On the mechanism of extractive electrospray ionization (EESI) in the dual-spray configuration
Dual-spray extractive electrospray ionization (EESI) mass spectrometry as a versatile analytical technique has attracted much interest due to its advantages over conventional electrospray ionization (ESI). The crucial difference between EESI and ESI is that in the EESI process, the analytes are introduced in nebulized form via a neutral spray and ionized by collisions with the charged droplets from an ESI source formed by spraying pure solvent. However, the mechanism of the droplet–droplet interactions in the EESI process is still not well understood. For example, it is unclear which type of droplet–droplet interaction is dominant: bounce, coalescence, disruption, or fragmentation? In this work, droplet–droplet interaction was investigated in detail based on a theoretical model. Phase Doppler anemometry (PDA) was employed to investigate the droplet behavior in the EESI plume and provide the experimental data (droplet size and velocity) necessary for theoretical analysis. Furthermore, numerical simulations were performed to clarify the influence of the sheath gas flow on the EESI process. No coalescence between the droplets in the ESI spray and the droplets in the sample spray was observed using various geometries and sample flow rates. Theoretical analysis, together with the PDA results, suggests that droplet fragmentation may be the dominant type of droplet–droplet interaction in the EESI. The interaction time between the ESI droplet and the sample droplet was estimated to be <5 μs. This work gives a clear picture of droplet–droplet interactions in the dual-spray EESI process and detailed information for the optimization of this method for future applications that require higher sensitivity.
KeywordsMass spectrometry Extractive electrospray Ionization mechanisms
We would like to thank Mr. Lukas Meier, Dr. Thomas Schmid, and Dr. Waisiang Law for their kind help and nice discussion. This project was supported by the Swiss National Science Foundation (grant no. 200020-124663).
- 23.Heine MC (2007) Particle dynamics at high aerosol concentrations and production rates. ETHZ, ZurichGoogle Scholar
- 25.Hindes WC (1999) Aerosol technology: properties, behavior, and measurement of airborne particles. Wiley, New YorkGoogle Scholar
- 28.Mackay GDM, Mason SG (1963) The gravity approach and coalescence of fluid drops at liquid interfaces. CanJChemEng 41:203–212Google Scholar
- 31.Cheng CS, Li YQ, Zhao LF (2009) Investigation of improving the model for binary collision regimes of hydrocarbon droplets. In: Wenbin H, Xin L (eds) 2009 International Conference on Information Engineering and Computer Science, Wuhan, China, 19–20 December 2009, IEEEGoogle Scholar
- 37.Lamb H (ed) (1932) Hydrodynamics, 6th edn. Dover, New YorkGoogle Scholar