激光剥蚀电感耦合等离子体质谱分析石笋样品中多元素比值及45种元素含量

Accurate Multi-element Content and Ratio Analysis of Stalagmites by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry

石笋样品的微量元素含量及Mg/Ca、Sr/Ca比值为高分辨的古气候重建提供重要指标。针对现有溶液分析技术易混合多个石笋微层、误差大的缺点,本文利用激光剥蚀电感耦合等离子体质谱技术(LA-ICP-MS)原位线扫描和点剥蚀方式对比分析了石笋生长轴方向的Mg/Ca和Sr/Ca空间分布趋势,研究表明二者均展现出显著的周期性变化特征,且周期性变化一致,其中40μm束斑线扫描更具有稳定性强、分辨率高、快速简便的优点。通过探讨碳酸盐标准样品MASC-3与玻璃标准样品NIST 610、NIST 612、KL2G、ATHO-G的相对灵敏度系数关系和元素分馏行为,确定基体效应是造成相对灵敏度系数变化的主要原因。同时建立了以MASC-3、NIST 610和NIST 612多外标结合内标Ca归一定量分析石笋中45种元素方法,针对石笋碳酸盐样品,将主量元素Ca、Mg变形为碳酸盐形式,与其他元素加和归一,不仅改变了国内外研究中需要预先采用其他分析技术来测定内标元素含量的计算方法,而且有效地避免了C元素无法准确检测的问题,能够实现与Ca内标法校正结果的吻合。

Mg/Ca, Sr/Ca ratios and trace element contents in stalagmites provide important indices for high resolution paleoclimate reconstruction. In situ LA-ICP-MS analysis is introduced here instead of solution methods due to their large errors and mixing with multi-micro layers. The spatial distributions of Mg/Ca and Sr/Ca parallel to the growth axis of stalagmite are compared in sampling ways of line scan and spot ablation respectively, which consistently show significant cyclical variations. The line scan ablation with 40 μm beam spot has the advantages of high stability, high resolution, and of being fast and simple. The relationship of relative sensitivity coefficients and element fractionation are discussed among NIST 610, NIST 612, KL2G, ATHO-G and MASC-3. Indications are that the matrix effect is the main reason for the relative sensitivity coefficient change. The calibration method of 45 major, minor and trace elements in stalagmites was established by using normalization with multi-external standards and internal standard element of Ca. The matrix normalization of Ca and Mg major elements in forms of CaCO3 and MgCO3 with other elements, not only changes the calculation method of the content of the internal standard elements in domestic and foreign studies, when using other analytical techniques, but also avoids the problem of inaccurate detection of carbon successfully, which is consistent with the result when using internal standard element Ca.