a) What are the most important reagent ions present in the methane reagent gas plasma?
Methane chiefly forms CH5+, m/z 17, C2H5+, m/z 29, and C3H5+, m/z 41, ions under CI conditions.
b) Which ions do mainly occur in the ammonia reagent gas plasma?
[NH4]+, m/z 18, and small cluster ions such as [(NH3)2+H]+, m/z 35, [(NH3)3+H]+, m/z 52, etc. .
c) Which ions effect protonation of the analyte in the isobutane reagent gas plasma?
The tert-butyl ions, C4H9+, m/z 57.
d) What is the basic difference between the creation of methane- and ammonia-derived reagent ions on one hand, and isobutane-derived reagent ions on the other?
Both methane- and ammonia-derived reagent ions are formed by bimolecular processes occurring between molecular or fragment ions of the gas with neutrals of the same species. Isobutane is different in that the tert-butyl ions result from unimolecular fragmentation of the isobutane molecular ions, i.e., they simply are [M-H]+ ions.