在复杂的天然基质中识别分子依赖于匹配所研究的离子的碎裂光谱和为相应的分析标准获得的光谱。目前,有许多实验测量的串联质谱数据库(如NIST,MzCloud,和Metlin),在使用组合,机器学习,和量子化学方法(如MetFrag,CFM-ID,和QCxMS)。然而,电喷雾电离分子可以在不同的位置电离(质子化或去质子化),和这些离子的碎片谱是不同的。这里,我们正在使用in-ESI源氢/氘交换反应和MSn片段化的组合来研究有机分子不同原聚体的片段化途径。表明,氘在碎片离子中的分布反映了不同质子的存在。对于几个分子,氘的分布可追溯到MS5的碎片化水平,揭示了许多不寻常和意想不到的影响。例如,我们调查了环丙沙星和诺氟沙星离子中HF的损失,并观察到对于在-COOH基团质子化的离子,消除的氢总是来自-NH基团。当离子在另一个位点质子化时,氢的消除以30%的概率从-NH基团发生,概率为70%,它起源于分子上的其他位点。以前没有描述过这样的效果。量子化学模拟用于质子化结构的验证和相应的碎裂光谱的模拟。
Identification of molecules in complex natural matrices relies on matching the fragmentation spectra of ions under investigation and the spectra acquired for the corresponding analytical standards. Currently, there are many databases of experimentally measured tandem mass spectrometry spectra (such as NIST, MzCloud, and Metlin), and considerable progress has been made in the development of software for predicting tandem mass spectrometry fragments in silico using combinatorial, machine learning, and quantum chemistry approaches (such as MetFrag, CFM-ID, and QCxMS). However, the electrospray ionization molecules can be ionized at different sites (protonated or deprotonated), and the fragmentation spectra of such ions are different. Here, we are using the combination of the in-ESI source hydrogen/deuterium exchange reaction and MSn fragmentation for the investigation of the fragmentation pathways for different protomers of organic molecules. It is shown that the distribution of the deuterium in the fragment ions reflects the presence of different protomers. For several molecules, the distribution of deuterium was traced up to the MS5 level of fragmentation revealing many unusual and unexpected effects. For example, we investigated the loss of HF from the ciprofloxacin and norfloxacin ions and observed that for ions protonated at -COOH group, the eliminating hydrogen always comes from -NH group. When ions are protonated at another site, the elimination of hydrogen with a probability of 30% occurs from the -NH group, and with a probability of 70%, it originates from other sites on the molecule. Such effects were not described previously. Quantum chemical simulation was used for the verification of the protonated structures and simulation of the corresponding fragmentation spectra.