In summary, source internal energy studies contradict the common intuition that small ions are produced via ion evaporation scenario whereas large ions are produced via the charged residue scenario: benzylpyridinium ions are smaller than peptides, but are produced via the charged residue mechanism, while peptides can be produced by ion evaporation or chain ejection. This could be at the origin of different characteristic temperatures observed for these two ion classes , although, as noted above, biases related to the E0 values used could also explain the difference. Further quantitative studies would thus be needed to shed a light on this matter. It would be interesting for example to study the interconnected effects of the emitter tip diameter, the electrothermal supercharging effect , and supercharging or stabilizing additives , from an ion internal energy point of view. Studying pure ion emission at reduced pressure instead of at atmospheric pressure could also prove interesting.