1、Designation: D2807 17aStandard Test Method forChromic Oxide in Leather (Perchloric Acid Oxidation)1This standard is issued under the fixed designation D2807; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. 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 U.S. Department of Defense.1. Scope1.1 This test method covers the determination of
3、chromicoxide in leathers that have been partly or completely tannedwith chromium compounds. In general the samples will con-tain between 1 and 5 % chromium, calculated as chromicoxide.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thiss
4、tandard.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, health and environmental practices and deter-mine the applicability of regulatory limitations prior
5、 to use.See Section 7 for specific safety hazards.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by
6、 the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D2617 Test Method for Total Ash in LeatherD2813 Practice for Sampling Leather for Physical andChemical TestsD2868 Test Method for Nitrogen Content (Kjeldahl) andHide Substance Content
7、of Leather, Wet Blue and WetWhiteD3495 Test Method for Hexane Extraction of LeatherD3790 Test Method for Volatile Matter (Moisture) ofLeather by Oven Drying3. Summary of Test Method3.1 The perchloric acid method is applied to the ashobtained in Test Method D2617. In the acid digestion, anyremaining
8、organic matter is destroyed and the chromiumoxidized to the hexavalent state. On dilution, the chromium istitrated volumetrically with thiosulfate or ferrous salt. Theperchloric acid method requires less manipulation than proce-dures based on fusion of the ash, but care must be takenbecause of poten
9、tial hazards in the use of this reagent.4. Significance and Use4.1 The procedure described is specific for chromium inleather. Vanadium is the only common interfering element andthis is rarely present in quantity. The precision and accuracy ofthe methods are usually at least as good as the sampling
10、of theleather itself.4.2 The chromium content of leather relates to the degree oftannage obtained, and hence may be a matter for specificationin the purchase of leather. The procedure described providesadequate accuracy for this purpose.5. Apparatus5.1 Potentiometric Titration EquipmentThis is requi
11、red inan alternative method for titrating chromium (Cr6+) withferrous ammonium sulfate solution. The equipment consists of:5.1.1 Stirrer.5.1.2 Calomel and Platinum Electrodes.5.1.3 PotentiometerA variety of instruments is satisfac-tory.3The most convenient common feature of these instru-ments is a n
12、ull-point device (either a cathode-ray electron tubeor galvanometer) that will signal the abrupt change occurringin the potential when the end point is reached.5.1.4 In carrying out the titration, the electrodes are im-mersed in the sample, the solution agitated by the stirrer, and1This test method
13、is under the jurisdiction ofASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.06 on Chemical Analysis Thistest method was developed in cooperation with the American Leather ChemistsAssn.Current edition approved Sept. 1, 2017. Published September 2017. Originallyapprov
14、ed in 1969. Last previous edition approved in 2017 as D2807 17. DOI:10.1520/D2807-17A.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
15、 page onthe ASTM website.3Satisfactory equipment include, among others the following: the Kelley,Serfass, and Fisher tritrimeters, Leeds & Northrup potentiometers, and Beckman pHmeters.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesTh
16、is international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (
17、TBT) Committee.1the potential balanced with the galvanometer or cathode-raytube. Titrant is added dropwise until a sharp permanent changein potential occurs.5.2 Perchloric Acid Hood.6. Reagents6.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is
18、intended thatall reagents shall conform to specifications of the Committeeon Analytical Reagents of the American Chemical Society,where such specifications are available.4Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use withou
19、t lessening theaccuracy of the determination.6.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean distilled water, deionizedwater, or water of equal purity.6.3 Ferrous Ammonium Sulfate, Standard Solution (0.1N)Dissolve 39.21 g of ferrous ammonium sulfate(Fe(NH
