5 Operating in CI Mode
To Use Other Reagent Gases
128 5977C GC/MSD Operating Manual
To Use Other Reagent Gases
This section describes the use of isobutane or ammonia as the reagent gas. You
should be familiar with operating the CI-equipped 5977C Series MSD with
methane reagent gas before attempting to use other reagent gases.
Changing the reagent gas from methane to either isobutane or ammonia
changes the chemistry of the ionization process and yields different ions. The
principal CI reactions encountered are described in general in the 5977C Series
Concepts Guide. If you are not experienced with CI, we suggest reviewing that
material before you proceed.
Do not use nitrous oxide as a reagent gas. It radically shortens the life span of
the filament.
Not all setup operations can be performed in all modes with all reagent gases.
(See Table 14 for details.)
Table 14 Reagent gases
Reagent gas/mode Reagent ion masses
PFDTD
Calibrant ions
Flow adj ions: Ratio
EI/PCI/NCI MSD Turbo pump
Recommended flow: 20% PCI 40% NCI
Methane/PCI 17, 29, 41
*
41, 267, 599 28/27: 1.5 – 5.0
Methane/NCI 17, 35, 235
†
185, 351, 449 N/A
Isobutane/PCI 39, 43, 57 N/A 57/43: 5.0 – 30.0
Isobutane/NCI 17, 35, 235 185, 351, 449 N/A
Ammonia/PCI 18, 35, 52 N/A 35/18: 0.1 – 1.0
Ammonia/NCI 17, 35, 235 185, 351, 517 N/A
* There are no PFDTD ions formed with any reagent gas but methane. Tune with methane and use the same parameters for the other
gas.
†There are no negativ e reagent gas ions formed. To pretune in negative mode, use background ions: 17 (OH-), 35 (Cl-), and 235
(ReO3-). These ions cannot be used for reagent gas flow adjustment. Set the flow to 40% for NCI and adjust as
necessary to get acceptable results for your application.
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