5521 International Standard (ISO INTE RNATIONAL ORGANIZATION FOR STANDARDIZATION MEKAYHAPOAHA OPrAHM3AMR nO CTAHAAPTM3ALWM·ORGANISATION INTE RNATIONALE DE NORMALISATION Fruits, vegetables and derived products Qualitative method for the detection of sulphur dioxide Fruits, légumes et produits dérivés -- Methode qualitative de recherche du dioxyde de soufre First edition - 1981-08-01 UDC 634/635 : 543.061 : 546.224-31 Ref. No. 1SO 5521-1981 (E) SO 5521-1981 (E) Descriptors : fruit and vegetable products, agricultural products, fruits, vegetables, qualitative analysis, detection, sulphur dioxide. Price based on 2 pages CopyightInternational Organizatio for Standardization 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 Inter- national 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. International Standard ISO 5521 was developed by Technical Committee ISO/TC 34, Agricultural food products, and was circulated to the member bodies in June 1979. It has been approved by the member bodies of the following countries : Australia Germany, F. R. New Zealand Austria Hungary Philippines Brazil India Poland Bulgaria Portugal Israel Kenya Canada Romania Cyprus Libyan Arab Jamahiriya South Africa, Rep. of Czechoslovakia Malaysia Spain Egypt, Arab Rep. of Mexico Thailand Netherlands France Yugoslavia No member body expressed disapproval of the document. International Organization for Standardization, 1981 C Printed in Switzerland Not for Resale ed without license from IHS ISO 5521-1981 (E) INTERNATIONAL STANDARD Fruits, vegetables and derived products - Qualitative method for the detection of sulphur dioxide 1 Scope and field of application 3.5 Phosphoric acid, approximately 50 % (m/m) solution, Q20 = 1,34 g/ml. This International Standard specifies a qualitative method for the detection of free or bound sulphur dioxide in fruits, 3.6 Sodium hydroxide, approximately 40 g/l solution. vegetables and derived products. The method is applicable to products having suiphur dioxide 4 Apparatus contents of 2 mg or more per kilogram (or per litre). Usual laboratory apparatus, not otherwise specified, and in par- For products containing garlic or onion, see clause 6. ticular : 2 Principle 4.1 Flasks, of clear glass, of capacity 150 ml, and having wide mouths and ground necks. 2.1 Free sulphur dioxide 4.2 Ground glass stoppers, to fit the flasks (4.1). After acidification of the test portion, decolouration by the liberated gaseous sulphur dioxide of a starch indicator paper, previously coloured blue by a trace of iodine vapour. 5 Procedure Bound sulphur dioxide 2.2 5.1 Preparation of starch indicator paper Addition of alkali to the test portion, followed by the procedure Immediately before use, wet a strip of starch paper (3.2) with described in 2.1 two drops of the potassium iodide solution (3.3) and attach it to the bottom of a glass stopper (4.2), for example by means of adhesive tape. Place a few millilitres of the iodine solution (3.4) 3 Reagents in one of the flasks (4.1). Insert the stopper (the starch paper shall be suspended in the air space above the iodine). Leave for All reagents shall be of recognized analytical quality. The water 5 to 10 s. A clearly visible pale blue colour will develop on the used shall be disilled water or water of at least equivalent starch indicator paper which has to be used immediately. purity, recently boiled. 5.2 Test portion 3.1 Starch, a