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- Maier, Michael P., et al.
(författare)
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Exploring Trends of C and N Isotope Fractionation to Trace Transformation Reactions of Diclofenac in Natural and Engineered Systems
- 2016
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 50:20, s. 10933-10942
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Tidskriftsartikel (refereegranskat)abstract
- Although diclofenac ranks among the most frequently detected pharmaceuticals in the urban water cycle, its environmental transformation reactions remain imperfectly understood. Biodegradation-induced changes in N-15/N-14 ratios (epsilon(N) = -7.1 parts per thousand +/- 0.4 parts per thousand) have indicated that compound-specific isotope analysis (CSIA) may detect diclofenac degradation. This singular observation warrants exploration for further transformation reactions. The present study surveys carbon and nitrogen isotope fractionation in other environmental and engineered transformation reactions of diclofenac. While carbon isotope fractionation was generally small, observed nitrogen isotope fractionation in degradation by MnO2 (epsilon(N) = -7.3 parts per thousand +/- 0.3 parts per thousand), photolysis (epsilon(N) = +1.9 parts per thousand +/- 0.1 parts per thousand), and ozonation (epsilon(N) = +1.5 parts per thousand +/- 0.2 parts per thousand) revealed distinct trends for different oxidative transformation reactions. The small, secondary isotope effect associated with ozonation suggests an attack of O-3 in a molecular position distant from the N atom. Model reactants for outer-sphere single electron transfer generated large inverse nitrogen isotope fractionation (epsilon(N) = +5.7 parts per thousand +/- 0.3 parts per thousand), ruling out this mechanism for biodegradation and transformation by MnO2. In a river model, isotope fractionation-derived degradation estimates agreed well with concentration mass balances, providing a proof-of-principle validation for assessing micropollutant degradation in river sediment. Our study highlights the prospect of combining CSIA with transformation product analysis for a better assessment of transformation reactions within the environmental life of diclofenac.
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- Bakkour, Rani, et al.
(författare)
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Molecularly Imprinted Polymers for Compound-Specific Isotope Analysis of Polar Organic Micropollutants in Aquatic Environments
- 2018
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 90:12, s. 7292-7301
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Tidskriftsartikel (refereegranskat)abstract
- Compound-specific isotope analysis (CSIA) of polar organic micropollutants in environmental waters requires a processing of large sample volumes to obtain the required analyte masses for analysis by gas chromatography/isotoperatio mass spectrometry (GC/IRMS). However, the accumulation of organic matter of unknown isotopic composition in standard enrichment procedures currently compromises the accurate determination of isotope ratios. We explored the use of molecularly imprinted polymers (MIPs) for selective analyte enrichment for C-13/C-12 and N-15/N-14 ratio measurements by GC/IRMS using 1H-benzotriazole, a typical corrosion inhibitor in dishwashing detergents, as example of a widely detected polar organic micropollutant. We developed procedures for the treatment of >10 L of water samples, in which custom-made MIPs enabled the selective cleanup of enriched analytes in organic solvents obtained through conventional solid-phase extractions. Hydrogen bonding interactions between the triazole moiety of 1H-benzotriazole, and the MIP were responsible for selective interactions through an assessment of interaction enthalpies and N-15 isotope effects. The procedure was applied successfully without causing isotope fractionation to river water samples, as well as in- and effluents of wastewater treatment plants containing mu g/L concentrations of 1H-benzotriazole and dissolved organic carbon (DOC) loads of up to 28 mg C/L. MIP-based treatments offer new perspectives for CSIA of organic micropollutants through the reduction of the DOC-to-micropollutant ratios.
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- Pati, Sarah G., et al.
(författare)
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Substrate and Enzyme Specificity of the Kinetic Isotope Effects Associated with the Dioxygenation of Nitroaromatic Contaminants
- 2016
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 50:13, s. 6708-6716
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Tidskriftsartikel (refereegranskat)abstract
- Compound-specific isotope analysis (CSIA) is a promising approach for tracking biotransformation of organic pollutants, but isotope fractionation associated with aromatic oxygenations is only poorly understood. We investigated the dioxygenation of a series of nitroaromatic compounds to the corresponding catechols by two enzymes, namely, nitrobenzene and 2-nitrotoluene dioxygenase (NBDO and 2NTDO) to elucidate the enzyme- and substrate-specificity of C and H isotope fractionation. While the apparent C-13- and H-2-kinetic isotope effects of nitrobenzene, nitrotoluene isomers, 2,6-dinitrotoluene, and naphthalene dioxygenation by NBDO varied considerably, the correlation of C and H isotope fractionation revealed a common mechanism for nitrobenzene and nitrotoluenes. Similar observations were made for the dioxygenation of these substrates by 2NTDO. Evaluation of reaction kinetics, isotope effects, and commitment-to-catalysis based on experiment and theory showed that rates of dioxygenation are determined by the enzymatic O-2 activation and aromatic C oxygenation. The contribution of enzymatic O-2 activation to the reaction rate varies for different nitroaromatic substrates of NBDO and 2NTDO. Because aromatic dioxygenation by nonheme iron dioxygenases is frequently the initial step of biodegradation, O-2 activation kinetics may also have been responsible for the minor isotope fractionation reported for the oxygenation of other aromatic contaminants.
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- Spahr, Stephanie, et al.
(författare)
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Compound-specific carbon, nitrogen, and hydrogen isotope analysis of N-nitrosodimethylamine in aqueous solutions
- 2015
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 87:5, s. 2916-2924
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Tidskriftsartikel (refereegranskat)abstract
- Mitigation of N-nitrosodimethylamine (NDMA) and other hazardous water disinfection byproducts (DBP) is currently hampered by a limited understanding of DBP formation mechanisms. Because variations of the stable isotope composition of NDMA can potentially reveal reaction pathways and precursor compounds, we developed a method for the compound-specific isotope analysis (CSIA) of (13)C/(12)C, (15)N/(14)N, and (2)H/(1)H ratios of NDMA by gas chromatography coupled to isotope ratio mass spectrometry (GC/IRMS). Method quantification limits for the accurate isotope analysis of NDMA, N-nitrosodiethyl-, -dipropyl-, and -dibutylamine as well as N-nitrosopyrrolidine were between 0.18 to 0.60 nmol C, 0.40 to 0.80 nmol N, and 2.2 to 5.8 nmol H injected on column. Coupling solid phase extraction (SPE) to GC/IRMS enabled the precise quantification of C, N, and H isotope ratios of NDMA in aqueous samples at concentrations of 0.6 μM (45 μg L(-1)). We validated the proposed method with a laboratory experiment, in which NDMA was formed with stoichiometric yield (97 ± 4%) through chloramination of the pharmaceutical ranitidine (3 μM). δ(13)C and δ(2)H values of NDMA remained constant during NDMA formation while its δ(15)N increased due to a reaction at a N atom in the rate-limiting step of NDMA formation. The δ(2)H value of NDMA determined by SPE-GC/IRMS also corresponded well to the δ(2)H value of the N(CH3)2-group of ranitidine measured by quantitative deuterium nuclear magnetic resonance spectroscopy. This observation implies that the N(CH3)2-moiety of ranitidine is transferred to NDMA without being chemically altered and illustrates the accuracy of the proposed method.
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