Many experiments in which an element or a mineral is evaporated or thermally decomposed under vacuum are known to consistently display unexpected behaviors. These include too low rates of evaporation, smaller (i.e. closer to 1) than predicted fractionation factors, and an inconsistent behavior of the stable isotope ratios of a given element (i.e. massindependent fractionation). This applies to ...

A carbon and sulfur isotope mass balance model has been constructed for calculating the variation of atmospheric O2 over Phanerozoic time. In order to obtain realistic O2 levels, rapid sediment recycling and O2-dependent isotope fractionation have been employed by the modelling. The dependence of isotope fractionation on O2 is based, for carbon, on the results of laboratory photosynthesis exper...

Introduction: High-precision measurements of Mg/Mg by multiple-collector inductively coupled plasma-source mass spectrometry (MC-ICPMS) have been used recently in our laboratory to constrain the thermal history of calcium aluminum-rich inclusions (CAIs) [1]. Presence of primary zoning profiles in at least some CAIs points to supersolidus and subsolidus diffusion as important factors in controll...

Analytical models were developed that simulate stable isotope ratios of volatile organic compounds (VOCs) near a point source contamination in the unsaturated zone. The models describe diffusive transport of VOCs, biodegradation and source ageing. The mass transport is governed by Fick's law for diffusion. The equation for reactive transport of VOCs in the soil gas phase was solved for differen...

The isotopic composition of U in nature is generally assumed to be invariant. Here, we report variations of the U/U isotope ratio in natural samples (basalts, granites, seawater, corals, black shales, suboxic sediments, ferromanganese crusts/ nodules and BIFs) of 1.3‰, exceeding by far the analytical precision of our method ( 0.06‰, 2SD). U isotopes were analyzed with MC-ICP-MS using a mixed U–...

The carbon isotope fractionation between tooth enamel bioapatite, breath CO2, and diet was measured for voles, rabbits, pigs, and cattle on controlled diets. The measured fractionation (expressed as isotope enrichment 3*) between enamel and diet was 11.5G 0.3&, 12.8G 0.7&, 13.3G 0.3&, and 14.6G 0.3& for these respective species. There is a 1:1 correlation between 3*breathediet and 3*enamelediet...

Fractionation of isotopes among distinct molecules or phases is a quantum effect which is often exploited to obtain insights on reaction mechanisms, biochemical, geochemical, and atmospheric phenomena. Accurate evaluation of isotope ratios in atomistic simulations is challenging, because one needs to perform a thermodynamic integration with respect to the isotope mass, along with time-consuming...

The common practice of measuring the change in isotope ratio for the whole molecule using isotope ratio measurement by mass spectrometry leads to the loss of significant information of potential interest, since it is the position-specific fractionation which most closely reflects the effect of physicochemical processes. We have shown for MTBE, a common ground water contaminant, that isotopic qu...