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1、INTERNATIONAL STANDARD First edition 1996-06-15 Animal and vegetable fats and oils - Determination of water content - Karl Fischer method Corps gras d origines animale et v6g6 tale - D 9 Procedure V is the volume, in millilitres, of Karl Fischer reagent used; 9.1 Preparation of the reaction vessel A
2、dd solvent (5.1) to the reaction vessel of the Karl Fis- cher apparatus (6.1) until the electrode is immersed. Whilst stirring, add the Karl Fischer reagent (5.2) until the endpoint is reached, as indicated by the instru- ment reading or by a change in colour. Disregard the amount of reagent used. p
3、 is the water equivalent of the Karl Fischer reagent, in grams per millilitre; m is the mass, in grams, of the test portion. Take as the result the arithmetic mean of the two determinations provided that the requirements for re- peatability (II .I) are met. 1) A suitable non-pyridine reagent is “Hyd
4、ranal-composite Z”, containing iodine, sulfur dioxide and an amine dissolved in the solvent. Hydranal-composite 2 is supplied by Riedel-de Haen AG, SeePze/Hannover, 3016 Germany. This information is given for the convenience of users of this International Standard and does not constitute an endorsem
5、ent by IS0 of this product. 2 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 20:41:48 MDTNo reproduction or networking permitted without license from IHS -,-,- 0 IS0 IS0 8534: 1
6、996(E) 11 Precision Details of an inter-laboratory test on the precision of the method are summarized in annex C. The values derived from this interlaboratory test may not be ap- plicable to concentration ranges and matrices other than those given. For the values obtained for repeatability and repro
7、- ducibility, a probability level of 95 % holds. test material in different laboratories with different operators using different equipment, should not be greater than: 30 % of the mean of the two results for water contents not exceeding 0,2 % (m/m); 20 % of the mean of the two results for water con
8、tents exceeding 0,2 % (m/m). 12 Test report 11 .I Repeatability The test report shall specify: The absolute difference between two independent single test results, obtained using 12 % of the mean of the two results for water contents exceeding 0,05 % (m/m). 11.2 Reproducibility The absolute differen
9、ce between two single test re- sults, obtained using the same method on identical - the method in accordance with which sampling was carried out, if known; - the method used; the test result(s) obtained; and - if the repeatability has been checked, the final quoted result obtained. It shall also men
10、tion all operating details not specified in this International Standard, or regarded as optional, together with details of any incidents which may have influenced the test result(s). The test report shall include all information necessary for the complete identification of the sample. 3 Copyright In
11、ternational Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 20:41:48 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 8534: 1996(E) IS0 Annex A (informative) Preparation of
12、Karl Fischer reagent containing pyridine Place 670 ml of methanol, containing not more than 500 mg/kg of water, or 2-methoxyethanol, containing not more than 500 mg/kg of water, in a dry 1 litre brown-glass flask, fitted with a ground glass stopper. As the reaction is exothermic, maintain the flask
13、at about 0 “C, for example by immersing it in an ice bath or in crushed solid carbon dioxide. Add about 85 g of iodine. Stopper the flask and shake it occasionally until the iodine is completely dissolved. Then add approximately 270 ml of pyridine containing not more than 500 mg/kg of water. Stopper
14、 the flask again and mix thoroughly. Using the method de- scribed below, dissolve 65 g of sulfur dioxide in this solution, ensuring that the temperature of the liquid does not exceed 20 “C. Replace the ground glass stopper by an attachment for introducing sulfur dioxide (consisting of a cork bearing
15、 a thermometer and glass inlet tube 6 mm x 8 mm, reaching to within IO mm of the bottom of the flask) and a small capillary tube for connecting to the atmosphere. Place the whole assembly with the cooling bath on a balance and weigh to the nearest 1 g. Connect the inlet attachment to a cylinder of s
16、ulfur dioxide by means of a flexible connection and a drying tube filled with desiccant and gently open the tap on the cylin- der . Adjust the rate of flow of sulfur dioxide so that all the gas is absorbed without the liquid showing any sign of rising up the inlet tube. Ensure that the temperature o
17、f the liquid does not rise above 20 “C. Close the tap on the cylinder as soon as the increase in mass reaches 65 g. Immediately remove the flexible connection and re- weigh the flask and its inlet attachment. The mass of dissolved sulfur dioxide should be between 60 g and 70 g. A slight excess is no
