Operating in Chemical Ionization (CI) Mode
4
5977 Series MSD Operation Manual
107
Isobutane CI
Isobutane (C
4
H
10
) is commonly used for chemical ionization when less
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
3
) is commonly used for chemical ionization when less
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
4
+
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
4
+,
NH
4
(NH
3
)+, and NH
4
(NH
3
)
2
+.
To adjust your MSD for isobutane or ammonia chemical ionization, use the
following procedure:
Procedure
1
Perform a standard Positive CI autotune with methane and PFDTD. See
“To Perform a PCI Autotune (Methane Only)”
2
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.
3
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.
4
Click
Isobutane
(or
Ammonia
)
Flow Adjust
on the
Execute
menu.
Summary of Contents for G7035A
Page 1: ...Agilent Technologies Agilent 5977 Series MSD Operation Manual ...
Page 30: ...30 5977 Series MSD Operation Manual 1 Introduction ...
Page 88: ...88 5977 Series MSD Operation Manual 3 Operating in Electron Ionization EI Mode ...
Page 170: ...170 5977 Series MSD Operation Manual 6 CI Maintenance ...
Page 171: ......