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1、 Reference numbers ISO 14673-1:2004(E) IDF 189-1:2004(E) ISO and IDF 2004 INTERNATIONAL STANDARD ISO 14673-1 IDF 189-1 Second edition 2004-02-01 Milk and milk products Determination of nitrate and nitrite contents Part 1: Method using cadmium reduction and spectrometry Lait et produits laitiers Dter
2、mination des teneurs en nitrates et en nitrites Partie 1: Mthode par rduction au cadmium et spectromtrie -,-,- ISO 14673-1:2004(E) IDF 189-1:2004(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall n
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5、table for use by ISO member bodies and IDF national committees. In the unlikely event that a problem relating to it is found, please inform the ISO Central Secretariat at the address given below. ISO and IDF 2004 All rights reserved. Unless otherwise specified, no part of this publication may be rep
6、roduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO or IDF at the respective address below. ISO copyright office International Dairy Federation Case postale 56 CH-1211 Geneva 20 Diamant Buildin
7、g Boulevard Auguste Reyers 80 B-1030 Brussels Tel. + 41 22 749 01 11 Tel. + 32 2 733 98 88 Fax + 41 22 749 09 47 Fax + 32 2 733 04 13 E-mail copyrightiso.org E-mail infofil-idf.org Web www.iso.org Web www.fil-idf.org Published in Switzerland ii ISO and IDF 2004 All rights reserved ISO 14673-1:2004(E
8、) IDF 189-1:2004(E) ISO and IDF 2004 All rights reserved iii Contents Page Forewordiv 1 Scope1 2 Normative references .1 3 Terms and definitions.2 4 Principle.2 5 Reagents2 6 Apparatus.4 7 Sampling5 8 Preparation of test sample.5 8.1 Dried milk and dried whey5 8.2 Caseins and caseinates5 8.3 Cheese6
9、 8.4 Whey cheese .6 9 Procedure.6 9.1 Preparation of the copperized cadmium column 6 9.2 Checking the reducing capacity of the column.6 9.3 Regeneration of the column.7 9.4 Preparation of test portion.7 9.5 Extraction and deproteination.8 9.6 Reduction of nitrate to nitrite.8 9.7 Blank test.9 9.8 De
10、termination9 9.9 Preparation of calibration graph .9 10 Calculation and expression of results9 10.1 Nitrite content9 10.2 Nitrate content.10 11 Precision10 11.1 General.10 11.2 Repeatability10 12 Test report11 Bibliography .13 ISO 14673-1:2004(E) IDF 189-1:2004(E) iv ISO and IDF 2004 All rights rese
11、rved Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for whic
12、h 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, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all ma
13、tters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circ
14、ulated 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 to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held respons
15、ible for identifying any or all such patent rights. ISO 14673-1IDF 189-1 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, and the International Dairy Federation (IDF), in collaboration with AOAC International. It is being published jointly by I
16、SO and IDF and separately by AOAC International. This second edition cancels and replaces the first edition (ISO 14673-1IDF 189-1:2001), of which it constitutes a minor revision. ISO 14673IDF 189 consists of the following parts, under the general title Milk and milk products Determination of nitrate
17、 and nitrite contents: Part 1: Method using cadmium reduction and spectrometry Part 2: Method using segmented flow analysis (Routine method) Part 3: Method using cadmium reduction and flow injection analysis with in-line dialysis (Routine method) ISO 14673-1:2004(E) IDF 189-1:2004(E) ISO and IDF 200
18、4 All rights reserved v Foreword IDF (the International Dairy Federation) is a worldwide federation of the dairy sector with a National Committee in every member country. Every National Committee has the right to be represented on the IDF Standing Committees carrying out the technical work. IDF coll
19、aborates with ISO and AOAC International in the development of standard methods of analysis and sampling for milk and milk products. Draft International Standards adopted by the Action Teams and Standing Committees are circulated to the National Committees for voting. Publication as an International
20、 Standard requires approval by at least 50 % of the National Committees casting a vote. ISO 14673-1IDF 189-1 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, and the International Dairy Federation (IDF), in collaboration with AOAC International
