Instrumental Chemistry Exam 3
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Peaks with greater m/z ratio than the molecular ion are either isotope peaks are this that are the cause of collision production peaks. The heights vary in accordance to abundance
increases with increasing pressure
Molecular ion peak
m/z corresponde to the MW of the singly charge molecule
- Analyte is bombarded by electrons
- hard ionization
- good for identification but not for MW
- it has a very low molecular peak and this is why it is not good for MW determination
- other disadvantage include that the molecules have to be vaporized and the vapor must be thermally stable.
- electron bombardment of vapor/ gas phase molecules
- molecules are excited
- The solvent ( ionization source)is methane because it is easily ionizable
- adds in proton transfer
- creates protonated end product molecules.
- this method produces less fragmentation than due EI
- common ions included the m=17 and ch5 and c2h5+
fast atom bombardment
- The analyte is bombarded with atom like argon helium.
- This is an example of ballistic collision
- This is in a glycerol solution in addition there is
electron spray ion
- soft ionization
- coulomb explosion
- the Analyte is ex[plodded into many charged particles that reduce in size as they get smaller
- this method allowed for the accumulation of multiple charges.
- there is a build up of negative charge and this what causes the Analyte molecules to explode
- generate pulse of ions
- separate ionsx passed on size
- they have the sam charge TOF has poor sensitivity and resolution
Matrix-assisted laser desorption/ionization
- This a soft method
- the anaylte is mixed with a UV absorber and made in a solution
- this causes the anaylte and the UV absorber to form a crystal
- The crystal is shot with a laser
- disadvantages included that the Analyte must have the ability to absorb UV light as well as be small in MW and it must also be able to crystalize.
Most intense ion ( abundant)
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