The spectrophotometric determination of nitrate in natural waters,with particular reference to sea-water

Nitrate can be reduced to nitrite in good yield by means of hydrazine in alkaline solution; the reaction is promoted by catalytic quantities of copper. The authors have established the optimum conditions for tlie reduction and applied the method to the determination of nitrate in fresh waters and in sea-waters. The nitrite formed is determined by Mellon and Rider's modification of the Griess-Ilosvay procedure. The reduction with hydrazine is carried out in the presence of 0.25 p.p.m. of copper at pH 9.6 in a solution buffered with sodium phenate. It is complete within 24 hours at room temperature. The method will detect ca. 0.3 μg NO₃$\text{N}\text{l}$ and gives a standard deviation of ca. 2% in the range 20-600 μg NO₃-$\text{N}\text{l}$. Up to 60 determinations can be made per 6 hour working period. The interference of nitrite has been investigated. Ammonium salts, urea, and amino acids do not interfere, at the concentrations at which they occur in sea-water.It is preferable to analyse samples immediately after collection, but if this is not possible, they should be filtered, sterilized with 2 p.p.m. of mercuric chloride and stored in glass containers.