Ion energization and thermalization in electrospray-ionization mass spectrometry

电喷雾电离（ESI）质谱是现代分析化学中最强大和最通用的方法之一。在很大程度上，它的实用性源于ESI过程的温和性质，它只向分析物分子提供相对少量的能量。通过这种方式，它允许将甚至弱结合的离子（例如生物分子或有机金属）转移到气相中而不解离。尽管其首要的重要性，在ESI过程中的能量沉积和随后的离子转移阶段的问题仍然没有完全理解。这种知识的缺乏反映了测量能量转移到分析物分子中的困难。最通用的方法是利用所谓的温度计离子，如果它们的内能超过它们的离解能，它们就会以明确的方式碎裂。将观察到的剩余完整温度计离子的分数与解离能相关联，提供了对离子所吸收的能量的测量。到目前为止，最常见的温度计离子是取代的苄基吡啶离子ArCH 2（NC 5 H4）+，其通过失去吡啶和形成苄基阳离子ArCH 2+而解离。然而，这些离子的相当高的解离能意味着它们在典型的ESI条件下仅经历非常少的碎裂，从而阻止了对离子的能量吸收的准确评估。为了解决这个问题，我们开发了对位取代的二苯甲基吡啶离子Ar 2CH（NC 5 H4）+，其具有显著较低的解离能。这些新的温度计离子已被证明非常适合表征ESI过程的能量条件。在拟议的工作中，我们首先寻求开发新的温度计离子，甚至更低的离解能。然后，我们将应用这些新的以及建立温度计离子探测离子的电离和热化在ESI飞行时间质谱仪。除了考察不同溶剂和不同ESI条件的影响外，我们还将探讨离子转移光学的影响。此外，我们将比较标准ESI与变体nanospray和cryo-spray电离。这项工作的结果有望推进我们对质谱的基本理解及其实际适用性。

Electrospray-ionization (ESI) mass spectrometry is among the most powerful and versatile methods of modern analytical chemistry. To a good deal, its utility results from the gentle nature of the ESI process, which imparts only relatively small amounts of energy into the analyte molecules. In this way, it permits the transfer of even weakly bound ions, such as biomolecules or organometallics, into the gas phase without their dissociation. Despite its prime importance, the problem of energy deposition during the ESI process and the subsequent ion-transfer stage remains incompletely understood. This lack of knowledge reflects the difficulty of measuring the energy transfer into the analyte molecules. The most versatile approach makes use of so-called thermometer ions, which fragment in a well-defined manner if their internal energies exceed their dissociation energies. Correlating the observed fractions of remaining intact thermometer ions with the dissociation energies affords a measure of the energy taken up by the ions. Until recently, the by far most common thermometer ions have been substituted benzylpyridinium ions ArCH2(NC5H4)+, which dissociate by the loss of pyridine and formation of benzyl cations ArCH2+. However, the rather high dissociation energies of these ions imply that they undergo only very little fragmentation under typical ESI conditions, thus preventing an accurate assessment of the energy uptake of the ions. To meet this problem, we have developed para-substituted benzhydrylpyridinium ions Ar2CH(NC5H4)+, which have significantly lower dissociation energies. These new thermometer ions have proven very well suited for characterizing the energetic conditions of ESI process. In the proposed work, we first seek to develop new thermometer ions with even lower dissociation energies. We will then apply these new as well as the established thermometer ions to probe ion energization and thermalization in an ESI time-of-flight mass spectrometer. Besides examining the effect of different solvents and different ESI conditions, we will also probe the influence of the ion-transfer optics. In addition, we will compare standard ESI with the variants nanospray and cryo-spray ionization. The results of this work promise to advance both our fundamental understanding of mass spectrometry and its practical applicability.