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.