Problems in obtaining precise and accurate Sr isotope analysis from geological materials using laser ablation MC-ICPMS |
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Authors: | P Z Vroon B van der Wagt J M Koornneef G R Davies |
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Institution: | (1) Department of Petrology, Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands |
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Abstract: | This paper reviews the problems encountered in eleven studies of Sr isotope analysis using laser ablation multicollector inductively
coupled plasma mass spectrometry (LA-MC-ICPMS) in the period 1995–2006. This technique has been shown to have great potential,
but the accuracy and precision are limited by: (1) large instrumental mass discrimination, (2) laser-induced isotopic and
elemental fractionations and (3) molecular interferences. The most important isobaric interferences are Kr and Rb, whereas
Ca dimer/argides and doubly charged rare earth elements (REE) are limited to sample materials which contain substantial amounts
of these elements. With modern laser (193 nm) and MC-ICPMS equipment, minerals with >500 ppm Sr content can be analysed with
a precision of better than 100 ppm and a spatial resolution (spot size) of approximately 100 μm. The LA MC-ICPMS analysis
of 87Sr/86Sr of both carbonate material and plagioclase is successful in all reported studies, although the higher 84Sr/86Sr ratios do suggest in some cases an influence of Ca dimer and/or argides. High Rb/Sr (>0.01) materials have been successfully
analysed by carefully measuring the 85Rb/87Rb in standard material and by applying the standard-sample bracketing method for accurate Rb corrections. However, published
LA-MC-ICPMS data on clinopyroxene, apatite and sphene records differences when compared with 87Sr/86Sr measured by thermal ionisation mass spectrometry (TIMS) and solution MC-ICPMS. This suggests that further studies are required
to ensure that the most optimal correction methods are applied for all isobaric interferences. |
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Keywords: | Laser ablation MC-ICPMS Sr isotopes In situ analysis Interferences |
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