Isotopic composition, mass spectrometric analysis

The major analytical complication in Mo isotope analysis is precise correction for isotope fractionation during Mo purification and mass spectrometric analysis. This subject is reviewed in general by Albarede and Beard (2004), and is discussed here in particular reference to Mo. It is important to recognize that this challenge is fundamentally dififerent in mass dependent stable isotope studies as compared to investigations of mass-independent Mo isotope variations produced by nucleosynthesis. The latter have received attention in recent years for high-precision determination of Mo isotope composition (e.g., Dauphas et al. 2002a,b Yin et al. 2002), but are not relevant here. 

Mass Spectrometric Analysis Combusted sample tubes were attached to a purification vacuum line connected to the inlet system of the mass spectrometer. Sample tubes were opened under vacuum using a tube-cracker (35), and the gases were passed through a dry ice trap to remove water vapor and a liquid nitrogen trap to collect CO 2. Noncondensible gases were pumped away. The purified CO2 was thawed and admitted into the inlet system of the mass spectrometer for determination of isotopic composition ... 

For most of the chemical elements, the relative abundances of their stable isotopes in the Sun and solar nebula are well known, so that any departures from those values that may be found in meteorites and planetary materials can then be interpreted in terms of planet-forming processes. This is best illustrated for the noble gases neon, argon, krypton, and xenon. The solar isotopic abundances are known through laboratory mass-spectrometric analysis of solar wind extracted from lunar soils (Eberhardt et al., 1970) and gas-rich meteorites. Noble gases in other meteorites and in the atmospheres of Earth and Mars show many substantial differences from the solar composition, due to a variety of nonsolar processes, e.g., excesses of " Ar and... 

The online mass spectrometric analysis of the evolving gas under open-circuit conditions and at different electrode potentials was carried out using nickel film sputter deposited onto a thin Teflon film as a working electrode, which was interfaced to the inlet of the mass spectrometer. Deuterium labeling allowed the rate of partial reactions (19.11) and (19.12) and the isotopic composition of the evolving gas to be monitored as a function of the electrode potential in parallel to faradaic current measurements, providing a solid evidence of the electrochemical mechanism of (electro) catalytic hypophosphite oxidation. 

Online mass spectrometry data listed in Table 19.1 show decrease in the deuterium content in the evolving gas from 36 mol% in Ni(II)-free solution to 5-10 mol% in the presence of Ni(II) under open-circuit conditions. This is in accordance with the literature data of mass spectrometric analysis of the isotopic composition of the gas evolved in various electroless plating solutions [64,65] and... 

Applications With the current use of soft ionisation techniques in LC-MS, i.e. ESI and APCI, the application of MS/MS is almost obligatory for confirmatory purposes. However, an alternative mass-spectrometric strategy may be based on the use of oaToF-MS, which enables accurate mass determination at 5 ppm. This allows calculation of the elemental composition of an unknown analyte. In combination with retention time data, UV spectra and the isotope pattern in the mass spectrum, this should permit straightforward identification of unknown analytes. Hogenboom et al. [132] used such an approach for identification and confirmation of analytes by means of on-line SPE-LC-ESI-oaToFMS. Off-line SPE-LC-APCI-MS has been used to determine fluorescence whitening agents (FWAs) in surface waters of a Catalan industrialised area [138]. Similarly, Alonso et al. [139] used off-line SPE-LC-DAD-ISP-MS for the analysis of industrial textile waters. SPE functions here mainly as a preconcentration device. 

The fragmentation of 2-acylpyrroles (6) and 3-pyridinols (7) on electron impact (El) has been elucidated and is shown for L -7 in Figure 7. The two numbers under each ion are the m/z values expected with the label at the alternative positions, the latter number within parantheses corresponding to labelled methyl carbon. Where the two m/z values differed, the peak at the first one always predominated in the El mass spectra of the labelled (J-7 obtained on GC/MS analysis of Extracts 1 and 3. This was in complete accordance with the 1 5C-NMR spectrometric results, but for several reasons the mass spectrometric results were less accurate and did not exclude up to 15 % of the label in the respective methyl groups. Most important, the spectra showed clusters of peaks at consecutive m/z values, including those of interest. The content was calculated by means of a computer program based on the somewhat doubtful assumption that ions in the same cluster differed only in hydrogen content and/or isotopic composition. 

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. 

