1、BRITISH STANDARD BS EN ISO 8968-3:2007 Incorporating amendment no. 1 (renumbers BS ISO 8968-3:2004 as BS EN ISO 8968-3:2007) Milk Determination of nitrogen content Part 3: Block-digestion method (Semi-micro rapid routine method) The European Standard EN ISO 8968-3:2007 has the status of a British St
2、andard ICS 67.100.10 BS EN ISO 8968-3:2007 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 9 September 2004 BSI 2007 ISBN 978 0 580 60071 5 National foreword This British Standard is the UK implementation of EN ISO 8968-3:2007. It is identica
3、l with ISO 8968-3:2004. The UK participation in its preparation was entrusted to Technical Committee AW/5, Milk and milk products. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisi
4、ons of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations. Amendments issued since publication Amd. No. Date Comments 17262 31 August 2007 Renumbers BS ISO 8968-3:2004 as BS EN ISO 8968-3:2007EUROPEANSTANDAR
5、D NORMEEUROPENNE EUROPISCHENORM ENISO89683 June2007 ICS67.100.10 EnglishVersion MilkDeterminationofnitrogencontentPart3:Blockdigestion method(Semimicrorapidroutinemethod)(ISO89683:2004) LaitDterminationdelateneurenazotePartie3: Mthodedeminralisationenbloc(Mthodederoutine semimicrorapide)(ISO89683:20
6、04) MilchBestimmungdesStickstoffgehaltesTeil3: BlockaufschlussVerfahren(HalbmikroSchnellverfahren) (ISO89683:2004) ThisEuropeanStandardwasapprovedbyCENon19May2007. CENmembersareboundtocomplywiththeCEN/CENELECInternalRegulationswhichstipulatetheconditionsforgivingthisEurope an Standardthestatusofanat
7、ionalstandardwithoutanyalteration.Uptodatelistsandbibliographicalreferencesconcernings uchnational standardsmaybeobtainedonapplicationtotheCENManagementCentreortoanyCENmember. ThisEuropeanStandardexistsinthreeofficialversions(English,French,German).Aversioninanyotherlanguagemadebytra nslation undert
8、heresponsibilityofaCENmemberintoitsownlanguageandnotifiedtotheCENManagementCentrehasthesamestatusas the officialversions. CENmembersarethenationalstandardsbodiesofAustria,Belgium,Bulgaria,Cyprus,CzechRepublic,Denmark,Estonia,Finland, France,Germany,Greece,Hungary,Iceland,Ireland,Italy,Latvia,Lithuan
9、ia,Luxembourg,Malta,Netherlands,Norway,Poland,P ortugal, Romania,Slovakia,Slovenia,Spain,Sweden,SwitzerlandandUnitedKingdom. EUROPEANCOMMITTEEFORSTANDARDIZATION COMITEUROPENDENORMALISATION EUROPISCHESKOMITEEFRNORMUNG ManagementCentre:ruedeStassart,36B1050Brussels 2007CEN Allrightsofexploitationinany
10、formandbyanymeansreserved worldwideforCENnationalMembers. Ref.No.ENISO89683:2007:E 2 Foreword The text of ISO 8968-3:2004 has been prepared by Technical Committee ISO/TC 34 “Agricultural food products” of the International Organization for Standardization (ISO) and has been taken over as EN ISO 8968
11、-3:2007 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 identical text or by endorsement, at the latest by Dece
12、mber 2007, and conflicting national standards shall be withdrawn at the latest by December 2007. 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, Cyprus, Czech
13、 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 The text of ISO 8968-3:2004 has
14、 been approved by CEN as EN ISO 8968-3:2007 without any modifications. EN ISO 8968-3:2007 Reference numbers ISO 8968-3:2004(E) IDF 20-3:2004(E)INTERNATIONAL NATSDRAD ISO 8-8693 FDI 02-3 tide tsriFino -400210-90 Milk Determination of nitrogen content Part 3: Block-digestion method (Semi-micro rapid r
15、outine method) Lait Dtermination de la teneur en azote Partie 3: Mthode de minralisation en bloc (Mthode de routine semi- micro rapide) Referecne unbmers OSI 3-8698002:)E(4 DI:3-02 F002)E(4INTERNATIONAL STANDARD ISO 8968-3 IDF 20-3 First edition 2004-09-01 eD kliMimretnitano fo ortingen tnoctne :3 t
16、raP -kcolBiditsegon temhod eS(m-iorcim or diparitune meohtd) tiaL D retmanitoid nl ea enetru ne azeto raPti:3 e Mtdohd em eirnsilaatoie nb nlco (Mtdohe r edtuonis emei- cimro rpai)ed EN ISO 8968-3:2007 ii iiiContents Page Foreword iv Foreword. v 1 Scope 1 2 Normative references . 1 3 Terms and defin
