Mass spectral patterns

Extensive mass spectral and electron impact studies have been reported for 3-hydroxy-1,2-benzisoxazole and its ethers. Similar work was also carried out with the isomeric A-alkyl-l,2-benzisoxazol-3-one (71DIS(B)4483). 1,2-Benzisoxazole A-oxide showed a mass spectral pattern than more closely resembled furoxans. The loss of NO predominated over the loss of O (Aft intense, [M— weak, [Af-30]" strong). 

Fig. 11. Mass spectral pattern of C02 pressure for Li2CO - Nb02F mixture (molar ratio 2 1, heating rate - 10°Cper minute) (after Agulyansky et al. [94]).

Fig. 15. Mass spectral pattern Polytherms of total pressure (P) and ionic currents of gaseous components in the form of ions separating from a TaiOs -NH4HF2 system versus heating temperature (after Agulyansky et al. [114]).

Mass spectrometers, workhorse instmments described in Chapter 2, require a vacuum to function. A mass spectrometer generates a beam of ions that is sorted according to specifications of the particular instrument. Usually, the sorting depends on differences in speed, trajectory, and mass. For instance, one type of mass spectrometer measures how long it takes ions to travel from one end of a tube to another. Residual gas must be removed from the tube to eliminate collisions between gas molecules and the ions that are being analyzed. As the diagram shows, collisions with unwanted gas molecules deflect the ions from their paths and change the expected mass spectral pattern. 

The low resolution electron impact mass spectral pattern of bromocriptine mesilate (fig. 7) corresponds quite nicely to those of the other non- and dihydrogenated ergot alcaloids (12, 13 and lit. quoted herein). 

Global proteomic profiling by MS is gaining significant attention as a tool for discovering disease biomarkers. Two basic approaches have been explored. With the first, MS analysis is performed with a material from a specific disease condition and the mass spectra are compared to those of normal individuals or related disease conditions. SELDI-TOF MS gained popularity in this area because of its simplicity and the requirement for only small amounts of samples.38"13 In MS-pattem based disease categorization, the mass spectral patterns are considered reflective of the proteins present in samples from distinct clinical conditions. 

Uk S, Himel CM, Dirks TF. 1972. Mass spectral pattern of mirex (dodecachlorooctahydro-1,3,4-metheno-2H-cyclobuta (cd) pentalene) and of Kepone (decachlorooctahydro-1,3,4-metheno-2H-cyclobuta (cd)- pentalen-2-one) and its application in residue analysis. Bull Environ Contam Toxicol 7(4) 207-215. 

Interestingly, Upper Freeport coal shows two distinct mass spectral patterns in 230-270 C range (Figure 6c), which contains homologous series at m/z 156,170,... 

Due to the distinctive mass spectral patterns caused by the presence of chlorine and bromine in a molecule, interpretation of a mass spectrum can be much easier if the results of the relative isotopic concentrations are known. The following table provides peak intensities (relative to the molecular ion (M+) at an intensity normalized to 100%) for various combinations of chlorine and bromine atoms, assuming the absence of all other elements except carbon and hydrogen.1 The mass abundance calculations were based on the most recent atomic mass data.1... 

One may ask why the FAB-MS technique, described in Chapter 3, would not save the day by simply obtaining the mass spectral pattern. As noted before and reemphasized here, FAB-MS is a powerful method and will give important information relative to the structure, but will not give a complete structure proof. First, it will not provide information on the stereochemical form, nor will it provide data on the positioning of the fatty acids on the presumed glycerol backbone and will not indicate the purity of the sample. Nonetheless, it is a masterful technique and if one has access to such sophisticated equipment, use it. 

Mass spectral fragmentation patterns in the spectra of these compounds are in accord with the formation of alkynes. The first step in the fragmentation of 1,2,3-selenadiazoles is the loss of N2 followed by extrusion of selenium and formation of the corresponding alkyne. The abundance of the alkynic ion in the mass spectrum appears to be dependent on the nature of the substituent group present in the selenadiazole. When the alkynic ion cannot be stabilized by the formation of a cation on the adjacent carbon atoms, the abundance of the alkynic ion decreases (10% in the parent compound and zero for 4-f-butyl-l,2,3-selenadiazole). On the basis of the mass spectral pattern it is possible to predict the yield of the alkynic compound formed through pyrolysis or photolysis of a given... 

Fig. 7. The mechanism for formation of b andy ions during fragmentation of protonated peptides and protein. The mass spectral pattern of b and y ions are used to determine the amino acid sequence...

Similar studies in a mass spectrometer, by using the electron beam to provide an initial distribution of excited ions, have bcHui interpreted semicpiantitatively in terms of the RRK model (D. P. Stevenson, private communication). However, the data are much less precise, and the assumptions needed to use them are open to considerable question. A similar theory has been used with some success to account for the mass spectral patterns of hydrocarbons, H. M. Rosenstock ct al., Proc. NaVl Acad. Sci. U.S.t 38, 667 (1962). 

For identification purposes, two basic approaches have been used. In the first, a purified protein is enzymatically digested, the product peptide mixture is analyzed and a mass spectral pattern is obtained. This pattern, called the MS fingerprint , is used to search in internet-available protein or DNA databases.17 Information about protein origin and an estimate of its MW are required in order to improve the chances of a correct match. The search algorithm then theoretically digests all appropriate proteins in the database with the specified enzyme, and matches the... 

In order to find a clue to the mechanism of the formation of the hydrocarbons stated above, we have studied the dependence of the TOF mass spectral pattern upon the power of the ablation laser. As a result, it will be proposed that the hydrocarbons are formed by reactions between large carbon clusters C (n 10) and hydrogen atoms which are produced from the buffer hydrogen gas thermally dissociated in the intense field of the ablation laser. 

In contrast, the TOF mass pattern obtained by MPI with the use of the third harmonics of a Nd YAG laser (355 nm = 3.5cV phoion) showed a bimodal distribution of products separated at about the cluster size n of C equal 30. Products of larger n values are known to have only even numbers of the carbon atom. This clear difference between the right and left panels of Figure 9.2 indicates that the mass spectral pattern obtained by MPI, especially clusters larger than C30, must be attributed to fragmentation of precursory larger clusters ( 100) due to intense ionization... 

Effect of Ablation Laser Power on the Mass Spectral Pattern... 

This paper discusses studies of sea surface films observed and collected in the southern California Bight and the U. S. Middle Atlantic Bight. The goals of these studies were to understand the relationship between chemical composition and surface elasticity in these complex natural films and to determine the range of surface elasticity typical of the ocean surface. Mass spectrometry was the principal analytical tool because of its capacity to characterise and identify chemical structures for many compound classes and to provide a quick assessment of compounds enriched in sea surface films. We present typical variations in SAOM chemical composition as reflected in mass spectral patterns and show the effect of these compositional variations on the film elasticity. 

Correlation studies of mass spectral patterns and elasticity of sea-slick materials... 

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