Two ionization methods – elect
Two ionization methods – electron ionization and chemicalionization. Briefly discuss the process involved in ion formationfor each method, and discuss the advantages/disadvantages of eachmethod in identification of an unknown compound.
Answer:
Electron ionization (EI,formerly known as electron impactionization[1] and electron bombardmentionization[2]) is an ionization method in whichenergetic electrons interact with solid or gas phase atoms ormolecules to produce ions.[3] EI was one of the firstionization techniques developed for massspectrometry.[4] However, this method is still a popularionization technique. This technique is considered a hard (highfragmentation) ionization method, since it uses high energeticelectrons to produce ions. This leads to extensive fragmentation,which can be helpful for structure determination of unknowncompounds.
Advantages | Disadvantages |
---|---|
Simple | Molecule must be volatile |
Sensitive | molecule must be thermally stable |
Fragmentation aids Identification of molecules | Extensive fragmentation- can’t interpret data |
Library-searchable fingerprint spectracalionization (CI) is an ionizationtechnique used in mass spectrometry. Chemical ionization (CI) is anionization technique used in mass spectrometry.Chemical ionization is a lower energy process thanelectron ionization (EI). The lower energy yieldsless or sometimes no fragmentation, and usually a simplerspectrum. Chemical IonizationAdvantages: Milder ionization than EI ;reduces fragmentation. Requires lower energy than EI. Often givesmolecular weight information through molecular-like ions such as[M+H]+, even when EI would not produce a molecular ion. Disadvantage :- no fragmentlibrary Need volatile samples,need thermalstability,picimolar samples, low mass compound(>1000DA) |
Useful mass range is low (<1000 Da) |
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