title: Novel laser spectroscopic technique for continuous analysis of N2O isotopomers--application and intercomparison with isotope ratio mass spectrometry.
abstract: BACKGROUND
  Nitrous oxide (N(2)O), a highly climate-relevant trace gas, is mainly derived from microbial denitrification and nitrification processes in soils. Apportioning N(2)O to these source processes is a challenging task, but better understanding of the processes is required to improve mitigation strategies. The N(2)O site-specific (15)N signatures from denitrification and nitrification have been shown to be clearly different, making this signature a potential tool for N(2)O source identification. We have applied for the first time quantum cascade laser absorption spectroscopy (QCLAS) for the continuous analysis of the intramolecular (15)N distribution of soil-derived N(2)O and compared this with state-of-the-art isotope ratio mass spectrometry (IRMS).
  
  
  METHODS
  Soil was amended with nitrate and sucrose and incubated in a laboratory setup. The N(2)O release was quantified by FTIR spectroscopy, while the N(2)O intramolecular (15)N distribution was continuously analyzed by online QCLAS at 1 Hz resolution. The QCLAS results on time-integrating flask samples were compared with those from the IRMS analysis.
  
  
  RESULTS
  The analytical precision (2σ) of QCLAS was around 0.3‰ for the δ(15)N(bulk) and the (15)N site preference (SP) for 1-min average values. Comparing the two techniques on flask samples, excellent agreement (R(2)= 0.99; offset of 1.2‰) was observed for the δ(15)N(bulk) values while for the SP values the correlation was less good (R(2 )= 0.76; offset of 0.9‰), presumably due to the lower precision of the IRMS SP measurements.
  
  
  CONCLUSIONS
  These findings validate QCLAS as a viable alternative technique with even higher precision than state-of-the-art IRMS. Thus, laser spectroscopy has the potential to contribute significantly to a better understanding of N turnover in soils, which is crucial for advancing strategies to mitigate emissions of this efficient greenhouse gas.
authors.affiliation: Institute of Plant Nutrition and Soil Science, Kiel University, Hermann-Rodewald-Str. 2, D-24118, Kiel, Germany. jrkoester@plantnutrition.uni-kiel.de
authors.forename: Jan Reent
authors.initials: JR
authors.lastname: Köster
authors.forename: Reinhard
authors.initials: R
authors.lastname: Well
authors.forename: Béla
authors.initials: B
authors.lastname: Tuzson
authors.forename: Roland
authors.initials: R
authors.lastname: Bol
authors.forename: Klaus
authors.initials: K
authors.lastname: Dittert
authors.forename: Anette
authors.initials: A
authors.lastname: Giesemann
authors.forename: Lukas
authors.initials: L
authors.lastname: Emmenegger
authors.forename: Albert
authors.initials: A
authors.lastname: Manninen
authors.forename: Laura
authors.initials: L
authors.lastname: Cárdenas
authors.forename: Joachim
authors.initials: J
authors.lastname: Mohn
mesh_terms: D054023:Lasers, Semiconductor; D013058:Mass Spectrometry / Q000379:methods*; D009566:Nitrates / Q000737:chemistry; D009587:Nitrogen Isotopes / Q000032:analysis* / Q000737:chemistry; D009609:Nitrous Oxide / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D010103:Oxygen Isotopes / Q000032:analysis* / Q000737:chemistry; D015203:Reproducibility of Results; D012987:Soil / Q000737:chemistry; D013055:Spectrophotometry, Infrared / Q000295:instrumentation / Q000379:methods; D013395:Sucrose / Q000737:chemistry
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D012987:Soil; D013395:Sucrose; D009609:Nitrous Oxide