1、BS ISO 6732:2010ICS 67.100.01NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDMilk and milk products Determinationof iron content Spectrometric method(Reference method)This British Standard was published under the authority of the Standards Policy and Strategy Co
2、mmittee on 31 July2010 BSI 2010ISBN 978 0 580 70103 0Amendments/corrigenda issued since publicationDate CommentsBS ISO 6732:2010National forewordThis British Standard is the UK implementation of ISO 6732:2010. Itsupersedes BS 6394-2:1985 which is withdrawn.The UK participation in its preparation was
3、 entrusted to TechnicalCommittee AW/5, Chemical analysis of milk and milk products.A list of organizations represented on this committee can be obtained onrequest to its secretary.This publication does not purport to include all the necessary provisionsof a contract. Users are responsible for its co
4、rrect application. Compliance with a British Standard cannot confer immunityfrom legal obligations.BS ISO 6732:2010Reference numbersISO 6732:2010(E)IDF 103:2010(E)ISO and IDF 2010INTERNATIONAL STANDARD ISO6732IDF103Second edition2010-06-01Milk and milk products Determination of iron content Spectrom
5、etric method (Reference method) Lait et produits laitiers Dtermination de la teneur en fer Mthode spectromtrique (Mthode de rfrence) BS ISO 6732:2010ISO 6732:2010(E) IDF 103:2010(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may
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11、and ii ISO and IDF 2010 All rights reservedBS ISO 6732:2010ISO 6732:2010(E) IDF 103:2010(E) ISO and IDF 2010 All rights reserved iiiForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing Inte
12、rnational 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-governmental, in liaison wi
13、th 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 main task of technic
14、al 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. Attention is drawn t
15、o 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 6732IDF 103 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products,
16、and the International Dairy Federation (IDF). It is being published jointly by ISO and IDF. This second edition of ISO 6732IDF 103 cancels and replaces the first edition (ISO 6732:1985), of which it constitutes a minor revision. BS ISO 6732:2010ISO 6732:2010(E) IDF 103:2010(E) iv ISO and IDF 2010 Al
17、l rights reservedForeword IDF (the International Dairy Federation) is a non-profit organization representing the dairy sector worldwide. IDF membership comprises National Committees in every member country as well as regional dairy associations having signed a formal agreement on cooperation with ID
18、F. All members of IDF have the right to be represented on the IDF Standing Committees carrying out the technical work. IDF collaborates with ISO in the development of standard methods of analysis and sampling for milk and milk products. The main task of Standing Committees is to prepare Internationa
19、l Standards. Draft International Standards adopted by the Standing Committees are circulated to the National Committees for endorsement prior to publication as an International Standard. Publication as an International Standard requires approval by at least 50% of IDF National Committees casting a v
20、ote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. IDF shall not be held responsible for identifying any or all such patent rights. ISO 6732IDF 103 was prepared by the International Dairy Federation (IDF) and Technical Committee
21、 ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products. It is being published jointly by IDF and ISO. All work was carried out by the former Joint ISO-IDF Action Team on Minor compounds, now part of the Standing Committee on Analytical methods for composition. This edition of ISO 6732I
22、DF 103 cancels and replaces IDF 103A:1986, of which it constitutes a minor revision. BS ISO 6732:2010INTERNATIONAL STANDARD ISO 6732:2010(E)IDF 103:2010(E) ISO and IDF 2010 All rights reserved 1Milk and milk products Determination of iron content Spectrometric method (Reference method) 1 Scope This
