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Status & Tuning Parameters
Source Tab
Repeller Voltage
Source Current
Temperature
Trap Current
8-4
Prima PRO & Sentinel PRO Mass Spectrometers User Guide
instruments and is set in on the
Centre.
A lower voltage setting will achieve a higher mass range as the mass
range is inversely proportional to ion energy. See
Technical Description:
The mass range is therefore about 200 amu at an ion energy setting
of 750 V.
Note All the tuning parameters need to be re-optimized and mass
scale recalibrated if the ion energy setting is changed.
The ion repeller is an electrode within the source block that ensures
ions move towards the ionization chamber exit slit. The voltage
applied to this plate affects sensitivity and may influence the peak
shape, linearity, and stability. The voltage applied to the ion repeller
is usually in the range 2 to 10 V, although it can be adjusted over the
range -10 V to +20 V.
The Source Current parameter represents the electrons emitted by the
filament that do not traverse the source to be collected at the trap
electrode. The proportion of the electrons traversing the source to the
trap electrode normally results in a source current 2 to 5 times greater
than that of the trap.
A source current ten times or greater than that of the trap suggests
that the filament may either be poorly aligned, have become
distorted, or the ion source has become contaminated, affecting the
number of electrons which can reach the trap.
Stability and linearity tend to be worse at higher source current / trap
current ratios.
Source
The ion source is heated by a cartridge heater in the ion source block,
and temperature is monitored by a platinum resistance thermometer
(PRT).
Source temperature is normally set within the range of 140°C to
200°C on the
dependant. Limits will be set accordingly.
The trap electrode is used to regulate and control the electron
emission through a control loop to the filament current drive.
Increasing this parameter will increase sensitivity, but care must be
taken to ensure that the biggest peaks can still be measured on the
lowest amplifier gain range.
As a guide, mass 28 should not be much set greater than 7 x 10
Mass Alignment tab
for more detail.
Heaters tab
of Control Centre but can be application
of Control
Appendix B:
-10
A
Thermo Fisher Scientific
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