Metal oxide (MOX) sensors are increasingly gaining attention in analytical applications. Their fundamental operation principle is based on conversion reactions of selected molecular species at their semiconducting surface. However, the exact turnover of analyte gas in relation to the concentration has not been investigated in detail to date. In the present study, two optical sensing techniques—luminescence quenching for molecular oxygen and infrared spectroscopy for carbon dioxide and methane—have been coupled for characterizing the behavior of an example semiconducting MOX methane gas sensor integrated into a recently developed low-volume gas cell. Thereby, oxygen consumption during MOX operation as well as the generation of carbon dioxide from the methane conversion reaction could be quantitatively monitored. The latter was analyzed via a direct mid-infrared gas sensor system based on substrate-integrated hollow waveguide (iHWG) technology combined with a portable Fourier transform infrared spectrometer, which has been able to not only detect the amount of generated carbon dioxide but also the consumption of methane during MOX operation. Hence, a method based entirely on direct optical detection schemes was developed for characterizing the actual signal generating processes—here for the detection of methane—via MOX sensing devices via near real-time online analysis.

Graphical Abstract

金属氧化物（MOX）传感器在分析应用中越来越受到关注。它们的基本操作原理基于所选分子种类在其半导体表面的转化反应。然而，迄今为止，尚未详细研究分析物气体相对于浓度的准确周转率。在本研究中，已将两种光学传感技术（用于分子氧的发光猝灭和用于二氧化碳和甲烷的红外光谱）耦合在一起，以表征集成到最近开发的小体积气室中的示例性半导体MOX甲烷气体传感器的性能。由此，可以定量地监测MOX操作期间的氧气消耗以及甲烷转化反应产生的二氧化碳。后者是通过直接中红外气体传感器系统进行分析的，该系统基于与基片集成的中空波导（iHWG）技术结合便携式傅里叶变换红外光谱仪，不仅能够检测产生的二氧化碳量，而且还能检测二氧化碳的含量。在MOX操作过程中消耗甲烷。因此，开发了一种完全基于直接光学检测方案的方法，用于通过近实时在线分析通过​​MOX传感设备表征实际信号生成过程（此处用于检测甲烷）。它不仅能够检测出产生的二氧化碳量，而且还能够检测MOX操作过程中的甲烷消耗量。因此，开发了一种完全基于直接光学检测方案的方法，用于通过近实时在线分析通过​​MOX传感设备表征实际信号生成过程（此处用于检测甲烷）。它不仅能够检测出产生的二氧化碳量，而且还能够检测MOX操作过程中的甲烷消耗量。因此，开发了一种完全基于直接光学检测方案的方法，用于通过近实时在线分析通过​​MOX传感设备表征实际信号生成过程（此处用于检测甲烷）。

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