Answer 5.3

a) What portion of the incoming neutral molecules becomes ionized in an EI ion source?

The ionization efficiency of an EI ion source ranges from 10-5 with old instruments to some 10-3 in advantageous cases.

b) Can you enumerate all techniques or sorts of inlet systems, if you like, for sample introduction into EI ion sources?

The most common sample introduction techniques in EI are direct insertion probe and gas chromatograph. Occasionally, samples are introduced via a reservoir inlet. Liquid chromatographs can be coupled to EI but are nowadays used with APCI or ESI ion sources. Direct exposure probes aren’t common any more.

c) Suggest suitable sample introduction for a

  • pure volatile liquid, e.g., xylene: reservoir inlet
  • mixture of many volatile compounds, e.g., gasoline: GC
  • moderately volatile solid sample, e.g., benzopyrene: DIP
  • solution of several moderately volatile organics, e.g., extract of N-heterocycles from coffee beans: GC