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Status & Tuning Parameters
Source Tab
Source Tab
Electron Energy
Emission
Filament Current
Filament Current
8-2
Prima PRO & Sentinel PRO Mass Spectrometers User Guide
This supply provides the energy to accelerate electrons (produced by
the filament) through to the ion source. Electrons subsequently
interact with molecules of the sample gases to create ions, a process
referred to as ionization.
The electron energy can be adjusted through on the
Control Centre; however it is typically set between 40 and 70 V.
The main effect of varying the Electron Energy parameter is to vary
the types and ratios of ions, the "fragmentation pattern" produced by
electron impact of the sample molecules.
In addition to dislodging one or more electrons from the sample
molecule (to produce singly or multiply charged positive ions), the
electron impact can also break molecular bonds to generate smaller
fragments. Lower electron energy tends to give a lower abundance of
fragment and multiply charged ions, which in certain applications
can help reduce the extent of component overlap and therefore
analytical complexity.
The Emission status is a "composite" status channel that shows when
all related parameters are within limits.
When the emission is switched on, the current through the filament
will be approximately 2.4 to 2.8 A when fitted with Thoria filaments.
When fitted with non standard Tungsten filaments, the current will
be closer to 3.7 A.
If the Filament Current value is close to zero, access Control Centre,
and check that the Trap Current setting (from
least 10 µA and the electron energy setting is at least 40 V.
Filament Current Limit is provided to protect the filament from being
Limit
overdriven and can be adjusted in Control Centre.
The current limits for common filaments are shown in the table
below.
Table 8–1. Current limits for common filaments
Filament
Thoriated iridium
Tungsten / ThO alloy
Sensitivity tab
Emission
tab) is at
Current Limit (Amps)
3.1
3.0
Thermo Fisher Scientific
of
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