1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS EN ISO 3656:2011Animal and vegetable fatsand oils Determinationof ultraviolet absorbanceexpressed as specific UVextinction (ISO 3656:2011)BS EN ISO 3656:2011 BRITISH STANDARDN
2、ational forewordThis British Standard is the UK implementation of EN ISO 3656:2011.It supersedes BS EN ISO 3656:2002 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee AW/307, Oil seeds, animal and vegetable fats and oilsand their by products.A list of org
3、anizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. BSI 2011 ISBN 978 0 580 66514 1 ICS 67.200.10 Compliance with a British Standa
4、rd cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 28 February 2011. Amendments issued since publicationDate T e x t a f f e c t e dEUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 3656 Febr
5、uary 2011 ICS 67.200.10 Supersedes EN ISO 3656:2002English Version Animal and vegetable fats and oils - Determination of ultraviolet absorbance expressed as specific UV extinction (ISO 3656:2011) Corps gras dorigines animale et vgtale - Dtermination de labsorbance dans lultraviolet, exprime sous la
6、forme dextinction spcifique en lumire ultraviolette (ISO 3656:2011) Tierische und pflanzliche Fette und le - Bestimmung der Ultraviolett-Absorption, ausgedrckt als spezifische UV-Extinktion (ISO 3656:2011) This European Standard was approved by CEN on 22 January 2011. CEN members are bound to comply
7、 with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC M
8、anagement Centre or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same
9、 status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Por
10、tugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels 2011 CEN All rights of exploitation in any form and by any mean
11、s reserved worldwide for CEN national Members. Ref. No. EN ISO 3656:2011: EBS EN ISO 3656:2011 EN ISO 3656:2011 (E) 3 Foreword This document (EN ISO 3656:2011) has been prepared by Technical Committee ISO/TC 34 “Food products“ in collaboration with Technical Committee CEN/TC 307 “Oilseeds, vegetable
12、 and animal fats and oils and their by-products - Methods of sampling and analysis” the secretariat of which is held by AFNOR. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by August 2011, and conf
13、licting national standards shall be withdrawn at the latest by August 2011. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. This docum
14、ent supersedes EN ISO 3656:2002. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany,
15、Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. Endorsement notice The text of ISO 3656:2011 has been approved by CEN as a EN ISO 3656:2011 without a
16、ny modification. BS EN ISO 3656:2011ISO 3656:2011(E) ISO 2011 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 International Standards is normally carried out thr
17、ough 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, also take part in the work. ISO collabo
18、rates 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 technical committees is to prepare International Stand
19、ards. 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 to the possibility that some of the elements of
20、this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 3656 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 11, Animal and vegetable fats and oils. This fourth edition cancels and replaces
21、the third edition (ISO 3656:2002), which has been technically revised. BS EN ISO 3656:2011ISO 3656:2011(E) iv ISO 2011 All rights reservedIntroduction This International Standard describes a method for the determination of the absorbance of light in the ultraviolet (UV) spectrum by fats and oils. Ch
22、anges in absorption in the UV region are used as quality, purity, and authenticity criteria for fats and oils. Refining causes the formation of conjugated dienes and trienes and increased values of K232and K268, which then indicate the presence of refined oils. The oxidation of linoleic and linoleni
23、c acids results in the formation of hydroperoxides in which the double bonds become conjugated. Furthermore, the formation of either carbon-carbon bonds or carbon-oxygen bonds (,-unsaturated carbonyl compounds) as secondary autoxidation products are observed. These compounds all lead to an increase
24、of the absorption in the region between 225 nm and 325 nm. The third edition of this International Standard allowed the determination of the UV absorbance at 232 nm and 268 nm using three different solvents (isooctane, cyclohexane or n-hexane). However, it is known that the solvents themselves have
25、an effect on the UV absorbance between 260 nm and 276 nm in vegetable oils. Recent investigations have shown that the measurement of K268and K270for the same oil in isooctane or in cyclohexane give significantly different results. In isooctane, the maxima appear at 267 nm to 268 nm whereas in cycloh
26、exane, the maxima appear at 268 nm to 269 nm. In the IOC standards for the determination of the ultraviolet absorbance of (virgin) olive oils, the specified wavelengths are 232 nm and 270 nm. Taking into account the above, the fourth edition of this International Standard specifies measurement at 26
27、8 nm when isooctane is used and measurement at 270 nm when cyclohexane is used. Moreover, the variation of the specific extinction, , for olive oils has been introduced. Precision data from a new collaborative trial have also been taken into consideration for this revision. BS EN ISO 3656:2011INTERN
28、ATIONAL STANDARD ISO 3656:2011(E) ISO 2011 All rights reserved 1Animal and vegetable fats and oils Determination of ultraviolet absorbance expressed as specific UV extinction 1 Scope This International Standard specifies a method for the determination of the absorbance at ultraviolet wavelengths of
29、animal and vegetable fats and oils. 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)
30、 applies. ISO 661, Animal and vegetable fats and oils Preparation of test sample 3 Terms and definitions NOTE The usual policy of ISO/TC 34/SC 11 of using symbols specified in International Standard 800005is not followed in this International Standard. The symbols are those used, for example, in Com
