A highly sensitive method for the determination of hydroxylamine in soils

Abstract Hydroxylamine (HA) is a crucial intermediate in the first step of nitrification, i.e., the oxidation of ammonium to nitrite. Due to its reactivity, HA may play a key role in soil N2O emission. To determine soil HA concentrations and to explore the correlation between soil HA concentrations and N2O emission rates, we developed a novel, extremely sensitive method based on fast extraction of HA from the soil at pH 1.7, oxidation of HA to N2O with Fe3 + and analysis of the N2O with gas chromatography (GC). The new method was tested on soil samples from a temperate Norway spruce forest, comparing soil HA concentrations with N2O emission rates determined with microincubations of the soil samples in GC vials. Our results demonstrate that the new GC method is extremely sensitive, being able to detect soil HA contents as low as 0.3 μg N kg− 1 dry soil. HA content in the forest soil samples ranged between 0.3 and 34.8 μg N kg− 1 dry soil. Moreover, N2O emission rates were significantly correlated with soil HA content (r2 = 0.80), suggesting a key role of HA in N2O formation under aerobic conditions.