1、BRITISH STANDARDBS EN ISO 14637:2006Incorporating amendment no. 1 (renumbers BS ISO 14637:2004 as BS EN ISO 14637:2006)Milk Determination of urea content Enzymatic method using difference in pH (Reference method)The European Standard EN ISO 14637:2006 has the status of a British StandardICS 67.100.1
2、0g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS EN ISO 14637:2006This British Standard was published under the authority of the Standards Policy
3、 and Strategy Committee on 31 October 2004 BSI 2007ISBN 0 580 44646 8National forewordThis British Standard was published by BSI. It is the UK implementation of EN ISO 14637:2006. It is identical with ISO 14637:2004.The UK participation in its preparation was entrusted to Technical Committee AW/5, M
4、ilk and milk products.A list of organizations represented on AW/5 can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer i
5、mmunity from legal obligations.Amendments issued since publicationAmd. No. Date Comments16903 28 February 2007 Renumbers BS ISO 14637:2004 as BS EN ISO 14637:2006.EUROPEAN STANDARDNORME EUROPENNEEUROPISCHE NORMEN ISO 14637December 2006ICS 67.100.10English VersionMilk - Determination of urea content
6、- Enzymatic method usingdifference in pH (Reference method) (ISO 14637:2004)Lait - Dtermination de la teneur en ure - Mthodeenzymatique par mesurage de pH diffrentiel (Mthode derfrence) (ISO 14637:2004)Milch - Bestimmung des Harnstoffgehaltes -Enzymatisches Verfahren mit pH-nderung(Referenzverfahren
7、) (ISO 14637:2004)This European Standard was approved by CEN on 13 November 2006.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bi
8、bliographical references concerning such nationalstandards may be obtained on application to the Central Secretariat or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of
9、 a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latv
10、ia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUROPEN DE NORMALISATIONEUROPISCHES KOMITEE FR NORMUNGManagement Centre: rue de Stassart, 36 B-1050 Brussels
11、2006 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN ISO 14637:2006: EForeword The text of ISO 14637:2004 has been prepared by Technical Committee ISO/TC 34 “Agricultural food products” of the International Organization for Standardi
12、zation (ISO) and has been taken over as EN ISO 14637:2006 by Technical Committee CEN/TC 302 “Milk and milk products - Methods of sampling and analysis“, the secretariat of which is held by NEN. This European Standard shall be given the status of a national standard, either by publication of an ident
13、ical text or by endorsement, at the latest by June 2007, and conflicting national standards shall be withdrawn at the latest by June 2007. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard:
14、 Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. Endorsement notice
15、 The text of ISO 14637:2004 has been approved by CEN as EN ISO 14637:2006 without any modifications. EN ISO 14637:2006Reference numbersISO 14637:2004(E)IDF 195:2004(E)OSI DI dnaF 4002INTERNATIONAL STANDARD ISO14637IDF195First edition2004-10-15Milk Determination of urea content Enzymatic method using
16、 difference in pH (Reference method) Lait Dtermination de la teneur en ure Mthode enzymatique utilisant les fluctuations du pH (Mthode de rfrence) EN ISO 14637:2006IS:73641 O4002(E) ID:591 F4002(E) DPlcsid Fremia ihTs PDF file may ctnoian emdebt dedyfepcaes. In ccaocnadrw eith Aebods licensilop gnic
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22、aID 4002 FA ll rihgtsser edevrIS:73641 O4002(E) ID:591 F002(4)E I SO dna ID 4002 F All irhgts seredevr iiiContents Page Foreword iv 1 Scope 1 2 Terms and definitions. 1 3 Principle . 1 4 Reagents 1 5 Apparatus. 2 6 Sampling 3 7 Preparation of test sample. 3 8 Procedure. 3 8.1 General. 3 8.2 Blank de
23、termination 3 8.3 Calibration 4 8.4 Checking the calibration 5 8.5 Determination 5 8.6 Checking the stability. 5 8.7 Checking the contamination of the electrodes 5 8.8 Cleaning procedure 5 9 Maintenance of the electrodes 5 9.1 Regeneration . 5 9.2 Strong regeneration 6 10 Calculation and expression
24、of results 6 10.1 Calculation. 6 10.2 Expression of results 6 11 Precision 6 11.1 Interlaboratory tests . 6 11.2 Repeatability 6 11.3 Reproducibility 7 12 Test report 7 Annex A (informative) Differential pH apparatus. 8 Annex B (informative) Interlaboratory tests. 9 Bibliography . 11 EN ISO 14637:20
25、06IS:73641 O4002(E) ID:591 F002(4)E iv I SO dna ID 4002 F All irhgts seredevrForeword 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
26、 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 collaborates cl
27、osely 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 Standards, Dr
28、aft International Standards adopted by the technical committee 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 this docu
29、ment may be the subject of patent rights, ISO shall not be held responsible for identifying any or all such patent rights, International Standard ISO 14637|IDF 195 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products, and the International Dairy Fed
30、eration (IDF), in collaboration with AOAC International. It is being published jointly by ISO and IDF and separately by AOAC International. EN ISO 14637:2006IS:73641 O4002(E) ID:591 F002(4)E I SO dna ID 4002 F All irhgts seredevr vForeword IDF (the International Dairy Federation) is a worldwide fede
