Determination of Nitrate Nitrogen in Mixed Fertilisers Using 1.2.4. Phenol-Disulphonic Acid

It is desirable to be able to determine nitrate in presence of other forms of nitrogen. The new reagent, N-(4-chlorobenzyl)-l- naphthylmethylamine (CBNMA) developed by Hutton, Salam and Stephen (1966, J. Chem. Soc. (A). 1573/1579) has been used with synthetic fertiliser solutions of known nitrate content. For comparison, results obtained by the use of nitron reagent are given. The average recovery given by the final version of the method using CBNMA reagent was 102% for chloride/nitrate concentration ratios of 0.53 to 1.15. With a ratio of 2.04, the recovery was 101 to 105% (average 103%). These high recoveries are due to co-precipitation of the reagent caused by the presence of chloride. They compare with an average of 99% using nitron. The new reagent has no advantage over nitron.