Re-examination of the determination of environmental nitrate as nitrite by reduction with hydrazine

Abstract

The determination of nitrate as nitrite remains the method of choice owing to the accuracy with which low concentrations of nitrite can be detected. A manual procedure for the reduction of nitrate to nitrite using hydrazine sulphate (HS) was described as impractical owing to the capricious nature of the reaction. The homogeneous catalysed reduction proposed in this work compares well with the usual heterogeneous catalysed cadmium reduction column technique without, however, being subject to interfering substances, and offers the possibility of increasing the number of simultaneous nitrate reductions using sample volumes down to a few microlitres. The relative standard deviation of the method is 0.7% with a detection limit of 0.2 µmol l^–1 of nitrate. It is demonstrated that uncontrolled fluctuations in the concentration of oxygen, present during the reduction, were the main cause of the earlier erratic results. The Mg²⁺ ion, also responsible for complete suppression of the reduction, was inactivated by pyrophosphate.