User:Benjah-bmm27/degree/3/PJG

=Mass spectrometry, PJG=

EI

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

CI

 * 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

 * 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
 * The analyte is mixed with a UV-active matrix compound and the mixture is co-crystallized
 * Common matrix compounds are 2,5-dihydroxybenzoic acid, sinapic acid, dithranol and alpha-cyano-4-hydroxycinnamic acid
 * UV laser excites the chromophores of matrix molecules, with the heat produced causing the matrix and analyte to evaporate (desorb)
 * Ion-molecule reactions transfer charge (H+ or metal cation, e.g. Na+) to analyte, resulting in [M+H]+ or e.g. [M+Na]+ ions
 * These analyte cations pass through an extraction grid and focussing lens into the mass spectrometer
 * 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

 * Mass spectrometry
 * Mass spectrum analysis
 * Mass-to-charge ratio
 * Ion sources
 * Gas phase ion chemistry
 * Mass spectrometry data format, e.g. JCAMP-DX

Resolution

 * Resolution (mass spectrometry)
 * Isobar (nuclide)
 * Isotope

Dissociation

 * Collision-induced dissociation
 * Electron capture dissociation

Types of MS

 * Inductively coupled plasma mass spectrometry
 * Secondary ion mass spectrometry
 * Time-of-flight mass spectrometry
 * Tandem mass spectrometry

Ionization techniques

 * Ionization
 * Chemical ionization
 * Atmospheric-pressure chemical ionization
 * Electrospray ionization
 * Matrix-assisted laser desorption/ionization
 * Ion attachment mass spectrometry

Analysers, traps and detectors

 * Quadrupole mass analyzer
 * Ion trap
 * Quadrupole ion trap