ISO 3188:1978

Starches and derived products — Determination of nitrogen content by the Kjeldahl method — Titrimetric method

The found value only includes free amino acids, compounds producing amino acids on hydrolysis and ammonium compounds. The principle consists in destruction of organic matter by sulphuric acid in the presence of a compound catalyst (see ISO 1871), alkalization of the reaction products, distillation of the liberated ammonia and collection in a boric acid solution, followed by titration with a standard volumetric sulphuric acid solution. The method applies to contents greater than 0,01 % (m/m). For products with contents less than 0,025 % (m/m), see ISO 5378.