Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan.
Physikalische Chemie, Freie Universität Berlin, Arnimallee 22, D-14195 Berlin, Germany.
J Chem Phys. 2019 Sep 21;151(11):114201. doi: 10.1063/1.5115191.
The application of soft X-ray absorption spectroscopy (XAS) to liquid cells based on microfluidics for chemical state analysis of light elements is much more difficult than hard X-ray absorption since soft X-rays cannot deeply penetrate a microfluidic cell. In this study, we have newly developed a microfluidic cell for spatially resolved XAS, where a 100 nm thick SiN membrane is used for the measurement window to transmit soft X-rays for keeping the microfluidic flow at a width and depth of 50 µm. The π peak of pyridine near the N K-edge XAS shows characteristic energy shifts near the liquid-liquid interface in a laminar flow of pyridine and water. The distributions of the molar fractions of pyridine and water near the liquid-liquid interface have been determined from the energy shifts of the π peak probed at different geometric positions, where pyridine is mixed in the water part of the laminar flow and vice versa. The spatial distribution of both species has also been studied by infrared microscopy, using the same microfluidic setup. The present work clearly shows that these spectroscopic techniques are easily applicable to chemical and biological reactions prepared by microfluidics.
软 X 射线吸收光谱（XAS）在基于微流控的液体池中的应用对于轻元素的化学态分析比硬 X 射线更为困难，因为软 X 射线无法深入穿透微流控池。在本研究中，我们新开发了一种用于空间分辨 XAS 的微流控池，其中使用 100nm 厚的 SiN 膜作为测量窗口来传输软 X 射线，以保持微流的宽度和深度为 50μm。在吡啶和水的层流中，靠近 N K 边 XAS 的吡啶的π 峰显示出在液-液界面附近的特征能量位移。从在不同几何位置探测到的π 峰的能量位移，可以确定在液-液界面附近吡啶和水的摩尔分数分布，其中吡啶混合在层流的水部分中，反之亦然。通过使用相同的微流控装置的红外显微镜，还研究了两种物质的空间分布。本工作清楚地表明，这些光谱技术易于应用于微流控制备的化学和生物反应。