18、t harmful. Stopper the flask, mix the solution and leave for at least 24 h before using it because the water equiva- lent of the reagent decreases rapidly to begin with and then much more slowly. The water equivalent of the reagent thus prepared should be between 3,5 mg/ml and 4,5 mg/ml. It should b
19、e determined daily if methanol has been used in its preparation, but may be determined less fre- quently if 2-methoxyethanol has been used. It is possible to prepare Karl Fischer reagent having a lower water content by diluting the solution prepared as described above with the solvent (5.1). Copyrig
20、ht International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 20:41:48 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 8534:1996(E) . Annex B (informative) Information o
21、n the use of the coulometric method In the coulometric variation of the Karl Fischer deter- mination of water, iodine necessary for the reaction with water is produced by the anodic oxidation of iod- ine. The iodine produced is proportional to the quantity of electricity consumed, the unit of which
22、is the cou- lomb. The commercial instruments which have been devel- oped to make use of this principle are sophisticated, usually being fully automated and computerized. Such an instrument contains two cells, anodic and cathodic, separated by a membrane and containing electrolytes into which platinu
23、m electrodes dip. The reaction takes place in the anodic cell. The rest of the instrument facilitates the reaction, the measurement of the num- ber of coulombs of electricity consumed and its con- version into the water content. The coulometric method is more sensitive than the volumetric method and
24、 permits the determination of lower water contents. It is also sensitive to at- mospheric moisture and chemical side reactions. It cannot be relied on for arbitration or referee pur- poses. Clause 11 is not applicable to results obtained using the coulometric method. 5 Copyright International Organi
25、zation for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 20:41:48 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 8534: 1996(E) IS0 Annex C (informative) Results of interlaboratory test T
26、he precision of the method has been established by an international interlaboratory test carried out in 1983 by AOAC, in accordance with IS0 5725. In this test 15 laboratories participated and samples with different water contents were investigated. The results are shown in table C.I. NOTE 3 These r
27、esults were obtained using a reagent con- taining pyridine. No results for interlaboratory tests using non-pyridine reagents are yet available. Table C.l Sample I II Ill IV Number of laboratories retained after eliminating outliers 12 14 13 15 Mean water content, % (ml m) 0,029 0,114 0,220 3,065 Coe
28、fficient of variation of repeatability, % 24,l 14,0 12,7 IO,4 Repeatability, 2,83 s,- 0,007 0,016 0,028 0,319 Coefficient of variation of reproducibility, % 31,0 28,9 18,1 20,3 Reproducibility, 2,83 sR 0,009 0,033 0,040 0,623 6 Copyright International Organization for Standardization Provided by IHS
29、 under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 20:41:48 MDTNo reproduction or networking permitted without license from IHS -,-,- Annex D (informative) Bibliography IS0 8534: 1996(E) I IS0 5555:1991, Animal and vegetable fats and oils - Sampling. 2
30、IS0 5725:1986, Precision of test methods - Determination of repeatability and reproducibility for a standard test method by inter-laboratory tests (now withdrawn), was used to obtain the precision data. 7 Copyright International Organization for Standardization Provided by IHS under license with ISO
31、 Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 20:41:48 MDTNo reproduction or networking permitted without license from IHS -,-,- This page intentionally left blank Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NA
32、SA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 20:41:48 MDTNo reproduction or networking permitted without license from IHS -,-,- This page intentionally left blank Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical
33、 Standards 1/9972545001 Not for Resale, 04/23/2007 20:41:48 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 8534:1996(E) IS0 ICS 67.200.10 Descriptors: agricultural products, animal products, plant products, food products, fats, oils, animal fats, animal oils, vegetable
34、 fats, vegetable oils, tests, determination of content, water, Karl Fischer method. Price based on 7 pages Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 20:41:48 MDTNo reproduction or networking permitted without license from IHS -,-,-