1、 ISO 2013 Starches and derived products Determination of sulfur dioxide content Acidimetric method and nephelometric method Amidons, fcules et produits drivs Dtermination de la teneur en dioxyde de soufre Dosage acidimtrique et dosage par nphlmtrie INTERNATIONAL STANDARD ISO 5379 Second edition 2013
2、-09-01 Reference number ISO 5379:2013(E) ISO 5379:2013(E)ii ISO 2013 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2013 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, i
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4、+ 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ISO 5379:2013(E) ISO 2013 All rights reserved iii Contents Page Foreword iv 1 Scope . 1 2 Acidimetric method . 1 2.1 Reagents 1 2.2 Apparatus 2 2.3 Procedure 4 2.4 Expression of results 6 3 Nephelometric method 6 3.1
5、Reagents 6 3.2 Apparatus 7 3.3 Procedure 7 3.4 Expression of results 8 4 Test report . 8 Bibliography 9 ISO 5379:2013(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International S
6、tandards 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-governmental, in liaison with ISO, als
7、o take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1.
8、In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2. www.iso.org/directives Attention is drawn to the possibility that some of the elements of
9、 this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received. www.
10、iso.org/patents Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement. The committee responsible for this document is ISO/TC 93, Starch (including derivatives and by-products). This second edition cancels and replaces ISO 5379:1
11、983, of which it constitutes a minor revision.iv ISO 2013 All rights reserved INTERNATIONAL ST ANDARD ISO 5379:2013(E) Starches and derived products Determination of sulfur dioxide content Acidimetric method and nephelometric method 1 Scope This International Standard specifies two methods (an acidi
12、metric method and a nephelometric method) for the determination of the sulfur dioxide content of starches and derived products. 2 Acidimetric method 2.1 Reagents WARNING All chemicals shall be handled with care. Consult the appropriate material safety data sheet for proper handling and disposal proc
13、edures. All reagents shall be of recognized analytical quality and be sulfate-free. 2.1.1 Water, distilled water or water of at least equivalent purity, recently boiled. 2.1.2 Nitrogen, oxygen-free. 2.1.3 Hydrogen peroxide, solution containing approximately 9 g to 10 g of H 2 O 2per litre c(H 2 O 2
14、) = 0,265 to 0,294 mol/l. Place 150 ml of 20 volumes (6 wt %, 2,08 mol/l) hydrogen peroxide solution or 30 ml of 110 volumes (30 wt %, 10,4 mol/l) hydrogen peroxide solution in a 1 l one-mark volumetric flask. Dilute to the mark with water. This solution should be freshly prepared. 2.1.4 Hydrochlori
15、c acid. To 500 ml of water in a 1 l beaker, slowly add 150 ml of concentrated hydrochloric acid ( 201,18 g/ml; 12 mol/l; 37 wt %) with stirring. Transfer this qualitatively to a 1 l volumetric flask and dilute to the mark. CAUTION Never add water to concentrated acid. 2.1.5 Bromophenol blue indicato
16、r solution. Dissolve 100 mg of bromophenol blue alternative names are , -bis(3,5-dibromo-4-hydroxyphenyl) toluene-2, sulfone or 3, 3, 5, 5-tetrabromophenol sulfonephthalein in 100 ml of 20 % (V/ V) ethanol. 2.1.6 Tashiro indicator solution. Dissolve 30 mg of methyl red 2-4-(dimethylamino)phenyl -azo
17、 benzoic acid and 50 mg of methylene blue 3,7-bis(dimethylamino)phenothiazin-5-ium chloride in 120 ml of 90 % (V/ V) ethanol. Dilute to 200 ml with water, mix and filter if necessary. NOTE The Tashiro indicator can only be used with the titrimetric method (2.3.4). The bromophenol blue indicator is a
18、ppropriate for the titrimetric method and does not hinder the further use of the nephelometric method (see Clause 3). Nevertheless, with this indicator, it is more difficult to detect the end-point. ISO 2013 All rights reserved 1 ISO 5379:2013(E) 2.1.7 Sodium hydroxide, standard volumetric solution,
19、 c(NaOH) = 0,1 mol/l; or sodium hydroxide, standard volumetric solution, c(NaOH) = 10 mmol/l. In order to obtain a sharp end-point, prepare this solution using carbon-dioxide-free water obtained by cooling boiled distilled water (2.1.1) under a flow of nitrogen (2.1.2). The use of sodium hydroxide,
20、standard volumetric solution, c(NaOH) = 0,1 mol/l is recommended and a piston-burette is useful for small volumes. If necessary, increase the mass of the test portion. 2.1.8 Iodine, standard volumetric solution, c(I 2 ) = 10 mmol/l. Potassium iodate (KIO 3 ) at the appropriate concentration is a sui
