Secondary Electrospray Ionization of Complex Vapor Mixtures. Theoretical and Experimental Approach

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-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.

Numerical modeling and experimental validation of a universal secondary electrospray ionization source for mass spectrometric gas analysis in real-time

“…This is crucial, since we know that this area plays a key role in SESI mechanism, as suggested by theoretical studies [30,31].…”

“…Theoretical models [30,31] consider two ionization mechanisms: i) ionization of molecules by ions via chemical ionization; and ii) ionization of vapors by droplets, where the neutral vapors are dissolved into the droplets and get ionized.…”

“…We based the numerical model of the SESI reaction kinetics on [30,31]. The evolution of the concentrations was modeled according to the ordinary differential equations system given by eq.…”

“…As a result, the macroscopic description of the process can be decoupled from the actual charge exchange mechanisms. This assumption led to the development of the first theoretical models that describe the ion concentration distribution: the model described in [30] predicts a uniform probability of ionization p i (defined as the ratio of the concentration ions generated over the concentration of molecules) in the limit of very low vapor concentrations, while the model described in [31] provides a more general relation between the concentration of charging ions (i.e., the primary ions produced by the spray) and sample ions (i.e., the ionized vapor molecules). These theories are in accordance with experimental measurements [17].…”

Analysis of pattern recognition and dimensionality reduction techniques for odor biometrics

“…The raw data analyzed in this study is a series of spectrum (each being a snapshot) that describes the time evolution of the concentration of the different species. More details describing the vapor ionization systems developed by SEADM can be found in [56,57].…”