SEADM S.L., Valladolid, Spain.
J Am Soc Mass Spectrom. 2012 Jun;23(6):1085-96. doi: 10.1007/s13361-012-0369-z. Epub 2012 Apr 17.
In secondary electrospray ionization (SESI) systems, gaseous analytes exposed to an electrospray plume become ionized after charge is transferred from the charging electrosprayed particles (the charging agent) to the vapor species. Currently available SESI models are valid for simplified systems having only one type of electrosprayed species, which ionizes only one single vapor species, and for the limit of low vapor concentration. More realistic models require considering other effects. Here we develop a theoretical model that accounts for the effects of high vapor concentration, saturation effects, interferences between different vapor species, and electrosprays producing different types of species from the liquid phase. In spite of the relatively high complexity of the problem, we find simple relations between the different ionic species concentrations that hold independently of the particular ion source configuration. Our model suggests that an ideal SESI system should use highly concentrated charging agents composed preferably of only one dominating species with low mobility. Experimental measurements with a MeOH-H(2)O-NH(3) electrospray and a mixture of fatty acids and lactic acid served to test the theory, which gives good qualitative results. These results also suggest that the SESI ionization mechanism is primarily based on ions rather than on charged droplets.
在次级电喷雾离子化（SESI）系统中，暴露于电喷雾羽流中的气态分析物在从带电的电喷雾颗粒（带电试剂）向蒸汽物种转移电荷后被离子化。目前可用的 SESI 模型对于仅有一种类型的电喷雾物种的简化系统、仅离子化一种单一蒸汽物种的系统以及蒸汽浓度低的情况是有效的。更现实的模型需要考虑其他影响。在这里，我们开发了一个理论模型，该模型考虑了高蒸汽浓度、饱和效应、不同蒸汽物种之间的干扰以及从液相产生不同类型物种的电喷雾的影响。尽管问题的相对复杂性很高，但我们发现不同离子物种浓度之间存在简单关系，这些关系独立于特定的离子源配置。我们的模型表明，理想的 SESI 系统应该使用高浓度的带电试剂，最好由低迁移率的单一主导物种组成。使用甲醇-H（2）O-NH（3）电喷雾和脂肪酸和乳酸混合物进行的实验测量用于测试该理论，该理论给出了良好的定性结果。这些结果还表明，SESI 离子化机制主要基于离子而不是带电液滴。
