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Tuesday, August 16, 2011

Influence of Na+ and K+ Concentration in solvents on Mass Spectra of Peptides in LC–ESI-MS
The effect of dispersing a solvent into charged droplets, when applying a high electric potential to an effluent capillary, was first described by Zeleny in 1917 (1). It was investigated in more detail in 1955 by Drozin (2) and used in pioneering work for an electrospray interface by Dole et al (3,4). This was continued in 1984 by Yamashita and Fenn (5,6), which finally resulted in a description of an LC–MS interface in 1985 (7). Today electrospray ionization (ESI) is the most widely used ionization technique in LC–MS. This is especially true in protein mass spectrometry, where series of multiply charged ions are observed and used to determine the molecular mass (8,9). Furthermore, after tryptic digestion, the resulting peptides can be measured with LC–ESI-MS, to obtain amino acid sequence information after a second MS/MS-step (10–14).
When characterizing peptides using LC–ESI-MS, often multiply charged ions are observed (usually doubly charged [M+2H]2+ ions in the instance of tryptic peptides). When the charge state is identified (15), the (monoisotopic) molecular mass can be calculated and the ion can be isolated to permit MS/MS for amino acid sequence information. With the growing demand for such data in bioscience (proteomics), the ability to do this in automated mode has been discussed (16–18). For this purpose, it is necessary to identify without doubt the correct doubly or multiply charged ions as precursors for MS/MS; in the ideal instance all relevant ions should occur at high abundance. However, this is not always the situation, because sometimes protonation is not the only ionization process. 
Joachim Emmert , Markus Pfluger , Fabian Wahl .
Spectroscopy, Feb 1, 2006 .



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