1、 g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58Iodometric titration methodICS 55.100; 79.100Cork stoppers Determination of oxidizing residues BRIT
2、ISH STANDARDBS ISO 21128:2006BS ISO 21128:2006This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 May 2007 BSI 2007ISBN 978 0 580 50755 7Amendments issued since publicationAmd. No. Date Commentscontract. Users are responsible for its correct a
3、pplication.Compliance with a British Standard cannot confer immunity from legal obligations.National forewordThis British Standard was published by BSI. It is the UK implementation of ISO 21128:2006. The UK participation in its preparation was entrusted to Technical Committee PRI/81, Cork.A list of
4、organizations represented on this committee can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a Reference numberISO 21128:2006(E)INTERNATIONAL STANDARD ISO21128First edition2006-02-01Cork stoppers Determination of oxidizing resid
5、ues Iodometric titration method Bouchons en lige Dosage des rsidus oxydants Mthode par titrage iodomtrique BS ISO 21128:2006ii iiiContents Page Foreword iv 1 Scope . 1 2 Normative references . 1 3 Terms and definitions. 1 4 Principe 1 5 Sampling 1 6 Conditioning 2 7 Reagents and materials . 2 8 Appa
6、ratus 2 9 Procedure 2 10 Calculation. 3 11 Test report . 3 Annex A (informative) Preparation of a starch solution, 0,1 % (m/V) 4 BS ISO 21128:2006iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work
7、of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-government
8、al, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The mai
9、n task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Att
10、ention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 21128 was prepared by Technical Committee ISO/TC 87, Cork. BS ISO 21128:20061Cork stoppers Determina
11、tion of oxidizing residues Iodometric titration method 1 Scope This International Standard specifies an iodometric titration method for determining the oxidizing residues released by cork stoppers ready to use. NOTE This Standard concerns cork stoppers previously submitted to treatments with oxidizi
12、ng products. It this is not the case, the result of the test method is probably negative. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition
13、 of the referenced document (including any amendments) applies. ISO 633:1), Cork Vocabulary 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 633 and the following apply. 3.1 oxidizing residues residues of bleaching products on the cork stoppers 4 Prin
14、cipe Titrimetric determination of iodine, formed by oxidation of the peroxide residues on the cork stoppers, by using thiosulfate in an acidic environment. The chemical reaction is: H2O2+ 2H+ 2I I2+ 2H2O (1) 2 S2O32+ I2 S4O62+ 2I(25 Sampling Take a gross sample, statistically representative of the c
15、ork stoppers to be characterized, by following a chosen sampling plan. 1) To be published. (Revision of ISO 633:1986) BS ISO 21128:20062 6 Conditioning Tests shall be carried out at a temperature of (21 4) C and a relative humidity of (60 20) %. 7 Reagents and materials Use only reagents of recogniz
16、ed analytical grade and distilled or demineralised water or water of equivalent purity. 7.1 Sulfuric acid (H2SO4), dilute, 25 %. 7.2 Potassium iodide solution (KI), 50 g/l. 7.3 Ammonium heptamolybdate solution, 3 %. 7.4 Sodium thiosulfate, standard solution, 0,02 N. 7.5 Iodine indicator or fresh sta
17、rch solution, 0,1 % (m/V) (see Annex A). 7.6 Acetic acid solution, 50 %. 7.7 Nitrogen. 8 Apparatus Usual laboratory apparatus and in particular, the following. 8.1 Volumetric pipettes, of capacity 1 ml, 5 ml and 25 ml. 8.2 Graduated burette, in 0,1 ml, class A. 8.3 Flasks with screw caps, of nominal
18、 capacity 250 ml and 500 ml. 8.4 Orbital stirrer with plate, adjustable to (150 10) rev/min. 9 Procedure Perform the test twice, on two groups, each one with 4 cork stoppers. Add to a screwed flask (8.3), in order, 25 ml of potassium iodide solution (7.2), 5 ml of dilute sulfuric acid (7.1), 5 ml of
19、 acetic acid solution (7.6), 1 ml of ammonium heptamolybdate solution (7.3), and iodine indicator (7.5). Introduce 4 cork stoppers into the flask. Add 200 ml of demineralised water and allow nitrogen (7.7) to flow through the obtained solution, or remove O2by ultrasounds. Close the flask and place i
20、t, for 2 h, on the plate of the orbital stirrer (8.4), protected from light. If the solution colour changes into blue, then oxidizing residues are present. Remove cork stoppers and titrate with the sodium thiosulfate solution 0,02 N (7.4), stirring frequently, until a persistant turning point is obt
21、ained for at least 10 s. Near the turning point, add iodine indicator (7.5). Report the volume of sodium thiosulfate 0,02 N used, expressed in millilitres. BS ISO 21128:20063If the solution colour does not change to blue, stop the test; that means that the solution does not contain any oxidizing res
22、idues. At the same time a blank test shall be carried out, where cork stoppers are absent. 10 Calculation The quantity of oxidizing residues for each group, expressed in milligrams of peroxide (H2O2) per stopper, shall be given by the formula: 0,02 174V where V is the volume, in millilitres, of thio
23、sulfate solution, rounded off to the nearest tenth, after subtracting the volume of thiosulfate required for the blank test. If the concentration of each solution used is not the one mentioned in Clause 7, corrections should be introduced. The test result is the greatest value obtained from the grou
24、ps, expressed in milligrams of peroxide per stopper, rounded off to the nearest tenth. 11 Test report The test report shall include at least the following information: a) a reference to this International Standard, i.e. ISO 21128; b) the complete identification of the product to be tested, including
25、 type, origin and manufacturers reference; c) the result obtained; d) any operation not included in this International Standard, or regarded as optional; e) any deviation from this International Standard, which may have changed the results. BS ISO 21128:20064 Annex A (informative) Preparation of a s
26、tarch solution, 0,1 % (m/V) A.1 Reagents A.1.1 Soluble starch, analytical grade. A.1.2 Demineralised water, or any equivalent quality. A.1.3 Sodium chloride, analytical grade. A.2 Apparatus A.2.1 Balance, with a resolution of 0,1 g. A.2.2 Watch glass. A.2.3 Graduated cylinder, of capacity 100 ml. A.
27、2.4 Mortar. A.2.5 Laboratory flask, of capacity 250 ml. A.2.6 Heating plate. A.2.7 Funnel. A.2.8 Whatman paper No.4 2), or similar filter paper. A.2.9 Glass flasks. A.3 Procedure Weigh 0,1 g of soluble starch (A.1.1). Carefully triturate with a few millilitres of cold demineralised water (A.1.2). Po
28、ur the paste obtained into 100 ml of boiling water containing 5 g of sodium chloride (A.1.3). Keep boiling for about 2 min until a persistent transparent solution is obtained. Filter the hot solution using Whatman paper No. 4 (A.2.8), or let it cool, to allow excess starch to precipitate at the bott
29、om of the flask and pour it off. 2) Whatman is an example of a suitable product available commercially. This information is given for the convenience of users of this International Standard and does not constitute an endorsement by ISO of this product. BS ISO 21128:20065A.4 Stock Keep the starch sol
30、ution in an identified glass flask (A.2.9). Starch solutions are an excellent environment to feed micro-organisms and therefore they quickly deteriorate. If the colour obtained during titration is brownish, instead of bluish, that means that the starch is spoiled and shall not be used as an indicato
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