Method for measuring nitrite and nitrate in aqueous medium

Abstract

A method is provided for measuring the concentration of nutrients such as nitrite and nitrate in aqueous media, e.g. the upper layers of the ocean where the concentrations of such nutrients are relatively low (i.e. in the tens of nanomoles per liter or less). The method is believed to be capable of such measurement capabilities at near real time sampling rates. The measurement of nitrite includes (a) treating an aliquot of the aqueous medium with a reagent that acidifies the aliquot, converts nitrite in the aliquot to nitrosium ion, and reacts with the nitrosium ion to yield a chemical species which fluoresces and (b) fluorometrically analyzing the resulting aliquot/reagent mixture to determine the concentration of such chemical species in the mixture, and thus to determine the concentration of nitrite in the aliquot and the aqueous medium from whence it came. The reagent is preferably an acidified solution in which the active ingredient is aniline. The measurement of nitrate is accomplished by treating a first aliquot of the aqueous medium in the manner described above to determine its nitrate concentration, treating a second aliquot (e.g. either sequentially with, or in parallel with the treatment of the first aliquot) to reduce the nitrate in the second aliquot to nitrite and measuring the resulting nitrite in the modified second aliquot in the manner described above, and using those two measurements to determine the concentration of nitrate in the second aliquot by difference.

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