Discussion on the need for correction during isotopic analysis of nitrogen by the denitrifier method

The nitrogen and oxygen isotopes of NO₃ ^- are effectively used to trace the main nitrogen sources and migration processes in the atmosphere, water and soil. NO₃ ^- can be converted into N₂O by the bacterial denitrification method, which is an advanced method with high sensitivity. However, due to the existence of a small but inevitable blank during the whole experimental process, the N isotopic signal of N₂O produced by denitrification superimposes on that of the N blank. Currently, the standard curve correction method is used to correct measured nitrogen isotope results to mitigate blank interference. It has been reported that high variability of the nitrogen isotope results have been produced by the denitrifier method by conducting an interlaboratory comparison of denitrifier methods and other methods on standards and environmental samples, and to reduce this problem, the nitrogen isotope calibration process with a standard curve is examined in depth in this paper, which uses PreCon-GC-IRMS to determine the nitrogen isotopes in N₂O. We demonstrate for the first time that reliable results can be obtained without correction for samples with nitrogen isotope composition ranging from -9.9 to 19.5‰, which covers the natural sample range. This study establishes the double test approach for the bacterial denitrification method, ensuring the accuracy and long-term stability of different batches of nitrogen isotope results.