Computational Simulation of Redox Reactions within a Metal Electrospray Emitter

Area of Science:

• Analytical Chemistry
• Computational Chemistry
• Electrochemistry

Background:

• Electrospray ionization mass spectrometry (ES-MS) is a powerful analytical technique.
• Understanding chemical reactions at the emitter interface is crucial for optimizing ES-MS performance.
• Computational modeling offers a way to study these complex interfacial processes.

Purpose of the Study:

• To develop and demonstrate a computational simulation for the oxidation of chemical species in a metal emitter electrospray ion source.
• To analyze the behavior of redox-active species, specifically ferrocene, under varying concentrations and solution conductivities.
• To predict interfacial potentials and reaction current densities within the emitter.

Main Methods:

• A boundary integral method was employed to solve the Laplace equation for electric potential and current.
• Standard activation and concentration polarization functions were incorporated for redox-active species.
• The simulation modeled an inert metal capillary emitter with a ferrocene solution in acetonitrile/water, varying analyte concentration and solution conductivity.

Main Results:

• The simulation successfully predicted interfacial potentials and current densities for water and ferrocene oxidation.
• The majority of current from redox reactions was found to be generated within a 200-300 μm region near the spray tip.
• Reaction extent upstream from the tip correlated inversely with the standard electrode potential (E(0)) of the reaction.

Conclusions:

• The developed computational simulation is capable of modeling interfacial redox reactions in ES-MS.
• Simulation results provide semiquantitative insights into the spatial distribution of electrochemical reactions within the emitter.
• The findings highlight the importance of the region near the spray tip for electrochemical current generation and reaction progression.