Fragmentation Reactions of Positive Ions

The terminology and the symbolism suggested by McLafferty [6,7] are used here as they have become universal. Moreover, the name McLafferty is associated with a rearrangement that we will discuss later. 

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This assumes that, in all reactions, only one fragment ion is formed from each decomposing molecular ion. The realtionships hold for reactions of negative ions, as well as for positive ions. 

Vrkic et al. [34] studied the fragmentation reactions of [M+H] of all 64 protonated ohgodeoxynucleotide trimers and of the 16 isomeric mixed-base tetramers in ion-trap MS-MS. Similar to negative-ion MS-MS, the first loss involves a nncleobase. The relative abundance of the resnlting fragment depends on the nncleobase (C G>A T) and its position (5 >3 >intemal). Fnrther MS experiments on the [M+H-BnH]" fragment ion result in 3 -C-0 phosphodiester cleavage to w- and (a-B)- ions. 

Low energy CAD of protonated phospholipids give a few typical fragments. In the positive ion mode, the main reaction is loss of a neutral phosphate ester, leaving the charge on the diacylglycerol fragment. The exception is phosphatidylcholine, where the choline... 

In the first investigation 20), ethylene in the collision chamber was bombarded with positive ions, and the intensities of the fragment ions, obtained after the charge exchange, were recorded. The mass spectra were thus not normalized. At low pressure only primary ions were observed that were formed from ethylene in the charge exchange, but at higher pressures also secondary and tertiary ions were obtained as a result of ion-molecule reactions between the primary ions and the ethylene molecules in the collision chamber. 

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