7-82 Routine maintenance
Measuring EI sensitivity from the solids probe
If you have any doubt about the sensitivity of the instrument, you must
perform a measurement of basic EI sensitivity. Do so at low resolution (1000)
in VSIR mode on the molecular ion of methyl stearate, m/z 298.3, introduced
into the source via the solids sample introduction probe.
The result gives a measure of the total number of ions produced and detected
for a known amount of sample, and is expressed in coulombs/µg.
To set up the instrument
1. If necessary, install the EI-only inner source chamber assembly.
See “Inserting the inner source chamber assembly into the outer source”
on page 7-33.
2. If necessary, pump-down (evacuate) the source until the Vacuum
Monitor window’s Source ion gauge display is 1 × 10
-6
mbar, or better.
3. Ensure that the GC column is withdrawn.
4. On the Vacuum tab, select Analyser 1.
5. Insert the solids sample introduction probe in the ion source.
See “Inserting the solids sample introduction probe in the ion source” on
page 6-9.
To set up the instrument conditions
1. On the Tune window’s EI Source tab, set Source Temp (C) to 0.
2. Allow the source to cool to less than 150 °C.
Warning: The probe components can be contaminated with toxic
materials. Wear nitrile gloves at all times while handling the
components.
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