Dabrowska Alicja, Lindner Stefan, Schwaighofer Andreas, Lendl Bernhard
Research Division of Environmental Analytics, Process Analytics and Sensors, Institute of Chemical Technologies and Analytics, Technische Universität Wien, Getreidemarkt 9/164-UPA, 1060 Vienna, Austria.
Research Division of Environmental Analytics, Process Analytics and Sensors, Institute of Chemical Technologies and Analytics, Technische Universität Wien, Getreidemarkt 9/164-UPA, 1060 Vienna, Austria.
Spectrochim Acta A Mol Biomol Spectrosc. 2023 Feb 5;286:122014. doi: 10.1016/j.saa.2022.122014. Epub 2022 Oct 20.
Mid-IR dispersion spectroscopy is an attractive, novel approach to liquid phase analysis that extends the possibilities of traditional methods based on the detection of absorption via intensity attenuation. This technique detects inherent refractive index changes (phase shifts) induced by IR light interaction with absorbing matter. In contrast to classic absorption spectroscopy, it provides extended dynamic range, baseline-free detection, constant sensitivity, and inherent immunity to power fluctuation. In this paper, we provide a detailed experimental and theoretical characterization and verification of this method with special focus on broadband liquid sample analysis. For this purpose, we develop a compact benchtop dispersion spectroscopy setup based on an EC-QCL coupled to a Mach-Zehnder interferometer. Phase-locked interferometric detection enables to fully harness the advantages of the technique. By instrument operation in the quadrature point combined with balanced detection, the full immunity towards laser power fluctuations and the environmental noise can be achieved. On the example of ethanol (0.5-50% v/v) dissolved in water, it is experimentally demonstrated that changes of the refractive index function are linearly related to concentration also for strongly absorbing, highly concentrated samples beyond the validity of the Beer-Lambert law. Characterization of the sensitivity and noise behavior indicates that the optimum applicable pathlength for liquid analysis can be extended beyond the ones for absorption spectroscopy. Experimental demonstration of the advantages over classical absorption spectroscopy illuminates the potential of dispersion spectroscopy as upcoming robust and sensitive way of recording IR spectra of liquid samples.
中红外色散光谱是一种极具吸引力的新型液相分析方法，它扩展了基于强度衰减检测吸收的传统方法的可能性。该技术检测红外光与吸收物质相互作用引起的固有折射率变化（相移）。与经典吸收光谱相比，它具有扩展的动态范围、无基线检测、恒定灵敏度以及对功率波动的固有免疫力。在本文中，我们对该方法进行了详细的实验和理论表征与验证，特别关注宽带液体样品分析。为此，我们基于与马赫 - 曾德尔干涉仪耦合的外腔量子级联激光器开发了一种紧凑型台式色散光谱装置。锁相干涉检测能够充分利用该技术的优势。通过在正交点进行仪器操作并结合平衡检测，可以实现对激光功率波动和环境噪声的完全免疫。以溶解在水中的乙醇（0.5 - 50% v/v）为例，实验证明，对于超出比尔 - 朗伯定律有效性的强吸收、高浓度样品，折射率函数的变化也与浓度呈线性关系。对灵敏度和噪声行为的表征表明，液体分析的最佳适用光程可以扩展到超过吸收光谱的光程。与经典吸收光谱相比的实验优势表明，色散光谱作为一种即将出现的记录液体样品红外光谱的强大且灵敏的方法具有潜力。
