Influence of the capillary temperature and the source pressure on the internal energy distribution of electrosprayed ions

The internal energy distributions in a heated capillary nano-electrospray source have been determined using the "survival yield" method. At low capillary temperatures, the internal energy distribution is characterized by a low-energy tail, which can be attributed to a fraction of ions not fully desolvated in the heated capillary. This low-energy tais is shown to disappear when the source pressure is increased. This explains why increased source pressure is favorable in the case of highly hydrophilic compounds or non-covalent complexes in order to achieve sufficient desolvation without fragmentation. It is also shown that "high temperature-low voltage" are not equivalent to "low temperature-high voltage" source conditions. These observations are important for fundamental issues as well as for source-CID mass spectral library searching applications.