20、4)2(SO4)26H2O) in water, add 25 mL of H2SO4, anddilute to 1 L.6.3.1 StandardizationDry potassium dichromate(K2Cr2O7) in an oven at 130 C for 2 h and cool in a desiccator.Weigh into a 250-mL glass-stoppered Erlenmeyer flask about0.200 g of K2Cr2O7to an accuracy of 0.0001 g. A beaker ispreferred if po
21、tentiometric titration is used. Dissolve in 75 to100 mL of water, add 20 mL of sulfuric acid (H2SO4, 1+1) andtitrate with the ferrous ammonium sulfate solution to bestandardized. Determine the end point eitherpotentiometrically, or with 1,10-phenanthroline ferrous sulfatesolution, 0.025 M,5as indica
22、tor. The potentiometric end pointis marked by a sharp decrease in oxidation potential. Theindicator end point is from blue-green to a red-brown. It ispreferable not to add the indicator until the end point isapproaching, as evidenced by the disappearance of ayellowish-green color and a gradual chang
23、e to blue-green.6.3.2 The titer of the ferrous ammonium sulfate solutiondecreases slowly because of oxidation of ferrous iron. Thischange may be retarded by storing the solution in a dark bottleand by adding a few pieces of mossy tin to the solution.However, the solution should be standardized daily
24、 wheneversamples are being analyzed. Calculate the normality of theferrous ammonium sulfate solutions as follows:Normality 5 A/0.04903 3 B! (1)where:A = grams of K2Cr2O7used, andB = millilitres required for titration.6.4 Nitric Acid (sp gr 1.42)Concentrated nitric acid(HNO3).6.5 Perchloric Acid (60
25、%)70 or 72 % perchloric acid(HClO4) may be substituted but storage is somewhat morehazardous.6.6 1,10-Phenanthroline-Ferrous Sulfate Solution (0.025M).56.7 Phosphoric Acid (40 %)Dilute 45 mL of 85 % phos-phoric acid (H3PO4) with water to 100 mL.6.8 Potassium Iodide Solution (10 %)Dissolve 10 g ofpot
26、assium iodide (KI) in 100 mL of water.6.9 Sodium Thiosulfate, Standard Solution (0.1 N)Dissolve 24.85 g of sodium thiosulfate (Na2S2O35H2O) inpreviously boiled water, add 1 g of sodium carbonate(Na2CO3), and dilute to 1 L.6.9.1 StandardizationDry potassium dichromate(K2Cr2O7) in an oven at 130 C for
27、 2 h and cool in a desiccator.Weigh into a 250-mL glass-stoppered Erlenmeyer flask about0.200 g of K2Cr2O7to an accuracy of 0.0001 g. Dissolve in 50mL of water; add 4 mL of hydrochloric acid (HCl, 1+1) 20 mLof KI solution, stopper the flask, and allow to stand 5 min in thedark. Titrate with the thio
28、sulfate solution to be standardized.When the color of the solution has faded to a brownish-green,add 2 mL of 2 % starch solution and continue titrating until thedeep blue color changes to a clear green. Record the titration.Calculate the normality of the thiosulfate solution as follows:Normality 5 A
29、/0.04903 3 B! (2)where:A = grams of K2Cr2O7used, andB = millilitres required for titration.6.9.2 The thiosulfate solution is quite stable but should berestandardized at least once a month.6.10 Starch Indicator Solution, prepared according to ac-cepted procedures available in analytical handbooks.6.1
30、1 Sulfuric Acid (sp gr 1.84)Concentrated sulfuric acid(H2SO4).7. Hazards7.1 The improper use of HClO4can lead to violent andserious explosions. In general, these can be traced to situationswhere concentrated HClO4has come in contact with organic oreasily oxidized materials.7.2 The exact procedures g
31、iven must be followed and thedigestions, once started, should be kept from possible contactwith other organic matter. The digestions should never beallowed to boil dry. HClO4should never be used withoutaccompanying use of HNO3and H2SO4.7.3 All spills involving HClO4should be flushed with water.Rags,
32、 sawdust, and other organic materials should never beused to mop up spilled acid.7.4 The use of a perchloric acid hood, reserved for perchlo-ric acid digestions, equipped with wash-down facilities andconstructed entirely of nonporous inorganic material is re-quired.4Reagent Chemicals, American Chemi
33、cal Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted 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. Pha
34、rmacopeial Convention, Inc. (USPC), Rockville,MD.5A satisfactory reagent, Ferroin, is commercially available.D2807 17a27.5 Perchloric acid bottles should be stored on a ceramictray or shelf and never on a wooden or pervious shelf. It isadvisable to keep only one 1-lb (0.45-kg) bottle of acid in thew
35、orking area.8. Test Specimen8.1 The specimen shall be 2 g leather from the compositesample prepared in accordance with Practice D2813, weighedand ashed according to Test Method D2617.9. Procedure9.1 Transfer the ash obtained from the determination of ash,Test Method D2617, to a 250-mL Erlenmeyer fla
