W-000.26.111 [2021-03] Nitrate in Water, Photometric Determination with 2,6-Dimethylphenol
Application/Purpose
The method describes how to determine the nitrate content of water photometrically with a cuvette test.
Scope of Application
Water intended for use as an ingredient in the production of beer (brewing liquor) or other foods
Nitrate ions can be found in ground and surface waters in a wide range of concentrations. These ions represent the final product in the oxidation of nitrogenous, organic substances. Therefore, they are much less concerning than the intermediate products of ammonia and nitrite.
Principle
In an acidic sulfurous solution containing phosphorus, nitrate ions react with 2,6-dimethylphenol to produce 4-nitro-2,6-dimethylphenol.
The method is suitable for determining approx. 0.5–25 mg/l NO3-. If the ratio of chloride to nitrate ions is larger than 10, this may interfere with the reaction (if this is the case, according to DEV D 9-3, follow DIN 38405); likewise, nitrite ions exceeding approx. 0.2 mg/l may also interfere with the reaction. For their removal, refer to Remarks below.