1、BRITISH STANDARDBS ISO 24698-2:2008Rubber, raw Determination of bound acrylonitrile content in acrylonitrile-butadiene rubber (NBR) Part 2: Kjeldahl methodICS 83.040.10g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g
2、53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS ISO 24698-2:2008This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 June 2008 BSI 2008ISBN 978 0 580 58389 6National forewordThis British Standard is the UK implementation
3、of ISO 24698-2:2008. The UK participation in its preparation was entrusted to Technical Committee PRI/23, Test methods for rubber and non-black compounding ingredients.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does not purport
4、to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.Amendments/corrigenda issued since publicationDate CommentsINTERNATIONALSTANDARDISO24698-2First edition2008-05-15R
5、eference numberISO 24698-2:2008(E)Rubber, raw Determination of bound acrylonitrile content in acrylonitrile-butadiene rubber (NBR) Part 2:Kjeldahl methodCaoutchouc brut Dtermination du contenu en acrylonitrile li dans le caoutchouc acrylonitrile-butadine (NBR) Partie 2: Mthode KjeldahlBS ISO 24698-2
6、:2008ii ISO 2008 All rights reserved iiiContents Page1 Scope 12 Normative references 13 Principle 14 Reagents and materials 15 Apparatus . 26 Sampling, preparation of the sample for the determination and preparation of reagents . 37 Procedure . 38 Calculation of bound acrylonitrile content 49 Precis
7、ion . 510 Test report 5Annex A (informative) Examples of automatic analysers based on the Kjeldahl method . 6Annex B (informative) Precision . 8BS ISO 24698-2:2008iv ISO 2008 All rights reservedForewordISO (the International Organization for Standardization) is a worldwide federation of national sta
8、ndards bodies(ISO member bodies). The work of preparing International Standards is normally carried out through ISOtechnical committees. Each member body interested in a subject for which a technical committee has beenestablished has the right to be represented on that committee. International organ
9、izations, governmental andnon-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the InternationalElectrotechnical Commission (IEC) on all matters of electrotechnical standardization.International Standards are drafted in accordance with the rules given in t
10、he ISO/IEC Directives, Part 2.The main task of technical committees is to prepare International Standards. Draft International Standardsadopted by the technical committees are circulated to the member bodies for voting. Publication as anInternational Standard requires approval by at least 75 % of th
11、e member bodies casting a vote.Attention is drawn to the possibility that some of the elements of this document may be the subject of patentrights. ISO shall not be held responsible for identifying any or all such patent rights.ISO 24698-2 was prepared by Technical Committee ISO/TC 45, Rubber and ru
12、bber products, SubcommitteeSC 2, Testing and analysis.ISO 24698 consists of the following parts, under the general title Rubber, raw Determination of boundacrylonitrile content in acrylonitrile-butadiene rubber (NBR): Part 1: Combustion (Dumas) method Part 2: Kjeldahl methodBS ISO 24698-2:2008 ISO 2
13、008 All rights reserved 1Rubber, raw Determination of bound acrylonitrile content in acrylonitrile-butadiene rubber (NBR) Part 2:Kjeldahl methodWARNING Persons using this part of ISO 24698 should be familiar with normal laboratory practice.This part of ISO 24698 does not purport to address all of th
14、e safety problems, if any, associated with itsuse. It is the responsibility of the user to establish appropriate safety and health practices and toensure compliance with any national regulatory conditions.CAUTION Certain procedures specified in this part of ISO 24698 may involve the use or generatio
15、n ofsubstances, or the generation of waste, that could constitute a local environmental hazard. Referenceshould be made to appropriate documentation on safe handling and disposal after use.1ScopeThis part of ISO 24698 specifies a method for the determination of the bound acrylonitrile content in NBR
16、 by anautomatic analyser which uses the Kjeldahl method.NOTE Parts 1 and 2 of this International Standard may not necessarily give the same result for any given rubber sample.2 Normative referencesThe following referenced documents are indispensable for the application of this document. For datedref
17、erences, only the edition cited applies. For undated references, the latest edition of the referenced document(including any amendments) applies.ISO 1407:1992, Rubber Determination of solvent extractISO 1795, Rubber, raw natural and raw synthetic Sampling and further preparative procedures3 Principl
