DISCRETE ANALYZER CHEMISTRY Nitrate/Nitrite (Hydrazine Reduction) Method
Method Description The sample is held in an alkaline solution of hydrazine sulfate ( SEALAnalyticalAQ NOx Hydrazine & SEALAnalyticalAQ NOx Hyd-Buffer ) with Cu (II) present for catalysis, which reduces nitrate in solution to nitrite. Both original nitrite and chemically reduced nitrite react with sulfanilamide, in dilute phosphoric acid, to form a diazonium compound. The reaction between the diazonium ion and NEDD results in the formation of an AZO bond (-C=N-) between the benzene ring and the naphthyl group, which is a reddish-purple AZO dye. The absorbance of this dye is measured photometrically at 520 nm. Note: It is essential to precisely adjust the volume of SEALAnalyticalAQ NOx Hydrazine used to ensure that equimolar Nitrate and Nitrite standards yield consistent results. An excess of hydrazine will lead to the reduction of Nitrite to nitrogen gas (N₂), while insufficient hydrazine will fail to completely reduce all Nitrate (NO₃⁻) to Nitrite (NO₂⁻). The required hydrazine concentration is influenced by several factors, including temperature, reaction time, pH, and metal ion concentration. Variations of ±25% from the original method are not uncommon.
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