17、itions. 1 4 Principle . 2 5 Reagents 2 6 Apparatus 3 7 Sampling 4 8 Preparation of test sample. 4 9 Procedure 4 9.1 Test portion and pretreatment. 4 9.2 Determination 5 9.3 Blank test . 6 9.4 Recovery tests. 6 10 Calculation and expression of results 7 10.1 Calculation of nitrogen content. 7 11 Prec
18、ision 8 12 Test report . 8 Annex A (informative) Results of interlaboratory test 9 Annex B (informative) Modified procedure for analysis of other milk products 10 Bibliography . 11 EN ISO 8968-3:2007iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of nat
19、ional 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 which a technical committee has been established has the right to be represented on that committee. Interna
20、tional 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 matters of electrotechnical standardization. International Standards are drafted in accordance with the r
21、ules 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 circulated to the member bodies for voting. Publication as an International Standard requires approval by a
22、t 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 responsible for identifying any or all such patent rights. ISO 8968-3IDF 20-3 was prepared by Technical Commit
23、tee 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 International. ISO 8968IDF 20 consists of the following parts, under th
24、e general title Milk Determination of nitrogen content: Part 1: Kjeldahl method Part 2: Block-digestion method (Macro method) Part 3: Block-digestion method (Semi-micro rapid routine method) Part 4: Determination of non-protein-nitrogen content Part 5: Determination of protein-nitrogen content EN IS
25、O 8968-3:2007 vForeword 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 collaborates
26、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 Standard
27、 requires approval by at least 50 % of IDF National Committees casting a vote. ISO 8968-3IDF 20-3 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 bei
28、ng published jointly by ISO and IDF and separately by AOAC International. 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 Mrs S. Berman (IL). This edition of ISO 8968-3IDF
29、20-3 cancels and replaces IDF 20-3:1993, which has been technically revised. ISO 8968IDF 20 consists of the following parts, under the general title Milk Determination of nitrogen content: Part 1: Kjeldahl method Part 2: Block-digestion method (Macro method) Part 3: Block-digestion method (Semi-micr
30、o rapid routine method) Part 4: Determination of non-protein-nitrogen content Part 5: Determination of protein-nitrogen content EN ISO 8968-3:2007blankNITERNATNOIAL STANDARD IS-8698 O3:(4002E) ID-02 F3:(4002E)1Milk Determination of nitrogen content Part 3: Block-digestion method (Semi-micro rapid ro
31、utine method) WARNING The use of this part of ISO 8968IDF 20 may involve the use of hazardous materials, operations and equipment. This standard does not purport to address all the safety risks associated with its use. It is the responsibility of the user of this standard to establish appropriate sa
32、fety and health practices and determine the applicability of local regulatory limitations prior to use. 1 Scope This part of ISO 8968IDF 20 specifies a method for the determination of the nitrogen content of liquid, whole or skimmed milk. It concerns a semi-micro rapid routine method following the b
33、lock-digestion principle. NOTE The method is a more rapid method than that described in ISO 8968-1IDF 20-1 and ISO 8968-2IDF 20-2 since the digestion time is reduced by taking a lower mass of test portion and using hydrogen peroxide together with sulfuric acid and a catalyst in the digestion. 2 Norm
34、ative 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 385: 1) , Laboratory glasswa
35、re Burettes 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 nitrogen content mass fraction of nitrogen determined by the procedure specified in this part of ISO 8968IDF 20. NOTE The nitrogen content is expressed as a percentage by mass. 1) To
