Analyzers and Collision Cell 7
Troubleshooting and Maintenance Manual 155
Ion focus
The voltage on the ion focus lens (Figure 27) can be varied from 0 to
–127 VDC. A typical voltage is between –70 and –90 VDC. In general:
• Increasing the ion focus voltage improves sensitivity at lower masses.
• Decreasing the ion focus voltage improves sensitivity at higher masses.
• Incorrect ion focus adjustment results in poor high mass response.
Entrance lens
The entrance lens (Figure 27) is at the entrance to the quadrupole mass filter.
This lens minimizes the fringing fields of the quadrupole which discriminate
against high-mass ions. There is a permanent +4.4 volt voltage added to the
entrance lens. The total voltage applied to the entrance lens is the sum of the
entrance lens offset and entrance lens gain and the +4.4 volt permanent offset.
Entrance lens voltage = +4.4 VDC + offset + (gain × mass)
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