Mass spectrometry

http://www.21stcenturybio.com/mass_spec_analytical/ms_cid.shtml

One of the most powerful tools available to the mass spectrometrist is MS/MS. Whereas fragmentation is virtually absent in electrospray mass spectrometry, it can be deliberately induced by MS/MS techniques. Tandem MS employs collision-induced dissociation (CID) to fragment a precursor ion.

Similarly, various amino acid modifications can be determined due to the gentle nature of ESI (versus MALDI, which tends to remove some modifications, such as phosphates). These include phosphorylation, glycosylation, acylation, nitronation, and many others.

Ionization source Advantages Disadvantages
Matrix associated desorption Ionization
(MALDI)
Simple sample application and acquisition,
high-throughput capable, low down-time
Variable sample preparation for
different samples

Electrospray Ionization (ESI) Consistent sample ionization efficiency,
capable of ionizing complex mixtures
Rigid sample preparation
requirements, can have high
downtime

• Amino acid
sequence can be
determined by
examining the mass
of the nested
fragments.
• Powerful
technique, does not
require protein
information.
• Not suitable for
complex protein
mixtures.