Colorimetric Determinations of Nitrite and Nitrate Nitrogen in Brackish Coastal Waters

A simple, rapid colorimetric procedure has been developed for determining the nitrite content of brackish coastal waters. A slight modification permits analysis of nitrate content. Both methods eliminate conflict with other ions. Each takes but 15 to 20 minutes. They can be used by persons who are not skilled chemists.

The procedures are presented as an aid to geologists and biologists who have had difficulty in correlating rapidly changing lateral, vertical and hourly chemical content with other brackish water data, especially near shore. The nitrite content of Mississippi's coastal water is 0.03 to 0.05 ppm. Nitrate content is 0.04 to 0.06 ppm.

The procedures are modifications of a 1954 method developed by Nelson, Kurtz and Bray for plant and soil analysis. Old colorimetric procedures are utilized in diazotization of sulfanilic acid by the nitrite ion and subsequent coupling with 1-napthylamine to form a red dye. As in the Nelson-Kurtz-Bray method, reagents are added as powdered mixtures which are stable for at least two months. One mixture is used for nitrite, only. The other is identical except that powdered zinc is added, to reduce nitrates to nitrites. Nitrate content is the difference between the nitrite determination and the determination after the nitrate is reduced to nitrite.