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Significance Statement
The analysis of volatile species is of great interest in a number of applications. For example, detection of explosives for homeland security, assessment of indoor and outdoor air quality and biomedical applications such as breath analysis for clinical diagnosis. Because of typical low gas-phase concentrations of analytes of interest in such applications, a pre-concentration step involving sample manipulation is often required for the detection of trace gases. This limits the opportunity to capture volatile changes of highly dynamic systems.
We present here a numerically optimized ion source based on secondary electrospray ionization technology. This device is compatible with major atmospheric pressure ionization mass spectrometry vendors. This plug and play add-on allows for real-time analysis of trace gas species at concentrations as low as parts-per-trillion without any sample manipulation. The range of applications is vast, as evidenced by recent studies documenting hundreds of metabolites emitted by plants and exhaled in human breath.
Journal Reference
Sensors and Actuators B: Chemical, Volume 223, February 2016, Pages 217–225.
César Barrios-Collado1,2,3, Guillermo Vidal-de-Miguel2,3 , Pablo Martinez-Lozano Sinues3
[expand title=”Show Affiliations”]- Department of Energy Engineering and Fluid Dynamics, University of Valladolid, Spain
- SEADM S.L., Spain
- Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland
Abstract
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 ∼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.
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