23、International Standard specifies a spectrometric reference method for the determination of the iron content of milk and milk products. This method is applicable to milk, skimmed milk, whey and buttermilk; plain yogurt and skimmed yogurt; evaporated milk and sweetened condensed milk; dried whole and
24、skimmed milk, dried whey and dried buttermilk; cream and butter; anhydrous butterfat, butteroil, butterfat and ghee; ice-cream; cheese of various ages, and processed cheese; caseins, caseinates and coprecipitates. 2 Terms and definitions For the purposes of this document, the following terms and def
25、initions apply. 2.1 iron content in milk and milk products mass fraction of substances determined by the procedure specified in this International Standard NOTE The iron content is conventionally expressed in milligrams per kilogram of sample. 3 Principle Organic material is digested with a mixture
26、of nitric and sulfuric acids, preceded, in the case of cream and anhydrous butterfat, butteroil, butterfat and ghee, by removal of the fat. In the case of butter, serum is separated and digested. BS ISO 6732:2010ISO 6732:2010(E) IDF 103:2010(E) 2 ISO and IDF 2010 All rights reservedIron(II) ions, ob
27、tained by reduction of iron(III) ions, are complexed with bathophenanthroline. The iron(II) compound is extracted with isoamyl alcohol. The absorbance of the red solution thus obtained is measured spectrometrically at a wavelength of 533 nm. 4 Reagents and materials IMPORTANT Maintain reagents, glas
28、sware and equipment, as well as the laboratory environment as clean as possible in order to avoid contamination by rust. Each laboratory should check and identify its own sources of contamination. Use only reagents of very pure analytical grade and which, with the exception of the iron standard solu
29、tions (4.14 and 4.15), are free from iron. 4.1 Water, complying with grade 2 as defined in ISO 36965. 4.2 Ethanol (C2H5OH), about 96 % volume fraction. Distil, if necessary, in an iron-free distillation unit. 4.3 Diethyl ether (C2H5OC2H5). Distil, if necessary, in an iron-free distillation unit. 4.4
30、 Light petroleum, boiling range 40 C to 60 C. Distil, if necessary, in an iron-free distillation unit. 4.5 Nitric acid (HNO3), concentrated, 20= 1,42 g/ml. Distil in an iron-free distillation unit. Discard the first 50 ml of distillate. Do not store the nitric acid in a brown glass bottle. 4.6 Sulfu
31、ric acid1)(H2SO4), concentrated, 20= 1,84 g/ml. 4.7 Potassium sulfate1), solution in sulfuric acid. Dissolve 25 g of anhydrous potassium sulfate (K2SO4) in sulfuric acid (4.6) and make up to 100 ml with the same acid. Filter the solution, without suction, through an all-glass, iron-free, filter cruc
32、ible, of porosity grade P 100 (pore diameter 40 m to 100 m). If the potassium sulfate available is not iron-free, purify it as follows. Dissolve 40 g of potassium sulfate in 500 ml of water (4.1) and add 3 ml of the hydroxylammonium chloride solution (4.10). Extract the solution with 10 ml of the ba
33、thophenanthroline solution (4.12). Remove the upper layer. Repeat these two operations until the upper layer remains colourless. Evaporate the water in a clean oven. 4.8 Hydrogen peroxide1)(H2O2), solution, 20= 1,099 g/ml to 1,103 g/ml. Store in a refrigerator. 1) Aristar, Suprapur and Ultrex reagen
34、ts are examples of suitable products available commercially. This information is given for the convenience of users of this International Standard and does not constitute an endorsement by ISO or IDF of these products. BS ISO 6732:2010ISO 6732:2010(E) IDF 103:2010(E) ISO and IDF 2010 All rights rese
35、rved 34.9 Sodium acetate1), saturated solution. Dissolve 232,5 g of anhydrous sodium acetate (CH3COONa) in 500 ml of water (4.1). If the sodium acetate available is not iron-free, purify it as follows. Dissolve 232,5 g of sodium acetate in 500 ml of water. Filter through a filter paper. Add 3 ml of
36、the hydroxylammonium chloride solution (4.10). Extract the solution with 10 ml of the bathophenanthroline solution (4.12). Remove the upper layer. Repeat these two operations until the upper layer remains colourless. 4.10 Hydroxylammonium chloride, solution. Dissolve 20 g of hydroxylammonium chlorid
