Since the late 1980s, so-called soft ionization techniques, such as laser desorption ionization (LDI) (Karas and Hillenkamp 1988; Tanaka et al. 1988) and electrospray ionization (ESI) (Fenn et al. 1989) were introduced in mass spectrometric analysis. Differently from classical ionization techniques, such as electronic impact and chemical ionization, soft ionization methods allow producing low fragmented ions from polymers and large biomolecules (with molecular masses exceeding 100,000 Da) and other nonvolatile and labile molecules (Siuzdak 2006). Due to their importance for chemical analysis, the development of soft ionization techniques was rewarded the Nobel Prize in Chemistry in 2002.