Pagnotti Vincent S, Chakrabarty Shubhashis, Wang Beixi, Trimpin Sarah, McEwen Charles N
Department of Chemistry and Biochemistry, University of the Sciences , Philadelphia, Pennsylvania 19104, United States.
Anal Chem. 2014 Aug 5;86(15):7343-50. doi: 10.1021/ac500132j. Epub 2014 Jul 11.
Introducing water or methanol containing a low concentration of volatile or nonvolatile analyte into an inlet tube cooled with dry ice linking atmospheric pressure and the first vacuum stage of a mass spectrometer produces gas-phase ions even of small proteins that can be detected by mass spectrometry. Collision-induced dissociation experiments conducted in the first vacuum region of the mass spectrometer suggest analyte ions being protected by a solvent cage. The charges may be produced by processes similar to those proposed for charge separation under freezing conditions in thunderclouds. By this process, the surface of an ice pellet is charged positive and the interior negative so that removal of surface results in charge separation. A reversal of surface charge is expected for a heated droplet surface, and this is observed by heating rather than cooling the inlet tube. These observations are consistent with charged supercooled droplets or ice particles as intermediates in the production of analyte ions under freezing conditions.
将含有低浓度挥发性或非挥发性分析物的水或甲醇引入用干冰冷却的进样管中，该进样管连接大气压和质谱仪的第一真空级，即使是小蛋白质也能产生气相离子，这些离子可通过质谱检测。在质谱仪的第一真空区域进行的碰撞诱导解离实验表明，分析物离子受到溶剂笼的保护。电荷的产生过程可能类似于雷云中冻结条件下电荷分离的过程。通过这个过程，冰粒表面带正电，内部带负电，因此去除表面会导致电荷分离。对于加热的液滴表面，预计表面电荷会反转，通过加热而不是冷却进样管可以观察到这一点。这些观察结果与带电的过冷液滴或冰粒子作为冷冻条件下分析物离子产生过程中的中间体一致。
