Search

Stable chlorine isotope analysis of organic compounds is potentially applicable in various fields in forensics and environmental analytics to investigate the fate of these substances in the environment, but a wider use of this technique is still hampered by the limited applicability of available offline and online techniques. In a previous study we presented a method for compound-specific chlorine isotope analysis of volatile organics including chlorinated methanes, ethanes and ethenes using gas chromatography interfaced with multiple-collector inductively coupled plasma mass spectrometry (GC-MC-ICPMS). In the current study we modified further the setup in order to extend the range of analytes towards semi-volatile organic substances with boiling points of up to 350 °C. The modified method was evaluated by using offline characterized in-house reference materials, such as chloroethenes, chloroacetic acid and hexachlorocyclohexenes. Additionally, analysis of various chlorinated benzenes, chlorinated phenols, chlordecone, dichlorodiphenyltrichloroethane (DDT) and related derivatives was demonstrated. The analytical precision (1σ) was usually better than ±0.2 mUr for single compound and ±0.3 mUr for compound-specific analysis of mixtures. Achieved accuracy was within ±0.2 mUr compared to available offline values. The isotopic detection limit could be significantly improved by one order of magnitude (250 pmol Cl on column, corresponding to ∼10 ng Cl) and is superior to other online state of the art approaches. The demonstrated method allows for the compound-specific stable chlorine isotope analysis of virtually all GC-compatible organics with versatility, high accuracy, and sensitivity. [ABSTRACT FROM AUTHOR]

Stable chlorine isotope analysis is increasingly used to characterize sources, transformation pathways, and sinks of organic aliphatic compounds, many of them being priority pollutants in groundwater and the atmosphere. A wider use of chlorine isotopes in environmental studies is still inhibited by limitations of the different analytical techniques such as high sample needs, offline preparation, confinement to few compounds and mediocre precision, respectively. Here we present a method for the d[sup 37]Cl determination in volatile aliphatic compounds using gas chromatography coupled with multiple-collector inductively coupled plasma mass spectrometry (GC-MC-ICPMS), which overcomes these limitations. The method was evaluated by using a suite of five previously offline characterized in-house standards and eight chlorinated methanes, ethanes, and ethenes. Other than in previous approaches using ICP methods for chlorine isotopes, isobaric interference of the [sup 36]ArH dimer with [sup 37]Cl was minimized by employing dry plasma conditions. Samples containing 2-3 nmol Cl injected on-column were sufficient to achieve a precision (s) of 0.1 mUr (1 milliurey = 0.001 = 1‰) or better. Long-term reproducibility and accuracy was always better than 0.3 mUr if organics were analyzed in compound mixtures. Standardization is carried out by using a two-point calibration approach. Drift, even though very small in this study, is corrected by referencing versus an internal standard. The presented method offers a direct, universal, and compound-specific procedure to measure the d[sup 37]Cl of a wide array of organic compounds overcoming limitations of previous techniques with the benefits of high sensitivity and accuracy comparable to the best existing approaches. [ABSTRACT FROM AUTHOR]

Volatilization causes changes in the isotopic composition of organic compounds as a result of different vapor pressures of molecules containing heavy and light isotopes. Both normal and inverse vapor pressure isotope effects (VPIE) have been observed, depending on molecular interactions in the liquid phase and the investigated element. Previous studies have focused mostly on pure compound volatilization or on compounds dissolved in organic liquids. Environmentally relevant scenarios, such as isotope fractionation during volatilization of organics from open water surfaces, have largely been neglected. In the current study, open-system volatilization experiments (focusing thereby on kinetic/ -nonequilibrium effects) were carried out at ambient temperatures for trichloromethane, trichloroethene, trichlorofluoromethane, trichlorotrifluoroethane, methanol, and ethanol dissolved in water and, if not previously reported in the literature for these compounds, for volatilization from pure liquids. Stable carbon isotopic signatures were measured using continuous flow isotope ratio mass spectrometry. The results demonstrate that volatilization of the four halogenated compounds from water does not cause a measurable change in the carbon isotopic composition, whereas for pure-phase evaporation, significant inverse isotope effects are consistently observed (+0.3 ‰ < ε < + 1.7 ‰). In contrast, methanol and ethanol showed normal isotope effects for evaporation of pure organic liquids (-3.9 ‰ and -1.9‰) and for volatilization of compounds dissolved in water (-4.4 ‰ and -2.9 ‰), respectively. This absence of measurable carbon isotope fractionation considerably facilitates the application of isotopic techniques for extraction of field samples and preconcentration of organohalogens known to be important pollutants in groundwater and in the atmosphere. [ABSTRACT FROM AUTHOR]

