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

The process by which ambient vapors are ionized upon interaction with electrosprays is not fully understood, compromising its optimization and widespread use. In this work we evaluated the different scales associated with the processes involved in secondary electrospray ionization (SESI), and developed a new numerical method that merges the analytical solution that describes the angle of aperture and the current of an ideal electrospray, with a finite element method that enables the evaluation of complex geometries. The numerical method showed that, despite the low ionization efficiency (i.e. ion concentration/neutral vapor concentration similar to 10(-4)), depletion of neutral vapors plays an important role. We used this method to optimize and design a low flow SESI source, which was coupled with a commercial high resolution/high mass accuracy mass spectrometer. The system was designed to be interfaced with virtually any pre-existing atmospheric pressure ionization mass spectrometer. The experimental validation for the detection of ambient vapors confirmed qualitatively the numerical predictions in terms of ionization efficiency as a function of sample flow rate. As a result of the optimization, this prototype showed a 5-fold sensitivity increase against standard SESI. This novel add-on is meant to upgrade mass spectrometers to analyze trace gases in real time by SESI technique. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (littp://creativecommons.org/licenses/by-nc-nd/4.01).