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1、International Standard INTERNATIONAL ORGANIZATION FOR STANDARDIZATlON.MEIKjjYHAPOflHAR OPrAHM3AUMR l-l0 CTAHL1APTM3ALU4MORGANISATION INTERNATIONALE DE NORMALISATION Milk and milk products - Determination of iron content - Spectrometric method (Reference method) Lait et prod 10; and 25 ml. 6.10 Gradu
2、ated pipettes, of capacities 1; 2; and 5 ml, graduated in divisions of 0,l ml, complying with the re- quirements of IS0 835. NOTE - Correct results cannot be expected if adequate mixing of the sample is not achieved or if the sample shows any evidence of churning or any other signs of abnormality. 6
3、.11 One-mark pipettes, delivering 1; 2; 3; 4; 5; 10; and 25 ml, complying with the requirements of IS0 648, class A. 8.1.5 Evaporated milk Shake the container thoroughly with frequent inversion. Open this container and pour the milk slowly into another container made of glass, provided with an airti
4、ght lid, taking care to in- corporate in the sample any fat or other constituents adhering to the wall of the original container. Stir vigorously and close the container. 6.12 Spectrometer, suitable for measuring absorbance at 533 nm, equipped with cells of optical path length 10 mm. 7 Sampling NOTE
5、 - Avoid contamination by iron. Heat the closed container in a water-bath at 40 to 60 OC. Remove and shake the container vigorously every 15 min. After 2 h, remove the container and cool to 20 + 2 OC. Remove the lid and mix thoroughly by stirring the sample with a spoon or spatula. 7.1 See IS0 707.
6、Store glass sampling jars in 10 % (m/m) nitric acid solution. NOTE - If the fat separates, correct results cannot be expected. Rinse them thoroughly and dry before use. 7.2 Store the sample in such a way change in composition are prevented. that deterioration and 8.1.6 Sweetened condensed milk Open
7、the container and thoroughly mix the milk with a spoon or spatula, using an up and down rotary movement in such a way that the top and bottom layers are moved and mixed. Take care to incorporate in the sample any milk adhering to the wall and ends of the container. 8 Procedure NOTE - Avoid contamina
8、tion by iron. Transfer the sample as completely as possible to a second con- tainer made of glass, provided with an airtight lid, and close this container. Heat the closed container in a water-bath at 30 to 40 OC. Cool to 20 + 2 OC. Stir the sample in the container thoroughly. Mix until the whole ma
9、ss is homogeneous. Close the container. 8.1 Preparation of the test sample 8.1.1 Milk, skimmed milk and whey Bring the sample to 20 1; 2; 3; 5; and 10 ml of the iron standard solution (5.14) into a series of six digestion flasks (6.7). Dilute with water to about 10 ml. Add to each flask 3 ml of the
10、nitric acid (5.4) and 1,8 ml of the potassium sulfate solu- tion (5.6). 5 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 21:38:57 MDTNo reproduction or networking permitted with
11、out license from IHS -,-,- IS0 6732-1985 (E) 8.7.2 Carry out the digestion as described in 8.3.1 and the colour development as described in 8.3.2. 8.7.3 Transfer each isoamyl alcohol (upper) layer, by means of a pipette, into a 10 mm cell (6.12). Measure the absorbance of each isoamyl alcohol layer
12、at 533 nm against water as reference. Subtract the value for the zero member from the values obtained for the other solutions. 8.7.4 Plot these absorbances against the amounts of iron contained in the calibration solutions. 8.7.5 Check the calibration graph weekly. 9 Expression of results 9.1 Method
13、 of calculation and formulae 9.1.1 Products other than butter The iron content, expressed in milligrams per kilogram, is equal to - where m. is the mass, in grams, of the test portion; ml is the mass, in micrograms, of iron, read from the calibration graph (or calculated from the regression line ob-
14、 tained by the method of least squares). 9.1.2 Butter Calculate the iron content of the butter serum as described in 9.1.1. The iron content of the butter, expressed in milligrams per kilogram, is equal to where m2 is the mass, in grams, of the butter transferred to the centrifuge tube (see 8.1.8) ;
15、 m3 is the mass, in grams, of butter serum, obtained in 8.1.8; WFe is the iron content, in milligrams per kilogram, of the butter serum, calculated as described in 9.1.1. 9.1.3 Result Take as the result the arithmetic mean of the results obtained, provided that the requirement for repeatability (see
16、 9.2) is satisfied. Express the result to the number of decimal places shown in the table. 9.2 Repeatability The difference between the results of duplicate determinations (results obtained almost simultaneously or in rapid succession by the same analyst) shall not be greater than the repeatability
17、value for the product analysed, as given in the table. Table - Expression of results and repeatability Expression of result to Product Repeatability the nearest w/kg WI/kg Milk 0,001 0,02 Skimmed milk 0,001 0,02 Whey 0,001 0,02 Buttermilk 0,001 0,03 Yogurt 0,001 0,03 Evaporated milk 0,Ol w Sweetened
18、 condensed milk 0,Ol OJ Dried whole milk 0,Ol 02 Dried skimmed milk 0,Ol 02 Dried whey, dried buttermilk 0,Ol 02 Cream 0,001 0,02 Butter 0,001 0,03 Butterfat 0,001 0,005 Ice cream 0,Ol 02 Cheese and processed cheese 0,Ol 02 Caseins, caseinates and coprecipitates w 0,4 10 Test report The test report
19、shall show the method used and the results ob- tained. It shall also mention any operating details not specified in this International Standard, or regarded as optional, together with details of any incidents likely to have influenced the results. The test report shall include all the information th
20、e complete identification of the sample. necessary for 6 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 21:38:57 MDTNo reproduction or networking permitted without license from IHS -,-,-