31、ration 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 collaborates with ISO and AOAC International in the development of standard methods of analysis a
32、nd 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 Standard requires approval by at least 50% of IDF National Committees casting a vote, Intern
33、ational Standard ISO 14637|IDF 195 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 ISO and IDF and separately by AOAC Inte
34、rnational. All work was carried out by the Joint ISO/IDF/AOAC Action Team, Nitrogen compounds, of the Standing Committee on Main components of milk, under the aegis of its project leader, Mr Ph. Trossat (FR). EN ISO 14637:2006blank4002:73641 OSI SBNITERNATNOIAL STANDARD IS:73641 O4002(E)ID:591 F002(
35、4)EI SO dna ID 4002 F All irhgts seredevr 1Milk Determination of urea content Enzymatic method using difference in pH (Reference method) 1 Scope This International Standard specifies an enzymatic method for the determination of the urea content of milk by measurement of the difference in pH. 2 Terms
36、 and definitions For the purpose of this document, the following terms and definitions apply. 2.1 urea content mass fraction of substances determined by the procedure specified in this International Standard NOTE The urea content is expressed in milligrams per litre. 3 Principle Urease is added to t
37、he test sample to split urea into ammonia and carbon dioxide. At pH 6,7, ammonia immediately hydrolyses thereby releasing hydroxyl ions, and carbon dioxide liberates protons that partly neutralize these hydroxyl ions. The balance between the ammonia and carbon dioxide hydrolysis and the resulting ne
38、utralization induces a change in pH. The pH change varies as a function of the urea content of the sample and is measured by using a differential pH analyser. 4 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or demineralized water or water of equ
39、ivalent purity. 4.1 Reagents for urea determination. 4.1.1 Buffer solution, pH 6,7. Dissolve 1,777 g of potassium monohydrogenphosphate (K2HPO4), 1,388 g of potassium dihydrogen-phosphate (KH2PO4), 7,600 g of potassium chloride (KCl), 1,00 g of sodium azide (NaN3), 0,010 g of acetazolamide (5-acetam
40、ido-1,3,4-thiadiazole-2-sulfonamide), 1,040 g of magnesium chloride hexahydrate (MgCl26H2O), 2 g of Triton X100, 1 g of Brij 35 and 20 ml of LM11)in a 1 000 ml volumetric flask (5.5). Dilute to the mark with water and mix. 1) This detergent is available from Valetudo S.r.l., BG, Italy, and is an exa
41、mple of a suitable product 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 this product. EN ISO 14637:2006IS:73641 O4002(E) ID:591 F002(4)E 2 I SO dna ID 4002 F All irhgts seredevrTh
42、e buffer solution may be kept for 6 months if stored at 4 C. 4.1.2 Urease enzyme solution. Dissolve 360 mg of lyophilized urease (EC 3.5.1.5) in 1 ml of a 50 % (volume fraction) aqueous solution of glycerol. The activity of the obtained urease enzyme solution shall be 2 100 units/ml 300 units/ml2).
43、The urease enzyme solution may be kept for 6 months if stored at 4 C. 4.1.3 Urea standard solution. Dissolve 1,000 g of dry urea (N2H4CO) (dried under vacuum in an oven at 90 C 1 C for 1 day), 7,45 g of potassium chloride (KCl) and 1,0 g of sodium azide (NaN3) in a 1 000 ml volumetric flask (5.5). D
44、ilute to the mark with water and mix. The urea standard solution may be kept for 6 months if stored at 4 C. 4.1.4 Zero milk. Add 20 l of urease solution (4.1.2) to 1 ml of raw milk. Mix and incubate the thus-prepared raw milk for 10 min in the water bath (5.3) set at 40 C. 4.2 Reagents for cleaning
45、and maintenance of electrodes. 4.2.1 Cleaning solution. Dissolve 1,742 g of potassium monohydrogenphosphate (K2HPO4), 1,361 g of potassium dihydrogen-phosphate (KH2PO4), 7,455 g of potassium chloride (KCl), 1,00 g of sodium azide (NaN3), 2 g of Triton X100, 2 g of Brij 35 and 3 g of LM11)in a 1 000
46、ml volumetric flask (5.5). Dilute to the mark with water and mix. The cleaning solution may be kept for 1 year if stored at room temperature. 4.2.2 Regenerating solution. Use hydrochloric acid of concentration, c(HCl) = 0,1 mol/l. The regenerating solution may be kept for 1 year if stored at room te
47、mperature. 4.2.3 Strong regenerating solution. Dissolve 30 g of nitric acid (HNO3) with a mass fraction of approximately 69 %, 30 g of hydrochloric acid (HCl) with a mass fraction of approximately 37 %, 30 g of sodium fluoride (NaF) and 1 g of Triton X100 in a 1 000 ml volumetric flask (5.5). Dilute
48、 to the mark with water and mix. The strong regenerating solution may be kept for 1 year if stored at room temperature. 5 Apparatus Usual laboratory equipment and, in particular, the following. 5.1 Analytical balance, capable of weighing to the nearest 1 mg. 2) This unit (often called the Internatio
49、nal Unit or Standard Unit) is defined as the amount of enzyme which will catalyse the transformation of one micromole of substrate per minute under standard conditions. EN ISO 14637:2006IS:73641 O4002(E) ID:591 F002(4)E I SO dna ID 4002 F All irhgts seredevr 35.2 Micropipettes (positive displacement), of capacities 15 l and 20 l. 5.3 Water bath, capable of being maintained at 38 C 1 C and at 40 C 1 C. 5.4 Differential pH apparatus, generally operating according to the scheme shown in Annex A. The arrangement
