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Forensic Applications for 1,4-Dioxane and Solvent Stabilizers
Published in Thomas K.G. Mohr, William H. DiGuiseppi, Janet K. Anderson, James W. Hatton, Jeremy Bishop, Barrie Selcoe, William B. Kappleman, Environmental Investigation and Remediation, 2020
Very sensitive isotope ratio mass spectrometers can measure the small differences in molecular mass to determine the ratios of the isotopes present, for example, the inclusion of heavier chlorine isotopes in a TCE molecule. Physical, chemical, or biological processes may favor heavier or lighter molecules and enrich or deplete the ratio of the rare to the most abundant isotope. The natural variations in the mass of the oxygen, hydrogen, and carbon atoms on the 1,4-dioxane molecule can potentially be used to interpret its fate in the subsurface, as discussed further in Section 10.2.5.
Characterisation of methane sources in Lutjewad, The Netherlands, using quasi-continuous isotopic composition measurements
Published in Tellus B: Chemical and Physical Meteorology, 2020
Malika Menoud, Carina van der Veen, Bert Scheeren, Huilin Chen, Barbara Szénási, Randulph P. Morales, Isabelle Pison, Philippe Bousquet, Dominik Brunner, Thomas Röckmann
The isotope measurement system is based on a continuous flow isotope ratio mass spectrometry (CF-IRMS) system. One IRMS instrument (Thermo Delta Plus XP, Thermo Fisher Scientific Inc., Germany) was used to measure alternatively 13C-CO2 and 2H-H2. Before injection into the mass spectrometer, CH4 needs to be isolated from the other air components and converted to CO2 or H2. To extract the CH4, ambient air is first pumped through magnesium perchlorate, a drying agent. Then, the dry air is sent through two successive cryogenic traps, cooled to −120 °C and filled with HayeSep D in the center and glass beads on each end. The cooling is achieved by a Polycold compact cooler compressor (Brooks Automation Inc., USA), filled with coolant PT-30. The cold end is attached to a copper block on which the traps are mounted. The traps are kept under vacuum to avoid condensation of water and to allow a fast and precise temperature control of each of them. The methane is released by heating the traps to −45 °C, and then it is converted to CO2 and H2 in combustion and pyrolysis furnaces, at temperatures of 1150 and 1350 °C, respectively. CO2 is further purified on a gas chromatography (GC) column, at a temperature between 0 and 10 °C. The whole extraction process is illustrated in Fig. S1, and described in more detail in Röckmann et al. (2016). A picture of the extraction system installed at Lutjewad is shown in Fig. S2.