FTMS event sequence

Figure 11.5. Example of an experimental sequence used in FTMS. Events such as the cell quench, ionization, and detection occur at different times during the experimental sequence. Events can be spaced by user-defined delays, allowing the timing of the FTMS experiment to be precisely controlled.

Figure 6 shows the sequence of events in a laser desorption FTMS experiment. First, a focused laser beam traverses the analyzer cell and strikes the crystal normal to the surface. Molecules desorbed by the thermal spike rapidly move away from the crystal and are ionized by an electron beam which passes through the cell parallel to the magnetic field and 3 cm in front of the crystal. 

Figure 6. The sequence of events in a laser desorption FTMS experiment, (a) The laser beam enters the cell and strikes the crystal, (b) Some of the desorbed molecules are ionized by an electron beam, (c) Ions are trapped in the analyzer cell by the magnetic and electric fields, (d) Ions are accelerated by an RF pulse and the resulting coherent image current signal is detected. Reproduced with permission from Ref. 18. Copyright 1935, North-Holland Physics Publishing.

The basis for FTMS is ion-cyclotron motion. A simple experimental sequence in FTMS is composed of four events quench, ion formation, excitation and ion detection. Ions are created in or injected into a cubic cell where they are held by an electric trapping potential and a constant magnetic field B. Each ion assumes... 

A fourth component of the FTMS is the data system. While the mechanical assembly of a FTMS system is relatively simple compared to other mass spectrometers, the data system is quite sophisticated. The FTMS data system consists of a pulse sequence generator to control the timing of the various events in a measurement cycle, a frequency synthesizer, a wideband excitation amphfierfor ion isolation and ion detection, and a transient digitizer. A computer controls all of these components and is used to acquire and process the data. 

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