5378 NTERNATIONAL STANDARD TSO INTERNATIONAL ORGANIZATION FOR STANDARDIZATION MEXAYHAPOAHAR OPTAHW3AWA nO CTAHAAPTW3ALWWORGANISATION INTE RNATIONALE DE NORMALISATION Starches and derived products -- Determination of nitrogen content by the Kjeldahl method -- Spectrophotometric method Amidons, fécules et produits derives - Dosage de I'azote selon la méthode de Kjeldahl - Methode spectrophotometrique First edition - 1978-06-15 ISO 5378-1978 (E) Ref. No. 1SO 5378-1978 (E) UDC 664.2 : 543.846 : 543.42 Descriptors : food products, starches, chemical analysis, fcontent,nitrogen,spectrophotometricanalysis. Price based on 3 pages Not for Resale FOREWORD ISo (the International Organization for Standardization) is a worldwide federation of national standards institutes (isO member bodies). The work of developing International Standards is carried out through ISO technical committees. Every member body interested in a subject for which a technical committee has been set up has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with IsO, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the Iso Council. StandardISO 5378was International developed by Technical Committee ISO/TC 93, (including derivatives and by-products), and was circulated Starch to the member bodies in March 1976. It has been approved by the member bodies of the following countries : Germany Australia Romania Hungary Austria Spain Chile Ireland Turkey Mexico United Kingdom Czechoslovakia Finland Netherlands Yugoslavia France Philippines The member body of the following country expressed disapproval of the document on technical grounds : Poland @ International Organization for Standardization, 1978 : Printed in Switzerland ed without license from IHS Not for Resale ISO 5378-1978 (E) INTERNATIONALSTANDARD Starches and derived products - Determination of nitrogen content by the Kjeldahl method - Spectrophotometric method 1 SCOPE AND FIELD OF APPLICATION 5 REAGENTS This International Standard specifies a spectrophotometric The reagents shall be of recognized analytical quality. method for the determination, by the Kjeldahl method, Ammonia-free distilled water or water of at least equivalent of the nitrogen content of starch and its derived products purity shall be used. whose presumed nitrogen content is less than 0,025 % (m/m).1) 5.1 Sulphuric acid, concentrated, P20 1,84 g/mi[96% (m/m)). NOTE -- In starches and their derived products to which nitrogen- ous materials have not been added, the nitrogen is present essen- 5.2 Sodium hydroxide, solution 30% (m/m), P20 tially in the form of protein and/or amino acids. 1,33 g/ml. 2 REFERENCES NOTE - This solution may be more concentrated. Iso 1227/Add. 2, Starch, including derivatives and by- 5.3 Compound catalyst3), consisting of, for example products -- Vocabulary, Addend. potassium sulphate : 97 g; ISO 1871, Agricultural food products - General directions for the determination of nitrogen by the Kjeldahl method. copper(ll) sulphate, anhydrous : 3 g. IsO 3188, Starches and derived products -- Determination of nitrogen content by the Kjeldahl method - Titrimetric 5.4 Ammonium sulphate, ammonium oxalate or am- method. monium chloride. 5.5 Sulphuric acid, approximately 0,1 N standard volu 3 DEFINITION metric solution. nitrogen content : The value found using the procedure specified. It includes the nitrogen content of free amino 5.6 Nessler reagent, prepared as follows at least 2 days acids, of compounds producing amino acids on hydrolysis before use : and of ammonium compounds. It does not include the nitrogen of nitrate and nitrite radicals, the nitrogen at- Dissolve 100 g of mercury(ll) iodide and 70 g of potassium tached directly to another nitrogen atom or the nitrogen iodide in 100 ml of water. Dissolve 224 g o