18、eThe nitrogen in a sample of raw rubber is converted into an ammonium salt by digestion with potassium sulfate,sulfuric acid and a copper sulfate catalyst. Ammonia is then released by the addition of strong alkali and steam-distilled into boric acid solution and titrated with standard volumetric aci
19、d solution.4 Reagents and materials4.1 Reference material: ammonium sulfate, purity .4.2 Standard volumetric acid solutions: sulfuric acid solution, ; hydrochloric acid solution, .4.3 Sulfuric acid, .greaterorequalslant 99,5 %0,05 mol/dm30,05 mol/dm3 = 1,84 g/cm3BS ISO 24698-2:20082 ISO 2008 All rig
20、hts reserved4.4 Sodium hydroxide solution, .4.5 Potassium sulfate (K2SO4).4.6 Copper sulfate (CuSO45H2O).4.7 Indicators, in accordance with the analyser manufacturers instructions: methyl red; methylene blue; bromophenol blue.4.8 Boric acid solution, in accordance with the analyser manufacturers ins
21、tructions (commonly, or solution).4.9 Ethanol, purity by volume.4.10 Methanol, purity by volume.5 Apparatus5.1 Automatic analyser.5.1.1 GeneralThe automatic analyser consists of the following components:a) a digestion unit, capable of maintaining a minimum operating temperature in accordance with th
22、emanufacturers instructions for digestion of the sample;b) a digestion tube, capable of being used for both digestion and distillation;c) a distillation unit, capable of introducing a fixed volume of sodium hydroxide into the digestion tube when itis placed in the unit and of steam-distilling, for a
23、 fixed time, the liberated NH3and condensing it into a fixedvolume of ammonia-absorbing boric acid solution in a titration vessel;d) a titration unit, capable of introducing the boric acid solution into the titration vessel before distillation and oftitrating the distillate with standard volumetric
24、acid solution photometrically using a photo-cell orpotentiometrically;e) a microprocessor, capable of calibrating the instrument with a reference material and of converting thetitration result into mass of nitrogen in the sample.5.1.2 Performance requirementsThe accuracy of the system shall be demon
25、strated by performing ten successive determinations using areference material such as ammonium sulfate. The mean of the ten determinations with the reference materialshall be within percentage points of the theoretical value. The relative standard deviation shall be withinby mass of nitrogen for the
26、 reference material.NOTE Relative standard deviation ( ) whereis the standard deviation;is the mean nitrogen content, in mass .5.2 Balance, weighing to the nearest .5.3 Extraction apparatus, as specified for method B in ISO 1407:1992.10 mol/dm33% 4%greaterorequalslant 95 %greaterorequalslant 99,8 %
27、0,20,5 % =swN 100swN%0,1 mgBS ISO 24698-2:2008 ISO 2008 All rights reserved 35.4 Beaker, capacity .5.5 Stirrer.5.6 Sieve, aperture .5.7 Absorbent tissue.5.8 Drying oven, capable of maintaining a temperature of .5.9 Roll mill, the temperature of whose rolls can be maintained at .6 Sampling, preparati
28、on of the sample for the determination and preparation of reagents6.1 Sampling and preparation of the sample for the determinationTake a sample of to in accordance with the method specified in ISO 1795, and pass the samplebetween the surfaces of the mill rolls with the nip set at and with the surfac
29、e temperature ofthe rolls maintained at .Take a portion of about to from the sample prepared as specified above.Extract this portion with ethanol by method B in ISO 1407:1992 and rinse the extracted material twice with asmall amount of fresh ethanol. Pour the contents of the flask onto a clean sieve
30、 to recover the extractedmaterial. Gently blot the extracted material with absorbent tissue to remove excess solvent, and dry the piecesof extracted rubber, separated from each other, in the oven at until the mass does not change bymore than over a period of .6.2 Preparation of reagents6.2.1 Catalys
31、t mixture: Prepare a mixture of potassium sulfate and copper sulfate in the fixed ratio inaccordance with the analyser manufacturers instructions.6.2.2 Indicator solution: Prepare an ethanolic indicator solution in accordance with the analysermanufacturers instructions.6.2.3 Boric acid solution: Pre
32、pare the ammonia-absorbing solution consisting of boric acid solution andindicator solution in accordance with the analyser manufacturers instructions.7 Procedure7.1 Operate the apparatus in accordance with the manufacturers instructions. A general procedure is asdescribed in 7.2 to 7.12.7.2 Take as
33、 the test portion to of the extracted material prepared by the method in 6.1 andweigh it to the nearest . The size of the test portion should preferably be chosen so that its total nitrogencontent is between and . Input the mass of the test portion into the microprocessor.7.3 Place the test portion
