Nanomolar concentrations of NH2OH in natural water sources were determined using an Fe 3+ 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 electroncapture 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.
In the euphotic layer of a dam lake (reservoir), we discovered a phenomenon that hydroxylamine (NH 2 OH) accumulates at a high concentration at the same time as the increase in Chl-a, which is an indicator of phytoplankton biomass. Therefore, to investigate the presence or absence of NH 2 OH production by phytoplankton, we conducted a culture experiment using a single sterile strain of cyanobacteria isolated from the dam lake. Our results confirmed that NH 2 OH increased with the increase in Chl-a, and the ability of cyanobacteria to produce NH 2 OH was clarified. This result suggests that NH 2 OH detected in the euphotic layer during the dominance of cyanobacteria in summer is produced by the cyanobacteria.
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