The use of differential mobility spectrometry (DMS) as a separation tool prior to mass analysis has increased in popularity over the years. However, the fundamental principles behind the difference between high- and low-field mobility is still a matter of debate-especially regarding the strong impact of solvent molecules added to the gas phase in chemically modified DMS environments. In this contribution, we aim to present a thorough model for the determination of the ion mobility over a wide range of field strengths and subsequent calculation of DMS dispersion plots. Our model relies on first principle calculations only, incorporating the modeling of the "hard-sphere" mobility, the change in CCS with field strength, and the degree of clustering of solvent molecules to the ion. We show that all three factors have to be taken into account to qualitatively predict dispersion plots. In particular, type A behavior (i.e., strong clustering) in DMS can only be explained by a significant change of the mean cluster size with field strengths. The fact that our model correctly predicts trends between differently strong binding solvents, as well as the solvent concentration and the background gas temperature, highlights the importance of clustering for differential mobility.

中文翻译：

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微分离子迁移率的第一原理模型：离子-溶剂聚集的影响。

多年来，在质量分析之前使用差分迁移谱 (DMS) 作为分离工具越来越受欢迎。然而，高场和低场迁移率差异背后的基本原理仍然存在争议，尤其是在化学改性的 DMS 环境中添加到气相中的溶剂分子的强烈影响。在这篇文章中，我们的目标是提供一个完整的模型，用于在广泛的场强范围内确定离子迁移率并随后计算 DMS 色散图。我们的模型仅依赖于第一性原理计算，结合了“硬球”迁移率的建模、CCS 随场强的变化以及溶剂分子与离子的聚集程度。我们表明，必须考虑所有三个因素才能定性预测离散图。特别是，DMS 中的 A 类行为（即强聚类）只能通过平均聚类大小随场强的显着变化来解释。我们的模型正确预测了不同强结合溶剂之间的趋势，以及溶剂浓度和背景气体温度，这一事实突出了聚类对差异迁移率的重要性。