Glow discharge electron impact ionization source for miniature mass spectrometers

2007 ◽  
Vol 42 (5) ◽  
pp. 675-680 ◽  
Author(s):  
Liang Gao ◽  
Qingyu Song ◽  
Robert J. Noll ◽  
Jason Duncan ◽  
R. Graham Cooks ◽  
...  
Keyword(s):  
Glow Discharge ◽  
Electron Impact ◽  
Impact Ionization ◽  
Electron Impact Ionization ◽  
Ionization Source ◽  
Mass Spectrometers ◽  
Miniature Mass Spectrometers ◽  
Electron Impact Ionization Source

The chemistry of peptides related to metabolites of Trichoderma Spp. 3. An unusual dehydration reaction of 2-methylalanine peptides after electron impact ionization

1986 ◽  
Vol 64 (2) ◽  
pp. 277-284 ◽  
Author(s):  
W. D. Jamieson ◽  
A. Taylor
Keyword(s):  
Electron Impact ◽  
Impact Ionization ◽  
Reaction Rates ◽  
Electron Impact Ionization ◽  
Molecular Ions ◽  
Dehydration Reaction ◽  
Ionization Source ◽  
Trichoderma Spp ◽  
C Terminus ◽  
Free Region

Peptides of 2-methylalanine, where this residue is not the C-terminus, give molecular ions of low abundance on electron impact ionization, but abundant ions are formed by loss of the elements of water from the molecular ion. The dehydration reaction does not occur in permethylated derivatives, nor under the milder ionization conditions in the chemical ionization source. The reaction does not appear to be time or temperature dependent, but depends on the steric hindrance of the NH group of the 2-methylalanine residue. The reaction occurs at sites where 2-methylalanine is not the C-terminal amino acid. In the cases of two pentapeptides where the dehydration reaction was of high probability, the correct sequence was found by semi-quantitative measurements of reaction rates in the first field-free region of a double focussing mass spectrometer.

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