The Chemical Reactions in Electrosprays of Water Do Not Always Correspond to Those at the Pristine Air-Water Interface

TL;DR

This study investigates whether chemical reactions observed in water electrosprays truly reflect those at the pristine air-water interface, revealing significant differences and emphasizing the need for complementary methods.

Contribution

The paper demonstrates that electrospray-induced reactions differ from natural interfacial chemistry, highlighting the importance of combining electrospray with surface-specific techniques and simulations.

Findings

Electrospray oligomerization involves reactive hydronium ions not present at the pristine interface.

Reactions in electrosprays do not accurately represent natural air-water interface chemistry.

Complementary surface-specific methods are necessary for reliable interfacial chemical analysis.

Abstract

The recent application of electrosprays to characterize the air-water interface, along with the reports on dramatically accelerated chemical reactions in aqueous electrosprays, have sparked a broad interest. Herein, we report on complementary laboratory and in silico experiments tracking the oligomerization of isoprene, an important biogenic gas, in electrosprays and isoprene-water emulsions to differentiate the contributions of interfacial effects from those of high voltages leading to charge-separation and concentration of reactants in the electrosprays. To this end, we employed electrospray ionization mass spectrometry, proton nuclear magnetic resonance, and quantum mechanical simulations. We found that the oligomerization of isoprene in aqueous electrosprays involved minimally hydrated and highly reactive hydronium ions. Those conditions, however, are non-existent at pristine air-water interfaces and oil-water emulsions under normal temperature and pressure. Thus, electrosprays should be complemented with surface-specific platforms and theoretical methods to reliably investigate chemistries at the pristine air-water interface.