Here we gather quantitative internal energy reports on sources where droplets are charged statistically instead of by applying a voltage to the emitter, and for which significantly lower average internal energies were observed than for ESI in the same interface and mass spectrometer settings. Other qualitative reports can be found on mechanospray ionization , Kelvin spray ionization , and vibrational sonic spray ionization ): these methods typically produce ions of lower charge states than electrospray, which favor the preservation of non-covalent complexes, and are thus thought to be softer than electrospray.