A Practical Method for Accurate Measurement of Trace Level Fluorine in Mg‐ and Fe‐Bearing Minerals and Glasses Using Electron Probe Microanalysis
A Practical Method for Accurate Measurement of Trace Level Fluorine in Mg‐ and Fe‐Bearing Minerals and Glasses Using Electron Probe Microanalysis
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DOI：
10.1111/j.1751-908x.2015.00390.x
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发表时间：
2016-09
影响因子：
3.8
通讯作者：
C. Zhang;J. Koepke;Lian-Xun Wang;Paul Eric Wolff;S. Wilke;A. Stechern;R. Almeev;F. Holtz
中科院分区：
文献类型：
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作者：
C. Zhang;J. Koepke;Lian-Xun Wang;Paul Eric Wolff;S. Wilke;A. Stechern;R. Almeev;F. Holtz
氟在岩浆和热液过程中起着重要作用，但由于其在地质样品中的丰度较低，用电子探针微量分析测定氟是困难的。使用W - Si多层假晶体代替邻苯二甲酸铊（TAP）作为衍射晶体，计数率明显提高，但在正常积分模式下，会引入FKα、fela α和MgKβ线之间的光谱干扰。在这项研究中，我们开发了一种使用W - Si多层假晶体精确测量矿物和玻璃中痕量F水平的方案。首先，我们在信号处理中使用了优化的PHA（脉冲高度分析）设置的差分模式，而不是普通的积分模式，这完全消除了二阶MgKβ线。其次，利用无氟矿物和硅酸盐玻璃定量校准了FKα峰上一阶FeLα的重叠，该重叠不能通过修改PHA设置来过滤。应用这种两步法，测定了许多参考玻璃中的F，以及由岩石参考物质AC‐E、GS‐N和DR‐N的粉末合成的玻璃中的F。我们的数据与其他方法测定的F浓度在误差范围内一致，证明了该方法的可靠性。
Fluorine plays an important role in magmatic and hydrothermal processes, but due to its low abundance in geological samples determining F is difficult by electron probe microanalysis. By using a W‐Si multi‐layered pseudocrystal as the diffraction crystal instead of thallium acid phthalate (TAP), count rates were considerably higher, which however introduced spectral interferences between FKα and FeLα and MgKβ lines when normal integral mode is applied. In this study, we developed a protocol using a W‐Si multi‐layered pseudocrystal for measuring accurately trace level F in both minerals and glasses. First, we used differential mode with an optimised PHA (pulse height analysis) setting in signal processing, instead of normal integral mode, which completely eliminated the second‐order MgKβ line. Second, the overlap of the first‐order FeLα on FKα peak, which cannot be filtered by modifying the PHA setting, was calibrated quantitatively using F‐free minerals and silicate glasses. Applying this two‐step method, F was determined in a number of reference glasses, as well as in glasses synthesised from powders of the rock reference materials AC‐E, GS‐N and DR‐N. Our data are consistent within error with F concentrations determined by other methods, demonstrating the reliability of this method.