Bayreuther Institut für Terrestrische Ökosystemforschung
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Lauf, J; Gebauer, G: On-line analysis of stable isotopes of nitrogen in NH3, NO and NO2 at natural abundance levels, Analytical Chemistry, 70, 2750-2756 (1998), doi:10.1021/ac9800053
Methods were developed for the on-line analysis of stable isotopes of nitrogen (at natural abundance levels) in NH3, NO and NO2 in order to study the contribution of these trace gases to nitrogen cycling in ecosystems. Standard methods for the combustion of organic substances to N2 (for the determination of the 15N/14N ratios by mass spectrometry) failed to satisfactorily oxidize or reduce the respective trace gases. The following oxidation or reduction techniques ensured quantitative conversion of the trace gases to N2 and analytical precision close to the internal precision of the instrument (precision +/-0.15 o/oo): (1) oxidation of NH3 to N2 at 1150 °C on a NiO surface (which needs a reoxidation before each NH3 analysis; measuring range 11.7-58.8 nmol of NH3, precision +/-0.3 o/oo); (2) reduction of NO to N2 at 1150 °C on a Ni surface (measuring range 33.3-133.3 nmol of NO, precision +/-0.28 o/oo); (3) reduction of NO2 to form NO at 420 °C on a Mo surface followed by further treatment as for NO (measuring range 26.0-129.9 nmol of NO2, precision +/-0.90 o/oo). This last technique was developed due to the poor chromatographic properties of NO2.
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