A novel method for the extraction and measurement of hydroxylamine in soils

Hydroxylamine (NH₂OH) is an intermediate in nitrification and a direct precursor for nitrous oxide (N₂O) in both enzymatic and abiotic reactions. Although its importance for N₂O emissions from soils has been recognized, NH₂OH has never been measured in soils except for one acidic forest soil. This is mostly due to a lack of an adequate extraction method in the presence of soil minerals. Therefore, we here developed a soil extraction method that stabilizes NH₂OH during the extraction by blocking its abiotic reactions by a combination of low pH, reducing agents and chelators. Furthermore, we optimized a colorimetric NH₂OH assay for the conditions encountered in such soil extracts. The colorimetric assay reacts NH₂OH with quinolin-8-ol under alkaline conditions and has a limit of detection of 0.5 µmol L^-1. In a next step, we target to purify the derivatization product with solid phase extraction to measure its concentration and isotopic composition via UPLC-Orbitrap mass spectrometry. The final goal is to provide a workflow for the ultra-sensitive NH₂OH measurement in soil ¹⁵N-tracer studies.