ASTM_D_3533_-_05.pdf

Designation:D 3533 05Standard Test Method forRubberNitrogen Content1This standard is issued under the fixed designation D 3533;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method outlines two procedures for the deter-mination of total nitrogen in natural and synthetic rubbers andlatexes,using variants of the Kjeldahl process.1.2 It is applicable to raw rubbers,cured or uncuredcompounds,and finished articles.1.3 Procedure A,the referee method,is a macro procedure.Procedure B,the alternative method,is a semimicro procedureusing the same reagent as in Procedure A.1.4 In the absence of other nitrogen-containing materials,the method can be used for the estimation of the NBR contentof NBR rubbers and rubber products.1.5 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.Specific warningsare given in 8.2 and 9.2.2.Referenced Documents2.1 ASTM Standards:2D 4483 Practice for Evaluating Precision for Test MethodStandards in the Rubber and Carbon Black ManufacturingIndustriesE 147 Specification for Apparatus For MicrodeterminationOf Nitrogen By Kjeldahl Method3.Summary of Method3.1 The procedures used are modifications of the Kjeldahlmethod using sulfuric acid,potassium sulfate,and catalyticamounts of copper sulfate and selenium in the digestionmixture.The distillate from a strongly alkaline solution of thedigested sample is caught in boric acid solution and titratedwith standard acid or in excess standard acid and back titratedwith standard base.4.Significance and Use4.1 The determination of nitrogen in natural rubber isusually carried out in order to arrive at an estimate of theprotein content.Minor amounts of non-proteinous nitrogen-containing constituents are also present,however,and in thedry solids prepared from natural rubber latex,these materialscan make a substantial contribution to the total nitrogencontent.4.2 In the absence of other nitrogen-containing materials,the method can be used for the estimation of the NBR contentof NBR rubbers and rubber products.4.3 In the absence of other nitrogen-containing materialsand if the acrylonitrile content of the NBR rubber is known,themethod can be used to estimate the amount of NBR rubber inmixtures.4.4 This method may be used for quality control,forpurchase and raw material uses,for processing studies,and forresearch and development.5.Apparatus5.1 Kjeldahl Digestion and Distillation Apparatus:5.2 For Procedure AMacro-Kjeldahl apparatus,prefer-ably having ground-glass joints and including an 800-cm3Kjeldahl flask,with electrical heating equipment for thedigestion apparatus.5.3 For Procedure BMicro-Kjeldahl digestion and distil-lation apparatus in accordance with Specification E 147,orsemimicro Kjeldahl digestion and distillation apparatus inwhich the digestion and distillation are carried out in the sameflask(30 to 100-cm3Kjeldahl flask that may be attached to thedistillation apparatus by means of a standard-taper joint).1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direct responsibility of Subcommittee D11.11 on Chemical Analysis.Current edition approved Dec.1,2005.Published January 2006.Originallyapproved in 1976.Last previous edition approved in 2001 as D 3533 90(2001).2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.6.Reagents6.1 Boric Acid Solution(40 g/dm3)Dissolve 40 g of boricacid(H3BO3)in warm water,dilute to nearly 1 dm3,cool toroom temperature,and dilute to 1 dm3.6.2 Catalyst MixturePrepare a finely divided,intimatemixture of 30 parts by mass of anhydrous potassium sulfate(K2SO4),4 parts of cupric sulfate(CuSO45H2O)and 1 part ofselenium powder.Alternatively,dissolve,with heating,110 gof K2SO4,14.7 g of CuSO45H2O and 3.7 g of selenium in 600cm3of H2SO4(density 1.89 Mg/m3).6.3 Indicator,Methyl RedMethylene BlueDissolve 0.1 gof methyl red and 0.05 g of methylene blue in 100 cm3ofalcohol.6.4 Indicator,Methyl RedBromcresol GreenDissolve0.08 g of methyl red and 0.4 g of bromcresol green in 100 cm3of alcohol.6.5 Sodium Hydroxide,Standard Solution(0.02 M),Carbonate-FreePrepare a 0.02 M carbonate-free solution ofsodium hydroxide