Open ion volume

For Cl to be efficient, the reagent partial pressure in the source must be between 1 and 5 torr. With classic sources described earlier, it is necessary to replace the open ion volume used in El by a closed ion volume (see Figure 3.10). Indeed, an open ion volume does not allow attainment of the necessary partial pressure in the reagent because the gas is sucked in by the pumping system at the level of the source. The closed ion volume is not completely closed it is pierced with a hole to allow the... 

FIGURE 3.10 Open ion volume (left) for El and closed ion volume (right) for CL... 

The change of ion volnme is problematic. Most of the time, it is necessary to break the vacnnm at the level of the source or even thronghout the total mass spectrometer device with all the consequences that this implies (see Chapter 2). Quadrupole nsers generally make little use of Cl for practical reasons. A few recent devices allow the nse of semi-open ion volumes, a compromise between open and closed ion volnmes. The main advantage is to avoid intervention at the source level when one wants to pass from one ionization mode to another. This type of ion volume is useful for working mainly on structural analyses bnt does not supply the best results for quantification. We will see below that the ion trap with internal ionization is the most practical device (and often the most efficient) when switching between ionization modes is required. 

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See also in sourсe #XX -- [ ]

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