ISO 5549:1978

Does not apply to caseins and caseinates containing ammonium caseinate or other ammonium compounds, or other nitrogenous nonprotein compounds. The principle of determination consists in digesting a test portion with a mixture of potassium sulphate and sulphuric acid, in the presence of copper(II) sulphate as catalyst, to convert organic nitrogen into ammoniacal nitrogen, distilling and absorbing the ammonia in boric acid solution, titrating with standard volumetric hydrochloric acid solution and multiplying the resualt by the factor 6.38.