microXAS Beamline Project, Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
Anal Chem. 2011 Aug 15;83(16):6259-66. doi: 10.1021/ac200899x. Epub 2011 Jul 15.
Quantitative chemical imaging of trace elements in heterogeneous media is important for the fundamental understanding of a broad range of chemical and physical processes. The primary aim of this study was to develop an analytical methodology for quantitative high spatial resolution chemical imaging based on the complementary use of independent microanalytical techniques. The selected scientific case study is focused on high spatially resolved quantitative imaging of major elements, minor elements, and a trace element (Cs) in Opalinus clay, which has been proposed as the host rock for high-level radioactive waste repositories. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), providing quantitative chemical information, and synchrotron radiation based micro-X-ray fluorescence (SR-microXRF), providing high spatial resolution images, were applied to study Cs migration into Opalinus clay rock. The results indicate that combining the outputs achievable by the two independent techniques enhances the imaging capabilities significantly. The qualitative high resolution image of SR-microXRF is in good agreement with the quantitative image recorded with lower spatial resolution by LA-ICPMS. Combining both techniques, it was possible to determine that the Opalinus clay sample contains two distinct domains: (i) a clay mineral rich domain and (ii) a calcium carbonate dominated domain. The two domains are separated by sharp boundaries. The spatial Cs distribution is highly correlated to the distribution of the clay. Furthermore, extended X-ray absorption fine structure analysis indicates that the trace element Cs preferentially migrates into clay interlayers rather than into the calcite domain, which complements the results acquired by LA-ICPMS and SR-microXRF. By using complementary techniques, the quantification robustness was improved to quantitative micrometer spatial resolution. Such quantitative, microscale chemical images allow a more detailed understanding of the chemical reactive transport process into and within heterogeneous media to be gained.
对非均相介质中微量元素的定量化学成像对于广泛的化学和物理过程的基本理解非常重要。本研究的主要目的是开发一种基于独立微分析技术互补使用的定量高空间分辨率化学成像分析方法。选定的科学案例研究侧重于对高放废物处置库候选岩土体之一的 Opalinus 粘土中的主要元素、次要元素和微量元素（Cs）进行高空间分辨率定量成像。激光烧蚀电感耦合等离子体质谱（LA-ICPMS）提供定量化学信息，同步辐射微 X 射线荧光（SR-microXRF）提供高空间分辨率图像，用于研究 Cs 在 Opalinus 粘土中的迁移。结果表明，将两种独立技术的输出结果相结合，可显著提高成像能力。SR-microXRF 的定性高分辨率图像与 LA-ICPMS 记录的低空间分辨率定量图像吻合良好。结合两种技术，可以确定 Opalinus 粘土样品包含两个不同的域：（i）富含粘土矿物的域和（ii）碳酸钙占主导地位的域。这两个域由明显的边界隔开。Cs 的空间分布与粘土的分布高度相关。此外，扩展 X 射线吸收精细结构分析表明，微量元素 Cs 优先迁移到粘土夹层中，而不是迁移到方解石域中，这补充了 LA-ICPMS 和 SR-microXRF 的结果。通过使用互补技术，提高了定量的稳健性，达到了定量的微米空间分辨率。这种定量的微尺度化学图像可以更详细地了解化学物质在非均相介质中的输运过程。
