MS spectrum

Laali and Lattimer (1989 see also Laali, 1990) observed arenediazonium ion/crown ether complexes in the gas phase by field desorption (FD) and by fast atom bombardment (FAB) mass spectrometry. The FAB-MS spectrum of benzenediazonium ion/18-crown-6 shows a 1 1 complex. In the FD spectrum, apart from the 1 1 complex, a one-cation/two-crown complex is also detected. Dicyclo-hexano-24-crown-6 appears to complex readily in the gas phase, whereas in solution this crown ether is rather poor for complexation (see earlier in this section) the presence of one or three methyl groups in the 2- or 2,4,6-positions respectively has little effect on the gas-phase complexation. With 4-nitrobenzenediazonium ion, 18-crown-6 even forms a 1 3 complex. The authors assume charge-transfer complexes such as 11.13 for all these species. There is also evidence for hydride ion transfer from the crown host within the 1 1 complex, and for either the arenediazonium ion or the aryl cation formed from it under the reaction conditions in the gas phase in tandem mass spectrometry (Laali, 1990). 

Figure 4.20 Product-ion MS-MS spectrum from the doubly charged molecular ion of the peptide glu-fibrinogen B generated during electrospray ionization. From applications literature published by Thermofinnigan, Hemel Hempstead, UK, and reproduced with permission.

Using Table 5.6 (see p. 156), propose a sequence for glu-fibrinopeptide B based on the product-ion MS-MS spectrum shown in Figure 4.20. 

Figure 5.20 shows an MS-MS spectrum produced from a peptide of molecular weight 1782.96 Da. The mass losses observed and corresponding amino acid assignments are shown in Table 5.11. 

Figure 5.20 LC-MS-MS spectrum of a tryptic peptide derived from spot 13 (see Figure 5.18) of the silver-stained two-dimensional gel of the proteins extracted from the yeast S. cerevisiae, showing the sequence information that may be extracted. From Poutanen, M., Salusjarui, L., Ruohonen, L., Penttila, M. and KaUddnen, N., Rapid Cotn-mun. Mass Spectrom., 15, 1678-1692, Copyright 2001. John Wiley Sons Limited. Reproduced with permission.

Table 5.11 Seqnence information extracted from the LC -MS -MS spectrum shown in Fignre 5.20...

Figure 5.31 LC-electrospray-MS-MS spectrum of the column eluate at around 22 min in the analysis of the peptide mixture from the tryptic digest of glycoprotein TIME-EA4 from silkworm diapause eggs. Reprinted from Bioorg. Med. Chem., 10, Kurahashi, T., Miyazaki, A., Murakami, Y., Suwan, S., Franz, T., Isobe, M., Tani, M. and Kai, H., Determination of a sugar chain and its linkage site on a glycoprotein TIME-EA4 from silkworm diapause eggs by means of LC-ESI-Q-TOF-MS and MS/MS , 1703-1710, Copyright (2002), with permission from Elsevier Science.

The RICs for m/z 614, indicating unchanged Indinavir, and m/z 630 and 646, i.e. those expected from its mono- and dihydroxymetabolites, are shown in Figure 5.41. This allows the presence of three monohydroxylated and one dihy-droxylated metabolite to be demonstrated the other responses observed were shown by the authors not to be associated with the drug. The MS-MS spectrum of the molecular species of the dihydroxylated compound did not allow its structure to be determined but those from the molecular species from the monohydroxylated compounds allowed the structures shown in Figure 5.42 to be proposed and these correlate well with the findings from other laboratories . 

The MS-MS data from metabolite 4 shows a series of ions, i.e. m/z 481, 437 and 380, at m/z values which are 16 greater than those in the MS-MS spectrum... 

The MS-MS spectrum of the (M + H)+ ion from the parent drug contains an ion at m/z 465, the structure of which is indicated in Figure 5.40. The mass spectrum of metabolite 1 indicates that it has a molecular weight of 482 Da, while the MS-MS spectrum from its MH+ ion contains both an ion at m/z 466 and aXm/z 364, also present in that from the MH+ of the parent drug. It is not unreasonable, although not necessarily always correct, to assume that the ion of... 

