fig 1. The simplified work-flow of this study. From rock digestion, NaCl doping, microsublimation to boron isotopes measurement by MC-ICPMS.
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Fig 2. The comparison of the boron isotopes results of international rock standards by this study and literature values.
Reference:
1. T. Ishikawa and E. Nakamura, Nature, 1994, 370, 205–208.
2. J. Hoefs, in Stable isotope geochemistry, Springer-Verlag, Berlin Heidelberg, 5th edn, 2004, ch. 2, pp. 45–
48.
3. G. E. Bebout, J. G. Ryan and W. P. Leeman, Geochim. Cosmochim. Acta, 1993, 51, 2227–2237.
4. E. Nakamura, T. Ishikawa, J. L. Birck and C. J. All´egre, Chem. Geol., 1992, 94, 193–204.
5. B. S. Wang, C. F. You, K. F. Huang, S. F. Wu, S. K. Aggarwal, C. H. Chung and P. Y. Lin, Talanta, 2010, 82, 1378-1384.
6. J. Gaillarde, D. Lemarchand, C. Göpel and G. Manhès, Geostand. Newsl., 2001, 25, 67-75.
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