The transfer of ions and charged nanoparticles from solution to the gas phase in electrosprays

The transfer of singly and multiply charged particles from solution to the gas phase in electrosprays has been studied, with the following conclusions: (1) Ion Field Evaporation is the mechanism responsible for the transfer of most small ions and singly charged ionic clusters produced in Electrospray Ionization. Furthermore, the kinetics of this process is well described by the Polarization Potential Model of Iribarne and Thomson (J. Chem. Phys. 64, 2287, 1976). (2) The multiply charged particles commonly observed in Electrospray Ionization (large ionic clusters, proteins and protein aggregates, etc.) are not field desorbed, but appear in the gas phase as charged residues after complete evaporation of the solvent. Although Coulomb explosions play an important role in the necessary subdivision of the original electrospray drops down to sizes of probably some ten nanometers, the final evolution of these nanodrops is governed by both the evaporation of their liquid phase and the field desorption of their surface charge. Ultimately, the Ion Field Evaporation mechanism fixes the charge state on the particles formed as charged residues. (3) Ions also evaporate from the surface of Taylor cones of dielectric liquids, provided that the surface electric field required for ion desorption is attained in the cone-jet. For the case of NaI dissolved in formamide, this phenomenon occurs when the electrical conductivity of the solution is larger than 1.5 S/m approx. This regime, first studied here, is characterized by the emission of large ionic currents from stable cone-jets, which can exceed that associated with emitted drops.;Through the process of explaining the phenomenon of Electrospray Ionization, the first condensation nucleous counter capable of detecting single ions of arbitrary small dimensions has been developed. This instrument is also able to determine the size or charge of nanoparticles, and has enabled a detailed investigation on the heterogeneous nucleation of charged nanoparticles.