37、e (HONH3Cl) in water (4.1) and make up to 100 ml. Filter through a filter paper. Extract the solution with 5 ml of the bathophenanthroline solution (4.12). Allow the layers to separate properly. Remove the upper layer. Repeat these two operations until the upper layer remains colourless. NOTE Genera
38、lly, five extractions are sufficient. If the solution was prepared more than 24 h before use, it is advisable to repeat the extraction with the bathophenanthroline. Instead of the hydroxylammonium chloride solution, a freshly prepared solution of ascorbic acid can be used as a reducing agent. The as
39、corbic acid solution can be made by dissolving 10 g of ascorbic acid in 100 ml of water. The solution should be extracted with the bathophenanthroline solution in exactly the same way as described for the hydroxylammonium chloride solution. It should be stored in a refrigerator. Instead of 3 ml of t
40、he hydroxylammonium chloride solution, 3 ml of this ascorbic acid solution can be used in 4.7, 4.9 and 8.2.1.4. 4.11 Isoamyl alcohol (3-methyl-1-butanol). Distil, if necessary, in an iron-free distillation unit. 4.12 Bathophenanthroline, solution. Dissolve 83,1 mg of bathophenanthroline 4,7-diphenyl
41、-1,10-phenanthroline (C24H16N2) in 100 ml of the isoamyl alcohol (4.11). 4.13 Potassium permanganate, solution. Dissolve 100 mg of potassium permanganate (KMnO4) in 50 ml of water (4.1). 4.14 Iron, standard solution corresponding to 1 000 mg of iron per litre. Dissolve 7,022 g of ammonium iron(II) s
42、ulfate hexahydrate (NH4)2Fe(SO4)26H2O in 250 ml of water (4.1). Add 8 ml of sulfuric acid (4.6) and cool to room temperature. Make up to 1 000 ml with water. A volume of 1 ml of this standard solution contains 1 mg of iron. NOTE Commercially available preparations which contain 1 000 mg of iron can
43、be used instead of the ammonium iron(II) sulfate hexahydrate. 4.15 Iron, standard solution corresponding to 1 mg of iron per litre. On the day of use, pipette (5.11) 1 ml of the standard iron solution (4.14) into 250 ml of water (4.1). Add 1 ml of sulfuric acid (4.6) and make up to 1 000 ml with wat
44、er. A volume of 1 ml of this standard solution contains 1 g of iron. BS ISO 6732:2010ISO 6732:2010(E) IDF 103:2010(E) 4 ISO and IDF 2010 All rights reserved5 Apparatus IMPORTANT Maintain glassware and equipment, as well as the laboratory environment as clean as possible in order to avoid contaminati
45、on by rust. Each laboratory should check and identify its own sources of contamination. Store clean glassware, including the glass beads (5.8), in 10 % mass fraction nitric acid solution. Rinse three times before use with distilled water and then three times with double-distilled water. If necessary
46、, dry by successively rinsing with ethanol (4.2) and diethyl ether (4.3). Usual laboratory equipment and in particular the following. 5.1 Analytical balance. 5.2 Centrifuge, capable of producing a radial acceleration of 2 500g, with tubes of capacity at least 150 ml. 5.3 Grinding device, appropriate
47、 to the nature of the sample. 5.4 Sieve, nominal size of openings 500 m, ISO 5651, made of iron-free material. 5.5 Water baths. 5.6 Micro-burners or electric heaters, which do not emit iron-containing particles. 5.7 Digestion flasks (Kjeldahl), capacity approximately 70 ml, with ground-glass stopper
48、s, calibrated on the lower part of the neck at 50 ml. 5.8 Glass beads, preferably made of quartz, which do not release iron during the digestion procedure (see 8.2.1). 5.9 Measuring cylinders, capacities 5 ml, 10 ml and 25 ml, ISO 47886. 5.10 Graduated pipettes, capacities 1 ml, 2 ml and 5 ml, gradu
49、ated in divisions of 0,1 ml, ISO 8354. 5.11 One-mark pipettes, capacities 1 ml, 2 ml, 3 ml, 4 ml, 5 ml, 10 ml and 25 ml, ISO 6482class A. 5.12 Spectrometer, suitable for measuring absorbance at 533 nm, equipped with cells of optical pathlength 10 mm. 6 Sampling IMPORTANT Avoid contamination by iron. Store glass sampling jars in 10 % mass fraction nitric acid solution. Rinse them thoroughly and dry before use. Sampling is not part of the method specified in this International Standa