36、 be published. (Revision of ISO 385-1:1984, ISO 385-2:1984 and ISO 385-3:1984) EN ISO 8968-3:20072 4 Principle A test portion is digested by using a block-digestion apparatus with a mixture of concentrated sulfuric acid, hydrogen peroxide and potassium sulfate, together with a catalyst to convert th
37、e organic nitrogen present to ammonium sulfate. Excess sodium hydroxide is added to the cooled digest to liberate ammonia. The liberated ammonia is distilled using a manual, semi-automatic or fully automatic steam distillation unit. In the case of manual or semi-automatic steam distillation, the amm
38、onia is distilled into excess boric acid solution then titrated with hydrochloric acid solution. Where a fully automatic distillation unit is employed, titration of the ammonia is carried out automatically with endpoint detection using a photometric or pH system. The nitrogen content is calculated f
39、rom the amount of ammonia produced. 5 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or demineralized water. 5.1 Kjeldahl catalyst tablets These tablets may be purchased commercially. Tablets comprising 3,5 g of potassium sulfate, 0,105 g of copp
40、er(II) sulfate pentahydrate and 0,105 g of titanium dioxide per tablet are suitable. Other types of tablet may be used provided that a) they contain a quantity of potassium sulfate such that 7 g of potassium sulfate can be dispensed using an integer number of whole tablets, and b) they contain no sa
41、lts of toxic metals such as selenium or mercury. 5.2 Sulfuric acid (H 2 SO 4 ), with mass fraction of at least 95 % to 98 %, nitrogen free 20 (H 2 SO 4 ) = 1,84 g/ml approximately. 5.3 Hydrogen peroxide solution (H 2 O 2 ), approximately 30 g of H 2 O 2per 100 ml. 5.4 Antifoaming agent A silicone pr
42、eparation is recommended, for example with a mass fraction of 30 % aqueous emulsion. 5.5 Sodium hydroxide solution (NaOH), nitrogen free, containing approximately 40 g of NaOH per 100 ml. 5.6 Boric acid solutions 5.6.1 Boric acid solution, c(H 3 BO 3 ) = 40,0 g/l. Dissolve 40,0 g of boric acid in 1
43、litre of hot water in a 1 000 ml one-mark volumetric flask. Allow the flask and its contents to cool to 20 C. Add 3 ml of indicator solution (5.7.1). Adjust to the mark with water and mix well. Store the solution, which will be light orange in colour, in a borosilicate glass bottle. Protect the solu
44、tion from light and sources of ammonia fumes during storage. 5.6.2 Boric acid solution, c(H 3 BO 3 ) = 10,0 g/l, to be used in the photometric endpoint titration. Dissolve 10,0 g of boric acid in 1 litre of hot water in a 1 000 ml one-mark volumetric flask. Allow the flask and its contents to cool t
45、o 20 C. Add 7 ml of methyl red solution (5.7.2) and 10 ml of bromocresol green solution (5.7.2) and mix. EN ISO 8968-3:2007 3Dilute to the 1 000 ml mark with water and mix well. Neutralize the boric acid solution with 0,1 mol/l sodium hydroxide until its colour changes to green. NOTE The addition of
46、 3 ml of 0,1 mol/l NaOH into 1 litre of 1 % boric acid usually gives good adjustments. 5.7 Indicator solutions 5.7.1 Indicator solution to be used in the pH endpoint titration Dissolve 0,1 g of methyl red in 95 % (volume fraction) ethanol. Dilute to 50 ml with the ethanol. Dissolve 0,5 g of bromocre
47、sol green in a small quantity of 95 % (volume fraction) ethanol. Dilute to 250 ml with the ethanol. Mix amounts of one part of methyl red solution with five parts of bromocresol green solution, or combine and mix both solutions. 5.7.2 Indicator solution to be used in the boric acid solution (5.6.2)
48、for the photometric endpoint titration a) Dissolve 0,1 g of bromocresol green in 100 ml of 95 % (volume fraction) ethanol. b) Dissolve 0,1 g of methyl red in 100 ml of 95 % (volume fraction) ethanol. 5.8 Hydrochloric acid standard volumetric solution, c(HCl) = (0,1 0,0005) mol/l. If the titration (9.2.3) is carried out manually, the use of a more diluted hydrochloric acid standard volumetric solution, c(HCl) = (0,05 0,0005) mol/l, is recommended. 5.9 Ammoniu
