SIMS-TOF and Post-Ionization

While few SIMS-TOF instruments have been developed for the analysis of large biological molecules, the development of ion microprobes capable of focusing an ion 

Schematic diagram of the liquid SIMS-TOF. (Reprinted with permission from reference 13). 

FIGURE 5.6 Liquid SIMS-TOF mass spectrum of a peptide obtained after 20 ps time delay between the ionizing and extraction pulses. The peaks marked by vertical lines belong to the y-ion series. 

Sputtering by kilovolt ion beams produces far more neutral species than ions. When static methods are employed, one can assume that a large percentage of these sputtered neutrals will be intact molecules. Thus, there is the very real possibility for improving detection limits (sensitivity) if these neutrals can be observed by post-ionization in the gas phase. Such techniques are known as secondary neutral mass spectrometry (SNMS).  

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