Fragments, mass spectrometry

The same enzymatic cleavage can then be applied to the unreduced enzyme. Pairs of peptide fragments remain linked by the S-S bridges. These crosslinked pairs can be separated, the disulfide bridges cleaved, and the resulting peptides identified, each as one of the already sequenced fragments. Mass spectrometry provides a rapid method for their identification.258... 

C. Sihlbom, I. D. Hard, M. E. Lidell, T. Noll, G. C. Hansson, and M. Backstrom, Localization of O-glycans in MUC1 glycoproteins using electron-capture dissociation fragmentation mass spectrometry, Glycobiology, 19 (2009) 375-381. 

Recently, a LC/MS method to determine OTA in wine and grape extracts by using Surface-Activated-Chemical-Ionization and multistage fragmentation mass spectrometry (LC/SACI-MS3), was proposed (Flamini et al., 2007). SACI is an ionization source developed to analyze medium-high polar compounds in a wide range of m/z ratios (100-4000 Da). This device, used in determination of compounds such as... 

Kan, Z.Y., Walters, B.T., Mayne, L., Englemder, S.W. (2013) Protein hydrogen exchange at residue resolution by proteolytic fragmentation mass spectrometry emeilysis. Proc Natl Acad Sci USA, 110 (41), 16438-16443. 

Z. Y. Kan, B. T. Walters, L. Mayne and S. W. Englander. (2013) Protein Hydrogen Exchange at Residue Resolution by Proteolytic Fragmentation Mass Spectrometry Analysis, Proceedings of the National Academy of Sciences USA, 110 (41), 16438-16443. 

Figure 10.6. Outline of the fragmentation/mass spectrometry method to determine structural details in small regions of proteins [44]. (Reproduced from C. Dass, Principles and Practice of Biological Mass Spectrometry, Wiley-Interscience, 2001.)...

Keywords CID Fragmentation Mass spectrometry Per- and polyfluorinated chemicals (PFC)... 

Four-level system, lasers, 171-173 Fragmentation, mass spectrometry, 551,552, 554,555,... 

Separation of families by merely increasing the resolution evidently can not be used when the two chemical families have the same molecular formula. This is particularly true for naphthenes and olefins of the formula, C H2 , which also happen to have very similar fragmentation patterns. Resolution of these two molecular types is one of the problems not yet solved by mass spectrometry, despite the efforts of numerous laboratories motivated by the refiner s major interest in being able to make the distinction. Olefins are in fact abundantly present in the products from conversion processes. 

Schlager H and Arnold F 1985 Balloon-borne fragment ion mass spectrometry studies of stratospheric positive ions unambiguous detection of H (CH3CN), (H20)-clusters Pianet. Space Sc/. 33 1363-6... 

Lover T efa/1997 Electrospray mass spectrometry of thiophenolate-capped clusters of CdS, CdSe and ZnS and cadmium and zinc thiophenolate complexes observation of fragmentation and metal, chalcogenide and ligand exchange processes Inorg. Chem. 36 3711... 

The first mass spectrometric investigation of the thiazole ring was done by Clarke et al. (271). Shortly after, Cooks et al., in a study devoted to bicydic aromatic systems, demonstrated the influence of the benzo ring in benzothiazole (272). Since this time, many studies have been devoted to the influence of various types of substitution upon fragmentation schemes and rearrangements, in the case of alkylthiazoles by Buttery (273) arylthiazoles by Aune et al. (276), Rix et al. (277), Khnulnitskii et al. (278) functional derivatives by Salmona el al. (279) and Entenmann (280) and thiazoles isotopically labeled with deuterium and C by Bojesen et al. (113). More recently, Witzhum et al. have detected the presence of simple derivatives of thiazole in food aromas by mass spectrometry (281). 

Although GGMS is the most widely used ana lytical method that combines a chromatographic sep aration with the identification power of mass spectrometry it is not the only one Chemists have coupled mass spectrometers to most of the mstru ments that are used to separate mixtures Perhaps the ultimate is mass spectrometry/mass spectrome try (MS/MS) m which one mass spectrometer gener ates and separates the molecular ions of the components of a mixture and a second mass spec trometer examines their fragmentation patterns ... 

As we have just seen interpreting the fragmentation patterns m a mass spectrum m terms of a molecule s structural units makes mass spectrometry much more than just a tool for determining molecular weights Nevertheless even the molecular weight can provide more information than you might think... 

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... 

Mass Spectrometry The molecular ion peak is usually quite small m the mass spec trum of an alcohol A peak corresponding to loss of water is often evident Alcohols also fragment readily by a pathway m which the molecular ion loses an alkyl group from the... 

Mass Spectrometry Aldehydes and ketones typically give a prominent molecular ion peak m their mass spectra Aldehydes also exhibit an M— 1 peak A major fragmentation pathway for both aldehydes and ketones leads to formation of acyl cations (acylium ions) by cleavage of an alkyl group from the carbonyl The most intense peak m the mass spectrum of diethyl ketone for example is m z 57 corresponding to loss of ethyl radi cal from the molecular ion... 

Mass Spectrometry Aside from a peak for the molecular ion which is normally easy to pick out aliphatic carboxylic acids undergo a variety of fragmentation processes The dominant fragmentation m aromatic acids corresponds to loss of OH then loss of CO... 

Amines have odd numbered molecular weights which helps identify them by mass spectrometry Fragmentation tends to be controlled by the formation of a nitrogen stabilized cation... 

Fragmentation pattern (Section 13 22) In mass spectrometry the ions produced by dissociation of the molecular ion... 

Although there has been some controversy concerning the processes involved in field ionization mass spectrometry, the general principles appear to be understood. Firstly, the ionization process itself produces little excess of vibrational and rotational energy in the ions, and, consequently, fragmentation is limited or nonexistent. This ionization process is one of the mild or soft methods available for producing excellent molecular mass information. The initially formed ions are either simple radical cations or radical anions (M ). 

If a sample solution is introduced into the center of the plasma, the constituent molecules are bombarded by the energetic atoms, ions, electrons, and even photons from the plasma itself. Under these vigorous conditions, sample molecules are both ionized and fragmented repeatedly until only their constituent elemental atoms or ions survive. The ions are drawn off into a mass analyzer for measurement of abundances and mJz values. Plasma torches provide a powerful method for introducing and ionizing a wide range of sample types into a mass spectrometer (inductively coupled plasma mass spectrometry, ICP/MS). 

To examine a sample by inductively coupled plasma mass spectrometry (ICP/MS) or inductively coupled plasma atomic-emission spectroscopy (ICP/AES) the sample must be transported into the flame of a plasma torch. Once in the flame, sample molecules are literally ripped apart to form ions of their constituent elements. These fragmentation and ionization processes are described in Chapters 6 and 14. To introduce samples into the center of the (plasma) flame, they must be transported there as gases, as finely dispersed droplets of a solution, or as fine particulate matter. The various methods of sample introduction are described here in three parts — A, B, and C Chapters 15, 16, and 17 — to cover gases, solutions (liquids), and solids. Some types of sample inlets are multipurpose and can be used with gases and liquids or with liquids and solids, but others have been designed specifically for only one kind of analysis. However, the principles governing the operation of inlet systems fall into a small number of categories. This chapter discusses specifically substances that are normally liquids at ambient temperatures. This sort of inlet is the commonest in analytical work. 

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