Mechanisms of Electrospray Ionization for Mass Spectrometry Analysis Jayo, Roxana
Electrospray ionization mass spectrometry (ESI-MS) is a choice method to accomplish the mass determination of large, non-volatile biomolecules including proteins, peptides, oligonucleotides, carbohydrates, polysaccharides and other compounds which are too large to be vaporized or too fragile to remain intact when other ionization methods are used. Since ions are generated directly from the liquid phase, ESI can be easily coupled to separation techniques such as high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). Although ESI has had an enormous impact on modern mass spectrometry, and has become one of the most important ionization techniques, some parts of the underlying processes have proven to be very difficult to establish. Such is the case of the mechanisms by which gas-phase ions are produced by the charged droplets. Two theories, the Charge Residue Model (CRM) and the Ion Evaporation Mechanism (IEM), have been proposed. Since electrochemistry is considered a fundamental aspect of the operation of the ESI ion source both for the fundamentals of gas-phase ion formation from the charged droplets, and for the analytical utility of the device, there has been considerable efforts in order to elucidate the electrochemical process associated to the operation of this ion source. The aim of the present report is to provide a concise and fundamental description of the mechanisms involved in the production of isolated ions by ESI, as well as, to present a brief account of the electrolytic nature of ESI.
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