36、sk, or otherappropriate glassware. Add, in the order named,20mLofHNO3, 15 mLof HClO4, and 10 mLof H2SO4.Add 3 to 5 glassbeads. In the perchloric acid hood, heat gently under refluxconditions, using a small funnel as a condenser in the neck ofthe flask, or a watch glass over the mouth of a beaker, un
37、til allorganic matter is destroyed and the color changes to a clearred-orange, indicating oxidation of chromium. Heat an addi-tional 2 min, cool quickly, rinse and remove the actingcondenser, and dilute to 125 mLwith water. Heat to boiling andcontinue boiling for 7 min. Cool and titrate by the proce
38、duregiven in 9.2 or 9.3.NOTE 1If the titration volume is less than 5 mL or more than 50 mL,adjust the size of the sample to give a titration volume between theselimits and repeat the determination.9.2 Titration with Na2S2O3SolutionAdd 30 mL of H3PO4and 20 mL of KI solution to the solution obtained i
39、n 9.1 andstopper the flask.Allow to stand 5 min in the dark. Titrate with0.1 N sodium thiosulfate solution standardized as described in6.9.1. When the color of the solution has faded to a brownish-green, add 2 mL of 2 % starch solution and continue thetitration until the deep blue color changes to a
40、 clear green.Record the titration. Calculate the results in accordance withSection 9.9.3 Titration with Ferrous Ammonium Sulfate SolutionAdd2mLofH3PO4and titrate with 0.1 N ferrous ammoniumsulfate solution standardized as described in 6.3.1. When thecolor of the solution has changed from yellow thro
41、ugh yellow-green to blue-green, add 5 drops of indicator5and continuetitrating until the blue-green solution changes to a red-brown.Record titration. Calculate results as described in Section 10.9.4 Alternatively, the titration may be done potentiometri-cally. After adding the H3PO4, transfer the so
42、lution to a 250-mL beaker and titrate with 0.1 N ferrous ammonium sulfatesolution, using the potentiometric apparatus described in 5.1.The end point is signaled by a sudden large change in potential.Record the titration. Calculate results as described in Section10.9.5 It is preferable to use the sam
43、e method of determiningthe end point in both the standardization of the ferrousammonium sulfate solution and in the analysis of the sample.10. Calculation10.1 Calculate the chromium content as percentage ofchromic oxide (Cr2O3) in the leather as follows:Cr2O3,%5 A 3 B 30.02533 3 100/C! (3)where:A =
44、millilitres of titrating solution used (either thiosulfateor ferrous ammonium sulfate),B = normality of titrating solution, andC = mass of leather. Use the mass of leather recorded asC B in Section 7 of Test Method D2617.10.2 If the determination of Cr2O3is performed on a leatherthat has been condit
45、ioned and weighed at constant temperatureand humidity, the fact should be indicated in reporting theresults.10.3 The above calculations give the Cr2O3content of theleather on an “as weighed” basis. If it is desired to express thison a moisture-free basis, a moisture determination should berun accord
46、ing to Test Method D3790 on a sample weighedfrom the same leather prepared at the same time according toPractice D2813. Unless otherwise specified, the chromiumcontent on a moisture-free basis shall be considered the defaultcalculation. If D is the percentage moisture found in thesample, calculate t
47、he Cr2O3, moisture-free basis, % as follows:Cr2O3,%moisture-free basis! 5A 3 B 30.02533 3100C 3100 2 D100(4)where A, B, and C have the same significance as above.10.4 If it is desired to express the Cr2O3content of theleather on a moisture-free and hexane-extractable basis, amoisture determination s
48、hould be run according to TestMethod D3790 and a hexane-extractable determination shouldbe run according to Test Method D3495. Samples should beweighed from the same leather prepared at the same timeaccording to Practice D2813.IfE is the percentage hexane-extractable material found in the sample, ca
49、lculate the Cr2O3moisture-free and hexane-extractable free basis, % as follows:Cr2CO3,%moisture-free and hexane-extractable-free basis!5A 3 B 30.02533 3100C 3100 2 D!1003100 2 E!100(5)where A, B,C, and D have the same significance as above.10.5 If it is desired to express the Cr2O3content of theleather on a hide substance basis, a moisture determinationshould be run according to Test Method D3790 and a hidesubstance determination should be run according to TestMethod D2868. Samples should be weighed from the sameleather prepared at the same tim
