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1、International Standard INTERNATIONAL ORGANIZATION FOR STANDARDIZATION.MEIltjJYHAPOHAR OPl-AHM3AUMfl IlO CTAHAPTkl3Al.WlORGANISATlON INTERNATIONALE DE NORMALISATION Fruits, vegetables and derived products - Qualitative method for the detection of sulphur dioxide Fruits, legumes et produits d&iv& - Me
2、thode qualitative de recherche du dioxyde de soufre First edition - 1981-08-01 UDC 634/635: 543.061: 546.224-31 Ref. No. ISO 5521-1981 (E) Descriptors : fruit and vegetable products, agricultural products, fruits, vegetables, qualitative analysis, detection, sulphur dioxide. Price based on 2 pages C
3、opyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 20:36:09 MDTNo reproduction or networking permitted without license from IHS -,-,- Foreword ISO (the International Organization for
4、 Standardization) is a worldwide federation of national Standards institutes (ISO member bedies). 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
5、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 Internat
6、ional 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. lt has been approved by the member bodies of the following countries : Australia Germany, F. R. Austri
7、a Hungary Brazil India Bulgaria Israel Canada Kenya Cyprus Libyan Arab Jamahiriya Czechoslovakia Malaysia Egypt, Arab Rep. of Mexico France Netherlands No member body expressed disapproval of the document. (c, International Organkation for Standardkation, 1981 New Zealand Philippines Poland Portugal
8、 Romania South Africa, Rep. of Spain Thailand Yugoslavia Printed in Switzerland Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 20:36:09 MDTNo reproduction or networking permitte
9、d without license from IHS -,-,- INTERNATIONALSTANDARD ISO 5521-1981 (E) Fruits, vegetables and derived products - Qualitative method for the detection of sulphur dioxide 1 Scope and field of application This International Standard specifies a qualitative method for the detection of free or bound su
10、lphur dioxide in fruits, vegetables and derived products. The method is applicable to products having sulphur dioxide contents of 2 mg or more per kilogram (or per litre). For products containing garlic or onion, see clause 6. 2 Principle 3.5 Phosphoric acid, approximately 50 % (mlm) Solution, e20 =
11、 1,34 g/ml. 3.6 Sodium hydroxide, approximately 40 g/l Solution. 4 Apparatus Usual laboratory apparatus, not otherwise specified, and in par- ticular : 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
12、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. 2.2 Bound sulphur dioxide Addition of alkali to the test Portion, followed by the procedure described i
13、n 2.1. 3 Reagents All reagents shall be of recognized analytical quality. The water used shall be distilled water or water of at least equivalent purity, recently boiled. 3.1 Starch, approximately 5 g/l Solution. During preparation, boil the Solution for 10 min. The Solution will keep only for a few
14、 days. 3.2 Starch Paper. Dip a white filter Paper, of close texture, into the starch solu- tion (3.1) three times and dry in an oven at 30 OC after each im- pregnation. Cut into Strips of 2 cm x 5 cm. 3.3 Potassium iodide, approximately 1 g/l Solution (free from iodate). 3.4 lodine, approximately 12
15、 g/l Solution. 5 Procedure 5.1 Preparation of starch indicator Paper Immediately before use, wet a Strip of starch Paper (3.2) with two drops of the potassium iodide Solution (3.3) and attach it to the bottom of a glass stopper (4.21, for example by means of adhesive tape. Place a few millilitres of
16、 the iodine Solution (3.4) 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 5 to 10 s. A clearly visible pale blue colour will develop on the starch indicator Paper which has to be used immediately. 5.2 Test Portion Pla
17、ce in another flask (4.1) about 20 ml of the product to be analysed (in the case of liquid products) or about 20 g of finely comminuted product (in the case of solid products) suspended in 20 ml of water. 5.3 Detection of free sulphur dioxide 53.1 Acidify the test Portion with a few drops of the pho
18、sphoric acid Solution (3.5). 5.3.2 Immediately close the flask by means of the stopper with the starch indicator Paper, prepared as described in 5.1, attached. In the presence of traces of sulphur dioxide 2 mg per kilogram (or per litre)l the indicator Paper will be decolorized in less than 5 min. 1
19、 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 20:36:09 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 5521-1981 (E) 5.4 Detection of bound sulph
20、ur dioxide 6 Note on procedure 54.1 In the absence of free sulphur dioxide, make the test Portion alkaline by adding the sodium hydroxide Solution (3.6) in slight excess. Allow to stand for 5 min and acidify with suffi- cient phosphoric acid Solution (3.5). Products containing garlic or onion releas
21、e a substance capable of decolorizing the starch indicator Paper when treated with the sodium hydroxide. Thus, they may be erroneously considered to contain bound sulphur dioxide. NOTE - The volume of phosphoric acid Solution required will be ap- proximately l/ 13 of the volume of sodium hydroxide S
22、olution used. 5.4.2 Proceed as specified in 5.32. However, the technique specified in 5.3 for the detection of free sulphur dioxide may be used without error for these pro- ducts. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 20:36:09 MDTNo reproduction or networking permitted without license from IHS -,-,-