21、. It is being published jointly by ISO and IDF and separately by AOAC International. All work was carried out by the Joint ISO/IDF/AOAC Action Team Minerals and minor compounds, of the Standing Committee on Minor components characterization of physical properties, under the aegis of its project lead
22、er, Mr G. Brthen (NO). This second edition, together with ISO 14673-2IDF 189-2 and ISO 14673-3IDF 189-3, cancels and replaces IDF 84A:1984, IDF 95A:1982, IDF 96A:1987, IDF 97A:1985 and IDF 120:1984, which have been technically revised. -,-,- -,-,- INTERNATIONAL STANDARD ISO 14673-1:2004(E) IDF 189-1
23、:2004(E) ISO and IDF 2004 All rights reserved 1 Milk and milk products Determination of nitrate and nitrite contents Part 1: Method using cadmium reduction and spectrometry WARNING The use of this International Standard may involve hazardous materials, operations and equipment. This standard does no
24、t purport to address all the safety problems associated with its use. It is the responsibility of the user of this standard to establish safety and health practices and determine the applicability of regulatory limitations prior to use. 1 Scope This part of ISO 14673IDF 189 specifies a method for th
25、e determination of the nitrate and nitrite contents of milk and milk products by cadmium reduction and spectrometry. The method is applicable to whole and partly skimmed and skimmed dried milk; hard, semi-hard and soft cheeses; processed cheese; whey cheese, caseins and caseinates, and dried whey. T
26、he method may be performed using automatic equipment, in particular by segmented flow analysis (SFA) or flow injection analysis (FIA), thus reducing cadmium contamination in laboratory work places and waste water. NOTE These methods are described in ISO 14673-2IDF 189-2 and ISO 14673-3IDF 189-3, res
27、pectively. 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 of the referenced document (including any amendments) applies. ISO 565, Test s
28、ieves Metal wire cloth, perforated metal plate and electroformed sheet Nominal sizes of openings ISO 648, Laboratory glassware One-mark pipettes ISO 835-1, Laboratory glassware Graduated pipettes Part 1: General requirements ISO 1042, Laboratory glassware One-mark volumetric flasks ISO 14673-1:2004(
29、E) IDF 189-1:2004(E) 2 ISO and IDF 2004 All rights reserved 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 nitrate content mass fraction of nitrate determined by the procedure specified in this part of ISO 14673IDF 189 NOTE The nitrate conte
30、nt is expressed as the mass in milligrams of nitrate ions (NO3) per kilogram of product. 3.2 nitrite content mass fraction of nitrite determined by the procedure specified in this part of ISO 14673IDF 189 NOTE The nitrite content is expressed as the mass in milligrams of nitrite ions (NO2) per kilog
31、ram of product. 4 Principle A test portion is dispersed in warm water, with precipitation of the fat and proteins, then filtration. The nitrate ions are reduced to nitrite ions in a portion of the filtrate by means of copperized cadmium. A red colour is developed in portions of both unreduced filtra
32、te and the reduced solution, by addition of sulfanilamide and N-1-naphthyl ethylenediamine dihydrochloride. Spectrometric measurements are carried out at a wavelength of 538 nm. The nitrite content of the sample and the total nitrite content after reduction of nitrate ions are calculated by comparin
33、g the measured absorbances with those of a set of sodium nitrite calibration solutions. The nitrate content is calculated from the difference between these two contents. 5 Reagents Use only reagents of recognized analytical grade unless otherwise specified. 5.1 Water, distilled or deionized, or wate
34、r of equivalent purity, free from nitrate and nitrite ions. To avoid the possible inclusion of small gas bubbles in the copperized cadmium column (9.1.6), freshly boil the distilled or deionized water and cool to room temperature. Use the thus-prepared water for the preparation of the column (9.1),
35、to check the reducing capacity of the column (9.2), and to regenerate the column (9.3). 5.2 Cadmium granules, of diameter 0,3 mm to 0,8 mm. Prepare cadmium granules, if not available commercially, as follows. Place a suitable number of zinc rods in a beaker. Cover the rods with cadmium sulfate solut
