FTICR and Orbitrap Analyzers

The same lack of apphcation to trace quantitative analysis appears to be true of a more recent innovation, the Orbitrap analyzer (Makarov 2000) indeed a recent extensive review of this device (Hu 2005) also does not mention quantitation at all. Like the FTICR analyzers, the Orbitrap operates under very high vacuum ( 10 torr) to achieve its ultimate performance it also uses image current detection. At this time neither of these analyzers appears to be suitable for trace level quantitation experiments of the kind discussed in this book. 

Historically, from the earliest days of mass spectrometry the most common method of ion activation has been coUisional activation (CA), whereby ions are accelerated through a defined potential drop and caused to collide with gas molecules that are deliberately introduced into the ion trajectory the history of this approach has been described in an excellent overview (Hu 1995). This involves conversion of part of the kinetic energy of the ion into internal energy (that in turn leads to fragmentation), and is still by far the most commonly used method. 

In general the timescale for the activation itself is appreciably shorter than that for the subsequent dissociation, and this two-step model appreciably simplifies theoretical descriptions of the phenomenon. This can be understood to some degree for the case of coUisional activation by estimating the time during which the fast ion interacts with its neutral collision partner. The velocity of an ion that has been accelerated through a potential difference from to zero was given previously (Section 6.4.4) as  

---