21、table substitute. 2.1.9 Starch, 5 g/l solution. Dissolve 0,5 g of Lintner starch or similar in 100 ml of water. Heat to boiling while stirring. Add 20 g of sodium chloride, stir and boil until dissolution is complete. Allow to cool to ambient temperature before use. 2.1.10 Sodium metabisulfite (c(SO
22、 2 ) = 7,8 mmol/l) and ethylenediaminetetraacetic acid (EDTA), disodium salt (c(EDTA) = 0,5 mmol/l). 1)Dissolve in water 0,74 g of sodium metabisulfite (Na 2 S 2 O 5 ) and 0,20 g of ethylenediaminetetraacetic acid disodium salt dihydrate (Na 2 H 2 EDTA2H 2 O). Transfer the solution quantitatively to
23、 a 1 l volumetric flask and make up to the mark with water. For accurate results, minimize exposure of this solution to the atmosphere. 2.2 Apparatus Glass apparatus should preferably be fitted with ground glass joints. Use ordinary laboratory apparatus, and in particular, the following. See Figure
24、1. 2.2.1 One-mark volumetric flasks, of capacity 1 l, complying with the requirements of ISO 1042, class A. 2.2.2 One-mark pipettes, of capacities 0,1 1 2 3 5 and 20 ml, complying with the requirements of ISO 648, class A. 2.2.3 Burettes, with capacities of 10 ml, 25 ml and 50 ml, complying with ISO
25、 385, smallest scale division, accuracy class A or AS. 2.2.4 Analytical balance, capable of weighing to the nearest 10 mg. 2.2.5 Magnetic stirrer, efficient, with heating, for use with the flask (A) (see Figure 1). 2.2.6 Entrainment apparatus, as shown in the Figure 1, or equivalent equipment for en
26、suring the displacement and entrainment of sulfur dioxide and its absorption in a solution of hydrogen peroxide. Avoid making connections with tubes between the condenser and the bubblers as this could lead to absorption of sulfur dioxide. 1) EDTA is used to retard any oxidation of sulfite by air in
27、 the presence of trace amounts of copper ion.2 ISO 2013 All rights reserved ISO 5379:2013(E) Dimensions in millimetres Key A round-bottom flask, of capacity 250 ml or greater, with a ground tubular allowing the introduction of a thermometer B vertical condenser of high efficiency, to fit the flask (
28、A) C separating funnel, fitted to the flask (A) D nitrogen inlet with an absorber containing an alkaline solution of pyrogallol E, E 2 bubblers in series, connected to the condenser (B) F thermometer Between two determinations, if the entrainment is sufficiently slow and moderate, only flask (A) nee
29、d be cleaned. Figure 1 Diagram of entrainment apparatus (Lieb and Zaccheri type) ISO 2013 All rights reserved 3 ISO 5379:2013(E) 2.2.7 Check tests The apparatus shall satisfy the following requirements. a) Place in the flask (A) 100 ml of water and proceed as specified in 2.3.3. The contents of the
30、bubblers shall remain neutral. b) Carry out the following operations. 1) Place in the flask (A) 100 ml of water. Introduce, using a pipette, 20 ml of the solution. Carry out the entrainment and the determination of sulfur dioxide as specified in 2.3.3 and 2.3.4. 2) Transfer, using a pipette, 20 ml o
31、f the iodine solution, 5 ml of the hydrochloric acid and 1 ml of the starch solution into a 100 ml conical flask.Titrate, using a burette, with the solution until the first coloration is discharged. The sulfur dioxide (SO 2 ) content can be calculated according to the below chemical equation: SO 2+
32、I 2+ 2 H 2 O SO 4 2+ 4 H + 2 I where I 2 is the chemical formula for iodine; H 2 O is the chemical formula for water; SO 2 is the chemical formula for sulfur dioxide; H + is the chemical symbol for the hydrogen ion; I is the chemical symbol for the iodide ion; SO 4 2 is the chemical symbol for the s
33、ulfate ion. The difference between the sulfur dioxide contents determined in Operations 1) and 2) shall not exceed 1 % of their arithmetic mean. Operation 2) shall not be carried out more than 15 min after completion of Operation 1) in order to avoid a possible change in the amount of sulfur dioxide
34、 contained in the sodium metabisulfite/ Na 2 H 2 EDTA solution. 2.3 Procedure 2.3.1 Preparation of test samples Thoroughly mix the laboratory sample. 2.3.2 Test portion Weigh, to the nearest 10 mg, a mass of the test sample (see 2.3.1) as specified in Table 1. Table 1 Mass of test sampleExpected sul
35、fur dioxide content Approximate mass of test portionmg/kg g 50 100 50 to 200 50 This quantity may be increased, particularly in the case of d-glucose.4 ISO 2013 All rights reserved ISO 5379:2013(E) If the expected content is greater than 200 mg/kg, reduce the test portion accordingly so that it does
