ASTM_D_3533_-_90_2001.pdf

Designation:D 3533 90(Reapproved 2001)Standard 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 method outlines two procedures for the determina-tion 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 as thestandard.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:D 1076 Specification for RubberConcentrated,AmmoniaPreserved,Creamed,and Centrifuged Natural Latex2D 3040 Practice for Preparing Precision Statements forStandards Related to Rubber and Rubber Testing3D 4483 Practice for Determining Precision for Test MethodStandards in the Rubber and Carbon Black Industries2E 147 Specification for Apparatus for Microdeterminationof Nitrogen by Kjeldahl Method4NOTE1The specific dated edition of Practice D 3040 that prevails inthis method is referenced in the Precision section.3.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 apparatus5inwhich 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).6.Reagents6.1 Boric Acid Solution(40 g/dm3)Dissolve 40 g of boricacid(H3BO3)in warm water,dilute to nearly 1 dm3,cool to1This method is under the jurisdiction of ASTM Committee D11 on Rubber andis the direct responsibility of Subcommittee D11.11 on Chemical Analysis.Current edition approved Oct.26,1990.Published May 1991.Originallypublished as D 3533 76.Last previous edition D 3533 82.2Annual Book of ASTM Standards,Vol 09.01.3Discontinuedsee 1986 Annual Book of ASTM Standards,Vols 09.01 and09.02.4Annual Book of ASTM Standards,Vol 14.04.5Suitable semimicro apparatus may be obtained from the American InstrumentCo.,8030 Georgia Ave.,Silver Spring,Md.,20910,and from the Scientific GlassApparatus Co.,737 Broad St.,Bloomfield,NJ 07003.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.room 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.