Fragmentation flight tube

This technique has been extended by inclusion of a pulsed ionization laser to vaporize the particles after their size has been determined by aerodynamic time of flight. This causes the particle to vaporize and the resulting fragments are partly ionized. Positive ions are accelerated into the flight tube of a mass spectrometer where their chemical composition is determined [141]... 

Figure 15.7. Typical configurations used in biological MS. In MALDI-TOF, the ions produced by a short laser pulse travel across a flight tube, arriving at different times at the detector. In ESI-triple quadrupole, the first quadrupole (Ql) is used to separate the sprayed ions, in the second (Q2, also called the fragmentation cell) argon atoms collide with the ions the resulting ions (daughter ions) are analyzed in Q3, and subsequently detected.

They are metastable ions that occur when excited species leaving the source fragment in the flight tube. Indeed, they do look like lumps that are a few mass units wide. 

A certain amonnt of structural information, snch as sequencing of peptides, can be obtained from single-analyzer MALDl-TOF systems used in the reflectron mode becanse some ions leaving the ion source are metastable (Section 3.3.1.2) and fragment as they move down the flight tube the process is called post-source decay (PSD). The technique is limited because it is not possible to preselect ions for fragmentation and becanse stepwise changes in the parameters of the reflectron are needed to obtain prodnct ion spectra. 

Because the flight-tube fragments continue to travel with the velocity of their precursor, the velocity of the b4-ion is calculated using the m/z = 556. Therefore,... 

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