A Novel Approach for Real-Time Determination of ¹⁵N-Enriched Hydroxylamine

Hydroxylamine (NH₂OH) is a critical precursor of nitrous oxide (N₂O) and key intermediate in the nitrogen cycle. However, the conversion of NH₂OH is very fast, and the lack of real-time ¹⁵N analytical methods for NH₂OH hinders the on-time capture of its biochemical signals in the N cycle. To bridge this gap, we developed a novel approach for real-time determination of ¹⁵N-enriched NH₂OH. In this approach, an automated sample inlet unit was coupled to a membrane-inlet mass spectrometer, and NH₂OH was converted to N₂O by sodium hypochlorite for analysis. The interference of carbon dioxide was successfully removed by an ascarite trap, and the N₂O signal showed good linearity over the targeted NH₂OH concentrations. The limit of detection and limit of quantification of this approach were 0.38 and 1.28 μM, respectively, and ¹⁵N enrichment can be accurately detected when the ¹⁵N enrichment is higher than 5 atom %. This approach provides a first online analytical tool to capture real-time NH₂OH transforming signals using the ¹⁵N tracing technique, which will advance mechanism studies of the N cycle.