Agilent Technologies G7035A Operation Manual page 107

5977 series msd
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Isobutane CI
Isobutane (C
fragmentation is desired in the chemical ionization spectrum. This is because
the proton affinity of isobutane is higher than that of methane; hence, less
energy is transferred in the ionization reaction.
Addition and proton transfer are the ionization mechanisms most often associated
with isobutane. The sample itself influences which mechanism dominates.
Ammonia CI
Ammonia (NH
fragmentation is desired in the chemical ionization spectrum. This is because
the proton affinity of ammonia is higher than that of methane; hence, less
energy is transferred in the ionization reaction.
Because many compounds of interest have insufficient proton affinities,
ammonia chemical-ionization spectra often result from the addition of NH
and then, in some cases, from the subsequent loss of water. Ammonia reagent
ion spectra have principal ions at m/z 18, 35, and 52, corresponding to NH
NH
To adjust your MSD for isobutane or ammonia chemical ionization, use the
following procedure:
Procedure
1
2
3
4
5977 Series MSD Operation Manual
H
) is commonly used for chemical ionization when less
4
10
) is commonly used for chemical ionization when less
3
) + , and NH
(NH
(NH
4
3
4
Perform a standard Positive CI autotune with methane and PFDTD. See
"To Perform a PCI Autotune (Methane Only)"
In the Tune and Vacuum Control view from the Tune menu, click Tune Wizard
and when prompted select Isobutane or Ammonia. This will change the
menus to use the selected gas and select appropriate default tune
parameters.
When prompted, select Gas B. (the port where Isobutane or Ammonia is
plumbed). Continue to the prompts from the Tune Wizard and set the gas
flow to 20%.
If you use an existing tune file, be sure to save it with a new name if you do
not want to overwrite the existing values. Accept the default temperature
and other settings.
Click Isobutane (or Ammonia) Flow Adjust on the Execute menu.
Operating in Chemical Ionization (CI) Mode
+ .
)
3
2
on page 111.
4
+
4
+ ,
4
107

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