36、 not contain more than 10 mg of sulfur dioxide and transfer it quantitatively to the flask (A). In the case of certain derived products, the mass of the test portion can be determined by difference by weighing of the container. Add 100 ml of water to the test portion and mix well by shaking. In the
37、case of a test portion of more than 100 g (for example d-glucose), the quantity of water added should be equal to that of the test portion. 2.3.3 Entrainment 2.3.3.1 Place in the funnel (C) 50 ml of the hydrochloric acid. 2.3.3.2 In each of the bubblers (E and E), place, by means of a pipette, 3 ml
38、of the hydrogen peroxide solution, 0,1 ml of the bromophenol blue indicator solution (see the note to 2.1.6 Tashiro indicator solution) and neutralize the hydrogen peroxide solution with the sodium hydroxide solution. 2.3.3.3 Connect the condenser (B) and the bubblers (E and E) to the apparatus, and
39、 slowly pass a current of nitrogen to expel the air from the whole equipment. Start the flow of water to the condenser. 2.3.3.4 Allow the hydrochloric acid contained in the funnel (C) to flow into the flask (A) (if necessary interrupt the flow of nitrogen for a moment). CAUTION With D on, there is p
40、ositive pressure in the assembly which may expel hydrochloric acid from C causing injury. D should be off when C is on. 2.3.3.5 Bring the mixture to boiling point in 30 min. Boil for 30 min, while passing a current of nitrogen and stirring with the magnetic stirrer. CAUTION This involves boiling an
41、acidic mixture under slightly positive pressure. The entrainment apparatus should be assembled in a fume hood and all joints should be leak-proof. 2.3.4 Titration Add quantitatively the content of the second bubbler to the content of the first bubbler, and titrate the sulfuric acid formed with the s
42、odium hydroxide solution depending on the expected sulfur dioxide content. If the end point is not sharp, owing to the presence of volatile organic acids, boil for 2 min and cool to room temperature before titrating. 2.3.5 Check If the volume V is less than 5 ml when the 10 mmol/l sodium hydroxide s
43、olution is used, or less than 0,5 ml when the 0,1 mol/l sodium hydroxide solution is used, carry out the determination by the nephelometric method (see Clause 3). 2.3.6 Number of determinations Carry out two determinations on the same test sample (2.3.1) ISO 2013 All rights reserved 5 ISO 5379:2013(
44、E) 2.4 Expression of results 2.4.1 Method of calculation and formulae If determination by the nephelometric method is not necessary (see 2.3.5), the sulfur dioxide content, expressed in milligrams per kilogram of sample, is given by the formula: , where m 0 is the mass, in grams, of test portion (2.
45、3.2); V is the volume, in milliliters, of 10 mmol/l sodium hydroxide, standard volumetric solution, or 10 times the volume of 0,l mol/l sodium hydroxide, standard volumetric solution used. Take as the result the arithmetic mean of the values obtained in two determinations (2.3.6), provided that the
46、requirement for repeatability (see 2.4.2) is satisfied. 2.4.2 Repeatability The absolute difference between the results of two determinations carried out simultaneously or in rapid succession by the same analyst on the same test sample shall not exceed 5 % of the mean value of the two determinations
47、. (See ISO 5725-2.) 2.4.3 Reproducibility The difference between the results of two determinations carried out in different laboratories on the same test sample shall not exceed 10 % of the mean value of the two determinations. (See ISO 5725-2.) 3 Nephelometric method If the volume V was less than 5
48、 ml when the 10 mol/l sodium hydroxide solution was used or was less than 0,5 ml when the 0,1 mol/l sodium hydroxide solution was used, determination only by the nephelometric method is valid. For a test portion of 100 g, this limit of 5 ml corresponds to a content of 16 mg of sulfur dioxide per kil
49、ogram. Above this limit, the acidimetric method is satisfactory. 3.1 Reagents All reagents shall be of recognized analytical quality and sulfate-free. The following reagents shall be used. 3.1.1 Water, distilled water or water of equivalent purity, recently boiled. 3.1.2 Sulfuric acid, standard solution. Place in a 1 l one-mark volumetric flask, 31,2 ml of 0,1 mol/l standard volumetric sulfuric acid solution and dilute to the mark with water. 1 ml of thi
