a) How are the ionizing electrons generated in electron ionization (EI)?
The beam of ionizing electrons is produced by thermionic emission from a resistively heated metal wire or filament typically made of rhenium or tungsten. The filament reaches up to 2000 °C during operation.
b) How are samples usually introduced into an EI ion source?
Sample introduction systems (also sample inlet systems or inlets) suitable for the combination with EI are: reservoir inlets, gas chromatographs, and direct insertion probes. Which of these inlet systems is to be preferred depends on the type of sample going to be analyzed. Whatever type the inlet system may be, it has to manage the same basic task, i.e., the transfer of the analyte from atmospheric conditions and to vaporize it into the high vacuum of the EI ion source.
d) Do EI spectra in general exhibit a high or a low degree of ion fragmentation?
Most of the molecular ions are in highly excited states and undergo rapid fragmentation within the ion source. Therefore, EI mass spectra exhibit a high degree of ion fragmentation.