ISO 5315:1984 Preview
Fertilizers -- Determination of total nitrogen content -- Titrimetric method after distillation
This standard was last reviewed and confirmed* in 2012.
*Therefore this version remains current
The method consists in reducing of nitrate to ammonia by chromium powder in acid medium, converting of organic and urea nitrogen into ammonium sulfate by digestion with concentrated sulfuric acid in the presence of a catalyst, distilling of the ammonia from an alkaline solution and absorbing in an excess of standard volumetric sodium hydroxide solution. The method is not recommended for materials containing more than 7 % of organic matter.