Leibniz University Hannover, Institute of Electrical Engineering and Measurement Technology, Department of Sensors and Measurement Technology, 30167 Hannover, Germany.
Anal Chem. 2022 Jul 19;94(28):9960-9969. doi: 10.1021/acs.analchem.2c00955. Epub 2022 Jul 6.
Efficient ionization of analyte molecules is a crucial step for the outstanding sensitivity of ion mobility spectrometers (IMS) used for trace gas detection. Here, we present a new ion source that combines the previously published extended field switching ion shutter with two switchable ionization sources and an optimized sample gas flow that leads to a focused laminar stream through the reaction region of the ion source. The X-ray ionization source allows for chemical gas phase ionization of analyte molecules, while the UV ionization source allows for direct ionization of analyte molecules. The optimized sample gas flow not only allows for quickly washing out analyte molecules from the reaction region but also has improved sensitivity by a factor of about 5 for protonated monomers, 20 for proton-bound dimers, and over 100 for the proton-bound trimer of 1-octanol. The resulting limits of detection using chemical X-ray ionization are in the subppt-range for protonated monomers and in the low ppt-range for proton-bound dimers, while the limits of detection using direct UV ionization are in the subppb-range. Especially, a direct comparison between chemical and direct ionization of ketones using this ultrasensitive ion source reveals a stepwise conversion from directly ionized monomers to proton-bound dimers via protonated monomers during direct UV ionization.
分析物分子的高效离化是用于痕量气体检测的离子淌度谱仪（IMS）具有出色灵敏度的关键步骤。在这里，我们提出了一种新的离子源，它结合了先前发表的扩展场切换离子快门以及两个可切换的离子源和优化的样品气流，这些气流通过离子源的反应区形成聚焦层流。X 射线离子源允许分析物分子的化学气相离化，而紫外离子源允许分析物分子的直接离化。优化的样品气流不仅允许快速将分析物分子从反应区冲洗出来，而且还将质子化单体的灵敏度提高了约 5 倍，质子结合二聚体提高了 20 倍，1-辛醇的质子结合三聚体提高了 100 倍以上。使用化学 X 射线离化的检测限达到亚 ppt 级，用于质子结合二聚体的检测限达到低 ppt 级，而使用直接紫外离化的检测限达到亚 ppb 级。特别是，使用这种超灵敏离子源对酮类化合物的化学和直接离化进行的直接比较表明，在直接紫外离化过程中，直接离化的单体通过质子化单体逐步转化为质子结合二聚体。
