Performance of a new coaxial ion–molecule reaction region for low-pressure chemical ionization mass spectrometry with reduced instrument wall interactions
Performance of a new coaxial ion–molecule reaction region for low-pressure chemical ionization mass spectrometry with reduced instrument wall interactions
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DOI：
10.5194/amt-12-5829-2019
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发表时间：
2019-11
影响因子：
3.8
通讯作者：
B. Palm;Xiaoxi Liu;J. Jimenez;J. Thornton
中科院分区：
文献类型：
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作者：
B. Palm;Xiaoxi Liu;J. Jimenez;J. Thornton
抽象。化学电离质谱（CIMS）技术已成为对挥发性相对较低的痕量气体进行采样的主要方法。这种气体通常被称为"粘性的"，即，由于分析物分子和仪器壁之间的相互作用，考虑到它们倾向于通过吸收或吸附过程与壁表面相互作用，具有测量伪像。这些表面相互作用会影响测量的精密度、准确度和检测限。我们引入了一个低压离子分子反应（IMR）区主要用于执行碘化物加合物电离，虽然其他加合物电离方案可以采用。设计目标是通过减少低压下壁相互作用的影响，同时保持足够的离子-分子反应时间，来改进以前的低压IMR版本。腔室测量表明IMR延迟时间（即，与以前的版本相比，新IMR中挥发性跨越5个数量级的一系列有机分子的壁相互作用的大小（即壁相互作用的大小）降低了3至10倍。尽管有这些改进，但壁相互作用仍然存在，需要理解。为此，我们还介绍了一个概念框架，考虑仪器壁的相互作用和测量协议，以准确地捕捉分析物浓度的时间依赖性。该方案使用总背景的短持续时间、高频率测量（即，快速零点）。该框架和相关术语适用于对易受壁相互作用影响的化合物进行采样的任何仪器和电离技术。
Abstract. Chemical ionization mass spectrometry (CIMS) techniques have become prominent methods for sampling trace gases of relatively low volatility. Such gases are often referred to as being “sticky”, i.e., having measurement artifacts due to interactions between analyte molecules and instrument walls, given their tendency to interact with wall surfaces via absorption or adsorption processes. These surface interactions can impact the precision, accuracy, and detection limits of the measurements. We introduce a low-pressure ion–molecule reaction (IMR) region primarily built for performing iodide-adduct ionization, though other adduct ionization schemes could be employed. The design goals were to improve upon previous low-pressure IMR versions by reducing impacts of wall interactions at low pressure while maintaining sufficient ion–molecule reaction times. Chamber measurements demonstrate that the IMR delay times (i.e., magnitude of wall interactions) for a range of organic molecules spanning 5 orders of magnitude in volatility are 3 to 10 times lower in the new IMR compared to previous versions. Despite these improvements, wall interactions are still present and need to be understood. To that end, we also introduce a conceptual framework for considering instrument wall interactions and a measurement protocol to accurately capture the time dependence of analyte concentrations. This protocol uses short-duration, high-frequency measurements of the total background (i.e., fast zeros) during ambient measurements as well as during calibration factor determinations. This framework and associated terminology applies to any instrument and ionization technique that samples compounds susceptible to wall interactions.