36、ion (5.3). Scrape the cadmium sponge from the rods from time to time over a period of 24 h. Remove the zinc rods and decant the liquid until only sufficient remains to cover the cadmium sponge. Wash the sponge two or three times with water. Transfer the cadmium sponge to a laboratory blender togethe
37、r with 400 ml of the hydrochloric acid working solution (5.7) and blend for a few seconds to obtain granules of the required size. Return the contents of the blender to the beaker and leave to stand for several hours, while stirring occasionally to remove bubbles. Decant most of the liquid and immed
38、iately copperize the granules as described in 9.1. WARNING Because of its toxicity, the used cadmium should be delivered as chemical waste to the relevant authorities. -,-,- ISO 14673-1:2004(E) IDF 189-1:2004(E) ISO and IDF 2004 All rights reserved 3 5.3 Cadmium sulfate solution, c(CdSO48H2O) = 40 g
39、/l. Dissolve 40 g of cadmium sulfate solution in water in a 1 000 ml volumetric flask (6.4). Dilute to the mark with water and mix. 5.4 Copper(II) sulfate solution, c(CuSO45H2O) = 20 g/l. Dissolve 20 g of copper(II) sulfate in water in a 1 000 ml volumetric flask (6.4). Dilute to the mark with water
40、 and mix. 5.5 Hydrochloric acid (HCl), (20 = 1,19 g/ml). 5.6 Dilute hydrochloric acid, c(HCl) 2 mol/l. Carefully add 160 ml of hydrochloric acid (5.5) to about 700 ml of water in a 1 000 ml volumetric flask (6.4) while regularly swirling the contents. Cool the contents to room temperature. Dilute to
41、 the mark with water and mix carefully. 5.7 Hydrochloric acid working solution, c(HCl) 0,1 mol/l. Add 50 ml of dilute hydrochloric acid (5.6) to a 1 000 ml volumetric flask (6.4). Dilute to the mark with water and mix. 5.8 Zinc sulfate solution, c(ZnSO47H2O) = 535 g/l. Dissolve 53,5 g of zinc sulfat
42、e in water in a 100 ml volumetric flask (6.4). Dilute to the mark with water and mix. 5.9 Potassium hexacyanoferrate(II) solution, c(K4Fe(CN)63H2O) = 172 g/l. Dissolve 17,2 g of potassium hexacyanoferrate(II) trihydrate in water in a 100 ml volumetric flask (6.4). Dilute to the mark with water and m
43、ix. 5.10 Disodium ethylenediaminetetraacetate dihydrate (EDTA) solution (Na2C10H14N2O82H2O). Dissolve 33,5 g of EDTA in about 900 ml water in a 1 000 ml volumetric flask (6.4). Dilute to the mark with water and mix. 5.11 Solution I. Carefully add 450 ml of hydrochloric acid (5.5) to a 1 000 ml volum
44、etric flask (6.4). Dilute to the mark with water and mix. 5.12 Solution II. Dissolve by heating on a water bath (6.15) 0,5 g of sulfanilamide (NH2C6H4SO2NH2) in a mixture of 75 ml of water and 5 ml of hydrochloric acid (5.5) in a 100 ml volumetric flask (6.4). Cool to room temperature. Dilute to the
45、 mark with water and mix. Filter the obtained solution, if necessary. 5.13 Solution III. Dissolve 0,1 g of N-1-naphthyl ethylenediamine dihydrochloride (C10H7NHCH2CH2NH22HCl) in water in a 100 ml volumetric flask (6.4). Dilute to the mark with water and mix. Filter the obtained solution, if necessar
46、y. The solution may be stored for up to 1 week in a well-stoppered brown bottle in a refrigerator. 5.14 Sodium nitrite stock solution (NaNO2). Dry a few grams of sodium nitrite in an oven (6.16) at 110 C to 120 C to constant mass (i.e. until the difference between two successive weighings does not e
47、xceed 1 mg). Dissolve 0,150 g of the sodium nitrite in water in a 1 000 ml volumetric flask (6.4). Dilute to the mark with water and mix. -,-,- ISO 14673-1:2004(E) IDF 189-1:2004(E) 4 ISO and IDF 2004 All rights reserved 5.15 Sodium nitrite working solution. Prepare the sodium nitrite working soluti
48、on on the day of use. Transfer with a pipette (6.5), 10 ml of the stock solution (5.14) and 20 ml of the buffer solution (5.19) to a 1 000 ml volumetric flask (6.4). Dilute to the mark with water and mix. The nitrite content of the sodium nitrite working solution is 1 g/ml. 5.16 Potassium nitrate stock solution (KNO3). Dry a few grams of potassium nitrate in an oven (6.16) at 110 C to 120 C to constant mass (i.e. until the difference between two successive weighings does not exceed 1 mg). Dissolve 1,468 g of the potassium nitrate in water in a 1 0