The electrospray mass spectrnm of metabolite 2 indicates it has a molecular weight of 522 Da, while the MS-MS spectrum of the (M + H)+ ion contains an intense ion at m/z 422, 1 Da greater than the base peak of the MS-MS spectrnm of the protonated molecnlar ion of the parent drug. If we assume a similar relationship between these ions as assnmed for m/z 465 and m/z 466 above, it is not nnreasonable to postnlate the strnctnre of metabolite 2 to be that shown in Fignre 5.44. 

One of the features of an ion-trap is that ion selection is carried out in time rather than space. In this type of instrument, MS-MS data are generated by ionizing the analyte of interest in the normal way but then, instead of causing ions of all m/z values to become unstable and reach the detector, ions other than those being studied by MS-MS are ejected from the trap. The selected ion is then caused to fragment, in the trap, and the ions so generated are made unstable in order to generate the MS-MS spectrum. The procedure may then be... 

Effect of dimer formation on deactivation. Another possible mode of deactivation is formation of inactive Co dimers or oligomers. To test for these species, we examined the ESI-mass spectram of fresh and deactivated Co-salen catalysts in dichloromethane solvent (22). The major peak in the mass spectram occurred at m/z of 603.5 for both Jacobsen s Co(II) and Co(III)-OAc salen catalysts, whereas much smaller peaks were observed in the m/z range of 1207 to 1251. The major feature at 603.5 corresponds to the parent peak of Jacobsen s Co(II) salen catalyst (formula weight = 603.76) and the minor peaks (1207 to 1251) are attributed to dimers in the solution or formed in the ESI-MS. The ESI-MS spectrum of the deactivated Co-salen catalyst, which was recovered after 12 h HKR reaction with epichlorohydrin, was similar to that of Co(II) and Co(III)-OAc salen. Evidently, only a small amount of dimer species was formed during the HKR reaction. However, the mass spectram of a fresh Co(III)-OAc salen catalyst diluted in dichloromethane for 24 h showed substantial formation of dimer. The activity and selectivity of HKR of epichlorohydrin with the dimerized catalyst recovered after 24 h exposure to dichloromethane were similar to those observed with a fresh Co-OAc salen catalyst. Therefore, we concluded that catalyst dimerization cannot account for the observed deactivation. 

FTICR-MS is capable of powerful mixture analysis, due to its high mass range and ultrahigh mass resolving power. However, in many cases it is still desirable to couple a chromatographic interface to the mass spectrometer for sample purification, preconcentration, and mixture separation. In the example given above, DTMS under HRMS conditions provides the elementary composition. Apart from DTMS, PyGC-MS can be performed to preseparate the mixture of molecules and to obtain the MS spectrum of a purified unknown. Direct comparison with the pure reference compound remains the best approach to obtain final proof. 

Figure 6.22 FD-MS spectrum of an equimolar mixture of polymer additives. After Jackson et al. [96]. Reprinted from A.T. Jackson et al., Rapid Communications in Mass Spectrometry, 10,1449-1458 (1996). Copyright 1996 John Wiley Sons, Ltd. Reproduced with permission...

MS/MS Duty Cycle Typical MS/MS analysis is a serial process, relying on the selection of precursors (peptides) in MS mode, followed by high-energy fragmentation in MS/MS. This process is termed data dependent acquisition (DDA). The duty cycle for the completion of MS and MS/MS cycles (the time necessary for MS/MS spectrum acquisition) is of primary importance. When the separation performance is viewed from the mass spectrometry perspective, the peak capacity can be characterized by the number of MS/MS scans, yielding successful... 

Figure 2.15 APCI (+) mass spectrum of the lipid extract obtained from a ceramic vessel recovered from the thirteenth century church of Sant Antimo in Piombino (Central Italy) (a). TheAPCI MS/MS spectrum obtained by selecting ions at m/z 315 (b). The latter made it possible to determine that ions at m/z 315 are due to protonated 7 oxodehydroabietic acid. (Adapted from ref. [29])...

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