The rapid determination of nitrate in fresh and saline waters

The method suggested by HARTLEY A. M. and ASAI R. I. for the determination of nitrate with 2,6- xylenol (see Wat. Pollut. Abstr., l960, 33, Abstr. No. 2226) has been modified to eliminate the need for preliminary removal of chloride. The reaction between 2,6- xylenol and nitrate is carried out in a sulphuric acid medium in the presence of ammonium chloride, and the concentration of the product is determined spectrophotometrically at 304 mm. The range of the method has been extended to 55 p.p.m. nitrate-nitrogen, and the need for evaporating more dilute samples has been eliminated by using 4 cm cells. The modified method has a sensitivity of 0.13 p.p.m. at 95 per cent confidence limits, and is applicable to fresh and estuarine waters and sewage-works effluents. There is no interference by nitrite, ferrous iron, or sulphamic acid. Some observations on a standard method for determination of nitrate using Devarda's alloy have shown that the blank value is affected by the slow absorption by the alloy of nitrogen from the air.