A Novel Approach\nfor Real-Time Determination of <sup>15</sup>N‑Enriched Hydroxylamine

Hydroxylamine (NH<sub>2</sub>OH) is a critical precursor\nof nitrous\noxide (N<sub>2</sub>O) and key intermediate in the nitrogen cycle.\nHowever, the conversion of NH<sub>2</sub>OH is very fast, and the\nlack of real-time <sup>15</sup>N analytical methods for NH<sub>2</sub>OH hinders the on-time capture of its biochemical signals in the\nN cycle. To bridge this gap, we developed a novel approach for real-time\ndetermination of <sup>15</sup>N-enriched NH<sub>2</sub>OH. In this\napproach, an automated sample inlet unit was coupled to a membrane-inlet\nmass spectrometer, and NH<sub>2</sub>OH was converted to N<sub>2</sub>O by sodium hypochlorite for analysis. The interference of carbon\ndioxide was successfully removed by an ascarite trap, and the N<sub>2</sub>O signal showed good linearity over the targeted NH<sub>2</sub>OH concentrations. The limit of detection and limit of quantification\nof this approach were 0.38 and 1.28 μM, respectively, and <sup>15</sup>N enrichment can be accurately detected when the <sup>15</sup>N enrichment is higher than 5 atom %. This approach provides a first\nonline analytical tool to capture real-time NH<sub>2</sub>OH transforming\nsignals using the <sup>15</sup>N tracing technique, which will advance\nmechanism studies of the N cycle.