title: Compound-specific carbon, nitrogen, and hydrogen isotope analysis of N-nitrosodimethylamine in aqueous solutions.
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.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology , CH-8600 Dübendorf, Switzerland.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Spahr
authors.forename: Jakov
authors.initials: J
authors.lastname: Bolotin
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schleucher
authors.forename: Ina
authors.initials: I
authors.lastname: Ehlers
authors.forename: Urs
authors.initials: U
authors.lastname: von Gunten
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Hofstetter
mesh_terms: D002247:Carbon Isotopes / Q000737:chemistry*; D004128:Dimethylnitrosamine / Q000032:analysis*; D004203:Disinfection; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006859:Hydrogen / Q000737:chemistry*; D007553:Isotope Labeling; D009682:Magnetic Resonance Spectroscopy; D009587:Nitrogen Isotopes / Q000737:chemistry*; D052616:Solid Phase Extraction; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D014874:Water Pollutants, Chemical; D014867:Water; D006859:Hydrogen; D004128:Dimethylnitrosamine