Spectrophotometric Determination of Nitrate Ion in Fresh Water

R. S. Lambert and R. J. DuBois (Anal. Chem., 43, 955, 1971) reported a method for the determination of nitrate ion in the concentration range of 1.5 to 9.0 mg/I in saline waters. In this method, the nitrate ion is reduced to a nitrite ion and a diazo coupling is made to form a species for suitable spectrophotometric determinations in 5-cm cells. This method has been adapted for use on fresh-water samples with nitrate ion levels ranging down to 10 mcg/l. The concentrations of reagents, and the volume of the sample have been changed. These changes, with the use of both 10-cm and 5-cm cells, have provided excellent results over a range of 10 to 5000 mcg/l. The method was quite successful for routine analysis in view of its facility of use and precision provided.