mass spec Flashcards
(8 cards)
4 general steps of process
The sample is vaporised and ionised (+ve or –ve)
The ions are subject to a filter to separate them according to their mass to charge ratio
The stream of mass-separated ions are detected
An electrical output is generated producing a plot of the signal intensity (number of ions in the sample!) for each mass to charge ratio (a spectrum)
how does electron impact ionization work
In Electron Impact (EI) ionisation the vaporised sample is bombarded with a stream of high energy electrons (ca. 70 eV)
Impact of a high energy electron with a molecule serves to eject an electron from the compound thus generating a high energy charged species (M+*)
what does electron impact ionization often lead to
can (and frequently does) breakdown into lower molecular weight fragment ion and radical
process of electron impact ionization
- Sample is vaporised and ionised
- The ions are accelerated in an electric field (many KV)
- In the magnetic sector (at rights angles to the stream of ions), circular flight path is adopted and this is dependent upon the mass to charge ratio (m/z)
- Changing the magnetic field strength allows only ions of the correct m/z ratio though to the detector
what is the meolcuolar ion peak and is it set at 100% intensity
- highest peak is the base peak and is set to 100% relative intensity
- The signal corresponding to the mass of the target compound is called the molecular ion peak
process of matriz assisted laser desorption ionisation
Cations formed by ionization and are repelled by the positively charged anode and attracted towards the negative cathode before leaving the source through a hole in the cathode
all same force, time of flight anmalysis as heavier ions will take longer to read detector
MALDI vs EI , type of radiaiton, prep, size
maldi soft, more prep, higher mass ranges
what is a Isotopologues
molecules that differ only in isotopic composition
