01. What are the selection guidelines for reaction gases used with CI and NCI?
Reaction gases used with CI/NCI include methane, isobutane, and ammonia. The question of which reaction gas to use for any given analysis is determined by trial and error with the measurement target. There are no general guidelines. Measurement must be re-executed using a different reaction gas when results are not satisfactory.
Isobutane is generally first considered as the reaction gas for CI. When the results with isobutane are not quite satisfactory, the reaction gas is changed to ammonia.
Methane may be used in cases where the molecular weight of the sample is small.
In the same way, NCI analyses also start with isobutane and then change to ammonia when the results are not satisfactory.