Agilent Technologies 5975C TAD VL MSD, Руководство по устранению неисправностей и техническому обслуживанию

Страница: 206 / 276

206 5975 Series MSD Troubleshooting and Maintenance Manual
7
Analyzer
Other Source Elements
Magnet
The field created by the magnet directs the electrons emitted by the filament
into and across the ionization chamber. The magnet assembly is a permanent
magnet with a charge of 350
gauss in the center of the field.
Repeller
The repeller ( Figure 46 ) forms one wall of the ionization chamber. A positive
charge on the repeller pushes positively-charged ions out of the source
through a series of lenses. The repeller voltage is also known as the ion energy,
although the ions only receive about 20% of the repeller energy. The repeller
voltage can be varied from 0 to +42.8
VDC. Some tune programs use a fixed
repeller voltage. Others ramp the repeller voltage to find the optimum setting.
•
Setting repeller voltage too low results in poor sensitivity and poor high
mass response.
•
Setting repeller voltage too high results in precursors (poor mass filtering)
and poor low mass resolution.
Drawout plate and cylinder
The drawout plate ( Figure 46 ) forms another wall of the ionization chamber.
The ion beam passes through the hole in the drawout plate and into the
drawout cylinder. The drawout cylinder is slotted. The slots correspond to
slots in the source body. These slots allow carrier gas and un-ionized sample
molecules or fragments to be pulled away by the vacuum system. The drawout
plate and drawout cylinder are both at ground potential.
Ion focus
The voltage on the ion focus lens ( Figure 46 ) 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.