title: Nitrogen isotopes determination in natural gas: analytical method and first results on magmatic, hydrothermal and soil gas samples.
abstract: A continuous-flow GC/IRMS technique has been developed to analyse delta(15)N values for molecular nitrogen in gas samples. This method provides reliable results with accuracy better than 0.15 per thousand and reproducibility (1sigma) within+/-0.1 per thousand for volumes of N(2) between 1.35 (about 56 nmol) and 48.9 muL (about 2 mumol). The method was tested on magmatic and hydrothermal gases as well as on natural gas samples collected from various sites. Since the analysis of nitrogen isotope composition may be prone to atmospheric contamination mainly in samples with low N(2) concentration, we set the instrument to determine also N(2) and (36)Ar contents in a single run. In fact, based on the simultaneously determined N(2)/(36)Ar ratios and assuming that (36)Ar content in crustal and mantle-derived fluids is negligible with respect to (36)Ar concentration in the atmosphere, for each sample, the degree of atmospheric contamination can be accurately evaluated. Therefore, the measured delta(15)N values can be properly corrected for air contamination.
authors.affiliation: Istituto Nazionale di Geofisica e Vulcanologia, Palermo, Italy.
authors.forename: Fausto
authors.initials: F
authors.lastname: Grassa
authors.forename: Giorgio
authors.initials: G
authors.lastname: Capasso
authors.forename: Ygor
authors.initials: Y
authors.lastname: Oliveri
authors.forename: Aldo
authors.initials: A
authors.lastname: Sollami
authors.forename: Paula
authors.initials: P
authors.lastname: Carreira
authors.forename: M
authors.initials: M
authors.lastname: Rosario Carvalho
authors.forename: Jose M
authors.initials: JM
authors.lastname: Marques
authors.forename: Joao C
authors.initials: JC
authors.lastname: Nunes
mesh_terms: D000393:Air Pollutants / Q000032:analysis / Q000737:chemistry; D001128:Argon / Q000032:analysis; D001272:Atmosphere / Q000737:chemistry; D005579:Fossil Fuels / Q000032:analysis*; D008401:Gas Chromatography-Mass Spectrometry; D005740:Gases / Q000032:analysis / Q000737:chemistry*; D045482:Hot Springs / Q000737:chemistry*; D009584:Nitrogen / Q000032:analysis; D009587:Nitrogen Isotopes / Q000032:analysis*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012987:Soil / Q000032:analysis*; D013696:Temperature
chemical_list: D000393:Air Pollutants; D005579:Fossil Fuels; D005740:Gases; D009587:Nitrogen Isotopes; D012987:Soil; D001128:Argon; D009584:Nitrogen