Varian 4000 GC, Hardware Operation Manual

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Ion Intensities for Standard CI Reagents
The CI Adjust function gives recommendations of an acceptable level of CI
reagent ions for each of the five standard CI reagents. The general principles
used in implementing these tests are:
Methane Adjust the reagent gas pressure so that the peak height at m/z 17
(CH
5
+
) is about 25% of that at m/z 29 (C
2
H
5
+
). The ratio of the ions at
m/z 17 to m/z 16 should be about 10:1. The ion at m/z 41 (C
3
H
5
+
)
should be visible.
Isobutane Adjust the reagent gas pressure so that the peak heights at m/z 57
[(CH
3
)
3
C
+
] and m/z 43 [(CH
3
)
2
CH
+
] are about equal. There may also
be an intense reagent ion at m/z 41 (C
3
H
5
+
).
Acetonitrile Adjust the reagent gas pressure so that the ion at m/z 42 [CH
3
CNH
+
]
is more than 5 times higher than at m/z 41. The valley between the
41/42 ions should reach a minimum at less than half the height of the
m/z 41 ion. The m/z 54 ion [CH
3
CHCNH
+
] will be present at 10 - 15%
the height of m/z 42. Too much acetonitrile in the trap can cause early
filament failures.
d3-Acetonitrile Adjust the reagent gas pressure so that the ion at m/z 46 [CD
3
CND
+
]
is more than 5 times higher than at m/z 44. The m/z 58 ion
[CD
3
CDCND
+
] will be present at 10 - 15% the height of m/z 46.
Methanol The ion at m/z 33 [(CH
3
OH)H
+
] will dominate the spectrum. No ion is
observed at m/z 32, but a small peak is observed at m/z 31 and m/z
47.
In each case, by following these guidelines, the reagent gas pressure in the ion
trap will be approximately 1 to 2 x 10
-5
Torr (about 1.3 to 2.6 x 10
-3
Pa). The CI
reagent molecules comprise about 1% of the gas pressure in the ion trap. He
atoms from column flow are present at 100 times this pressure.
Setting Flows of CI Reagents in External Configuration
In External Configuration CI reagent flow is set using the ion gauge pressure
measured in Manual Control.
1. Open the main valve of the methane (or isobutane) CI Gas cylinder and set
the second—stage regulator pressure to 20 psi.
2. Open System Control. Turn on the CI and Ion Gauge using the check boxes
beneath the 4000 MS icon. If the CI line has not been evacuated already,
allow a few minutes for this process.
3. Adjust the CI valve so that the ion gauge reading is between 50 – 80 µTorr.
Setting Flows of CI Reagents in Hybrid Configuration
See the 4000 MS Operations Manual for advice on setting flows for CI reagents.
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