How ‘Soft’ are ‘Soft ionization methods’?

Liquid compounds containing no acidic hydrogens produce [M]+˙ ions of high energy in low yield upon particle bombardment. The molecular ions undergo fragmentation in a similar way, as if the compounds were ionized by electron impact. ‘Soft ionization’ spectra produced by fast atom bombardment mass spectrometry and liquid secondary ion mass spectrometry are actually spectra obtained from ions already existing in the matrix. The main feature of the bombarding particles is to sputter the ions, not to ionize neutral molecules.