Sensitive Gas Chromatography Detection of Nanomolar Hydroxylamine in Environmental Water by Fe(III) Oxidation

Nanomolar concentrations of NH₂OH in natural water sources were determined using an Fe³⁺ oxidation method. A pH of 2.35 - 2.50 was used, which was adjusted by adding a chloroacetate buffer. Equal amounts (1.0 mL) of the chloroacetate solution and ferric chloride solution were added to the water sample (70 mL) to oxidize NH₂OH to N₂O. The resulting N₂O in the sample water was then quantified by headspace analysis using a gas chromatograph with an electron-capture detector (ECD), where a limit of detection of 0.2 μgN L^-1 (14 nmol L^-1) was achieved. This method was successfully applied to samples of freshwater, brackish water, and seawater, and despite the various salinities no interfering substances were observed. Furthermore, NH₂OH was successfully detected in samples collected from the Hii River and Lakes Shinji and Nakaumi (Shimane Prefecture, Japan). In addition, the proposed method was also applicable to samples rich in organic substance derived from phytoplankton.