User:Benjah-bmm27/degree/3/PJG

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Mass spectrometry, PJG[edit]

Major topics[edit]

EI[edit]

  • Summary:
    • Best suited to highly volatile, thermally stable analytes
    • Low-mass limit
    • Forms radical ions
    • Usually observe loads of fragment ions
  • Electron ionisation

CI[edit]

  • Summary:
    • Like EI, best suited to highly volatile analytes
    • Low-mass limit
    • Form protonated molecules
    • Unlike EI, see only a few fragment ions
  • Chemical ionisation

MALDI[edit]

  • Summary – best suited to:
    • Involatile or thermally unstable analytes
    • Highly functionalised or protected analytes
    • Biologically important analytes – proteins, peptides, sugars, etc.
  • Matrix-assisted laser desorption/ionization (MALDI)
  • Evolved from an older technique called laser desorption
  • MALDI involves blasting a solid mixture of analyte and UV-absorbing matrix with a UV laser
  • MALDI is a low energy ionisation technique since the analyte becomes charged via a chemical reaction – generates low energy [M+H]+ ions
    • Analyte remains intact, no fragmentation
  • MALDI is not suitable for small molecules
    • Matrix molecules are present and also have low masses, so they interfere with the mass spectrum
    • Molecules with mass < 1000 Da will be lost in the matrix signal
  • MALDI is ideal for ionising large biomolecules (e.g. peptides, proteins, DNA) and synthetic polymers, which might otherwise fragment and prevent the molecular ion from being observed
    • Can very easily obtain the mass each protein in a mixture of proteins by MALDI-MS
    • In fact, MALDI is the only way to detect the masses of proteins directly
    • The technique is very fast and very sensitive

General topics[edit]

Resolution[edit]

Dissociation[edit]

Types of MS[edit]

Ionization techniques[edit]

Analysers, traps and detectors[edit]