Gentle nano-electrospray ion source for reliable and efficient generation of microsolvated ions.

We present herein the design of a nano-electrospray ion source capable of reliable generation of large quantities of microsolvated ions. The source is based on a triple molecular skimmer scheme and can be quickly tuned to generate bare ions or their ionic complexes with up to more than 100 solvent molecules retained from solution. The performance of this source is illustrated by recording the mass spectra of distributions of ionic complexes of protonated water, amino acids, and a small protein ubiquitin. Protonated water complexes with more than 110 molecules and amino acids with more than 45 water molecules could be generated. Although the commercial ion source based on the double ion funnel design with orthogonal injection, which we used in our laboratory, is more efficient in generating ions than our triple skimmer ion source, they both exhibit comparable short-term stability in generating bare ions. In return, only the new source is capable of generating microsolvated ions.