Modeling a Continuously Operating Electrospray Ionization Emitter Using Molecular Dynamics Simulations: From Bulk...

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Computational Chemistry

Background:

• Electrospray ionization (ESI) is crucial for mass spectrometry (MS) analysis, converting solution species into gas-phase ions.
• However, the detailed mechanisms of ESI, particularly droplet formation and ion release, remain incompletely understood.
• Existing molecular dynamics (MD) simulations of ESI have been limited to finite solution volumes, restricting analysis to short bursts.

Purpose of the Study:

• To develop and validate a novel MD algorithm for simulating continuous electrospray ionization (ESI) from an emitter capillary.
• To enable sustained, long-term MD simulations of the entire ESI process, overcoming previous computational limitations.
• To provide unprecedented insights into the physics of the Taylor cone and nascent droplet behavior during ESI.

Main Methods:

• Development of a new MD algorithm combining trajectory stitching with "solution recycling" for continuous simulation.
• Implementation of a method to periodically remove ejected droplets and replenish the emitter with fresh solution.
• Simulation of aqueous NaCl solution ESI from an emitter capillary over 50 ns.

Main Results:

• The novel algorithm enables continuous MD-based ESI simulations, a significant advancement over previous methods.
• Computational efficiency was dramatically improved, reducing an estimated 5000 days of wall clock time to 20 days for a 50 ns simulation.
• Detailed insights into the Taylor cone dynamics and the behavior of newly formed ESI droplets were obtained.

Conclusions:

• The developed MD approach provides the first comprehensive, continuous simulation of the entire ESI process.
• This method significantly enhances the feasibility of detailed mechanistic studies in ESI-MS.
• The findings offer a deeper understanding of ESI fundamental processes, from solution to ion generation.