1、Designation: D2868 10Standard Test Method forNitrogen Content (Kjeldahl) and Hide Substance Content ofLeather, Wet Blue and Wet White1This standard is issued under the fixed designation D2868; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 metho
3、d covers the determination of the nitro-gen content of all types of leather, wet blue and wet white. Thenitrogen content is used to calculate the hide substance (proteinfiber) content of leather, wet blue and wet white.NOTE 1The original test method for leather was essentially a com-posite of Method
4、 6441 of Federal Test Method Standard No. 311 andMethod B5 of the American Leather Chemists Association.NOTE 2Melamine, if present in bonded leather, could give an artifi-cially high value for the calculation of protein fiber.1.2 The values stated in SI units are to be regarded asstandard. No other
5、units of measurement are included in thisstandard.1.3 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 r
6、egulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D2813 Practice for Sampling Leather for Physical andChemical TestsD6659 Practice for Sampling and Preparation of Wet Bluefor Physical and Chemical TestsE177 Practice for Use of the Terms Precision and Bias inASTM Test Meth
7、odsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Summary of Test Method3.1 The specimen prepared according to an accepted proce-dure (see Note 3) is digested with acid in the presence of acatalyst to convert the nitrogen to ammonium ion. The ammo-
8、nium ion formed is nonvolatile under these highly acidconditions.NOTE 3For leather use specimen prepared per Practice D2813. Forwet blue and wet white, use specimen prepared per Practice D6659.3.2 The acid mixture is then made alkaline and the ammonialiberated is distilled into either a boric acid s
9、olution whichabsorbs the ammonia, or a sulfuric acid solution which absorbsthe ammonia.3.3 When the boric acid solution is used, the amount ofammonia in the boric acid is then determined by back titrationwith standardized acid using a sharp color change indicator(green to purple) to determine the en
10、d point. When the sulfuricacid solution is used, the amount of ammonia in the sulfuricacid solution is then determined by back titration with stan-dardized base using a sharp color change indicator (purple togreen-blue) to determine the end point.4. Significance and Use4.1 The nitrogen content as de
11、termined by this test methodis normally 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
12、 of animal hides, but it cannot be 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 thesevar
13、iations, the true factor for any given leather may beexpected to vary from 5.44 to 5.80 or about 63%.31This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.06 on ChemicalAnalysis. Thistest method was developed in cooperation
14、with the American Leather ChemistsAssn. (Standard Method B5 1954).Current edition approved Nov. 1, 2010. Published December 2010. Originallyapproved in 1970. Last previous edition approved in 2007 as D2868 07. DOI:10.1520/D2868-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org,
15、 orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Dahl, S., “Determination of Hide Substance in the Kjeldahl Method,” inChemistry and Technology of Leather, Vol 4, Reinhold Publis
16、hing Co., New York,NY, 1965.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2 A given leather sample may contain nitrogenous sub-stances other than hide substance (protein fiber) which will beanalyzed for by this test method, such
17、as resins, dyestuffs, etc.,that contain nitrogen. Therefore, although this 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
18、on other chemical determinations of agiven leather. Any errors, such as those described in 4.1.1 and4.2, will be carried over into these other analytical calculations.5. Apparatus5.1 Kjeldahl Apparatus consisting of:5.1.1 Kjeldahl Flask, of 500 or 800-mL capacity for diges-tion of the sample.5.1.2 H
19、eater, (gas or electric) for the Kjeldahl flask withfume hood 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
