ASTM D2868-2007 Standard Test Method for Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather《皮革的氮含量(基尔达斯法)和皮革物质含量的标准试验方法》.pdf
《ASTM D2868-2007 Standard Test Method for Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather《皮革的氮含量(基尔达斯法)和皮革物质含量的标准试验方法》.pdf》由会员分享,可在线阅读,更多相关《ASTM D2868-2007 Standard Test Method for Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather《皮革的氮含量(基尔达斯法)和皮革物质含量的标准试验方法》.pdf(3页珍藏版)》请在麦多课文档分享上搜索。
1、Designation: D 2868 07Standard Test Method forNitrogen Content (Kjeldahl) and Hide Substance Content ofLeather1This standard is issued under the fixed designation D 2868; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、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.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method covers the determin
3、ation of the nitro-gen content of all types of leather. The nitrogen content is usedto calculate the hide substance (protein fiber) content of leather.NOTE 1This test method is essentially a composite of Method 6441 ofFederal Test Method Standard No. 311 and Method B 5 of the AmericanLeather Chemist
4、s Association.1.2 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.2
5、. Referenced Documents2.1 ASTM Standards:2D 2813 Practice for Sampling Leather for Physical andChemical TestsE 180 Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial and Spe-cialty Chemicals3. Summary of Test Method3.1 The ground leather specimen prepared ac
6、cording to anaccepted procedure3is digested with acid in the presence of acatalyst to convert the nitrogen to ammonium ion. The ammo-nium ion formed is nonvolatile under these highly acidconditions.3.2 The acid mixture is then made alkaline and the ammonialiberated is distilled into a boric acid sol
7、ution which absorbsthe ammonia.3.3 The amount of ammonia in the boric acid is thendetermined by back titration with standardized acid using asharp color change indicator (green to purple) to determine theend point.4. Significance and Use4.1 The nitrogen content as determined by this test methodis no
8、rmally considered to be related to the amount of hidesubstance (protein fiber) present in the leather sample. A factorof 5.62 is normally used to calculate the hide substance fromthe nitrogen content.4.1.1 The 5.62 factor represents the average result of manyanalyses of animal hides, but it cannot b
9、e considered to beaccurate since it varies somewhat from hide to hide of the sametype, from type of hide to type of hide, and also with thethickness of hide retained in the final leather (split thickness ascompared to original hide thickness). As a result of thesevariations, the true factor for any
10、given leather may beexpected to vary from 5.44 to 5.80 or about 63%.44.2 A given leather sample may contain nitrogenous sub-stances other than hide substance (protein fiber) which will beanalyzed for by this test method, such as resins, dyestuffs, etc.,that contain nitrogen. Therefore, although this
11、 test method isfairly accurate for determining the nitrogen content of leather,its use for determining hide substance may result in largeerrors.4.3 The hide substance value derived from this determina-tion has a large bearing on other chemical determinations of agiven leather. Any errors, such as th
12、ose described in 4.1.1 and4.2, will be carried over into these other analytical calculations.5. Apparatus5.1 Kjeldahl Apparatus consisting of:1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.06 on ChemicalAnalysis. Thist
13、est method was developed in cooperation with the American Leather ChemistsAssn. (Standard Method B 5 1954).Current edition approved April 1, 2007. Published April 2007. Originallyapproved in 1970. Last previous edition approved in 2001 as D 2868 96 (2001).2For referenced ASTM standards, visit the AS
14、TM 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.3Acceptable procedures are published in Journal of the American LeatherChemists Association, Vol 51, 1956
15、 p. 497; or Offcial Methods of Analysis, Am.Leather Chemists Assn., available through the Office of the Secretary-Treasurer,Campus Station, Cincinnati, Ohio 45221; see Practice D 2813.4Dahl, S., “Determination of Hide Substance in the Kjeldahl Method,” inChemistry and Technology of Leather, Vol 4, R
16、einhold Publishing Co., New York,NY, 1965.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.1.1 Kjeldahl Flask, of 500 or 800-mL capacity for diges-tion of the sample.5.1.2 Heater, (gas or electric) for the Kjeldahl flask withfume ho
17、od or other exhaust system.5.1.3 Distillation Apparatus, consisting of an efficient vaportrap that can be sealed tightly in the top of the Kjeldahl flaskand a condenser connected to the top of the trap. All elementsof the distillation system shall be constructed of block tin,borosilicate glass, or o
18、ther materials known not to react withhot ammonia vapor.5.2 Comparable semi-automated equipment may be avail-able. The sample sizes may need to be adjusted and resultsshould be compared to the above equipment to determinesuitability.6. Reagents6.1 Purity of ReagentsReagent grade chemicals shall beus
19、ed in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.5Other grades may beused, provided it is first ascertained that the reage
20、nt is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.6.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean distilled water or water ofequal purity.6.3 Boric Acid Indicator SolutionDissolve 40 g of boricacid (H3B
21、O3) (borax-free) in water, add 10 mL of mixedindicator solution (5.5) and dilute to 1 L.6.4 Catalyst Digestion Mixture6,7 20.0 g K2SO4+ 0.6 gCuSO4+ 0.2 g pumice.6.5 Mixed Indicator SolutionDissolve 0.060 g of methylred indicator and 0.040 g of methylene blue indicator in 100mL of 95 % ethyl alcohol.
22、6.6 Sodium Hydroxide, Concentrated Solution (450 g/L)Dissolve 450 g of sodium hydroxide (NaOH) pellets (98 %) inwater and dilute to 1 L.6.7 Sodium Hydroxide, Standard Solution (0.1 N)Dissolve 10 mL of the concentrated NaOH solution (6.6)in1L of boiled and cooled water. Determine the exact normality
23、bytitration against the standard sulfuric acid (6.11) using themixed indicator (6.5) for the end point.6.8 Sodium Thiosulfate Solution (80 g/L)Dissolve 80 g ofsodium thiosulfate (Na2S2O35H2O) in water and dilute to 1 L.6.9 Sucrose (C11H22O11).6.10 Sulfuric Acid (sp gr 1.84)Concentrated sulfuric acid
24、(H2SO4), free from nitrogen.6.11 Sulfuric Acid, Standard (0.3 N)Dissolve 9 mL ofconcentrated H2SO4(5.10) in water and dilute to 1 L. Deter-mine the exact normality by titration against an equivalentsolution of a primary standard such as anhydrous sodiumcarbonate or tris (hydroxymethyl) amino methane
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