Fragmentation techniques Tandem mass spectrometry

The ionization techniques most widely used for LC-MS, however, are termed soft ionization in that they produce primarily molecular species with little fragmentation. It is unlikely that the molecular weight alone will allow a structural assignment to be made and it is therefore desirable to be able to generate structural information from such techniques. There are two ways in which this may be done, one of which, the so-called cone-voltage or in-source fragmentation, is associated specifically with the ionization techniques of electiospray and APCl and is discussed later in Section 4.7.4. The other, termed mass spectrometry-mass spectrometry (MS-MS) or tandem mass spectrometry, is applicable to all forms of ionization, provided that appropriate hardware is available, and is described here. 

However, mass spectrometry itself offers two additional degrees of freedom . One can either resolve the complexity of a sample by going to high or even ultra-high mass resolution or one can employ tandem MS techniques to separate the fragmentation pattern of a single component from that of others in a mixture. [2,3] In practice, the coupling of separation techniques to mass spectrometry is often combined with advanced MS techniques to achieve the desired level of accuracy and reliability of analytical information. [1,7,24-27]... 

Peptide and protein sequencing and its importance in the proteomics field were discussed in Section 2.2.3. The following gives a brief description of the mass spectrometry methods used to achieve sequencing. First, to produce protein or oligonucleotide structural/sequence information by mass spectro-metric techniques, one needs to use tandem mass spectrometry (MS-MS). In this technique, a sample is first fragmented and analyzed in one mass spec-... 

A considerable amount of information has been accumulated during the review period with respect to fragmentation studies of flavonoid aglycones and their glycosides using ionization techniques such as El and CID (Figure 2.17). Tandem mass spectrometry with soft ionization methods such as FAB, ESI, and APCI have been used for the structural characterization of a variety of flavonoids, and both deprotonation ° ° and... 

FAB and LSIMS are matrix-mediated desorption techniques that use energetic particle bombardment to simultaneously ionize samples like carotenoids and transfer them to the gas phase for mass spectrometric analysis. Molecular ions and/or protonated molecules are usually abundant and fragmentation is minimal. Tandem mass spectrometry with collision-induced dissociation (CID) may be used to produce abundant structurally significant fragment ions from molecular ion precursors (formed using FAB or any suitable ionization technique) for additional characterization and identification of chlorophylls and their derivatives. Continuous-flow FAB/LSIMS may be interfaced to an HPLC system for high-throughput flow-injection analysis or on-line LC/MS. 

Polypeptides of up to approximately 25 residues can be sequenced by the technique of mass spectrometry (MS), which involves an ionization technique called fast atom bombardment (FAB) in concert with a tandem mass spectrometer (two mass spectrometers coupled in series). The sequence of the polypeptide can be obtained from the molecular masses of the various fragments produced in the ionization stage in only a few minutes compared to the hour required for just one cycle of Edman degradation. In addition, mass spectrometry can be used to sequence several polypeptides in a mixture, alleviating the need to completely... 

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