Nitrogen isotopes determination in natural gas: analytical method and first results on magmatic, hydrothermal and soil gas samples.
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.
Grassa
Fausto
F
Istituto Nazionale di Geofisica e Vulcanologia, Palermo, Italy.
Capasso
Giorgio
G
Oliveri
Ygor
Y
Sollami
Aldo
A
Carreira
Paula
P
Rosario Carvalho
M
M
Marques
Jose M
JM
Nunes
Joao C
JC
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
D000393:Air Pollutants; D005579:Fossil Fuels; D005740:Gases; D009587:Nitrogen Isotopes; D012987:Soil; D001128:Argon; D009584:Nitrogen