Ionization Sources

Card Set Information

Author:
saitclt
ID:
203451
Filename:
Ionization Sources
Updated:
2013-02-25 23:11:22
Tags:
INST395
Folders:

Description:
Mass Spec
Show Answers:

Home > Flashcards > Print Preview

The flashcards below were created by user saitclt on FreezingBlue Flashcards. What would you like to do?


  1. EI - Electron Impact Ionization?
    uses el- to bombard analyte molecules to produce molecular ions and fragments
  2. MI - Molecular Ionization?
    analyte molecule interacts w electron, the energy absorbed will remove a non-bonding electron.
  3. Hard Ionization Technique?
    • Removal of an electron from the molecule.
    • Lots of fragmentations
  4. Soft Ionization Technique?
    • transfer of charge from a matrix or solvent.
    • less fragmentation, more parent or molecular ion.
  5. 3 ionization methods
    Gas-phase, Desorption, and spray
  6. Gas-Phase Ioniz Methods
    EI/CI
  7. CI - Chemical Ionization?
    ionization source s filled w reagent gas (methane, isobutane, ammonia). reag gas is converted to ions in rxn w energetuc el- therefore reacts w analytye to produce protonated molecules.
  8. Desorption Ioniz Method
    • MALDI
    • FAB
  9. MALDI?
    Matrix-assisted Laser Desorption Methods. Analyte suspended in solvent, solvent is evap creating solid solution of matrix and analyte. Laser causes sublimation of matrix molecules.
  10. FAB?
    Fast Atom Bombardment - energy stream of atoms of noble gases focused onto analyte molecules. charge transfer occurs. (for proteins and peptides, thermally unstable (labile) and high MW)
  11. Spray Ioniz Methods?
    ESI/APCI
  12. ESI?
    Electrospray Ionization. Soft. solvent & analyte pass thru metallic capillary - create electrically charged spray, reduce droplet size, liberate desolvated ion.
  13. APCI?
    Atmospheric Pressure Chem Ioniz - sample introduced to nebulizer, hot N2 gas forces sample through, thin fog is formed, sample molecules are desorbed and ionized with corona discharge.
  14. ADV/DIS of CI
    • ADV - parent ion present, selective & sensitive
    • DIS - sample must be volatile, not good for high MW or therm unstable, dirty, needs high pump, no frag, not universal
  15. ADV/DIS of EI?
    • ADV - frag, use w insoluble samples, interface w GC, non-polar samples
    • DIS - less stable molecules = no parent identification, requires volatile sample, not goo for high MW or thrm unstbl
  16. mass chromatogram vs mass spec?
    • mass chrom - time of x-axis
    • mass spec - m/z on x-axis
  17. why are FAB & MALDI not ideal for quant analysis?
    poor reproducibility (depending on sample prep)
  18. Mass Accuracy?
    difference between theoretical and observed mass. (milliamu)

What would you like to do?

Home > Flashcards > Print Preview