Fragmentation vaporized peptide molecules

Other Methods of Ionization. There are several other methods for ionization in addition to ESI and MALDI. However, most of them are not commonly used in proteomics. Some of these include chemical ionization, electron ionization, fast atom bombardment (FAB), and many others. Most of these lead to disintegration or fragmentation of analyte molecules and are not commonly used in proteomics. However, FAB has some application in the analysis of proteins and peptides, because this is a soft ionization procedure and does not cause the fragmentation of molecules under analysis. In the FAB method, a nonvolatile matrix such as m-nitrobenzyle alcohol is used to hold the analyte molecules. Analyte molecules are vaporized and ionized by bombardment with the high-energy beam of xenon or cesium from a probe inserted directly into the device containing the sample. Ionized molecules thus obtained are then subjected to separation by the mass... 

The utilization of the previous techniques is limited by the necessity of evaporating compounds with a very low vapor pressure which are also often thermo-labile. Nevertheless, the vaporization at high temperature is often more rapid than the decomposition reactions of the ions produced after passage into the vapor phase (reverse of the situation at lower temperatures). Thus, Anderson et al. [68] introduced the flash desorption technique , in which the sample is brought from 25 to 1000°C in less than 0.5 second and is ionized by electron impact. This technique appears to be much more efficient than the conventional technique. It is sufficiently powerful to obtain the vaporization of a polypeptide so as to obtain intense protonated molecules, MH and identifiable fragmentations, leading to the peptide sequence. 

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