Ultra-precise stable Fe isotope measurements by high resolution multiple-collector inductively coupled plasma mass spectrometry with a ⁵⁷Fe-⁵⁸Fe double spike

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• 作者：Marc-Alban Millet ; ^{marc-alban.millet@vuw.ac.nz} ; Joel A. Baker ; Constance E. Payne
• 关键词：Iron isotopes ; Ultra-high precision ; Double spike ; High resolution MC-ICP-MS ; Standards
• 刊名：Chemical Geology
• 出版年：2012
• 期刊代码：12_00092541
• 类别：ear
• 出版时间：18 April, 2012
• 卷：304-305
• 期：Complete
• 页码：18-25
• 文件大小：952 K

摘要

We have developed a method for high precision measurement of stable Fe isotopes by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), utilizing a ⁵⁷Fe-⁵⁸Fe double spike to correct for instrumental mass bias. Polyatomic interferences of ⁴⁰Ar¹⁴N⁺, ⁴⁰Ar¹⁶O⁺ and ⁴⁰Ar¹⁶O¹H⁺ on Fe isotopes are minimized by the use of a desolvating nebulizer and pseudo-high resolution mass spectrometry with typical mass resolutions of 3300, 3100 and 2700 on ⁵⁴Fe⁺, ⁵⁶Fe⁺ and ⁵⁷Fe⁺, respectively. Sample-standard bracketing with double spiked IRMM-014 Fe isotope standards accounts for residual tails from these interferences beneath the Fe ion peaks.

A range of analytical tests demonstrates that it is possible to attain internal precisions (2 se) of 卤 0.02 to 0.04鈥?on a single 15 min analysis. Long-term reproducibility (2 sd) of 卤 0.02鈥?was obtained by replicate (n = 51) analyses of IRMM-14 over a 6-month period. Replicate digestions and analyses of the basalt standard BHVO-2 (未⁵⁶Fe = + 0.128 卤 0.019鈥? demonstrate that this external reproducibility is also obtainable on natural samples.

Utilizing this new technique, we present high precision stable Fe isotope data for a range of international reference materials (BHVO-2, BCR-2, JB2, BIR-1, AGV-2, JA1, GSP-1, JG3a, JR1, RGM-1 and JF2). Data for this range of igneous standards (basalt, andesite, granodiorite, rhyolite) are in good agreement with previously published values obtained by high precision sample-standard bracketing techniques, and highlight that BIR-1 is the best calibrated standard available with a reference 未⁵⁶Fe value of + 0.052 卤 0.009鈥?(95%c.i.). Other reference values for BHVO-2, BCR-2, JB2, BIR-1, AGV-2 are also presented. Stable Fe isotope data for the JF2 alkali feldspar from a pegmatite are markedly heavy (未⁵⁶Fe = + 0.816 卤 0.025鈥?, perhaps due to the incorporation of isotopically heavy magmatic Fe³⁺ into the feldspar mineral structure during crystallization.