Methyl chloride and methyl bromide (CH 3 Cl and CH 3 Br) are the largest natural sources of chlorine and bromine, respectively, to the stratosphere, where they contribute to ozone depletion. We report the anthropogenic production of CH 3 Cl and CH 3 Br during breadbaking, and suggest this production is an abiotic process involving the methyl ester functional groups in pectin and lignin structural polymers of plant cells. Wide variations in baking styles allow only rough estimates of this flux of methyl halides on a global basis. A simple model suggests that CH 3 Br emissions from breadbaking likely peaked circa 1990 at approximately 200 tonnes per year (about 0.3% of industrial production), prior to restrictions on the dough conditioner potassium bromate. In contrast, CH 3 Cl emissions from breadbaking may be of similar magnitude as acknowledged present-day CH 3 Cl industrial emissions. Because the mechanisms involve functional groups and compounds widely found in plant materials, this type of methyl halide production may occur in other cooking techniques as well. [ABSTRACT FROM AUTHOR]

Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), controlled substances due to their role in stratospheric ozone loss, also occur as dissolved contaminants in groundwaters. Stable carbon isotopic signatures may provide valuable new information on the fate of these compounds as has been seen for other priority hydrocarbon contaminants, but to date no method for extraction and isotopic analysis of dissolved CFCs from groundwaters has been developed. Here we describe a cryogenic purge and trap system coupled to continuous flow compound-specific stable carbon isotope analysis mass spectrometry for concentrations as low as 35 µg/L. The method is validated by comparing isotopic signatures from water extracted CFCs against a new suite of isotopic CFC standards. Fractionation of CFCs in volatilization experiments from pure-phase CFC-11 and CFC-113 resulted in enrichment factors (ε) of +1.7 ± 0.1‰ and +1.1 ± 0.1‰, respectively, indicating that such volatile loss, if significant, would produce a more 13C depleted signature in the remaining CFCs. Importantly, no significant fractionation was observed during volatile extraction of dissolved CFCs from aqueous solutions. δ13C values for groundwaters from a CFC-contaminated site were, on average, more enriched than δ13C values for pure compounds. Such enriched δ13C values have been seen in other hydrocarbon contaminants such as chlorinated ethenes and ethanes due to in situ degradation, but definitive interpretation of such enriched signatures in field samples requires additional experiments to characterize fractionation of CFCs during biodegradation. The establishment of a robust and sensitive method of extraction and analysis, as described here, provides the foundation for such future directions. [ABSTRACT FROM AUTHOR]

Methyl bromide (CH3Br) emitted from plants constitutes a natural source of bromine to the atmosphere, and is a component in the currently unbalanced global CH3Br budget. In the stratosphere, CH3Br contributes to ozone loss processes. Studies of stable isotope composition may reduce uncertainties in the atmospheric CH3Br budget, but require well-constrained isotope fingerprints of the source end members. Here we report the first measurements of stable bromine isotopes (δ81Br) in CH3Br from abiotic plant emissions. Incubations of both KBr-fortified pectin, a ubiquitous cell-stabilizing macromolecule, and of a natural halophyte (Salicornia fruticosa), yielded an enrichment factor (ε) of −2.00±0.23‰ (1σ, n =8) for pectin and −1.82±0.02‰ (1σ, n =4) for Salicornia (the relative amount of the heavier 81Br was decreased in CH3Br compared to the substrate salt). For short incubations, and up to 10% consumption of the salt substrate, this isotope effect was similar for temperatures from 30 up to 300°C. For longer incubations of up to 90h at 180°C the δ81Br values increased from −2‰ to 0‰ for pectin and to −1‰ for Salicornia. These δ81Br source signatures of CH3Br formation from plant matter combine with similar data for carbon isotopes to facilitate multidimensional isotope diagnostics of the CH3Br budget. [ABSTRACT FROM AUTHOR]

