5 Operating in CI Mode
To Use Other Reagent Gases
130 5977C GC/MSD Operating Manual
4 Click Isobutane (or Ammonia) Flow Adjust on the Execute menu.
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 5975 Series MSDs” (5989-5170EN).
Ammonia tends to break down vacuum pump fluids and seals. Ammonia CI
makes more frequent vacuum system maintenance necessary. Refer to the
Agilent 5977C 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
CI 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.
Use of ammonia affects the maintenance requirements of the MSD. (See “CI
Maintenance” on page 203 for more information.)
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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