Sequential fragmentation

Diagram showing the relation between the designation MS" and the number of sequential fragmentation steps involved. 

Other radicals undergo rearrangement in competition with bimolecular processes. An example is the 5-hexenyl radical (5). The 6-heptenoyloxy radical (4) undergoes sequential fragmentation and cyclization (Scheme 3.8).1S... 

The dendrons were initially incubated with TFA to afford their amine salts, which dissolved in dimethylsulfoxide (DMSO). Then, the solutions were diluted into methanol with 10% triethylamine. The sequential fragmentation of compounds... 

Dendritic molecules 33 and 34 were then incubated with PGA in PBS (pH 7.4) at 37 °C. Control solutions were composed of buffer without the enzyme. The sequential fragmentation illustrated in Fig. 5.31 was monitored by observing the disappearance of dendrons 33 or 34 and the release of 4-nitroaniline by RP-HPLC. As expected, dendron 33 could not be activated by PGA and remained intact for 72 h (data not shown). However, dendron 34 showed clear activation upon incubation with PGA and its corresponding peak completely disappeared from the HPLC chromatogram as 4-nitroaniline appeared (Fig. 5.32). No 4-nitroaniline was observed in the control experiment when dendron 34 was incubated in the buffer without PGA. 

In the ion trap technology, ions are captured in three-dimensional electric fields. The continuous beam of ions fills the trap up to the limit of their space charge. When additional electric fields are applied, ions are ejected sequentially and detected. Accumulation of ions in the trap results in high sensitivity for these instruments. The trap can be operated in MS and MS/MS modes. In the latter, the ions of interest are maintained in the trap, whereas the other ions are excluded. Sequential fragmentation steps can be performed to generate MSn spectra, highly valuable for structural characterization studies. 

QIT The quadrupole ion trap (QIT) utilizes a cylindrical ring and two end-cap electrodes to create a three-dimensional (3D) quadrupolar field for mass analysis. These instruments are capable of selectively trapping or ejecting ions and are often used for the sequential fragmentation and analysis experiments of product ion MS/MS. Also known as a 3D trap due to the configuration (March, 1997). 

A significant difference between the two types of trapping instruments is that in the ion trap mass spectrometers, ions are expelled from the trap to be analysed. Hence they can be observed only once at the end of the process. In FTMS, they can be observed non-destructively, and hence measured at each step in the sequential fragmentation process. 

FIGURE 35.3 The MS spectrum of AZAl produced using QIT MS. The sequential fragmentation of AZAl produces product ions by processes shown by the annotations. 

Fig. 6. ES MS" spectra of the pentaglycosylated saponin 4 from the fruit methanolic extract of P. dodecandra (Phytotaccaceae). Sample (1 mg/ml) injected by a syringe pump (5pl/min) (infusion experiment). For LC/MS conditions, see experimental. This experiment allowed a sequential fragmentation of the saponin sugar chain (cleavage of only one sugar at each MS/MS step), clarifying the structural determination.

Figure I. The ESI-MS spectrum (positive ion-mode) and sequential fragmentation spectrum (MS ) of a-PHB telechelic obtained in the polymerization of (R,S) P-butyrolactone initiated by l8-Crown-6 complex of 4-hydroxybutanoic acid sodium salt and terminated with bromoethanol.

In order to estimate rates for sequential fragmentation, we consider for each value of 7 the continuum states describing a Ne atom plus a triatomic He — I2 molecule in a given n" state, where /2 is in a lower v < v vibrational level... 

In principle, both instrumental concepts can be expanded to allow for multiple-stage mass spectrometry, i.e., multiple stages of precursor ion selection followed by product ion detection for successive n generation product ions [6]. While it is convenient to talk about MS/MS, acronyms like MS/MS/MS are clearly out of place. Therefore, it is common practice to use MS, MS, and generally MS" to denote the number of stages of a tandem mass spectrometric experiment. Accordingly, in the sequential fragmentation scheme... 

Because of the low cost, high sensitivity, large mass range, and ability to perform many sequential fragmentation experiments (MS ), ion traps played an important role in pharmaceutical studies, especially in drug metabolites identification. 

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