Nitrite removal improves hydroxylamine analysis in aqueous solution by conversion with iron(III)

Abstract

Environmental context Nitrogen is an essential nutrient for marine organisms, and thus an understanding of the marine nitrogen cycle is a crucial factor in predicting the sensitivity of marine life to environmental change. Hydroxylamine is a short-lived intermediate in nitrogen transformation processes, and reliable detection of this compound in seawater can help to identify these processes within the marine nitrogen cycle. Abstract Dissolved hydroxylamine (NH2OH) is a short-lived compound produced in the oceanic environment during nitrification and dissimilatory reduction of nitrate to ammonium (DNRA). The ferric ammonium sulfate (FAS) conversion method is the only method available so far to determine dissolved NH2OH in nanomolar concentrations in seawater. We show that side reactions of dissolved nitrite (NO2–) can result in a significant bias in the NH2OH concentration measurements when applying the FAS conversion method. We propose to scavenge dissolved NO2– by addition of sulfanilamide to suppress effectively the undesired side reactions by NO2–. This modification of the FAS conversion method will allow a NH2OH determination even in oceanic regions with high NO2– concentrations. A reliable detection of NH2OH in seawater samples can give us a clue about the occurrence of active nitrification or DNRA in the ocean and, therefore, will provide further insights about the oceanic nitrogen cycle.