Card Set Information
EI - Electron Impact Ionization?
uses el- to bombard analyte molecules to produce molecular ions and fragments
MI - Molecular Ionization?
analyte molecule interacts w electron, the energy absorbed will remove a non-bonding electron.
Hard Ionization Technique?
Removal of an electron from the molecule.
Lots of fragmentations
Soft Ionization Technique?
transfer of charge from a matrix or solvent.
less fragmentation, more parent or molecular ion.
3 ionization methods
Gas-phase, Desorption, and spray
Gas-Phase Ioniz Methods
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.
Desorption Ioniz Method
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.
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)
Spray Ioniz Methods?
Electrospray Ionization. Soft. solvent & analyte pass thru metallic capillary - create electrically charged spray, reduce droplet size, liberate desolvated ion.
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.
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
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
mass chromatogram vs mass spec?
mass chrom - time of x-axis
mass spec - m/z on x-axis
why are FAB & MALDI not ideal for quant analysis?
poor reproducibility (depending on sample prep)
difference between theoretical and observed mass. (milliamu)