Isotopics derivatives, spectroscopy mass spectrometry

In this review results from two surface science methods are presented. Electron Spectroscopy for Chemical Analysis (ESCA or XPS) is a widely used method for the study of organic and polymeric surfaces, metal corrosion and passivation studies and metallization of polymers (la). However, one major accent of our work has been the development of complementary ion beam methods for polymer surface analysis. Of the techniques deriving from ion beam interactions, Secondary Ion Mass Spectrometry (SIMS), used as a surface analytical method, has many advantages over electron spectroscopies. Such benefits include superior elemental sensitivity with a ppm to ppb detection limit, the ability to detect molecular secondary ions which are directly related to the molecular structure, surface compositional sensitivity due in part to the matrix sensitivity of secondary emission, and mass spectrometric isotopic sensitivity. The major difficulties which limit routine analysis with SIMS include sample damage due to sputtering, a poor understanding of the relationship between matrix dependent secondary emission and molecular surface composition, and difficulty in obtaining reproducible, accurate quantitative molecular information. Thus, we have worked to overcome the limitations for quantitation, and the present work will report the results of these studies. 

As the glucose is metabolized, the metabolic derivatives become enriched with the isotopic carbon label and are detected using advanced technologies such as mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. Importantly, incorporation of isotopes into molecules can alter reaction mechanisms including the rate of a reaction-this is termed isotopic substitution and forms the basis of the kinetic isotope effect. 

Isotopically labelled fatty acids and the lipids derived from them are used in studies of reaction mechanism (e.g. hydrogenation) and of lipid biosynthesis and metabolism. Compounds containing radioactive isotopes ( H, are studied by liquid-scintillation counting or radio gas chromatography. Non-radio-active labels are studied by mass spectrometry or by NMR spectroscopy. 

The main specifications concern the uranium content in UFg by gravimetric and titrimetric methods, isotopic composition (as listed earlier), el ental impurities by atomic absorption, ICP-AES, spectrographic, colorimetric, titrimetric, spark source mass spectroscopy and radiochemical (alpha and gamma spectrometry and neutron absorption) methods, and organic impurities like hydrocarbons and their derivatives. Modern methods also deploy ICPMS techniques for the determination of impurities and isotopic composition (C1287 2010). It is beyond the scope of this book to present all these methods in detail so a number of examples are shown later. 

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