Soft ionization methods such as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) ) revolutionized mass spectrometry, notably because they were much softer than electron ionization (EI) and chemical ionization (CI). But although intact molecular ions are effortlessly produced by ESI and MALDI, ions just emitted from ESI or MALDI are hotter than the ambient temperature (~500-600 K for ESI , ~800-1000 K for MALDI ). More importantly, for atmospheric pressure ionization, the transfer interface modulates this ion internal energy further, through collisional activation/deactivation processes that depend on source pressure, hardware geometry and voltages applied. Thus, using ESI does not guarantee against in-source activation and in-source fragmentation.