Establishing the accuracy of position-specific carbon isotope analysis of propane by GC-pyrolysis-GC-IRMS.

Rationale: Position-specific (PS) δ C values of propane have proven their ability to provide valuable information on the evolution history of natural gases. Two major approaches to measure PS δ C values of propane are isotopic C nuclear magnetic resonance (NMR) and gas chromatography-pyrolysis-gas chromatography-isotope ratio mass spectrometry (GC-Py-GC-IRMS). Measurement accuracy of the isotopic C NMR has been verified, but the requirements of large sample size and long experimental time limit its applications.

Low C-C abundances in abiotic ethane.

Distinguishing biotic compounds from abiotic ones is important in resource geology, biogeochemistry, and the search for life in the universe. Stable isotopes have traditionally been used to discriminate the origins of organic materials, with particular focus on hydrocarbons. However, despite extensive efforts, unequivocal distinction of abiotic hydrocarbons remains challenging.

Position-specific isotope effects during alkaline hydrolysis of 2,4-dinitroanisole resolved by compound-specific isotope analysis, C NMR, and density-functional theory.

Compound-specific isotope analysis (CSIA), position-specific isotope analysis (PSIA), and computational modeling (e.g., quantum mechanical models; reactive-transport models) are increasingly being used to monitor and predict biotic and abiotic transformations of organic contaminants in the field.

Trichloroethene (TCE) hydrodechlorination by NiFe nanoparticles: Influence of aqueous anions on catalytic pathways.

Amending bulk and nanoscale zero-valent iron (ZVI) with catalytic metals significantly accelerates hydrodechlorination of groundwater contaminants such as trichloroethene (TCE). The bimetallic design benefits from a strong synergy between Ni and Fe in facilitating the production of active hydrogen for TCE reduction, and it is of research and practical interest to understand the impacts of common groundwater solutes on catalyst and ZVI functionality. In this study, TCE hydrodechlorination reaction was conducted using fresh NiFe bimetallic nanoparticles (NiFe BNPs) and those aged in chloride, sulfate, phosphate, and humic acid solutions with concurrent analysis of carbon fractionation of TCE and its daughter products.

The use of chlorate, nitrate, and perchlorate to promote crude oil mineralization in salt marsh sediments.

Due to the high volume of crude oil released by the Deepwater Horizon oil spill, the salt marshes along the gulf coast were contaminated with crude oil. Biodegradation of crude oil in salt marshes is primarily limited by oxygen availability due to the high organic carbon content of the soil, high flux rate of S(2-), and saturated conditions. Chlorate, nitrate, and perchlorate were evaluated for use as electron acceptors in comparison to oxygen by comparing oil transformation and mineralization in mesocosms consisting of oiled salt marsh sediment from an area impacted by the BP Horizon oil spill.

Carbon-bearing iron phases and the carbon isotope composition of the deep Earth.

The carbon budget and dynamics of the Earth's interior, including the core, are currently very poorly understood. Diamond-bearing, mantle-derived rocks show a very well defined peak at δ(13)C ≈ -5 ± 3‰ with a very broad distribution to lower values (∼-40‰). The processes that have produced the wide δ(13)C distributions to the observed low δ(13)C values in the deep Earth have been extensively debated, but few viable models have been proposed.

Stable carbon and nitrogen isotope ratios of sodium and potassium cyanide as a forensic signature.

Sodium and potassium cyanide are highly toxic, produced in large amounts by the chemical industry, and linked to numerous high-profile crimes. The U.S.

Polarization behavior of water in extreme aqueous environments: A molecular dynamics study based on the Gaussian charge polarizable water model.

We study the polarization behavior of water under geologically relevant extreme aqueous environments along four equidistant supercritical isotherms, 773 View Article and Find Full Text PDF

Liquid-vapor equilibrium isotopic fractionation of water: how well can classical water models predict it?

The liquid-vapor equilibrium isotopic fractionation of water is determined by molecular-based simulation, via Gibbs ensemble Monte Carlo and isothermal-isochoric molecular dynamics involving two radically different but realistic models, the extended simple point charge, and the Gaussian charge polarizable models. The predicted temperature dependence of the liquid-vapor equilibrium isotopic fractionation factors for H(2) (18)O/H(2) (16)O, H(2) (17)O/H(2) (16)O, and (2)H(1)H(16)O/(1)H(2) (16)O are compared against the most accurate experimental datasets to assess the ability of these intermolecular potential models to describe quantum effects according to the Kirkwood-Wigner free energy perturbation variant Planck's over h(2)-expansion. Predictions of the vapor pressure isotopic effect for the H(2) (18)O/H(2) (16)O and H(2) (17)O/H(2) (16)O pairs are also presented in comparison with experimental data and two recently proposed thermodynamic modeling approaches.

Isotope effects in the evaporation of water: a status report of the Craig-Gordon model.

The Craig-Gordon model (C-G model) [H. Craig, L.I.

Liquid-vapor isotopic fractionation factors of diatomic fluids: a direct comparison between molecular simulation and experiment.

Liquid-vapor fractionation factors of molecular fluids are studied by molecular-based simulation, Gibbs ensemble Monte Carlo, and isothermal-isochoric molecular dynamics of realistic models for N(2), O(2), and CO. The temperature dependence of the fractionation factors for (15)N(14)N(14)N(2), (15)N(2)(14)N(2), (18)O(16)O(16)O(2), (18)O(2)(16)O(2), (13)C(16)O(12)C(16)O, and (12)C(18)O(12)C(16)O along the vapor-liquid coexistence curves as predicted by simulation is compared with the existing experimental data to assess the accuracy of Planck's(2)-order Kirkwood-Wigner free energy expansion for specific model parametrizations. Predictions of the fractionation factors for other isotopologue pairs, including (18)O(17)O(16)O(2), (16)O(17)O(16)O(2), and (17)O(2)(16)O(2), as well as tests of some approximations behind the microscopic interpretation of the fractionation factors are also given.

Perchlorate isotope forensics.

Perchlorate has been detected recently in a variety of soils, waters, plants, and food products at levels that may be detrimental to human health. These discoveries have generated considerable interest in perchlorate source identification. In this study, comprehensive stable isotope analyses (37Cl/35Cl and 18O/17O/16O) of perchlorate from known synthetic and natural sources reveal systematic differences in isotopic characteristics that are related to the formation mechanisms.

Stable-isotope fingerprints of biological agents as forensic tools.

Naturally occurring stable isotopes of light elements in chemical and biological agents may possess unique "stable-isotope fingerprints" depending on their sources and manufacturing processes. To test this hypothesis, two strains of bacteria (Bacillus globigii and Erwinia agglomerans) were grown under controlled laboratory conditions. We observed that cultured bacteria cells faithfully inherited the isotopic composition (hydrogen, carbon, and nitrogen) of media waters and substrates in predictable manners in terms of bacterial metabolism and that even bacterial cells of the same strain, which grew in media water and substrates of different isotopic compositions, have readily distinguishable isotopic signatures.

Carbon isotopic fractionations associated with thermophilic bacteria Thermotoga maritima and Persephonella marina.

Stable carbon isotopes can provide insight into carbon cycling pathways in natural environments. We examined carbon isotope fractionations associated with a hyperthermophilic fermentative bacterium, Thermotoga maritima, and a thermophilic chemolithoautotrophic bacterium Persephonella marina. In T.