Mass Spectrometry (MS) part:4

Mass Spectrometry of Biomolecules

1.Ionization methods: Because of the high molecular weights of biomolecules, it is not possible to bring them in the vapour phase so that electron impact or chemical ionization can be applied. Therefore ionization techniques such as fast-atom bombardment (FAB) and the related secondary ion mass spectrometry (SIMS), electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) are needed. The typical ranges of application of these ionization techniques are as follows:

2.Amino acid with exact mass(-18 With water mol)

3.Fragmentation of positive ions of peptides and proteins, once created by FAB, ESI, or MALDI, can occur spontaneously and be detected by separating the ions. It can also be induced by socalled tandem mass spectrometry in which the ions are made to undergo collisions (collisioninduced dissociation) with inert gas molecules (e.g. Ar) at low pressure in an ion trap or quadrupole. Peptides and proteins have a convenient tendency to fragment somewhere near the amide bond. The fragment peaks arising from fragmentation due to breaking of the C-C, C-N, or N-C bonds are labelled by the so-called Roepstorff-Fohlman-Biemann nomenclature, of which details as:

Fig:Fragmentation of protonated peptide in FAB/MS. (A) Positive ions may be generated at the C- or N-terminal side of peptide bonds. (B) Main-chain fragmentation. (C) Side-chain fragmentation. Note that dn and wn-type ions allow distinction of isomers such as Leu and Ile

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