I am gonna do some analyses / detection on plant secondary metabolites (Terpenes and mostly volatile ones), Was wondering which method might be more beneficial- GC-MS-EI or CI?
In most recent papers both methods have been used. I know based on different purposes one can be chosen; but Why?
any suggestion?
Thanks
The difference is in ionization method: EI (electron impact) and CI (chemical ionization).
The CI is a "mild" ionization technique which usually do not destroy you molecule and very likely will give you the molecular ion of your material. This is very useful for determining the molecular weight and helps in identification.
On the other hand, IE is quite a "harsh" method, so it does not normally give you the molecular ion (unless it is very stable), but will rather provide you a set of fragments to which your molecule is broken (under typically used 60-90 EV electrons energy).
For the experienced mass-spectrometrist fragmentation can be very useful for structure elucidation, but the information about the molecular mass is also quite important. Therefore, if possible, use both methods.
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