202 5977B Series MSD Troubleshooting and Maintenance Manual
7 Analyzer
HES Post extractor lens 1 and 2
The post extractor lenses are part of the lens stack in the EI HES source only.
A voltage is applied to the two lenses to increase ion focusing through the
source.
Ion focus
The voltage on the ion focus lens 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 is at the entrance to the quadrupole mass filter. This lens
minimizes the fringing fields of the quadrupole which discriminate against
high-mass ions.
Entrance lens offset
The entrance lens offset (EntOff) controls the fixed voltage applied to the
entrance lens. It can be varied from 0 to –64 VDC (–20 V is typical). Increasing
the entrance lens offset generally increases the abundance of ions at low
masses without substantially decreasing the abundance of high mass ions.
Entrance lens gain
Entrance lens gain (EntLens) controls the variable voltage applied to the
entrance lens. It determines how many volts are applied for each m/z. It can be
varied from 0 to –128 mV/(m/z). A typical range is 0 to –40 mV/amu.
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