20、 shall be constructed of block tin,borosilicate glass, or other materials known not to react withhot ammonia vapor.5.2 Semi-automated equipment (Kjeltec/micro-Kjeldahl)produce comparable results and may be substituted forKjeldahl apparatus. See Precision and Bias (12.1 12.4).6. Reagents6.1 Purity of
21、 ReagentsReagent grade chemicals shall beused 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.4Other grades may beused, prov
22、ided it is first ascertained that the reagent 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 Indica
23、tor SolutionDissolve 40 g of boricacid (H3BO3) (borax-free) in water, add 10 mL of mixedindicator solution (6.5) and dilute to 1 L.6.4 Catalyst Digestion Mixture5,6 20.0 g K2SO4+ 0.6 gCuSO4+ 0.2 g pumice.6.5 Mixed Indicator Solution7Dissolve 0.060 g of methylred indicator and 0.040 g of methylene bl
24、ue indicator in 100mL of 95 % ethyl alcohol.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
25、cooled water. Determine the exact normality bytitration against the standard sulfuric acid (6.10) using themixed indicator (6.5) for the end point.6.8 Sucrose (C11H22O11).6.9 Sulfuric Acid (sp gr 1.84)Concentrated sulfuric acid(H2SO4), free from nitrogen.6.10 Sulfuric Acid, Standard (0.3 N)Dissolve
26、9 mL ofconcentrated H2SO4(6.9) in water and dilute to 1 L. Determinethe exact normality by titration against an equivalent solutionof a primary standard such as anhydrous sodium carbonate ortris (hydroxymethyl) amino methane.6.11 Sulfuric Acid, Standard (0.5 N)Available commer-cially. Determine the
27、exact normality by titration against anequivalent solution of a primary standard wuch as anhydroussodium carbonate or tris (hydroxymethyl) amino methane.6.12 Sodium Hydroxide (0.5 N)Available commercially.Determine the exact normality by titration against a knownsolution of a primary standard such a
28、s potassium hydrogenphthalate.7. Hazards7.1 All reagents and chemicals should be handled with care.Before using any chemical, read and follow all safety precau-tions and instructions on the manufacturers label or MSDS(Material Safety Data Sheet).8. Standardization8.1 BlanksRun a blank determination
29、substituting 1.0 g ofsucrose in place of the leather specimen by the procedureshown in Section 9. Calculate the blank results, as shown inSection 9.5.8.2 StandardTris (hydroxymethyl) amino methane can beused as an internal nitrogen standard for the method. Weigh outto 0.001 g approximately1goftris (
30、hydroxymethyl) aminomethane and transfer to the Kjeldahl flask. Run this standard bythe same procedure shown in Section 9. One gram of thisreagent is equal to 0.1156 g of N2or 8.255 meq of N2.9. Procedure9.1 Sample and Specimen:9.1.1 LeatherWeigh out two specimens from the preparedsample of 0.5 6 0.
31、05 g accurately to 0.001 g and record theweight of each specimen.9.1.2 Wet Blue or Wet WhiteWeigh out two specimensfrom the prepared sample of 0.05 1.0 g accurately to 0.001 gand record the weight of each specimen.NOTE 4If the sample size is 0.5 g, five replicates must be analyzed.NOTE 5The specimen
32、s for all chemical tests to be performed on theleather, wet blue or wet white, should be weighed at the same time to keepthe moisture content constant among the specimens. If only the nitrogencontent is being analyzed for, then specimens for moisture analysis shouldbe weighed out at the same time as
33、 those for the nitrogen analyses.9.2 DigestionTransfer the specimen to a Kjeldahl flask,being careful that all the powder is shaken down into the main4Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents no
34、tlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.5Dahl, S., and Oehler, R., “The Determination of Nitrogen in Leath
35、er by theKjeldahl Method,” JALCA, Vol 46, 1951, pp. 317355.6Available as a prepared catalyst mixture from some laboratory supply compa-nies, for example, Alfie Packers, #20P.7Available as prepared solution from some laboratory supply companies. HachBromcresol Green Methyl Red Indicator.D2868 102bulb
36、 of the flask. Add 10 6 0.5 g of the catalyst digestionmixture, a few glass beads or other anti-bumping agents, and25 mL of H2SO4. Mix the contents by gently swirling until allof the powder is wet by the acid. Place the flask over the heaterin the fume hood with the flask inclined at about 45. Adjus
