How are completely desolvated ions produced in electrospray ionization: insights from molecular dynamics simulations

We apply molecular dynamics (MD) simulations to study the final phase of electrospray ionization (ESI), where an ion loses all of its associated solvent molecules. By applying an electric field to a cluster of H(2)O molecules solvating an ion and including a surrounding gas of varying pressure, we demonstrate that collisions with the gas play a major role in removing this final layer of solvent. We make quantitative predictions of the critical velocity required for the cluster to start losing molecules via collisions with gas and propose that this should be important in real ESI experiments. Such collisions have heretofore not been explicitly considered in discussions of the ESI process.