Mass Spectrometry: Methods of Ionization (Applied to Biopolymers)
Ionization: the process of converting atoms or molecules to ions. In the context of biopolymer mass spectrometry, this usually involves the addition or removal of protons.
The mass spectrometric analysis of biopolymers such as proteins, peptides, oligonucleotides, and carbohydrates has been revolutionized by the development of two key ionization methods: electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI). Both methods facilitate the transfer of large, polar biomolecules from the condensed phase in to the gas phase, permitting determination of their mass/charge ratios (m/z). In the case of ESI, ionization of the biomolecules takes place in solution, under the influence of a strong electric field and before evaporative desolvation of the analyte. MALDI is achieved by embedding the biomolecule in a crystalline matrix capable of absorbing energy from laser irradiation, which causes both desorption and ionization. For large...
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