37、tthe heat so that the contents boil gently (the condensate lineshould be within the neck of the flask) and maintain this boilingfor 1.5 h. Cool and dilute with 250 to 300 mL of water.NOTE 6For distillation, use either boric acid solution (9.3) or sulfuricacid (9.4) in the receiving flasks.9.3 Distil
38、lation (Boric acid solution):9.3.1 Measure out 125 mL of the H3BO3solution with agraduate and transfer to a 500-mL Erlenmeyer receiving flask.Place the receiving flask under the outlet tube from thecondenser so that the end of the tube dips below the surface ofthe H3BO3solution.9.3.2 Carefully pour
39、an amount of the concentrated NaOHsolution, sufficient to make the contents of the flask stronglyalkaline, slowly down the side of the digestion flask so that thecaustic settles to the bottom and does not mix with the acidlayer. The amount of concentrated NaOH solution required isabout 95 mL. Connec
40、t the Kjeldahl flask to the trap immedi-ately and be sure that the rubber stopper is tightly in place.Swirl the contents gently to mix the two layers and then heatsufficiently to boil the solution in the flask. Continue heatinguntil 150 to 200 mL has distilled over and been collected in theH3BO3solu
41、tion in the receiver. Disconnect the flask and trapbefore turning off the heat to prevent sucking the solution fromthe receiver back into the flask. Disconnect the condenseroutlet tube and rinse it off into the receiver. Dilute the contentsof the receiver to approximately 350 mL.9.4 Distillation (Su
42、lfuric acid solution):9.4.1 Measure out 25.0 mL of the 0.5 N H2SO4solutionfrom a buret into a 500-mL Erlenmeyer receiving flask. Add0.5 mL of the mixed indicator solution. Adjust the volume tothe 100 mL mark with DI water. Place the receving flask underthe outlet tube from the condenser so that the
43、end of the tubedips below the surface of the acidic receiving solution. Preparea receiving flask for each sample, plus a separate flask for theblank.9.4.2 Carefully pour an amount of the concentrated NaOHsolution, sufficient to make the contents of the flask stronglyalkaline, slowly down the side of
44、 the digestion flask so that thecaustic settles to the bottom and does not mix with the acidlayer. The amount of concentrated HaOH solution required isabout 95 mL. Connect the Kjeldahl flask to the trap immedi-ately and be sure that the rubber stopper is tightly in place.Swirl the contents gently to
45、 mix the two layers and then heatsufficiently to boil the solution in the flask. Continue heatinguntil 150 to 200 mL has distilled over and been collected in thesolution in the receiver. Disconnect the flask and trap beforeturning off the heat to prevent sucking the solution from thereceiver back in
46、to the flask. Disconnect the condenser outlettube and rinse it off into the receiver. Dilute the contents of thereceiver to approximately 350 mL.9.5 Titration (Boric acid solution)Titrate the receivercontents of the blank distillate immediately with the 0.3 NH2SO4(6.10) to a purple end point (pH abo
47、ut 4.9). Blankdeterminations run in accordance with 8.1 may require titrationwith alkali (if they are purple at the end of the distillation). Inthis case, titrate with the 0.1 N NaOH solution.9.6 Titration (Sulfuric acid solution)Titrate the receivercontents of the blank distillate immediately with
48、the 0.5 NNaOH (6.12) to a blue-green end point. Record the volume oftitrant for the blank. Titrate the receiving flasks for the samplesto the same end-point. Record the volume of titrant for eachsample.10. Calculations10.1 Blank (Boric acid solution)If the blank was acid(purple) and required titrati
49、on by the 0.1 N NaOH solution,then convert this value to equivalent millilitres of 0.3 N H2SO4as follows:B 5 blank, mL of standard 5 VbNb/Na(1)where:Vb= millilitres of NaOH solution required for titration ofthe blank,Nb= normality of the NaOH solution, andNa= normality of the H2SO4.10.2 Nitrogen in Sample (Boric acid solution)Calculate asfollows for the as received basis:Nitrogen, % 5 A 6 B! 3 N 3 0.014!/W 3 100 (2)where:A = millilitres of H2SO4required for titration of thesample,B = millilitres of H2SO4required for titration of the blank(or eq
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