Equilibrating of 15N-Gases by Electrodeless Discharge: A Method of Indirect Mass Spectrometric Analysis of 30N2 for Denitrification Studies in Soils

Abstract The estimation of denitrification in soil by the 15N tracer technique includes isotope analysis of gas samples with a nonrandom distribution of the N2 mole masses of 28, 29 and 30. In that case the emission of total 15N is underestimated by calculating 15N atom fractions from the 29N2/28N2 ratio if 30N2 is not considered. 30N2 can be measured indirectly in N2 enriched with 15N with nonrandom distribution of mole masses by mass spectrometric analysis. The nitrogen fraction of gas samples was transferred to discharge tubes. Microwaves (60 sec) generated an electrodeless discharge of the gas which caused a temporary split-up of N2 molecules and thus established an equilibrium distribution of the mole masses. The 29N2/28N2 ratio was measured in equilibrated and in untreated samples to calculate the real emission of 15N. The measurements of 15N standard gases by this method satisfactorily coincided with calculated values for 15N atom fraction above a concentration of 50 δ‰.