Fig. 1. A simple illustration of the ESI environment. For simplicity, droplets are presented with positive charges. According to the model presented by Loo et al.27 opposing charges may also be present in the gas phase ion. Under an electric field, elevated temperature but at ambient pressure, the sprayed analyte solution undergoes the simultaneous processes of the droplet splitting, generation of highly charged droplets, repeated splitting and shrinkage of the droplets, solvent evaporation, and removal under a directed gas (typically N2) stream. These progeny droplets themselves undergo subsequent and repeated evaporation and splitting, and this process is repeated until only gas-phase ions are generated.76 The ions are then drawn under negative pressure into the mass spectrometer.
