A study was performed of the reactions of protonated acetic acid hydrates, CH3COOHH+(H2O)n, with acetone molecules, CH3COCH3, using a selected ion flow-drift tube (SIFDT). The rationale for this study is that hydrated protonated organic molecules are major product ions in secondary electrospray ionization mass spectrometry (SESI-MS) and ion mobility spectrometry (IMS). Yet the formation and reactivity of these hydrates are only poorly understood, and kinetics data are only sparse. The existing SIFDT instrument in our laboratory was upgraded to include an octupole ion guide and a separate drift tube by which hydrated protonated ions can be selectively injected into the drift tube reactor and their reactions with molecules studied under controlled conditions. This case study shows that, in these hydrated ion reactions with acetone molecules, the dominant reaction process is ligand switching producing mostly proton-bound dimer ions (CH3COCH3)H+(CH3COOH), with minor branching into (CH3COCH3)H+(H2O). This switching reaction was observed to proceed at the collisional rate, while other studied hydrated ions reacted more slowly. An attempt is made to understand the reaction mechanisms and the structures of the reaction intermediate ions at the molecular level. Secondary switching reactions of the asymmetric proton-bound dimer ions lead to a formation of strongly bound symmetrical dimers (CH3COCH3)2H+, the terminating ion in this ion chemistry. These results strongly suggest that, in SESI-MS and IMS, the presence of a polar compound, like acetone in exhaled breath, can suppress the analyte ions of low concentration compounds like acetic acid thus compromising their quantification.

中文翻译：

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配体转换离子化学：质子化乙酸水合物与丙酮的初级和次级反应的 SIFDT 案例研究。

使用选定的离子流漂移管 (SIFDT) 对质子化乙酸水合物 CH3COOHH+(H2O)n 与丙酮分子 CH3COCH3 的反应进行了研究。这项研究的基本原理是水合质子化有机分子是二次电喷雾电离质谱 (SESI-MS) 和离子迁移谱 (IMS) 中的主要产物离子。然而，人们对这些水合物的形成和反应性知之甚少，动力学数据也很少。我们实验室现有的 SIFDT 仪器升级为包括一个八极离子导向器和一个单独的漂移管，通过它可以将水合质子化离子选择性地注入漂移管反应器，并在受控条件下研究它们与分子的反应。这个案例研究表明，在这些与丙酮分子的水合离子反应中，主要的反应过程是配体转换，主要产生质子结合的二聚体离子 (CH3COCH3)H+(CH3COOH)，少量分支为 (CH3COCH3)H+(H2O)。观察到这种转换反应以碰撞速率进行，而其他研究的水合离子反应更慢。试图在分子水平上理解反应机制和反应中间离子的结构。不对称质子结合二聚体离子的二次转换反应导致形成强结合的对称二聚体 (CH3COCH3)2H+，这是该离子化学中的终止离子。这些结果强烈表明，在 SESI-MS 和 IMS 中，极性化合物（如呼出气中的丙酮）的存在可以抑制低浓度化合物（如乙酸）的分析物离子，从而影响其定量。