Department of Chemistry, University of California, Berkeley, California 94720-1460, USA.
Analyst. 2018 Dec 17;144(1):237-248. doi: 10.1039/c8an01824c.
The location of gaseous ion formation in electrospray ionization under native mass spectrometry conditions was investigated using theta emitters with tip diameters between 317 nm and 4.4 μm to produce droplets with lifetimes between 1 and 50 μs. Mass spectra of β-lactoglobulin do not depend on instrument source temperatures between 160 and 300 °C with the smallest tips. A high charge-state distribution is observed for larger tips that produce droplets with lifetimes ≥10 μs and this distribution increases at higher source temperatures. These and other results show that gaseous protein ions originating from the smallest droplets are formed outside of the mass spectrometer whereas the majority of protein ions formed from the larger droplets are formed inside of the mass spectrometer where thermal heating of the droplet and concomitant protein unfolding inside of the droplet occurs. These results show that small emitter tips are advantageous in native mass spectrometry by eliminating effects of thermal destabilization of proteins in droplets inside of the mass spectrometer, eliminating the effects of non-specific protein dimerization and aggregation that can occur in larger droplets that contain more than one protein molecule, and significantly reducing salt adduction.
在 native 质谱条件下，使用发射角为 theta 的发射器（尖端直径为 317nm 至 4.4μm）产生具有 1 至 50μs 寿命的液滴，研究了电喷雾电离中气态离子形成的位置。对于最小尖端，β-乳球蛋白的质谱不依赖于仪器源温度在 160 至 300°C 之间。对于产生具有寿命≥10μs 的液滴的较大尖端，观察到高电荷态分布，并且在较高的源温度下，这种分布增加。这些和其他结果表明，源自最小液滴的气态蛋白质离子是在质谱仪外部形成的，而大多数由较大液滴形成的蛋白质离子是在质谱仪内部形成的，在那里液滴被热加热，并且伴随的蛋白质在液滴内部展开。这些结果表明，小发射器尖端在 native 质谱中是有利的，因为它消除了质谱仪内部液滴中蛋白质热不稳定性的影响，消除了在含有多个蛋白质分子的较大液滴中可能发生的非特异性蛋白质二聚体化和聚集的影响，并且显著减少了盐加合物的形成。
