Abstract
The authors have perceived that nitrate ion could be reduced almost completely, close to 100%, to nitrite ion by zinc under selected conditions in the presence of appropriate salt and acid, which, in this experiment, were sodium acetate and sulfanilic acid.
To 25 ml of sample solution are added, in the order, 15.0 ml of 30% solution of sodium acetate, 0.07 g of sulfanilic acid and 0.3 g of zinc powder. After a 10 min shaking, a 10 ml aliquot of the filtrate was taken and mixed with 1.50 ml of 35% hydrochloric acid and 1.0 ml of 0.1% n-naphthylethylenediamine solution. The absorbance of the developed azo-dye was measured at 550 mμ after about 20 min. Nitrite initially present in sample was not destroyed by this procedure, and hence the values estimated were the sum of nitrate and nitrite ions. Alternatively, the nitrate ion was determined directly by heating the sample with sulfanilic acid for 10 min in a boiling water bath to destroy nitrite, and then by carrying through the procedure from the addition of sodium acetate.
A sample containing only a small amount of nitrate with a large amount of nitrite is treated conveniently by the latter procedure.
The error was±2.5% for 0.2 ppm nitrate-nitrogen, and the sensitivity represented as absorbance was 0.159 for 0.1 ppm nitrate-nitrogen.