31、mission Regulation (EEC) No 2568/916. For the purposes of this document, the following terms and definitions apply. 3.1 specific extinction (K232 K268 K270) absorbance of 1 g sample, dissolved in 100 ml isooctane or cyclohexane, measured in a 10 mm cell at the specific wavelengths 232 nm, 268 nm, an
32、d 270 nm 4 Principle A sample is dissolved in isooctane or cyclohexane and the absorbance is measured spectrophotometrically in a specified ultraviolet wavelength range. The specific absorbance at 232 nm and 268 nm in isooctane or 232 nm and 270 nm in cyclohexane for a concentration of 1 g per 100 m
33、l in a 10 mm cell is calculated. 5 Reagents WARNING Attention is drawn to the regulations which specify the handling of hazardous substances. Technical, organizational and personal safety measures shall be followed. During the analysis, unless otherwise stated, use only reagents of recognized analyt
34、ical grade and distilled or demineralized water or water of equivalent purity. 5.1 Solvent: isooctane (2,2,4-trimethylpentane) for the measurement at 232 nm and 268 nm or cyclohexane for the measurement at 232 nm and 270 nm, having an absorbance less than 0,12 at 232 nm and less than 0,05 at 250 nm
35、against water, measured in a 10 mm cell. BS EN ISO 3656:2011ISO 3656:2011(E) 2 ISO 2011 All rights reserved6 Apparatus The glassware used for the determination shall be thoroughly cleaned and rinsed with the solvent (5.1) before use so that it is free from impurities having an absorbance within the
36、wavelength range of 220 nm to 360 nm. Usual laboratory apparatus and, in particular, the following. 6.1 One-mark volumetric flasks, capacity 25 ml, ISO 10421class A. 6.2 Analytical balance, capable of being read to the nearest 0,000 1 g. 6.3 Spectrometer, with quartz cells of pathlength 10 mm, suita
37、ble for measurements at ultraviolet wavelengths (220 nm to 360 nm). 6.3.1 General. Before use it is recommended that the wavelength and absorbance scales of the spectrometer be checked as specified in 6.3.2 and 6.3.3. 6.3.2 Wavelength scale. Check this using a reference material consisting of an opt
38、ical glass filter containing holmium oxide which has distinct absorption bands. The reference material is designed for the verification and calibration of the wavelength scales of visible and ultraviolet spectrophotometers having nominal spectral bandwidths of 5 nm or less. The holmium glass filter
39、is measured in the absorbance mode against an air blank, over the wavelength range 640 nm to 240 nm. For each spectral bandwidth (0,10, 0,25, 0,50, 1,00, 1,50, 2,00, and 3,00), a baseline correction is performed with an empty cell holder. The wavelengths of the spectral bandwidth are listed in the c
40、ertificate of the reference material1). 6.3.3 Absorbance scale. This may be checked using a reference material consisting of four solutions of potassium dichromate in perchloric acid sealed in far UV quartz cells to measure the linearity and photometric accuracy reference in the UV. The potassium di
41、chromate filled cells (40 mg/ml, 60 mg/ml, 80 mg/ml and 100 mg/ml) are measured against a perchloric acid blank (see Reference 7). The net absorbance values are listed in the certificate of the reference material1). 7 Sampling Sampling is not part of the method specified in this International Standa
42、rd. A recommended sampling method is given in ISO 55552. It is important the laboratory receive a truly representative sample which has not been damaged or changed during transport or storage. 8 Preparation of test sample Prepare the test sample in accordance with ISO 661. Ensure that the test sampl
43、e is perfectly homogeneous and contains no suspended impurities. Filter oils which are liquid at ambient temperature through paper at a temperature of approximately 30 C. Homogenize and filter hard fats at a temperature of not more than 10 C above their melting point. 1) Suitable holmium filters and
44、 potassium dichromate-sealed cells are available commercially, e.g. from Starna Scientific (). This information is given for the convenience of users of this document and does not constitute an endorsement by ISO of this supplier. BS EN ISO 3656:2011ISO 3656:2011(E) ISO 2011 All rights reserved 39 P
45、rocedure 9.1 Test portion and preparation of the test solution 9.1.1 Weigh, to the nearest 0,1 mg (6.2), an amount of the test sample, generally 0,05 g to 0,25 g, necessary to obtain absorbance values between 0,2 and 0,8, into a 25 ml volumetric flask (6.1). 9.1.2 K232/K268. Dissolve the test portio
46、n at ambient temperature in a few millilitres of isooctane (5.1) for the determination of the specific absorbance at 232 nm and 268 nm and then make up to the mark with the same solvent. Mix thoroughly. 9.1.3 K232/K270. Dissolve the test portion at ambient temperature in a few millilitres of cyclohe
47、xane (5.1) for the measurement of the specific absorbance at 232 nm and 270 nm and then make up to the mark with the same solvent. Mix thoroughly. 9.1.4 Ensure that the solutions prepared in 9.1.2 and 9.1.3 are perfectly clear. If opalescence or turbidity is present, filter quickly through paper. If
48、 the concentration of test sample in the test solution is greater than 1 g per 100 ml of solution, this shall be stated in the test report. 9.2 Determination Rinse a quartz cell (6.3) three times with the test solution (9.1). Fill the cell with the test solution and measure the absorbance against th
49、e solvent used for dilution, by means of the spectrometer (6.3), over the wavelength range 220 nm to 360 nm, either continuously or at intervals of 1 nm or 2 nm, reducing the intervals to 0,5 nm in the regions of maximum and minimum absorbance. NOTE It is possible that it is not necessary to measure the absorbance over the full wavelength range. If the absorbance value obtained exceeds 0,8, dilute the test solution as appropriate and repeat the determination. 10 Expression of results 10.1 Specific ext
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