飞秒激光剥蚀-多接收等离子体质谱原位分析玄武岩玻璃样品Mg同位素组成

In Situ Analysis of Mg Isotopic Compositions of Basalt Glasses by Femtosecond Laser Ablation Multi-collector Inductively Coupled Mass Spectrometry

建立了飞秒激光剥蚀多接收等离子体质谱(fs LA-MC-ICP-MS)原位微区分析玄武岩玻璃中Mg同位素的方法。溶液进样-干气溶胶条件下浓度匹配实验表明,样品和标准样品中Mg浓度比在0.4~3.0时,可获得准确样品Mg同位素组成。激光剥蚀条件对Mg同位素的准确测定有明显的影响,激光剥蚀斑束和扫描速率变化,使得质谱仪的质量歧视效应随进样负载量不同而产生较大的变化,并影响样品Mg同位素组成;激光剥蚀频率与δ^(25)Mg正相关,与δ^(26)Mg负相关,当剥蚀频率大于4 Hz时,δ^(25)Mg和δ^(26)Mg趋于平稳;超快激光的能量密度对Mg同位素组成影响较小。利用本方法对国际标准样品的分析结果与参考值在误差范围内一致。本方法具有制样简单、快速的特点,且测试结果准确可靠,为火山玻璃中Mg同位素分析提供了有效的分析手段。

A method was developed for the in situ analysis of magnesium isotopes by femtosecond laser ablation multi-collector inductively coupled mass spectrometry （fsLA-MC-ICP-MS）. Concentration matching experiment revealed that the Mg isotopic composition could be measured accurately when Mg concentration difference between sample and standard was in the range of 0.4- 3.0. The Mg isotopic composition was affected by the femtosecond laser conditions, including laser spot size and scanning speed, due to mass discrimination changing which was caused by different mass loading into mass spectrometer. The amount of ablated aerosol was correlated with laser frequency, laser ablation spot size, scanning speed. However, the laser energy density showed negligible effect on the accuracy of Mg isotope measurement due to the high energy output of femtosecond which was higher than the ablation threshold. To obtain reliable Mg isotopic compositions, the laser ablation spot size, laser frequency and scanning speed should be consistent during one analytical section and the difference of Mg concentration between standard and samples should be in 3 times. The analytical resuhs of two reference materials uncertainties. The developed method is simple, analysis of volcanic glasses and silicate minerals agreed well with the published values within 2 s analytical reliable and accurate, and can be used for the Mg isotope