In electrospray ionization, how much pull does an ion need to escape its droplet prison?

This article assumes that (1) that solute ions from a charged droplet are formed by field-assisted desorption, (2) that the charges on such a droplet are equidistantly spaced in a uniform array on the droplet surface, and (3) that the distance between charges on an evaporated ion cannot be less than the distance between charges on the droplet surface when that ion desorbed. These assumptions, together with mass spectral data for poly(ethylene glycols) and available information on the structure of their electrospray ions, allow us to determine that intercharge distance and thus the magnitude of the droplet surface field when these ions desorbed. Values of this desorption field for methanol-water droplets are 2.66, 1.55, and 1.46 V/nm for the smallest oligomer ions having respectively 2, 3 and 6 charges (Na+). (C) 1997 American Society for Mass Spectrometry.