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Functional Description
Mass Spectrometer
24 TSQ Series Hardware Manual Thermo Scientific
The ion sweep cone is a metallic cone over the ion transfer tube. The ion sweep cone channels
the sweep gas towards the entrance of the tube.
The ion source interface is enclosed in a vacuum chamber that is evacuated by the forepump
to a pressure of approximately 1.5 Torr.
Figure 15. Ion transfer tube
Ion Optics
The ion optics focus the ions produced in the API source and transmit them to the mass
analyzer. The TSQ mass spectrometer uses two ion optics elements:
•Q00 ion optics
•Q0 ion optics
Q00 Ion Optics
The Q00 ion optics are the ion optics that are located closest to the API source. Q00 ion
optics include either the tube lens and skimmer or the S-lens and exit lens, the Q00 rf lens,
the ion source interface cage, and the lens L0. See Figure 14.
On the TSQ Quantum Access, TSQ Quantum Access MAX, and TSQ Quantum Ultra mass
spectrometers, ions from the ion transfer tube enter the tube lens. See Figure 16. The tube
lens has a mass-dependent potential applied to it to focus the ions toward the opening of the
skimmer. An additional potential of between 0 and ±250 V (positive for positive ions and
negative for negative ions), called the tube lens offset voltage, can be applied to the tube lens.
This accelerates the ions into background gas that is present in the ion transfer tube-skimmer
region. Collisions with the background gas aid in the desolvation of the ions and increase
sensitivity. If the tube lens offset voltage is too high, however, collisions with the background
gas can be energetic enough to cause ion fragmentation. This fragmentation, called ion source
collision-induced dissociation (CID), decreases sensitivity. When you tune the TSQ mass
spectrometer, you adjust the tube lens offset voltage to maximize sensitivity by balancing
desolvation with fragmentation.
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