Identification Of Individual Components Research Articles

New methods of identifying organic compounds

A 'reversed' geometry mass spectrometer, in which the ion beam passes through the magnetic sector before the electric sector, offers several advantages for the study of large organic molecules. The method used is to select individual ionic species formed in the ion source in turn by using the magnet and to study the fragmentation of these species in the field-free region in front of the electric sector. Either unimolecular or collision-induced fragmentations can be investigated, the masses of the daughter species being determined by scanning the electric sector. By selecting a variety of individual ions, a comprehensive fragmentation ‘ map' of the molecular species can be constructed. Because it is a voltage that is scanned, the instrument can readily be computer controlled which gives improved reproducibility of scanning, together with other advantages. The several pathways that often link a particular fragment ion with the molecular ion provide complementary information concerning ion structure. The fragmentation pattern of any ion is often sufficiently characteristic of the ion structure to allow direct identification of structural features present to be made by comparing the pattern from the relevant ion with that of an ion formed from a known reference compound. By using these methods the molecular structure of large organic molecules can often be deduced. Large isomeric molecules such as steroids, differing only in the structure of a side chain, can be distinguished by selecting only ions containing the side chain for study. The new methods also offer advantages for the detection and identification of individual components in mixtures.

Sur l'arǒme de viande de bœuf grillée III. Pyrrolo [1,2‐a]pyrazines, identification et synthèse

Synthesis of alkylpyrrolo[1,2‐a]pyrazines, roasted meat flavor constituentsSeven alkylpyrrolo[1,2‐a]pyrazines have been identified for the first time in a roasted meat aroma obtained by thermolysis of the hydrosoluble flavor precursors of raw meat. Identification of individual components was done by capillary gas chromatography/mass spectroscopy coupling. The structure of these nitrogen heterocyclic compounds was for some time in doubt because of the similarity of the MS. with those of other diazaindene and diazanaphthalene derivatives such as benzimidazoles, indazoles, cyclopenta [b]pyrazines and dihydroquinoxalines. The structure of these new flavor components was completely elucidated in some cases by interpretation of NMR. spectra, the others being deduced by analogy. Hypotheses are formulated concerning the formation of this skeleton by a non‐enzymatic browning reaction between carbohydrates and amino acids. Four different schemes have been adopted to synthesize substituted isomers selectively.

Studies of the acidic components of the Colorado Green River Formation oil shale: Mass spectrometric identification of the methyl esters of extractable acids

A study of solvent extractable acidic constituents of oil shale from the Colorado Green River Formation (ca. 50·10 6 years) is presented. Identification of individual components is based upon gas chromatographic and mass spectrometric data obtained for their respective methyl esters. Normal acids (C 7–C 12), isoprenoidal acids (C 9, C 10), α, ω-dicarboxylic acids (C 12–C 18), mono-α-methyl dicarboxylic acids (C 13, C 15) and methyl ketoacids (C 11, C 14) were identified. In addition, the presence of monocyclic, benzoic, phenylalkanoic and naphthyl-carboxylic acids, as well as cycloaromatic acids, is demonstrated by partial identification.