Mass spectrometry, structure analysis

The most frequently used techniques for the structural elucidation of photodegradation products are IR spectroscopy, mass spectrometry, elemental analysis, and nuclear resonance spectroscopy. Degradation products for use with these methods... 

Reaction of triquinphosphorane (95) with BF3 etherate gave a mixture of two isomeric BF3 adducts (96ab), in which the hydrophosphorane structure was preserved. The products were characterised by mass spectrometry, elemental analysis, IR, multinuclear ( B, F, P) NMR and X-ray... 

The methanol-soluble fraction was of sufficiently low molecular weight that peaks could be observed in the field ionization mass spectrometry experiment. Analysis of the predominant series of peaks were consistent with the structure shown in Fig. 4.28, where the end and head groups are -CH = CH2 and -CgF and n=2, 3, 4, 5, 6, and 7 (m/z=382, 476, 570, 664, 758 and 852, respectively). The H and F nmr spectra confirmed the presence of vinyl and pentafluorophenyl groups in the methanol-soluble fraction. 

If combinatorial libraries consist of compound mixtures (e.g., after cleavage from the resin beads), a reliable analytical characterization is difficult. In this case the utilization of mass spectrometry for analysis is based on the prediction of mass distribution of the library. Computer-generated distribution profiles can be compared with the actual profile obtained from the compound library [93,94]. Evaluation of mass distribution detects synthetic problems based on incomplete coupling (shift toward lower molecular masses), incomplete deprotection, or unwanted library modification, such as oxidation, acylation, or alkylation (shift toward higher molecular masses). However, for a larger library of compound mixtures many different compounds will have the same molecular mass. This greatly complicates structural determination and even makes it impossible at a certain mixture complexity. 

Myung, S., Wiseman, J.M., Valentine, S.J., Takats, Z., Cooks, R.G., Clemmer, D.E., Coupling desorption electrospray ionization with ion mohihty/mass spectrometry for analysis of protein structure evidence for desorption of folded and denatured states. J. Phys. Chem. B 2006,110, 5045. 

Gu, C., Pivovarov, A., Garcia, R., Stevie, E, Griffis, D., Moran, I, Kulig, L., Richards, J.F. (2004) Secondary ion mass spectrometry backside analysis of barrier layers for copper diffusion. Journal of Vacuum Science Technology B Microelectronics and Nanometer Structures, 22,350-354. 

Under routine conditions, enrichment and isolation of single anthocyanins followed by classical structural elucidation (mass spectrometry, elemental analysis, UVA IS absorbance evaluation using shift reagents, NMR, thin layer chromatography of sugars and anthocyanidins) is rarely necessary, hence will not be discussed in detail. Routine analysis focuses on the quantification and the distribution of known anthocyanins to confirm the content and source of anthocyanins. 

Although several technologies have been used in lipidomics to identify, quantify, and understand the structure and function of lipids in biological systems, it is clear that the progress of lipidomics has been accelerated by the development of modern mass spectrometry (e.g., electrospray ionization (ESI) and matrix-assisted laser desorption/ionization). Mass spectrometric analysis of lipids plays a key role in the discipline. Therefore, this book is focused on the mass spectrometry of lipids that has occurred in these years. Other technologies for analysis of lipids, particularly those with chromatography, can be found in the book entitled Lipid Analysis Isolation, Separation, Identification and Lipidomic Analysis written by Drs William W. Christie and Xianlin Han. Readers who are interested in classical techniques and applications of mass spectrometry for analysis of lipids should refer to Dr Robert C. Murphy s book entitled Mass Spectrometry of Lipids. 

Wen DX, Livingston BD, Medzihradszky KF, Kelm S, Burlingame AL, et al. Primary Structure of Galbetal,3(4)GlcNAc 2,3-Sialyltransferase Determined by Mass Spectrometry Sequence Analysis and Molecular Cloning—Evidence for a Protein Motif in the Sialyltransferase Gene Family. 7. Biol. Chem. 1992 267 21011 21019. 

Wen, D. X., Livingston, B. D., Medzihradszky, K. F., Kelm, S., Burlingname, A. L., and Paulson, J. C., 1992, Primary structure of Galpl,3(4)GlcNAc a2,3-sialyltransferase determined by mass spectrometry sequence analysis and molecular cloning, J. Biol. Chem. 267 21011-21019. 

One has seen that the number of individual components in a hydrocarbon cut increases rapidly with its boiling point. It is thereby out of the question to resolve such a cut to its individual components instead of the analysis by family given by mass spectrometry, one may prefer a distribution by type of carbon. This can be done by infrared absorption spectrometry which also has other applications in the petroleum industry. Another distribution is possible which describes a cut in tei ns of a set of structural patterns using nuclear magnetic resonance of hydrogen (or carbon) this can thus describe the average molecule in the fraction under study. 

Ions are also used to initiate secondary ion mass spectrometry (SIMS) [ ], as described in section BI.25.3. In SIMS, the ions sputtered from the surface are measured with a mass spectrometer. SIMS provides an accurate measure of the surface composition with extremely good sensitivity. SIMS can be collected in the static mode in which the surface is only minimally disrupted, or in the dynamic mode in which material is removed so that the composition can be detemiined as a fiinction of depth below the surface. SIMS has also been used along with a shadow and blocking cone analysis as a probe of surface structure [70]. 

Section 13 22 Mass spectrometry exploits the information obtained when a molecule is ionized by electron impact and then dissociates to smaller fragments Pos itive ions are separated and detected according to their mass to charge (m/z) ratio By examining the fragments and by knowing how classes of molecules dissociate on electron impact one can deduce the structure of a compound Mass spectrometry is quite sensitive as little as 10 g of compound is sufficient for analysis... 

The techniques described thus far cope well with samples up to 10 kDa. Molecular mass determinations on peptides can be used to identify modifications occurring after the protein has been assembled according to its DNA code (post-translation), to map a protein structure, or simply to confirm the composition of a peptide. For samples with molecular masses in excess of 10 kDa, the sensitivity of FAB is quite low, and such analyses are far from routine. Two new developments have extended the scope of mass spectrometry even further to the analysis of peptides and proteins of high mass. 

Sputtered Neutral Mass Spectrometry (SNMS) is the mass spectrometric analysis of sputtered atoms ejected from a solid surface by energetic ion bombardment. The sputtered atoms are ionized for mass spectrometric analysis by a mechanism separate from the sputtering atomization. As such, SNMS is complementary to Secondary Ion Mass Spectrometry (SIMS), which is the mass spectrometric analysis of sputtered ions, as distinct from sputtered atoms. The forte of SNMS analysis, compared to SIMS, is the accurate measurement of concentration depth profiles through chemically complex thin-film structures, including interfaces, with excellent depth resolution and to trace concentration levels. Genetically both SALI and GDMS are specific examples of SNMS. In this article we concentrate on post ionization only by electron impact. 

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