Describe how the electrons in EI are found
From a hot filament and then accelerated via a … V electric field
Describe how the energy of the electrons have influence on the amount of fragmentation
High energy = more fragmentation
Low energy = less fragmentation
Describe 3 advantages of EI
- It produces reproducible spectra that can easily be matched with spectral libraries.
- Highly efficient (& straightforward)
- Low-cost
Describe the applicability of EI
mostly volatile and thermally stable compounds <800 Da
Describe the type of ions that CI vs EI generate
CI –> [M+H]+ or [M+X]+ –> even number of electrons
EI –> radical cation M.+ –> odd number of electrons
Describe 2 chemical reagents used in CI and how they become charged
Both become charged by EI
Methane CH4:
CH4 + e –> CH4.+ + H.
CH4.+ + CH4 –> CH5+ + CH3.
Ammonia NH3:
NH3 + e –> NH3.+ + e
NH3.+ + NH3 –> NH4+ + NH2.
Describe ions that form during CI with Methane
[M+H]
[M+C2H5]
[M+C3H5]
Describe ions that form during CI with Ammonia
[M+H]
Explain why separation before MS can have advantages
Most real samples are complex mixtures. Direct infusion leads to spectra overlap and ion suppression, making it impossible to identify single compounds. Separation separates the mixture and MZ analyses 1 compound at a time
Describe Pyrolysis-GC-MS
Pyrolysis is thermal decomposition in atmosphere withour oxygen. Coupled to GC-(EI)MS. This is often used for Synthetic polymers (micro and nano plastics). The EI mass spectrum is a unique chemical fingerprint.
Name the 4 main mechanisms behind EI fragmentation
- Sigma bond cleavage
- Homolytic (radical side driven) cleavage
- Heterolytic (charge side driven) cleavage
- (Mc lafferty’s) Rearrangements
Describe the even-electron rule and how you can use it
Odd-electron ions (molecular ion) can give rise to [Even]+ and R., or [Odd]+. and n
Even-electron ions (fragments/protonated ions) can give rise to [Even]+ + n.
Basically: Molecular ion can loose radical and neutral. Fragments can only loose fragments.
Describe how size has influence on stability of cations
Smaller is less stable than large
Describe how hybridisation has influence on stability of cations
sp3(single)>sp2(double)>sp(triple)
Describe how branching has influence on stability of cations
tertiary > secondary > primary
