The Plasma Desorption Mass Spectrometer

FIGURE 4.2 Schematic diagram of a plasma desorption mass spectrometer. Because the TDC is a multistop device, each ionization and recording cycle produces time-interval measurements for several ions. In the example shown. 3 and 4 ions are recorded in the first and second cycles, respectively. 

FIGURE 4.3 PDMS spectrum of insulin. Note in the low mass portion of the spectrum that there is a broad peak resulting from the fission fragments themselves, whose velocities TeVImy are approximately I 

FIGURE 4.4 Schematic diagram of a coincidence time-of-flight mass spectrometer. In contrast to current TDCs, the TPHC is a single-stop device that outputs pulses, whose amplitudes are proportional to flight times and are assigned to an appropriate channel by a PHA. 

Because the flight time of each ion is the time interval that begins with detection of an electron released in the same ionization event, this is a coincidence instrument. The only requirement for such instruments is that ionization events occur (predom-inandy) at intervals longer than the time-of-flight measurement. 

FIGURE 4.5 Pulses processed by (a) a low-level discriminator, and (b) a constant-fraction discriminator. 

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