Leibniz Institute of Photonic Technology , 07745 Jena , Germany.
Max-Planck-Institute for Biogeochemistry , 07745 Jena , Germany.
Anal Chem. 2019 Jun 18;91(12):7562-7569. doi: 10.1021/acs.analchem.8b05684. Epub 2019 May 3.
Stable isotopes are used in ecology to track and disentangle different processes and pathways. Especially for studies focused on the gas exchange of plants, sensing techniques that offer oxygen (O) and carbon dioxide (CO) sensitivity with isotopic discrimination are highly sought after. Addressing this challenge, fiber-enhanced Raman gas spectroscopy is introduced as a fast optical technique directly combining CO and CO as well as O and O measurements in one instrument. We demonstrate how a new type of optical hollow-core fiber, the so-called revolver fiber, is utilized for enhanced Raman gas sensing. Carbon dioxide and oxygen isotopologues were measured at concentrations expected when using C- and O-labeled gases in plant experiments. Limits of detection have been determined to be 25 ppm for CO and 150 ppm for O. The combination of measurements with different integration times allows the creation of highly resolved broadband spectra. With the help of calculations based on density functional theory, the line at 1512 cm occurring in the oxygen spectrum is assigned to OO. The relative abundances of the isotopologues OO and nitrogen NN were in good agreement with typical values. For CO, fiber-enhanced Raman spectra show the Fermi diad and hotbands of CO, CO, and COO. Several weak lines were observed, and the line at 1426 cm was identified as originating from the (0 4 0 2) → (0 2 0 2) transition of CO. With the demonstrated sensitivity and discriminatory power, fiber-enhanced Raman spectroscopy is a possible alternative means to investigate plant metabolism, directly combining CO and CO measurements with O and O measurements in one instrument. The presented method thus has large potential for basic analytical investigations as well as for applications in the environmental sciences.
稳定同位素在生态学中用于追踪和理清不同的过程和途径。特别是对于专注于植物气体交换的研究，具有氧 (O) 和二氧化碳 (CO) 敏感性以及同位素分辨能力的传感技术是非常需要的。为了应对这一挑战，纤维增强拉曼气体光谱学被引入作为一种快速光学技术，直接在一台仪器中同时测量 CO 和 CO 以及 O 和 O。我们展示了如何利用一种新型光学中空纤维，即所谓的左轮手枪纤维，来增强拉曼气体传感。在植物实验中使用 C 和 O 标记气体时，测量了预期浓度的二氧化碳和氧气同位素。确定 CO 的检测限为 25 ppm，O 的检测限为 150 ppm。通过使用不同的积分时间进行组合测量，可以创建高度分辨的宽带光谱。借助基于密度泛函理论的计算，将在氧气光谱中出现的 1512 cm 处的线分配给 OO。OO 和氮 NN 同位素的相对丰度与典型值吻合良好。对于 CO，纤维增强拉曼光谱显示了 CO 的费米二联体和热带，以及 CO、CO 和 COO 的费米二联体。观察到几条弱线，并且 1426 cm 处的线被鉴定为源自 CO 的 (0 4 0 2) → (0 2 0 2) 跃迁。纤维增强拉曼光谱具有所展示的灵敏度和分辨能力，是一种可能的替代方法，可以直接在一台仪器中同时测量 CO 和 CO 以及 O 和 O，用于研究植物代谢。该方法因此在基础分析研究以及在环境科学中的应用中具有很大的潜力。
