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

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. 

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

About the author

César Barrios-Collado is M. Eng. in Industrial Engineering (energy engineering specialization) at the University of Valladolid (Spain). Since 2011, he has worked at SEADM S.L. (Spain) on the development of a transversal modulation ion mobility spectrometer (TMIMS), with emphasis on the understanding of the ion optics within the TMIMS device. He is currently preparing his PhD dissertation at the University of Valladolid, under the supervision of Dr. Guillermo Vidal-de-Miguel. He became a Marie-Curie fellow in 2014, throughout a collaborative project between SEADM and ETH-Zürich (Switzerland), where he focused in the development of the optimized low flow secondary electrospray ionization (LFSESI) source and its applications with Dr. Guillermo Vidal-de-Miguel and Dr. Pablo Martínez-Lozano-Sinues.

About the author

Guillermo Vidal de Miguel completed his degree in aeronautical engineering in 2006 and joined the group of Prof. F. de la Mora (mechanical engineering, Yale University) to improve a SESI source specifically optimized for explosives detection. In this period, he was appointed as CTO of SEADM (a start-up at the time), and returned to Spain to combine a PhD program in fluid mechanics with the new position. Based on the initial configuration developed by Martinez-Lozano, GVM focused on the fluid mechanics and the electrostatics of the configuration, and was able to improve the ionization efficiency by almost two orders of magnitude. In the same period, GVM invented the Transversal Modulation Ion Mobility Spectrometry (TMIMS), and developed the first demonstrators. After completing his PhD, in order to get the perspectives of the scientists that use the instruments, he joined the analytical chemistry group of Prof. Zenobi and Martinez-Lozano at ETH-Z to develop an optimized SESI configuration for breath analysis. In parallel, he developed a pre-commercial TMIMS in a collaboration with Thermo Fisher Bremen.

Spinning out from these experiences, GVM founded Fossil Ion Technology (FIT) in 2015 to further develop the SESI and the TMIMS technologies and to serve the proteomics and metabolomics scientists. Currently, and after a long lasting collaboration, GVM and Martinez-Lozano work together to improve the limits of detection of the system and to bring the best SESI source into the market.

About the author

PD Dr. Pablo Martinez-Lozano Sinues is senior lecturer at ETH Zurich (Department of Chemistry and Applied Bioscience) since 2011. He graduated in Chemistry at the University of Murcia and earned his PhD in Mechanical Engineering at the University Carlos III of Madrid (2006). He has been postdoctoral fellow at Yale University and the Italian National Research Council. His research interests include the mass spectrometric analysis of trace gases for various interdisciplinary applications with a focus on breath analysis.  

 

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

Show Affiliations
  1. Department of Energy Engineering and Fluid Dynamics, University of Valladolid, Spain
  2. SEADM S.L., Spain
  3. 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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