Ion mobility spectrometry allows one to determine ion collision cross sections, which are related to ion size and shape. Collision cross sections (CCS) are usually discussed based on the peak center, yet the width of each peak contains further information on the distribution of collision cross sections of each conformational ensemble. Here, we analyze how to convert arrival time distributions (ATD) to CCS distributions (CCSD). With a calibration curve taking into account the CCS dependence of the time spent outside the mobility region, one can reconstruct CCS distributions with correct peak center values. However, the peak widths are incorrectly rendered because ion diffusion, which affects the peak width in the time domain, is irrelevant to collision cross sections. For drift tube ion mobility, we describe a new method, coined “FWHMstep”, using a step-field experiment and processing the peak’s full width at half-maximum to reconstruct CCSDs. The width of the CCS distribution helps to characterize the analyte’s structural heterogeneity, and/or its flexibility (i.e., the variety of ways the analyte ions can rearrange following electrospray into kinetically stable gas-phase conformations).

中文翻译：

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漂移管离子淌度：如何从到达时间分布重构碰撞截面分布？

离子迁移谱法可以确定与离子尺寸和形状有关的离子碰撞截面。通常基于峰中心讨论碰撞横截面（CCS），但是每个峰的宽度包含有关每个构象整体的碰撞横截面分布的进一步信息。在这里，我们分析了如何将到达时间分布（ATD）转换为CCS分布（CCSD）。借助考虑到流动性区域之外所花费时间的CCS依赖性的校准曲线，可以重建具有正确峰中心值的CCS分布。但是，峰宽被错误地绘制，因为在时域中影响峰宽的离子扩散与碰撞截面无关。对于漂移管离子迁移率，我们描述了一种新方法，称为“ FWHMstep”，使用阶跃场实验并处理峰的最大半峰全宽以重建CCSD。CCS分布的宽度有助于表征分析物的结构异质性和/或其柔韧性（即，在电喷雾成动力学稳定的气相构象后，分析物离子可以重排的多种方式）。