108 5977 Series MSD Operation Manual
4 Operating in Chemical Ionization (CI) Mode
There is no CI autotune for isobutane or ammonia in PCI.
If you wish to run NCI with isobutane or ammonia, load NCICH4.U or an
existing NCI tune file for the specific gas. For more information on CI
operation using ammonia, refer to Agilent Application Note “Implementation
of Ammonia Reagent Gas for Chemical Ionization on the Agilent 5977 Series
MSDs” (5989-5170EN).
Ammonia tends to break down vacuum pump fluids and seals. Ammonia CI
makes more frequent vacuum system maintenance necessary. (See the 5977
Series MSD Troubleshooting and Maintenance Manual.)
Frequently, a mixture of 5% ammonia and 95% helium or 5% ammonia and 95%
methane is used as a CI reagent gas. This is enough ammonia to achieve good
chemical ionization while minimizing its negative effects.
Carbon dioxide CI
Carbon dioxide is often used as a reagent gas for CI. It has obvious advantages
of availability and safety.
CAUTION
Use of ammonia affects the maintenance requirements of the MSD. See “CI
Maintenance” on page 153 for more information.
CAUTION
The pressure of the ammonia supply must be less than 5 psig. Higher pressures can
result in ammonia condensing from a gas to a liquid.
Always keep the ammonia tank in an upright position, below the level of the flow
module. Coil the ammonia supply tubing into several vertical loops by wrapping the
tubing around a can or bottle. This will help keep any liquid ammonia out of the flow
module.
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