Mauersberger (1981), utilizing in situ mass spectrometric measurements, demonstrated that ozone possesses a large 0 enrichment. The O isotopic composition was not determined and the mass-independent isotopic composition could not be detected. As reviewed by Thiemens (1999), Weston (1999), and Johnston and Thiemens (2003), there now exists an extensive literature on stratospheric ozone isotopic measurements obtained by different techniques. Measurements by Mauersberger (1987) confirmed that stratospheric ozone was mass-independently fractionated as displayed in the 1983 laboratory experiments of Thiemens and Heidenreich. Return ozone isotopic analysis by Schueler et al. (1990) demonstrated that stratospheric ozone possessed an isotopic composition entirely consistent with laboratory observations. Tropospheric ozone has also been studied for its 5 0 isotopic... 

Mass spectra have been used principally for the determination of molecular weights and deduction of the detailed composition of the molecule from the isotopic patterns of the various ions. Structural information can also be obtained from a detailed analysis of the fragmentation pattern. The clusters which have been studied by mass spectrometric methods have largely been carbonyl, 7r-cyclopentadienyl, and carbonyl hydride clusters, and references to these studies have been included in Tables II, VIII, and III, respectively. 

A stock solution was prepared by dissolving the enriched isotope. Diluted solutions were prepared from this stock solution on a weight basis. The isotopic composition of this solution was determined experimentally by GC-MS analysis of the chelate. The internal standard solution was calibrated by reverse isotope dilution GC-MS using the atomic absorption primary standard. Weighed amounts of the primary standard solution were mixed with weighed amounts of the enriched isotope solution. Chelates were prepared from the spiked samples (as described below) and were used for mass spectrometric determination of isotope ratios. Concentration of the trace metal in the spike solution was calculated using the experimentally determined isotope ratios, the weights of the standard and... 

Once a sample is collected, the isotopic composition of uranium must be determined as the content is one of the main factors that determine the price of the product. Several mass spectrometric techniques have been developed for direct isotope analysis of gaseous UFg and for indirect analysis (usually after hydrolysis) of liquid and gaseous UFg samples. The use of a thermal ionization mass spectrometer (TIMS), nowadays equipped with several detectors (i.e., multicollector TIMS), has been the method of choice for many years, but the sample must be hydrolyzed to liquid form (uranyl fluoride or uranyl nitrate solutions) and the uranium must be purified (usually not a problem for UFg samples), as mentioned, for example, by ASTM (C1413 2011). The method is used for hydrolyzed samples of UFg (UOjFj (uranyl fluoride)) or for... 

These include chemical methods (reduction by ferrons snlfate and titrimetric determination), gravimetric methods for 0 U ratio, moistnre analysis by conlomet-ric techniques, and determination of H, C, N, Cl, and E with a specific method for each of these elements. In addition, the isotopic composition is determined by mass spectrometric methods and several metallic and nomnetallic impnrity elements are determined by spectrochemical methods. 

Probably the most comprehensive published assay of DU used in armor pen-etrators was reported on the basis of analysis of an unfired CHARM-3 penetrator (Trueman et al. 2004). A sample from the penetrator was dissolved in 9 M HCl, spiked with U as a yield monitor, and the uranium was separated from impurities on an ion-exchange resin. The isotopic composition of uranium was determined by mass spectrometric techniques. Actinides ( - Am and Np) were determined in the uranium-free solution by gamma spectrometry and 239+24opy and Pu were measured by alpha spectrometry and their presence was confirmed by ICPMS. Technetium-99 was determined by ICPMS when rhenium was used as a carrier and interferences from iron were eliminated by precipitating with ammonia while ruthenium and molybdenum were removed by separation on a chromatographic resin. The content of these radioactive nuclides is summarized in Table 2.7. 

Determination of uranium in soil samples can be carried out by nondestructive analysis (NDA) methods that do not require separation of uranium (needed for alpha spectrometry or TIMS) or even digestion of the soil for analysis by ICPMS, ICPAES, or some other spectroscopic methods. These NDA methods can be divided into passive techniques that utilize the natural radioactive mission (gamma and x-ray) of the uranium and progeny radionuclides or active methods where neutrons or electromagnetic radiation are used to excite the uranium and the resultant emissions (gamma, x-rays, or neutrons) are monitored. In many cases, sample preparation is simpler for these nondestructive methods but the requiranent of a neutron source (from a nuclear reactor in many cases) or a radioactive source (x-ray or gamma) and relatively complex calibration and data interpretation procedures make the use of these techniques competitive only in some applications. In addition, the detection limits are usually inferior to the mass spectrometric techniques and the isotopic composition is not readily obtainable. 

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