34、and the fixed amount of catalyst mixture in the digestion tube and pour the fixedamount of sulfuric acid into the tube.7.4 Place the digestion tube in the digestion unit and start to digest at the fixed temperature. Allow thedigestion to continue until the solution in the tube turns from yellow to a
35、 clear blue-green colour and thencontinue for longer (the digestion time can be determined before starting the analysis).300 cm3150m100C 2C100C 5C10 g 50 g0,2 mm 0,05 mm100C 5C3g 5g150m100C 2C0,1 mg 10 min50 mg 500 mg0,1 mg5mg 15 mg30 minBS ISO 24698-2:20084 ISO 2008 All rights reserved7.5 On comple
36、tion of the digestion, allow the tube to cool to room temperature and then dilute with the fixedamount of water.7.6 Place the digestion tube in the distillation unit.7.7 The fixed amount of sodium hydroxide solution and water is poured into the tube, and steam distillation iscarried out for a fixed
37、length of time or until a fixed amount of distillate has been collected.7.8 The distillate is collected by absorbtion in boric acid solution in the titration vessel.7.9 The collected distillate is then titrated with standard volumetric acid solution either photometrically using aphoto-cell or potent
38、iometrically.7.10 After the titration, the solution in the titration vessel is exhausted automatically.7.11 Carry out a blank determination in the same way.7.12 The microprocessor converts the titration result into the nitrogen content of the test portion, in mass .8 Calculation of bound acrylonitri
39、le content8.1 When sulfuric acid ( ) is used as the standard volumetric solutionCalculate the bound acrylonitrile content of the sample, in mass , from the following equation:whereis the exact concentration of the sulfuric acid solution, in ;is the volume of sulfuric acid solution required for the t
40、itration, in ;is the volume of sulfuric acid solution required for the blank determination, in ;is the mass of the test portion, in g.The test result is the value from a single determination of bound acrylonitrile content.8.2 When hydrochloric acid ( ) is used as the standard volumetric solutionCalc
41、ulate the bound acrylonitrile content of the sample, in mass , from the following equation:whereis the exact concentration of the hydrochloric acid solution, in ;is the volume of hydrochloric acid solution required for the titration, in ;is the volume of hydrochloric acid solution required for the b
42、lank determination, in ;is the mass of the test portion, in g.%0,05 mol/dm3wA%wA=10,61 cS(V1 V2)mcSmol/dm3V1cm3V2cm3m0,05 mol/dm3wA%wA=5,306 cH(Vprime1 Vprime2)mcHmol/dm3Vprime1cm3Vprime2cm3mBS ISO 24698-2:2008 ISO 2008 All rights reserved 5The test result is the value from a single determination of
43、 bound acrylonitrile content.9PrecisionAn interlaboratory test programme to determine the precision of this Kjeldahl method using automatic analyserswas conducted on NBR in 2006 (see Annex B).10 Test reportThe test report shall include the following particulars:a) a reference to this part of ISO 246
44、98;b) full identification of the rubber tested;c) full identification of the apparatus used;d) the standard volumetric acid solution used;e) the result of the test;f) the date of the test.BS ISO 24698-2:20086 ISO 2008 All rights reservedAnnex A(informative)Examples of automatic analysers based on th
45、e Kjeldahl methodA.1 GeneralThere are differences between automatic analysers with regard to the digestion conditions (including thedigestion temperature) and the catalyst. There are also differences with regard to the methods of distillation,absorption and titration of the ammonia. However, all aut
46、omatic analysers based on the Kjeldahl digestionmethod which meet the performance requirements specified in 5.1.2 are suitable for the determination of thebound acrylonitrile content of NBR by the method specified in this part of ISO 24698.A.2 Examples of suitable automatic analysers System A, which
47、 is composed of a QDS-10M digestion unit and a KJEL-AUTO DTP-3S distillation andtitration unit (Nakayama Rika Seisakusho Inc.); System B, which is composed of a Buchi K-435 digestion unit, a B-324 distillation unit (Shibata ScientificTechnology Ltd.) and a COM-1500 titration unit (Hiranuma Sangyo Co
48、., Ltd.).NOTE These are examples of suitable equipment available commercially. This information is given for the convenience ofusers of this part of ISO 24698 and does not constitute an endorsement by ISO of this equipment.A.3 Examples of determination conditionsExamples of suitable conditions are g
49、iven in Table A.1. The following should be noted:a) Excess sulfuric acid (over and above the amount consumed during the digestion) is needed and the amountdepends on the size of the digestion tube.b) The ratio of K2SO4to CuSO45H2O is between 9:1 and 8:1. The exact ratio and the amount of catalystmixture used should be determined in advance in accordance with the equipment manufacturersinstructions.c) The t
