Electron Impact (EI) Ionisation
Definition
A hard ionisation mode at 70 eV used in GC-MS that produces extensive, reproducible fragmentation. The fragmentation pattern is matched against libraries such as NIST and Wiley for compound identification.
- Ionisation energy
- 70 eV
- Result
- Extensive, reproducible fragmentation
- Used with
- GC-MS
- Matched against
- NIST and Wiley libraries
Common questions
Why is fragmentation reproducibility important for compound identification?+
Because the fragmentation pattern at 70 eV is highly consistent across instruments, a spectrum generated in one lab can be confidently compared against a reference spectrum recorded elsewhere, which is the basis for automated library search and match scoring.
What happens when a compound's spectrum does not match any library entry?+
The analyst interprets the fragment masses manually using knowledge of common fragmentation pathways to propose a structure, or runs the sample under a softer ionisation technique to recover the molecular ion, since EI often destroys it through extensive fragmentation.
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