Electron impact ionization/quadrupole mass filter

There are many types of ionization modes and mass separation filters, the discussion of which is beyond the scope of this book. In forensic science applications, the most common design is an electron impact ionization/quadrupole mass filter (Figure 5.62) interfaced to a capillary GC. The small flows of the capillary column, on the order of 1 mL/minute or less, are managed by a simple vacuum system, allowing for a direct insertion of the column into the ionization region. Ionization and fragmentation are achieved by the collisions between... 

Undoubtedly, the technique most suited to tackle polyatomic multichannel reactions is the crossed molecular beam (CMB) scattering technique with mass spectrometric detection and time-of-flight (TOF) analysis. This technique, based on universal electron-impact (El) ionization coupled with a quadrupole mass filter for mass selection, has been central in the investigation of the dynamics of bimolecular reactions during the past 35 years.1,9-11 El ionization affords, in principle, a universal detection method for all possible reaction products of even a complex reaction exhibiting multiple reaction pathways. Although the technique is not usually able to provide state-resolved information, especially on a polyatomic... 

Typical residual gas analyzers employ electron impact to generate ions and a quadrupole mass filter to obtain the mass-to-charge ratio of these species. Mass ranges for these analyzers vary 2-80 atomic mass units for small units 1-500 on larger, more expensive gas analyzers. Electron impact ionization of the gas is achieved using a hot filament as the source. Many instruments are equipped with a second filament which can be switched into use in the event of a failure of the first. When a robust detector of moderate sensitivity is needed, a... 

In a typical CMB experiment, beams of atoms and molecules with narrow angular and velocity spread are crossed in a vacuum chamber and the angular and time-of-flight (TOF) distributions of the products are recorded after well defined collisional events take place. The detector is an electron-impact ionizer followed by a quadrupole mass spectrometer (QMS) filter the whole detector unit can be rotated in the collision plane around the axis passing through the collision center (Figure 14.1). The crossed beam machine used in the present experiments has been described in detail elsewhere [67, 79,80]. Briefly, it consists of two source chambers (10 mbar), a stainless-steel scattering chamber (10 mbar), and a rotatable, differentially pumped quadrupole mass spectrometric detector ( <8 X 10" mbar). 

The ion drift times through the quadrupole mass filter can also be determined in the hole-burning experiment. By taking the hole-burning spectra of the parent and fragment ions formed in electron impact ionization of the parent molecule, the corresponding arrival times (t) and masses (m) of these ions are used to fit the equation t = -t-1, where to is the... 

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