6
Operating in CI Mode
CI Autotune
7000/7010 Series TQ GC/MS Operating Manual
135
CI Autotune
After the reagent gas flow is set, the lenses and electronics of the MS should be
tuned. (See
.) Perfluoro-5,8-dimethyl-3,6,9-trioxidodecane (PFDTD) is
used as the calibrant. Instead of flooding the entire vacuum chamber, the PFDTD
is introduced directly into the ionization chamber through the GC/MS interface
by means of the gas flow control module.
There are no tune performance criteria. If CI autotune completes, it passes.
EMV at or above 2600 V, however, indicates a problem. If your method requires
EMV set at +400, you may not have adequate sensitivity in your data acquisition.
CAUTION
After the source is changed from EI to CI or vented for any other reason, the MS
must be purged and baked out for at least 2 hours before tuning. Longer
bakeout is recommended before running samples requiring optimal sensitivity.
CAUTION
Always verify MS performance in EI before switching to CI operation.
Table 11 CI tune default settings
Parameter
Methane
Isobutane
Ammonia
Ion polarity
Positive
Negative
Positive
Negative
Positive
Negative
Emission
150 µA
50 µA
150 µA
50 µA
150 µA
50 µA
Electron energy
150 eV
150 eV
150 eV
150 eV
150 eV
150 eV
Filament
1
1
1
1
1
1
Repeller
3 V
3 V
3 V
3 V
3 V
3 V
Ion focus
130 V
130 V
130 V
130 V
130 V
130 V
Entrance lens offset
20 V
20 V
20 V
20 V
20 V
20 V
EM volts
1200
1400
1200
1400
1200
1400
Shutoff valve
Open
Open
Open
Open
Open
Open
Gas select
A
A
B
B
B
B
Suggested flow
20%
40%
20%
40%
20%
40%
Source temp
250 °C
150 °C
250 °C
150 °C
250 °C
150 °C