Chapter 9. “Soft” ionisation mass spectrometry of large molecules
Chapter Summary: This chapter deals with the derivatisation methods used for the structural and quantitative analysis of large molecules by “soft” ionisation mass spectrometry such as FAB, MALDI, ESI and, rarely, APCI or SIMS. Only proteins and peptides, oligosaccharides and synthetic polymers will be considered where the application of derivatisation methods is particularly effective. In order to obtain structural information, low- and high-energy CID, in-source or post-source decay (PSD) are used to promote the decomposition of such parent ions. To do this, various experimental techniques, such as ESI ion trap, ESI-triple-quadrupoles, ESI-Q-ToF and MALDI-ToF/ToF, are employed. Nevertheless, additional derivatisation methods are not only helpful in many cases, but also sometimes necessary for solving structural and quantitative problems. Because the ionisation principles of the soft ionisation methods are somewhat similar, the employed derivatisation approaches frequently resemble each other.