An enhanced technique for automated determination of 15N signatures of N2, (N2+N2O) and N2O in gas samples

Abstract

RATIONALE An enhanced analytical approach for analyzing gaseous products from 15N-enriched pools has been developed. This technique can be used to quantify nitrous oxide (N2O) and dinitrogen (N2) fluxes from denitrification. It can also help in distinguishing different N 2- and N2O-forming processes, such as denitrification, nitrification, anaerobic ammonium oxidation or co-denitrification. METHODS The measurement instrumentation was based on a commercially available automatic preparation system allowing collection and separation of gaseous samples. The sample transfer paths, valves, liquid nitrogen traps, gas chromatography column and open split of the original system were modified. A reduction oven (Cu) was added in order to eliminate oxygen and measure N2O-N as N 2. Gases leaving the separation system entered an isotope ratio mass spectrometer where masses 28N2, 29N2 and 30N2 were measured. RESULTS The enhanced technique enabled rapid simultaneous measurement of stable isotope ratios 29N2/28N2 and 30N 2/28N2 originating from dinitrogen alone (N2) and from the sum of the denitrification products (N 2+N2O) as well as the determination of 15N enrichment in N2O. The 15N fraction in the N pool undergoing N2 and N2O production (15X N) and the contribution of N2 and N2O originating from this pool (d) were determined with satisfactory accuracy of better than 3.3% and 2.9%, respectively. CONCLUSIONS The precision and accuracy of this method were comparable with or better than previously reported for similar measurements. The proposed method allows for the analysis of all quantities within one run, thus reducing the measurement and sample preparation time as well as increasing the reliability of the results. Copyright © 2013 John Wiley & Sons, Ltd. Copyright © 2013 John Wiley & Sons, Ltd.