Secondary Electrospray Ionization of Complex Vapor Mixtures. Theoretical and Experimental Approach |
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Authors: | Guillermo Vidal-de-Miguel Ana Herrero |
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Institution: | (1) SEADM S.L., Valladolid, Spain;(2) Energy and Fluid Mechanics Engineering Department, Valladolid University, Valladolid, Spain |
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Abstract: | 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-H2O-NH3 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. |
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