A system was developed for collecting from the ambient atmosphere the methyl halides CH3Cl and CH3Br in quantities sufficient for chlorine and bromine isotope analysis. The construction and operation of the novel cryogenic collection system (cryosampler) and sample purification system developed for this task are described. This study demonstrates the capability of the cryosampler by quantifying the CH3Cl and CH3Br collected from atmospheric samples and the nonfractionating bromine isotope fingerprint of CH3Br from synthetic air samples of controlled composition. An optimized cryosampler operation time of 4 h at a flow rate of 15 L min−1 is applied to yield the nearly 40 ng required for subsequent δ81Br-CH3Br analyses. The sample purification system is designed around a packed column gas chromatography-quadropole-mass spectrometry (GCqMS) system with three additional cryotraps and backflushing capacity. The system's suitability was tested by observing both the mass recovery and the lack of Δ81Br isotope fractionation induced during sample purification under varying flow rates and loading scenarios. To demonstrate that the entire system samples and dependably delivers CH3Br to the isotope analysis system without inducing isotope fractionation, diluted synthetic air mixtures prepared from standard gases were processed through the entire system, yielding a Δ81Br-CH3Br of +0.03‰ ± 0.10‰ relative to their starting composition. Finally, the combined cryosampler-purification and analysis system was applied to demonstrate the first-ever δ81Br-CH3Br in the ambient atmosphere with two samples collected in the autumn of 2011, yielding −0.08‰ ± 0.43‰ and +1.75‰ ± 0.13‰ versus standard mean ocean bromide for samples collected at a suburban Stockholm, Sweden, site. [ABSTRACT FROM AUTHOR]

Tropospheric methyl bromide (CH3Br) is the largest source of bromine to the stratosphere and plays an important role in ozone depletion. Here, the first stable bromine isotope composition (δ81Br) of atmospheric CH3Br is presented. The δ81Br of higher concentration Stockholm samples and free air subarctic Abisko samples suggest a source/background value of −0.04±0.28‰ ranging up to +1.75±0.12‰. The Stockholm δ81Br versus concentration relationship corresponds to an apparent isotope enrichment factor of −4.7±3.7‰, representing the combined reaction sink. This study demonstrates the scientific potential of atmospheric δ81Br measurements, which in the future may be combined with other isotope systems in a top-down inverse approach to further understand key source and sink processes of methyl bromide. [ABSTRACT FROM AUTHOR]

Stable Isotopes (strontium-87, deuterium and oxygen-18, carbon-13) have been used to reveal different sources of groundwater and mixing processes in the aquifer of the Silao-Romita Valley in the state of Guanajuato, Mexico. Calcite dissolution appeared to be the main process of strontium release leading to relatively equal 87Sr/86Sr ratios of 0.7042-0.7062 throughout the study area which could be confirmed by samples of carbonate rocks having similar Sr ratios (0.7041-0.7073). δ13C values (-11.91- -6.87‰ VPDB) of groundwaters confirmed the solution of carbonates but indicated furthermore influences of soil-CO2. Deuterium and 18O contents showed a relatively narrow range of-80.1- -70.0 ‰ VSMOW and-10.2- -8.8 ‰, VSMOW, respectively but are affected by evaporation and mixing processes. The use of δ13C together with 87Sr/86Sr revealed three possible sources: (i) carbonate-controlled waters showing generally higher Sr-concentrations, (ii) fissure waters with low-strontium contents and (iii) infiltrating water which is characterized by low δ13C and 87Sr/86Sr ratios. The third component is affected by evaporation processes taking place before and during infiltration which might be increased by extraction and reinfiltration (irrigation return flow). [ABSTRACT FROM AUTHOR]

• We review Prof. Sherwood Lollar's contributions to Compound Specific Isotope Analysis. • We address contributions to contaminant hydrogeology and environmental chemistry. • We discuss contributions to fundamental science and to the remediation industry. Here, we review the contributions of Professor Barbara Sherwood Lollar to Compound Specific Isotope Analysis (CSIA) in contaminant hydrogeology and environmental chemistry. We first discuss the seminal work by Professor Sherwood Lollar's lab on establishing CSIA as a quantitative tool for contaminant (bio)transformation at contaminated groundwater sites. We describe the critical research by her lab in the development and validation of sample collection techniques, single- and multi-element CSIA, and isotope data evaluation for reliable interpretations. We highlight the contributions of Professor Sherwood Lollar's lab towards the development of best practices for the successful application of CSIA by industry to demonstrate the occurrence of (bio)transformation, identify (bio)transformation mechanisms, quantify the extent and rate of degradation and differentiate among potential contaminant sources. We then explore Professor Sherwood Lollar's applications of CSIA to hydrogeology of the deep subsurface and the fast widening of the field to new environments (e.g., sediments), contaminants (e.g., chlorofluorocarbons, pesticides), and systems (e.g., plant, enzymes). [ABSTRACT FROM AUTHOR]