Internal Energy - Practical Implications

The time span of ion accumulation can easily extend from milliseconds to seconds, the passage between functional units of the instrument may take tens of microseconds to milliseconds, and the m/z analysis requires storage times from milliseconds (QIT, LIT) to seconds (FT-ICR, orbitrap). 

In an El mass spectrum of ABYZ, all ionic species would be detected which are formed as a result of numerous coiipeting and consecutive reactions, but there is no simple rule which of them should give rise to intensive peaks and which of them would be hardly noticed. 

Obviously, the first-generation fragment ions should be more closely related to the initial structure of ABYZ than those of the second or even third generation. Fortunately, such higher generation (and therefore low-mass) fragment ions can also reveal relevant information on the constitution of the analyte. In particular, they yield reliable information on the presence of functional groups (Chap. 6). 

Fragmentation trees similar to that shown here can be constructed from any FI mass spectrum, providing ten thousands of examples for the sixth assunption of QET, that fragment ions may again be subject to dissociation, provided their internal energy suffices. 

Note The assumptions of QET have turned into basic statements governing the behavior of isolated ions in the gas phase and thus, in mass spectrometry in general. 

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Note in Fig. 9.9 how the threshold energy curve rises sharply as short power is reduced to values approaching the threshold power. The resulting cross-hatched area is a Safe Zone. Internal shorts with power or energy characteristics within this region will not induce thermal runaway. In practice, the threshold power is a more critical parameter, since in the field there are no practical means to interrupt an internal short once it has been initiated. Implications of the threshold energy curve s shape will be discussed in a future publication. 

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